37? /iBii 9$%8 LIGHT SPECTRA DISTRIBUTIONS IN TEMPERATE CONIFER-FOREST CANOPY GAPS, OREGON AND IN TROPICAL CLOUD-FOREST CANOPY, VENEZUELA DISSERTATION Presented to the Graduate Council of the University of North Texas in Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY By Susan Monteleone, B.S., M.S. Denton, TX December, 1997
198
Embed
digital.library.unt.edu/67531/metadc279052/m2/1/high_re… · Monteleone, Susan, Light spectra distributions in temperate conifer-forest canopy gaps. Oregon and in tropical cloud
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
37? /iBii
9$%8
LIGHT SPECTRA DISTRIBUTIONS IN TEMPERATE CONIFER-FOREST CANOPY
GAPS, OREGON AND IN TROPICAL CLOUD-FOREST
CANOPY, VENEZUELA
DISSERTATION
Presented to the Graduate Council of the
University of North Texas in Partial
Fulfillment of the Requirements
For the Degree of
DOCTOR OF PHILOSOPHY
By
Susan Monteleone, B.S., M.S.
Denton, TX
December, 1997
Monteleone, Susan, Light spectra distributions in temperate conifer-forest
canopy gaps. Oregon and in tropical cloud forest canopy. Venezuela. Doctor of
Philosophy (Biology), December 1997,198 pp., 5 tables, 66 illustrations,
references, 117 titles.
Light spectra distributions were measured in two different montane
forests: temperate and tropical. Spectral light measurements were made in
different sized canopy gaps in the conifer forest at H. J. Andrews Experimental
Forest in Oregon, USA. Researchers at Oregon State University created these
gaps of 20 m, 30 m, and 50 m in diameter. In the tropical cloud forest, spectral
light measurements were made in two plots that were permanently established at
La Mucuy Parque Nacional in Venezuela, in collaboration with researchers at
Universidad de Los Andes.
In both studies, spectra and distributions of physiologically active light
were analyzed: red, far-red, R/FR ratio, and blue light. Horizontal light
measurements were taken at 1.0 m above the forest floor. Also, light was
measured in vertical profiles. Oregon light measurements were regressed with
numbers of conifer seedlings and basal areas surveyed in the gaps.
Horizontal light distributions varied in both temperate and tropical
systems. Distribution patterns were predicted by the morphology of the canopy
gaps in Oregon, and the relief patterns in Venezuela. Attenuation of light in
forest systems is often assumed exponential following Beer's law, i.e., an
homogeneous path through plant canopy. In Oregon, vertical profiles showed
light in canopy gaps were often not homogeneous. Profiles in Venezuela were
heterogeneous because measurements were taken in full plant canopy.
As distribution of red, far red, and blue light wavelengths, and R/FR ratios
changed along cardinal axes in gaps of different sizes, species' seedling
associations changed. Significant relationships (p < 0.05) between conifer
seedling numbers and basal areas were found. More than 50% of the variation
in seedlings was explained by patterns in light-color distribution. In 30 m gaps,
western Hemlock seedlings were highly significantly affected by red and far red
light (R2 > 90; p < 0.001). Only R/FR ratios were associated significantly with
species distributions in 20 m gaps. Gap sizes strongly affected associations.
37? /iBii
9$%8
LIGHT SPECTRA DISTRIBUTIONS IN TEMPERATE CONIFER-FOREST CANOPY
GAPS, OREGON AND IN TROPICAL CLOUD-FOREST
CANOPY, VENEZUELA
DISSERTATION
Presented to the Graduate Council of the
University of North Texas in Partial
Fulfillment of the Requirements
For the Degree of
DOCTOR OF PHILOSOPHY
By
Susan Monteleone, B.S., M.S.
Denton, TX
December, 1997
ACKNOWLEDGMENTS
This project is the culmination of many hours contributed by willing and
supportive assistants: Magdiel Ablan, and Diana Victoria Acevedo. I thank Dr.
Miguel Acevedo for his encouragement to pursue this research and for making
possible the opportunity to work in Venezuela.
Many thanks are extended to Oregon State University and to H. J.
Andrews Experimental Forest Research Facility. Special thanks to Drs. Andrew
Gray and Thomas Spies for their collaboration on this project and their
cooperation during our stay at H. J. Andrews; and to Art McKee for his logistical
assistance in the use of H. J. Andrews Experimental Forest and associated
facilities.
At the Universidad de Los Andes in Venezuela for their support of this
project. My sincere gratitude and appreciation goes to Dra. Michele Ataroff at
the Center for Ecological Research for her collaboration and tireless support,
and further thanks to Dr. Carlos Estrada for his invaluable assistance while
working on this project at La Mucuy.
TABLE OF CONTENTS
Page
Chapter
1. ROLE OF SHADE AND LIGHT SPECTRA IN FOREST DYNAMICS 1
Introduction Plant perception of shade
Changes in light intensity Changes in light spectra
Proposed mechanisms of light perception in plants Plant photoreceptors Phytochrome Blue absorbing pigment Regulatory function of light via phytochrome Adaptive significance of photoreceptors
Dynamics of light in forest canopies
2. LIGHT SPECTRA SURVEY IN CANOPY GAPS OF A TEMPERATE MONTANE CONIFEROUS FOREST 22
Introduction Methods
Site description Study area Data collection and management Sample plots and one-meter ground measurements Vertical light profiles and attenuation coefficients
Results One-meter ground measurements Vertical light profiles and attenuation coefficients
Discussion
3. LIGHT SPECTRA IN CANOPY GAPS AND TREE SEEDLING ESTABLISHMENT IN A TEMPERATE MONTANE CONIFER FOREST 66
Introduction Methods
Site description and study area Seedling survey Spectral data collection and management PAR in gaps Statistical analysis
Results PAR in gaps Distribution of light and seedlings
Number of seedlings Seedling basal area
Regression of seedling establishment and light quality Analyses by gap size Analyses by axes
Step-wise regression analyses Discussion
4. LIGHT SPECTRA SURVEY IN A TROPICAL MONTANE FOREST LA MUCUY PARQUE NACIONAL IN VENEZUELA 100
Introduction Methods
Site description Data collection and management Sample plots One-meter ground measurements Vertical profiles and attenuation coefficients Hemispherical photographs
Results PAR in forest canopy One-meter ground measurements
Plot A Plot B
Vertical light profiles Plot A Plot B
Extinction coefficients Plot A Plot B
Open-canopy area calculated from hemispherical photographs
Discussion
5. CONCLUSIONS 151
Objectives
6. APPENDIX: TABLES OF RESULTS FROM LINEAR REGRESSION ANALYSIS OF SEEDLING DATA AND CANOPY GAP LIGHT 1623
Table 1 Table 2
7. LITERATURE CITED 180
CHAPTER 1
ROLE OF SHADE AND LIGHT SPECTRA
IN FOREST DYNAMICS
Introduction
Light is one of the most limiting of environmental factors that affects the
establishment, growth, and development of plants. Light has two important
aspects, fluence rates or light intensity and spectral quality, both of which are
effectively altered by shade environments. The plant's perception of shade in
canopy gaps is based on a dichotomy of plant photosynthetic and
photomorphological responses to the light environment.
Plant Perception of Shade
Changes in Light Intensity. -Vegetative canopies present the greatest
adaptive challenge of terrestrial plants to changes in light environments (Holmes
1981). Plants must receive adequate light intensity in a photosynthetically-
active range of radiation (PAR; 400 nm- 700 nm) to maintain their net
photosynthetic capacity. When intensity falls frequently below light compensa-
tion points, the irradiance at which loss of assimilation due to respiration is
balanced by rates of photosynthesis, plants
must adapt to survive. Canopy shade is a reduction in light intensity that causes
2
plant adaptation to maximize net photosynthesis (Schwartz and Koller 1978;
Barrett and Fox 1994; Hirose and Werger 1995).
Plants adapt to radiation environments in vegetation canopies with a
range of shade-tolerant and shade-intolerant responses. In the coniferous
forests of the Oregon Cascades in the Pacific northwest (PNW), Douglas-fir is a
shade-intolerant species, whereas western hemlock and Pacific silver fir are
shade-tolerant species (Franklin 1963; Spies and Franklin 1989,1991; Gray
1995). Shade-tolerant species are morphologically adapted to low light
intensities (Salisbury and Ross 1985). Leaf size, thickness of palisade cells,
and the activation of phytochrome results in the increased production of
chlorophyll to compensate for low light conditions (Kasperbauer 1988).
Seedlings can be shade-tolerant as juveniles to gain early establishment in the
canopy understory. They are maintained in low light until they are released from
light-limited growth in the event of a canopy-gap creation (Oliver and Larson
1996).
Many shade-tolerant species appear to require openings in the canopy to
become established (Uhl et al. 1988; White and Pickett 1985), but some species
are capable of growing directly up into canopies that have reduced densities
(Canham 1989). In the Oregon Cascade old-growth forests, Douglas-fir and
western hemlock are co-dominant in forest stands where major disturbances
have not occurred. Western hemlock canopies are typically dense, reducing
forest-floor light intensities to less than 5% of full sunlight (Spies and Franklin
1989). Seedlings of Douglas-fir, a shade-intolerant species are unable to
3
become established in canopy gaps smaller than 1000 m2. Further, typical gap-
creation events in H. J. Andrews forest, an old-growth experimental forest area
in the PNW, are from standing snags that allow less light to the forest floor than
gaps created by fallen trees.
In the tropics, ecological groups of species have been defined by their
light tolerances (Swaine and Whitmore 1988; Smith and Huston 1989). Pioneer
species are shown to be dependent on gap-phase regeneration for germination
and growth. The trigger for germination in all tropical species (reviewed by
Swaine and Whitmore, 1988) required increased red light observed after canopy
removal, or increased temperatures of soil exposed to direct radiation. Pioneer
species generally show a tendency toward longer seed dormancy than non-
pioneer species, and germination is cued to disturbance indicators linked to
changes in light quality (Brokaw 1985a).
Within non-pioneer or climax species, there is a gradient of seedling
growth responses to exposure to greater amounts of radiation found in different
gap sizes (Swaine and Whitmore 1988). One end of the response continuum
requires great amount of light to grow rapidly. These species tend to have high
mortality in low canopy shade. At the other extreme, some species do not
require great amounts of light for release. These species have slower growth
rates and are less likely to regenerate following catastrophic loss of canopy
cover.
Changes in Light Spectra.-Perception of shade by vegetation is not limited
4
to reduction in light intensities; changes in spectral quality have been shown to
precede alterations in plant resource allocations. One microclimate factor that
has received relatively little attention is the color of light in forest canopy and
gap environments (Woodward 1989; Canham 1989; Poulson and Piatt 1989;
Smith etal. 1992; Clark etal. 1993; Cornelissen 1993; Endler 1993; Jans etal.
1993; Ackerly and Bazzaz 1995), specifically the spatial patterns of color and its
role in the successful establishment and growth of species in a forest gap
(Franco 1986; Casal etal. 1990; Endler 1993). Understanding patterns of the
distribution of colors of light in forest gaps might help to elucidate functional
mechanisms that work in tandem with molecular light receptors in the plant's
cellular membrane (Frankland and Letendre 1978; Raven 1983; Smith etal.
1990; Fosket 1994). Measurements of light across a forest gap show spatial
patterns of color might be correlated to physiological activities of seeds and
seedlings of colonizing species during the forest regeneration phase.
Proposed Mechanism of Light Perception in Plants
Photomorphogenesis is defined as the control of plant development by
ambient light conditions (Smith 1984). Plants respond to variable light
environments with relatively-sophisticated physiological adjustments, e.g.,
protein synthesis or resource allocation. Such responses could account for a
great degree of the morphological plasticity observed in higher plants, e.g.,
heterophylly. Plants use a complex array of photoreceptors to sense and
respond to light conditions as environmental cues. Plant pigments such as
chlorophyll and carotenoids mediate the photosynthetic response in plants.
5
There are photoreceptors in plants such as photochrome, a pigment protein;
cryptochrome, which responds to visible- (primary peak between 420-480 nm)
and near- (secondary peak between 340-380 nm) UV wavelengths; and the blue
light photoreceptor with which plants respond to blue photon fluence rates (Taiz
and Zeiger 1991).
Plant Photoreceptors. - Plants have photoactive pigments that function as
photoreceptors in the perception of changes in spectral quality under vegetation
canopies. Photoreceptor molecules or biological pigments absorb light at
specific wavelengths, activating the signal transduction pathway (Robinson et al.
1993; Fosket 1994). Light is perceived by the plant at the environmental level
via a molecular receptor. Empirical evidence indicates that activation of a
photoreceptor enhances movement of proton and calcium ions across cell
membranes (Raven 1983). Modulation of these ion ports could be important
action sites for photoreceptors.
Photoreceptors are classified into five categories based on structure
(Hendry 1993). Chlorophylls are tetrapyrroles in their cyclic form and
phytochromes are tetrapyrroles in their linear form. Chlorophyll a and b are
dominant in terrestrial plants and have peak absorption in blue, yellow, and red
wavelength ranges. Chlorophylls are the primary pigments in the photosynthetic
activity of plants.
Phytochrome.- Phytochrome belongs to a group of pigments called
tetrapyrroles and accompanies the chlorophylls and hemes. Phytochrome is
composed of an apoprotein covalently attached to a linear tetrapyrrole
6
chromophore (McNellis and Deng 1995). It exists in two interconvertible forms:
Pr, which responds to red (650-680 nm) photon fluence rates and Pfr, which is
converted from Pr when exposed to far red (710-740 nm) photon fluence rates
(Taiz and Zeiger 1991). Phytochrome is synthesized as Pr, the bioactive form.
When exposed to saturating red light, with an absorbance maximum at 665 nm,
about 80% is converted to Pfr in vivo (McNellis and Deng 1995). There are
fluctuations in the pools of Pr and Pfr by synthesis of Pr, by destruction of the Pfr
form by proteolysis, and by slow reversion of Pfr back to the Pr conformation that
takes place in the dark (Taiz and Zeiger 1991).
There are several types of phytochromes identified in Arabidopsis, a
model species for transgenic plants; these molecules are thought to be encoded
by five distinct genes: PHYA, PHYB, PHYC, PHYD, and PHYE. Phytochrome A
is a light-labile protein and is generally isolated in light-etiolated plant tissues
(McNellis and Deng 1995). Concentrations of phytochrome A decrease 100-fold
when plants are exposed to white light. It is held to be the principal receptor for
continuous far red light. High FR/R ratios is one means by that phytochrome A
is thought to facilitate the emergence of seedlings from soil in deep shade light
environments (McNellis and Deng 1995).
Germinability of seeds under plant canopies is dependent, in many
situations, on the red-to-far red ratios (R/FR) reaching the seeds (Grime 1981;
Mohr and Drumm-Herrel 1983). Canopy shade results in the alteration of
spectral composition of light that influences successful regeneration of seedlings
by affecting seed germination and seedling growth. Germination in certain seed
7
species are inhibited by the depletion of red wavelengths as light is filtered
through the canopy. These species normally require a canopy gap to maximize
their germination success. Thus, light conditions of red light relative to far red
light at the top microzone of soils in canopy gaps is a focal factor in the
germination of forest species' seeds (Foster and Janson 1985; Forget 1992 a, b\
Alvarez-Buylla and Garcia-Barrios 1991; Kennedy and Swaine 1992; Hammond
and Brown 1995; Rokich and Bell 1995; Loiselle etal. 1996).
Phytochrome B is a light-stable protein, as are phytochromes C, D, and E.
However, phytochrome B is proposed as the principal receptor for red light, and
hence is postulated to mediate red-light-induced phytochrome responses such
as day length perception via R/FR equilibrium (Vince-Prue 1983; McCormac et
al. 1992) and shade-avoidance responses (Aphalo etal. 1991; McNellis and
Deng 1995).
Plant photoreceptors possibly initiate early signaling events that plants
use to initiate cellular development, and consequently affect morphogenetic
patterns. The hypothesized mode of action for phytochrome regulation of plant
functions is a signal transduction sequence (Raven 1983) perhaps mediated by
calcium uptake and calmodulin activity (Taiz and Zeiger 1991).
Mediation of membrane functions is especially evident during perceived
phytochrome activity in plants. This might be the interaction necessary to
facilitate the controlled uptake of calcium through cell membranes via
membrane-interactive phytochrome. This membrane interactivity could explain
the amplified effects of low concentrations of phytochrome in plant systems
8
through a calmodulin-mediated system (Raven 1983; Taiz and Zeiger 1991).
The effect of phytochrome on plants is categorized by the intensity of light
required to elicit the response (Taiz and Zeiger 1991). Some responses are
elicited by fluence rates as low as 0.1 nmol m2 s"1 (or one-tenth the light emitted
from a single flash of a firefly!) and are called very low fluence (VLF) responses.
This low amount of red light would convert less than 0.02% of the total
phytochrome to Pfr. Exposure to far red light converts 97% of Pfr to Pr, leaving
3% as Pfr, more than enough to elicit VLF responses. Note that far red light
cannot reverse VLF responses. Low fluence (LF) responses are not initiated
until fluence rates reach 1.0 p.mol m2 s"1. These are the classic photoconversion
responses, e.g., lettuce seed germination. Another category of responses is
elicited by high fluences (HF). Continuous radiation periods are required for
hours at fluences in excess of 10 nmol m2. Action spectra for HF responses are
in the far red and blue regions and are not photoreversible.
When responses require such high intensities of light, it might be found
that more than one photoreceptor is involved. Mancinelli (1989) explained that it
is possible that cryptochrome and phytochrome interact and even very low levels
of Pfr might be enough to elicit the interaction. Because it is not possible to
remove all Pfr from plants, we cannot control for the effect of Pfr to isolate the
effect elicited by blue light acting on cryptochrome.
Blue Absorbing Pigment.- There is evidence that suggests that
phytochrome and blue/UV photoreceptors interact at the molecular level ( Mohr
and Drumm-Herrel 1983; Mancinelli 1989; Elmlinger etal. 1994). However, both
9
the mode of expression and the mechanisms of interaction have not been
elucidated. There are four modes of interaction postulated (Mancinelli 1989): 1)
direct interaction between photoreceptors; 2) interaction at the level of the signal
transduction chain; 3) interaction at the level of post-signal transduction
processes; or, 4) independent action. Note that postulate 1 is a photoreceptor
interaction, whereas postulates 2-4 are interactions between products of actions
of the photoreceptors. Both photoreceptors are involved in photoregulation of
plant growth and development (Mancinelli 1989); however, this is not taken as
evidence of interaction. The nature of cryptochrome is yet unknown and
phytochrome is responsive to UV and blue light as well as red and far red light.
Thus, responses to blue light can be mediated by either phytochrome or
cryptochrome.
It has been argued that no blue light receptor exists because only a few
photochemical responses have been observed only when plants are exposed to
blue light. Isolation of the pigment was further confounded by the observed
response of phytochrome to blue wavelengths (Tanno 1983) and the
photoreversal of blue effects by FR exposure (Briggs and lino 1983; Obrenovic
1992). Also, there is an obligate sequence in which the blue "receptor" must be
activated before phytochrome can be initiated in the synthesis of anthocyanins
(Mohrand Drumm-Herrel 1983).
More evidence for the existence of a blue light receptor lies in the
controlled response of stomatal closure by blue light. Both blue and red light are
effective in photosynthesis and also effect stomatal closure. However, blue light
10
was more than twice as effective than red light in stomatal regulation, especially
under low light conditions. Zeiger et al. (1983) have isolated a blue light
photosystem that regulates changes in stomatal opening in Paphiopedilum
harrisianum (family Orchidaceae), a species whose guard cells do not contain
chlorophyll, which regulates uptake of potassium ions. Blue light is thought to
cause potassium ion movement independent of carbon dioxide or auxin
concentrations (Salisbury and Ross 1985). Zeiger etal. (1983) also attributes
any response to red light as an indirect effect to exposure, such as intercellular
changes in carbon dioxide concentrations from photosynthesis or activity of
chlorophyll receptors, an argument that further solidifies their evidence in
support of the existence of a blue light receptor.
Levels of red and blue light vary temporally, seasonally, and with cloud
cover (Holmes and Smith 1977). Generally, blue light is associated with shorter
internodes, smaller leaf areas, reduced growth rates, and increased nitrogen to
carbon ratios (Thomas 1981). Relative amounts of red and blue light in nature
are probably more important than intensities, suggesting that the interaction
between blue light and red and far red light photoreceptors is of evolutionary
importance.
Regulatory Function of Light via Phytochrome.- Phytochrome has a
regulatory function in the expression of nuclear genes, which might play an
integral role in controlling plant functions. Light-regulated elements have been
identified as promoter regions on plant genomes (Taiz and Zeiger 1991). A
protein factor called GT-1 was isolated by Kay et al. (1989). This factor binds to
11
the light-regulated regions of the rbcS genes of different species, making a
promoter not regulated by light into one influenced by light. This is one means
by which phytochrome can act upon the regulation of the expression of genes by
environmental light cues.
In a study by Elmlinger etal. (1994), levels of glutamine synthetase (GS)
in Scots pine was investigated. GS synthesis is reportedly regulated by light in
the genus Pinus. The study of the light-regulated coaction of the synthesis of
isoforms GS2 and Fd-GOGAT showed coordination of both enzymes via
phytochrome and a blue/UV photoreceptor (Elmlinger et al. 1994). In seedlings
less than 10 days old, phytochrome was the photoreceptor regulating enzyme
synthesis. After 20 days, blue light becomes necessary for any further enzyme
synthesis. Further investigation using dichromatic light showed that
phytochrome was the "effector" of GS synthesis under all conditions, and blue
light amplifies the responsiveness of the system towards Pfr. However, if Pfr
levels were kept low, blue light was not able to elicit the synthesis of GS protein.
On the basis of evidence from earlier studies corroborating the current results, it
was observed that coarse regulation of gene expression is mediated by
phytochrome, and "fine-tuning" takes place at the translational or post-
translational level (Elmlinger et al. 1994).
Adaptive Significance of Photoreceptors.- Mohr and Drumm-Herrel (1983)
argue that the amplification of anthocyanin synthesis in response to blue/UV
light is an evolutionary adaptation to production of a protective mechanism to
damaging UV radiation. Other effects of light cues on plant development has an
12
adaptive significance, e.g., shade-avoidance responses. Allocation of resources
toward stem growth to avoid light competition is one such avoidance response to
shading. Neighbor effect due to reflected FR light has been shown to be of
adaptive value to plants on the basis that plants are able to detect slight
changes in the spectral balance via the phytochrome photoreceptor
Ballare etal. 1987, 1990,1991; Smith etal. 1990).
This process is adaptive because strong selection pressure is exerted to
allocate resources on the basis of an economic principal. The more rapidly
competitive situations are detected, the more advantageous is the adaptive
response, and the advantage goes to the most responsive individuals (Bjorkman
and Powles 1981; Franco 1986; Ballare etal. 1987,1990,1991; Begonia and
Aldrich 1990; Casal et al. 1990; Smith et a\. 1990; Baraldi et al. 1992; Davis and
Simmons 1994).
Dynamics of Light in Forest Canopies
The conceptual model of vegetation as a dynamic mosaic, called the gap-
mosaic concept (Watt 1947; Bormann and Likens 1979; Shugart and Urban
1989), has generated an interest in the spatial dynamics of canopy gaps and
understory canopies in forest systems. In the northeastern United States,
researchers have investigated the relative importance of gap geometry or
various predominant microsite factors that are known to affect seedling
establishment and growth, such as changes in soil nutrients and moisture
resulting from gap creation and vegetation succession (Runkle 1982, 1985;
Runkle and Yetter 1987; Whitmore 1989; Battles etal. 1995, 1996; Battles and
13
Fahey 1996).
In the Pacific northwest of the US, where portions of this light study was
conducted, researchers have investigated the spatial and biological dynamics of
natural and artificial gaps and have related the information to the ability of
dominant species to use these sites as regeneration niches. Franklin (1963)
studied the species and the success of regeneration in different types of clear-
cuttings in H. J. Andrews forest. He studied strips oriented north and south,
strips oriented east and west, small patches 0.25-4 acres in size, seed-tree
cutting, and staggered-setting clear cuts. Oriented clear-cutting strips were
distributed across various elevations (2,025-2,650 feet) and slopes (60-40%).
Seed-tree cuttings were designed to leave trees in the clearing to act to reduce
soil temperatures by providing shade in the gap, and to act as a proximal source
of seeds for the regeneration effort.
Stand shade was established using a method described by Silen (1960,
cited in Franklin 1963). This method relates tree height to solar elevation, and
slope percent to amount of shade cast from a stand edge. A significant
relationship (p < 0.05) was determined when stand shade was related to the
establishment of natural regeneration of Douglas-fir seedlings (measured in
number per unit area). And when data from the three major types of cuttings
were pooled (east-west strips, north-south strips, and patch clear cuts), a highly-
significant relationship (p < 0.01) between gap shading and regeneration was
found. The east-to-west-oriented strips and patches tended to have stronger
relationships than plots oriented north-to-south. Apparently, in north-to-south-
14
oriented gaps, soil surfaces reached temperatures that were damaging to the
delicate, newly-established seedlings, whereas, in east-to-west gaps,
intermittent sunlight was less damaging than the continuous exposures in other
gaps.
Shugart (1987) compared the mode of tree death to the mode of tree
regeneration to determine that had the greater effect on observed patterns of
species in the forest. Whereas most biologists group factors affecting tree
regeneration and death into broad categories, Shugart coupled these modes into
four roles that trees play in a forest ecosystem based on the dichotomy of
whether species can produce a gap upon death and whether species require a
gap for regeneration. In role 1, species both require a gap for regeneration and
produce a gap upon their death. Role 2 categorizes species that create a gap
upon death but do not require a gap for regeneration. The third category, role 3,
is a tree that needs a gap to regenerate but does not produce gaps at its own
death. And role 4, trees neither create a gap nor do they require a gap to
regenerate.
A representative species from role 1, the yellow poplar (Uriodendron
tulipifera) or tulip tree commonly found in temperate forests in the southern
Appalachians, is described as a species that attains a large size and creates
gaps upon its demise. In addition, these trees require a canopy gap to
regenerate. Seed germination success is best for this species in sites with
adequate moisture and light, i.e., canopy gaps. Seeds are wind dispersed and
survive for long periods in the seed bank, approximately seven years. Hence,
15
these seeds more than likely use a regeneration event quickly when the
opportunity presents itself. Mature trees of yellow poplar are shade tolerant,
and grow to 50-55 m in the canopy. These trees generally die from windthrow,
and standing snags from this species are rare. Yellow poplar provides an
example of a mode of persistence referred to as "gap-phase replacement"
(Shugart 1987). It is important to note that, although species can be assigned to
the roles Shugart described, the effects are not mutually exclusive; hence,
creation of a gap by a species in role 1 can be used as a regeneration niche by
species occupying role 3 in a forest ecosystem, a species that requires a gap for
regeneration but does not create gaps upon its death.
Boreal species at higher latitudes might be affected strongly by the angle
of incident sunlight. At high latitudes, sun angles are elongated relative to the
earth's surface. Thus, shadows cast by standing trees are longer and the area
shaded by trees in this habitat would be larger than trees of the same type found
at lower latitudes. At higher latitudes, the death of solitary trees and the creation
of a small opening in the canopy might not be effective in releasing subdominant
trees in the lower canopy from their competitive disadvantage. Either their death
would not create a gap of sufficient size to affect shade-intolerant species that
require gap creation (role 3), or boreal trees, if shade-tolerant, would neither
create nor require gaps in their regenerative process and could be categorized
as role 4 species.
After studying a range of spatial and temporal scales of disturbances and
the stereogeometry of gaps created by such disturbances in coniferous forests
16
of the PNW, Spies and Franklin (1989) discussed the dynamics of species
interactions during post-disturbance succession. Douglas-fir, a shade-intolerant
pioneer (Swaine and Whitmore 1988; Whitmore 1989), is known to dominate the
canopy after coarse-scale disturbances that open broad patches in the forest
canopy. Douglas-fir does not regenerate well in small, closed gaps where
shade-tolerant species such as western hemlock, western redcedar, and Pacific
silver fir can invade and eventually dominate the canopy.
Fine-scaled disturbance often affect little more than the crown structure of
overstory species (Spies and Franklin 1989), but coarser-scale disturbances
such as root pathogens, wind damage, or pest infestation tend to change
uniform patches in forest canopy created by narrow-crowned, tall species such
as Douglas-fir or broad-crowned shorter species such as hemlock or redcedar,
into a mosaic of openings used as regeneration niches by established seedlings
in the lower canopy. Even shade-tolerant species usually require canopy gaps
to reach the upper strata in old-growth coniferous forests.
Seedling densities (in number m"2) were greater in gaps of both mature
and old-growth forests than in growth under the canopy. In gaps surveyed,
western hemlock seedlings were found, but Douglas-fir seedlings were not found
to be growing in gaps because gap sizes were insufficient for this shade-
intolerant species that requires gaps 300-1000 m2 in size (Spies et al. 1990). In
addition, gaps tended to play a more important role in old-growth forest
regeneration of hemlock. In mature stands, Douglas-fir crowns transmit a
greater amount of light than in old-growth forests because of canopy morphology
17
differences. Crowns were affected by low leaf-areas in younger trees and by
canopy mortality patterns. Hence, increased light availability is rarely due to the
formation of gaps in mature forests, and hemlock, an extremely shade-tolerant
species, is not limited by this low light environment. In old-growth forests, the
canopy is dominated by western hemlock, a broad, closed-canopied species,
and light beneath is extremely limited. Hence, regeneration in old-growth conifer
forests tends to be limited to areas of gap formation.
In the tropics, investigators have studied canopy gap regimes in context
of the intermediate disturbance hypothesis (Levin and Paine 1974; Connell
1978; Terborgh 1992; Terborgh etal. 1996; Vandermeer etal. 1996) that
presents an explanation for the observation that diversity begets stability in
areas that experience low intensity disturbances, but with greater frequency
(Denslow 1980; Brokaw 1985a, 19856,1987; Alvarez-Buy I la and Garcia-Barrios
n CL » o 3 C (0 to i s o w •Jo £ £ 8" p c « s C <D — sz
g> o
0 (0 c -o .2 S
1 £ S g> i I .2 a>
I £ (0 -*£ — CO y> F L. XI <D O) 0 = m H
. § ? e
I J " •§ E"
<" c 3 • 3 J?
« 5 S
i fci
mi
*>W:
;k'
$ ;v. v
vV-V-. -f V <. >/ h.' ,?
>«:5^ "X 44
^ . *
(LU) d e o A d o u e o u ; I L | 6 | 9 H
35
Table 2. Maximum transmissii R/FR ratio values in all ga
on and ps.
Diameter (m) Gap1 % Red % Far Red % Blue R/FR ratio
20 104 0.03 0.03 0.12 8.38
30 106 94.52 191.21 57.60 0.92
50 110 390.22 701.60 69.91 1.61
20 204 0.11 0.18 0.52 1.28
30 206 21.1 28.59 10.66 0.79
50 210 45.69 64.48 27.97 1.09 t Caveat: Gap 110 data are suspect because a different computer program was used to collect values in this gap versus remaining gaps.
Data were presented graphically by gap and also as averages between
two replicate gaps to simplify the comparison of the distribution of light across
the primary axes in the gaps. Because axis ordinates differed between gap
sizes, axes used with averaged data were standardized to facilitate direct
comparisons between sites on each axis. Spectral maps were composed to
assess patterns or trends in the distribution of light in forest gaps of different
sizes. Normalized data were used in these graphical presentations. Also,
maximal values were presented graphically for comparison across all gap sizes.
Results
One-meter Ground Measurements
Figure 3 shows the distribution of the maximal values reported in Table 2
for comparison across gap sizes. R/FR ratio values are read on the secondary
36
oiiBJ y j / y
CO <D
</> T>
CC * £ Li. DC CM CM
0
01 a:
\ i o£ m CM CM
[]
or m
11
( % ) UOjSSIlUSUBJJ_
37
axis. There was a clearly increasing trend in maximum values with increasing
gap size. Differences between replicate gaps were also evident. Percent
transmission for red light (1R and 2R) showed large differences for gaps of the
same size.
The following figures show comparisons of light in different gap sizes
across two primary gap axes, north to south and east to west. Along the north to
south axis, all gap sizes received greater average percent transmissions in red
light toward the northern axis (Figure 4). Along the east to west axis, red light
transmission was more irregular but showed increased values toward the center
for all gap sizes.
The distribution of average far red transmissions was similar to red
transmissions along both the north to south and east to west axes in all gaps
(Figure 5). Patterns were complicated for R/FR ratios. Along the north to south
axis, the trend of R/FR ratios was similar between the 30 m and 50 m gaps, but
R/FR ratios switched and were greatest in the north axis of the 30 m-diameter
gaps (Figure 6). Patterns were bimodal for the 50 m gap; peaks occurred in
both sides of the axes. The smaller gaps generally showed greater R/FR ratios
along the west axis.
The distribution of blue light transmission along gap axes showed a clear
pattern in 20 m-diameter gaps, an increasing trend from one side of the gap to
the other was evident along both cardinal axes (Figure 7).
Distribution maps for all wavelengths in one 20 m-diameter gap, gap 104,
38
Figure 4. Distribution of red light averaged between gap replicates (n=2) by size. Data are standardized to the maximum percent transmission value in each individual gap before averaging.
Distribution of red light All gaps avg by size
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 Fraction of diameter N(+) to S(-)
Distribution of red light All gaps avg by size
C 1 o '</)
.22 0.8 E 0.8 </> sz 2 0.6 h-"D <D 0.4 N 75 E 0.2 o Z o i
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 Fraction of diameter E(+) to W(-)
39
Figure 5. Distribution of far red light averaged between gap replicates (n=2) by size. Data are standardized to the maximum percent transmission value in each individual gap before averaging.
Distribution of far red light All gaps avg by size
c o
'</> CO
E CO c CO
0.8
0.6
o Z
"§0.4 N
I 0.2
! : :
t
: ! !
•:
i • i
20
30
50
0 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8
Fraction of diameter N(+) to S(-)
Distribution of far red light All gaps avg by size
£ 0.8
co 0 . 6
2 0.2
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 Fraction of diameter E(+) to W(-)
40
Figure 6. Distribution of RFR ratios averaged between gap replicates (n=2) by size. Data are standardized to the maximum percent transmission value in each individual gap before averaging.
Distribution of RFR ratios All gaps avg by size
x j 0 . 6
| 0.4
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 Fraction of diameter N(+) to S(-)
0.8
Distribution of RFR ratios All gaps avg by size
£ 0.8
co 0 . 4
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 Fraction of diameter E(+) to W(-)
0.8
41
Figure 7. Distribution of blue light averaged between gap replicates (n=2) by size. Data are standardized to the maximum percent transmission value in each individual gap before averaging.
Distribution of blue light All gaps avg by size
c 1 o
"(/)
.£2 0.8 E 0.8
CO c CO 0.6
"D CD 0.4
#N 15 E i
0.2 hmm
o z. 0
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 Fraction of diameter N(+) to S(-)
0.8
Distribution of blue light All gaps avg by size
£ 0.8
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 Fraction of diameter E(+) to W(-)
42
were compared in Figure 8. Similar patterns were observed for red and blue
light along cardinal axes. Comparing far red transmissions and R/FR ratios, an
inverse pattern was observed. Where far red transmissions were low, along the
west and south plot axes, higher R/FR ratios were seen. Transmission
differences were apparently greater in these areas of the gap than where both
red and far red transmissions were high, along the north and east plot axes.
In the second 20 m gap, gap 204, patterns were more complex (Figure 9).
Red and far red transmissions were low along the west axis, but R/FR ratios
were no higher along this axis than others in the gap. Blue transmissions were
uniform, peaking near the center of the gap and declining toward the axes
boundaries, as was also shown in gap 104 (20 m).
In 30 m and 50 m gaps, percent transmission values were distinctly lower
than was found in gaps 20 m in diameter. In the 30 m gaps, few points along the
cardinal axes showed peaks in transmission, and were generally near the center
of the gaps, except for peaks in all wavelengths along the west axis in gap 206
(Figures 10-11). No obstruction or nearby debris in the gap was noted at this
site. And in both gaps, although red and far red transmissions were low,
patterns in R/FR ratios were pronounced, peaking near the center of the gaps
and declining toward the gap edges.
In gap 110, red, far red, and blue transmissions were more pronounced
along the west axis (Figure 12). In gap 210, peaks were observed in red, far
red, and blue wavelengths near the center of the gap, and extended further
43 >* a.
o S-CO
"O m 0 C N 3 = O) (0 uz P 4-1 £ jz O CD c = <D "O u. <n CO 2: CO C
<5 c Q o
ai "o n ? CO
0
tn JQ
8 Jt-r" *-* ~ m
T3
E § o — CM O)
s i CO
rv CD ro £
? 8
! o
D) C CM -2 0 s |
i— O o
O 0 o
"S -b-
Q. o
(0 CL
E « d
g £ S •4= C 3 — „
& -C
» 1 - S b g »
co E ro
e | l S. x ® •S> <S o u. E —
CO
CD u>
; ; / ' * rmm
/ - > /: "v \ X X
x. V\\
,\x ( \ v r i v ® « /£! B
8 8 8 - o b
i
I / / / / / \CEB325S/
I ) - w \ : v
i ii 1 < m
I M l *
8 8 8 ^ o d
! / / / v \ J •' / < \ N X "
/ X > .* : 7 v \ \ 5
i* • / \_" \/ "^\\f ' "
S / \ \ ) \ X 55 \ /•>. 7.. / ... /» 3 S V >•, \ /cT
greatly reduced in the PAR range (400-700 nm) at heights below 4.2 m. Peaks at
the infra-red end of the spectrum (> 700 nm) remained in evidence throughout
the profile, although greatly reduced in some sites. Readings in the UV portion
of the spectrum were greatly increased near the forest floor as opposed to in the
upper canopy, Only at sites S8 and W8, above 4.2 m heights, were greater
percent transmissions measured in PAR in the upper canopy. At site W8, far red
wavelengths (~ 730 nm) peaked at 4.8 and 5.4 m heights in the canopy.
There was a preponderance of far red light relative to other wavelengths
measured throughout the entire vertical profile at all four sites in plot A (Figure
23). Percent transmissions were highest at site W8 and lowest at site N4. At
sites S8 and E4, transmission of far red light was highest in the lower strata of
the profile. At site W8, far red transmissions were highest above 4.2 m. There
was no trend in far red light distribution at site N4. Blue light was distributed
mostly in the upper strata of the canopy, except at site E4. Red light
transmission was uniform at sites N4 and E4. At S8 and W8, red light
transmissions were greatest in the upper strata, but percent transmissions were
much less at site S8 higher in the canopy.
Plot B.- In Figures 24 a and b, vertical profiles of selected spectra in 1.2
m increments on the north-to-south axis in plot B at sites N4 and S8 are shown,.
The tree canopy did not go beyond the 4.2 m height at site S8. There were
distinct differences in the spectral patterns between sites. Percent transmissions
for all spectral curves were below 0.12%. At 6.6 m in the canopy at site N4, the
138
o Q. c >» Q. O c 8 (0 0
(0 O CL O 0 x: jc o> 3 P
i L l j l i j B L j L i j L i i L i l L i l l <o <o v>
00 <N <D
(U.11H9I3H <D O CO <N <0 O ^ 00 <o<o»o ^ T r < o c o o i * -
(uu) 1H0I3H "O 0 0) (0 (0 C l
W CO -*«» -C D)
O 0
O
8 •E 5 CO CM
£ 3 D)
2 iM
(D (0 ID (ujl 1H0I3H CO CN r-< p O ^ C O < N < 0 0 ^ 0 0 (O <6 lf> ^ «0 CO CN T-* > ^ to
(w) 1HQI3H
139
Figure 24 a. Vertical spectrum for selected heights at sites N4 and S8 in plot B, at La Mucuy, Venezuela. Light sampling done to 4.2 m only at site S8.
N4 S8
WAVELENGTH (nm)
WAVELENGTH (nm)
WAVELENGTH (nm) WAVELENGTH (nm)
WAVELENGTH (nm)
WAVELENGTH (nm)
WAVELENGTH (nm)
140
Figure 24b. Vertical spectrum for selected heights at sites E4 and W8 in plot B, at La Mucuy, Venezuela.
E4 S8
WAVELENOTH <nm)
WAVELENOTH <nm)
WAVE LENGTH (nm)
WAVELENOTH <nm)
WAVELENOTH (nm)
WAVELENOTH (nm)
FET
WAVELENOTH (nm)
WAVELENOTH (nm)
WAVEUENOTH | n m ) WAVELENOTH (nm)
141
spectral distribution was greatest in the PAR wavelengths, 400-700 nm.
Compared to site S8 where UV wavelengths, ~ 300-330 nm, peaked
above other wavelengths at 3.0 m and 4.2 m, percent transmission in UV
wavelengths were attenuated at site N4. Peaks in far red wavelengths were
acute at 6.6 m at site N4, near the canopy top, and again at 4.2 m at site S8 near
the canopy top.
In Figure 24 b, most percent transmission values were below 0.035% at
both sites E4 and W8 on the east-to-west axis in plot B. Peaks in wavelengths
near 300 nm were pronounced at all heights in the canopy for both sites, except
height 6.6 m at site E4, where most light was extremely attenuated. It is possible
the sample fiber was immediately under an object, such as a tree branch, which
obstructed the light path, although care was taken to avoid this circumstance.
Percent transmission in the PAR range was reduced at all heights at both sites;
no values exceeded 0.0025%. Far red wavelengths (730 nm) were uniform at all
heights at site E4, except at 6.6 m where light was greatly attenuated. And at site
W8, far red wavelengths peaked near the top of the canopy, at 6.6 m, and
showed a decreasing trend with increased depth in the canopy, as did UV
wavelengths (300 nm).
In plot B, sites N4 and S8, transmission in red, far red, and blue light
decreased from greater transmissions higher in the canopy (6.6 m) to lower
transmissions deeper in the canopy (1.8 m; Figure 25). Figure 25 shows percent
transmissions were extremely reduced at both sites E4 and W8, < 0.02%. This is
"8 0)
l - i » m
o Q. C
GL O
c s CO 9>
8 QL O
(D JC
jC CD 3 O
TJ 0 (0 CO CO QL
<0 (0
CD
O Q . C
- C D)
0 0
1 Q .
1
iri CM
2 3 CD
L .
"I'D CD
1 4 2
Ul 111 fc: <o
J3- A
s
• n e a it , * rf <4 (u i ) lH9iaH
3 5
I CO
JSL • J L
( - ) 1H0I3H 3 3
"O CD
a)
i i 73 <D
TJ <1)
(D *-
I I K "O 0
- r tu
fc i
1 2 X 0
J Q I" z S 8
s s o CO
g z
d i 111 fiu
8
(W) IHDI3H e < t ( » N i o o « n id wi *1 w ^
( f ) 1HOI3H
143
not unexpected given the reduction in percent transmission in PAR shown at
sites E4 and W8 in Figure 24 b.
Extinction Coefficients
Plot A.- As was found in the smaller gaps in H. J. Andrews Experimental
Forest in Oregon, the vertical attenuation coefficients at La Mucuy, Venezuela
were not uniform throughout the profile because of variability of absorption at
different heights in the canopy (refer to Chapter 2). It appears that the canopy at
La Mucuy was not homogeneous, and that Beer's law might not apply in broad-
leaved tropical montane forests. In plot A, several strata in the canopy appeared
to absorb light at different rates (Figure 26). Greater extinction values were
interpreted as greater light extinction. Strata in which the coefficient values
increased abruptly might indicate areas in the canopy where greater leaf area
ratios might be found.
Changes in distribution of percent transmission values resulted from
abrupt changes in extinction coefficients in the canopy profile. For example, at
site W8 in Figure 23, percent transmission values decrease greatly for red and
blue light transmission between 4.2 m and 4.8 m heights, and more gradually for
far red light transmission. In Figure 26, extinction coefficients decreased at the
4.2 m height in the canopy; attenuation patterns were blue > red > far red, as the
transmission profile indicated.
Plot B.- In Figure 27, extinction coefficients of light in plot B are shown for
the four sites sampled. At site N4, increased attenuation of light occurred at 5.4
m and 2.4 m in the canopy. At other sites, attenuation of light varied at different
magnitudes, even in areas where transmission values were < 0.02%.
Open-Canopy Area Calculated from Hemispherical Photos
The percent open area in canopy over each site in plot A was calculated
from an analysis procedure using hemispherical photos taken at each site in the
plot. Areas of open-sky were regressed with percent transmission of red, far red,
and blue light, and with R/FR ratios measured at each site in the plot. No
significant relationships were found between areas of open canopy and spectral
percent transmission (R2 = 0; p > 0.9832).
Discussion
Light becomes the most limiting environmental factors in tropical montane
forests, assuming that moisture is abundant in cloud forests, even during dry
seasons. At La Mucuy, apart from a few areas in the plots that were exposed to
sunflecks or areas of brief increased solar intensity, most percent transmission
values in these plots were extremely low, generally less than 5%. PAR
measurements in the reference gap indicated that incident light was less than
400 nE m'2 s"1 throughout most of the sampling period. Additionally, cloud cover
becomes a salient factor in the reduction of incident radiation by late afternoons.
Removal of the saturated and near-saturated values from the light
distribution pattern provided a means to determine if low percent transmission
ranges were variable or uniform. The distribution of percent transmissions
across the forest floor showed light under this canopy was extremely variable,
147
even at low percent transmissions. Measurements of fluency rates in each
wavelength were not recorded in this study. Thus, it is difficult to discuss the
physiological relevance of spectral values at such low percent transmissions,
other than to say that if these data typify the light environment in this habitat,
plants that thrive there must be able to function efficiently under such low light
conditions.
The distribution of R/FR ratios in plot A was not uniform. This plot was on
an east-facing hillside with a gentle-to-steep slope in different parts of the plot.
The east edge of the plot was facing the reference light gap and the slope to the
east of the primary north to south cross axis was much steeper, > 30%. The
western half of the plot was on the apex of this slope where the gradient leveled
off. Light transmissions might have been more pronounced on the eastern side
of the plot because of the aspect of the plot or its proximity to the light gap. This
might have resulted in greater R/FR ratios because less red light was
attenuated. However, no patterns were observed in the distribution of red light in
this portion of the gap. Likewise, no pattern was discerned for far red light.
Distributions appeared random and variable. Only when ratioed did the pattern
become evident. The significance of in a difference between 0.2% and 0.4%
transmissions is a matter for further research.
Lee (1987) described R/FR ratios, based on quantum ratios between 658-
662 nm and 728-732 nm, in two tropical forests, La Selva in Costa Rica and
Barro Colorado Island (BCI) in Panama. In full sunlight, R/FR ratios were
148
typically 1.28. In gaps of undefined size, R/FR ratios ranged from 0.59-1.25 and
0.97-1.17, respectively. In sunflecks with diameters < 0.5 m, R/FR ratios ranged
from 0.37-1.17 and 0.58-1.3, respectively. In a typical understory shade
environment, R/FR ratios ranged from 0.17-0.7 and 0.13-0.67, respectively.
Light environments in the understory of a tropical montane forest appear
potentially to be comparable to those found in these other tropical forests. In plot
A, R/FR ratios ranged from 0.085-1.746. In plot B, R/FR ratios ranged from
0.025-1.525. However, the larger ratios were found in sites where sunflecks
occurred at the time of sampling and were atypical of the light environment in
these plots. In general, R/FR ratios were much less than the maximum values
observed, making this type of forest extremely light limited.
The distribution of blue light (430 nm) was random; no trends were
observed in either plot A or plot B. Even with the maximal values removed,
percent transmissions in blue light were very low. Peaks in blue transmission at
sites scattered throughout the plots, although < 0.12% in plot A and < 0.3% in
plot B, might be due to increased scatter from plants adjacent to the sampling
site. Values at these sites do not correspond to peaks in red or far red light, that
would suggest they result from sunflecks occurring through the forest canopy.
Not only was light under a forest canopy heterogeneous, but the vertical
light environment was variable. In plot A, transmission of far red slightly
increased with depth in the canopy. These data were supported by the
distribution of extinction coefficients in plot A. Less far red light was attenuated
149
in the lower strata. Changes in extinction coefficients throughout the canopy
showed that apparent physical differences in the light path were affecting the
light.
In plot B, extinction coefficients were not uniformly distributed throughout
the entire canopy, as in plot A. Distinct patterns in the profiles indicated where
greater attenuation of color occurred. These patterns were supported by the
pattern of color distribution found in this plot.
The distribution of light in a canopy is assumed to follow Beer's law of
exponential absorption if the light path transverses a homogeneous matrix. This
study has shown that light, for the most part, was different in each unique 0.6 m
slice of the forest canopy. Extinction coefficients in both plots showed that the
canopy environment is heterogeneous, and light passing through this canopy is
altered at different rates at different heights in the canopy.
Interpretation of fluctuating coefficient values by the magnitude of change
was a subjective procedure, at best. In future work at this site, extinction values
might be used to predict which strata in the canopy are supporting epiphytic
plant growth. Studies of epiphytes in rainforests is likely to be highly correlated
to the distribution patterns of light in the upper strata of tropical systems. Also,
information about vertical light profiles could elucidate how mature species affect
the nursery of seedlings gaining establishment in their understory. Lastly,
studies of the relationships between species' leaf area ratios and leaf
physiognomy could benefit from a better understanding of how light behaves in
150
different stands of forest trees.
CHAPTER 5
CONCLUSIONS
Objectives
The objectives of this study were to describe the distribution of light
wavelengths in plant canopies. In Oregon, permanently-marked canopy gaps of
different sizes were surveyed to assess patterns of light distribution in conifer
canopy gaps. In Venezuela, two 32 m x 32 m permanent plots were surveyed to
assess patterns of light distribution in tropical montane cloud forest canopy.
Vertical profiles were measured at the center of conifer canopy gaps and
at four points in each square plot in tropical canopy. Extinction coefficients were
calculated and the vertical distribution of light spectra and actinic wavelengths
were assessed.
In Oregon, the relationships between species' seedlings, surveyed in H.
J. Andrews Experimental Forest by Gray (1995), to light spectra in conifer
canopy gaps were determined using linear regression analyses. Seedling
numbers and seedling basal areas (cm2) were used in the analyses.
One of the most important limiting resources in a forest is the light
environment, a heterogeneous resource that varies spatially and temporally in a
forest environment. The complexity of forests, both vertically and horizontally,
directly affects the distribution of light intensity and color. A few guiding
4CL4
152
principles have emerged from decades of research on how light behaves in plant
canopies. Observations of changes in the RFR ratios with plant shading has
been well documented by many researchers. Also, it is usually assumed that
light varies vertically in a forest canopy according to Beer's law of exponential
light attenuation.
Conflicting methodologies in the study of light in different forest systems
have not facilitated our understanding of the relationship between seedling
establishment and patterns of shade and light on forest floors. Although limited
spectral surveys have been conducted in temperate and tropical systems,
essentially no data are available on the distribution of different wavelengths in
temperate canopy gaps or in tropical understory.
The goal of this study was to determine if there are distinguishable
patterns in the distribution of spectral light in contrasting forest environments.
First, spectral surveys were conducted in conifer forest gaps of different sizes.
In this survey, the distribution of light was measured along the cardinal axes that
dissected the canopy openings. Information about seedling establishment and
growth, from a survey conducted by Gray (1995), was examined to determine if
there was a correlation between the patterns of color in forest gaps and numbers
of seedlings or seedling basal areas.
The effect of intensity of light on seedlings is well established; however,
the effects of light color on seedling establishment and growth is less-well
understood. However, no previous study was found which applied the logic that
153
patterns in seedling distribution might correlate to the distribution patterns of
color found in forest gaps. Red, far red, and blue wavelengths affect the
developmental processes in seedlings, and R/FR ratios, and blue light are
known to affect seedling germination. Also, alterations in R/FR ratios have been
shown to affect stem elongation, leaf area ratios, and resource allocation
patterns in plants.
Second, spectral surveys were conducted in a tropical montane cloud
forest. In this survey, the distribution of light was measured in two, 32 m x 32 m
plots under the forest canopy. These data provided a baseline on the spectra of
light found in this light-limited environment.
Light was determined to be distributed in predictable patterns in gaps,
especially contrasting near-center sites with near-edge sites in the temperate
forest. Patterns of shading were controlled in these plots by the southern stand
of trees in a gap (Gray 1995). Early morning light first illuminated the west edge
of the gaps. By mid-day in the 50 m gaps, light was in all but the southern edge
of the gap that did not see much sunlight until later in the afternoon. In addition
to the effect of the path of the sun in northern latitudes, shading in the gap was
affected by standing snags (dead, standing debris), shrubs and brush (such as
Viney maples), and downed logs and stumps left in the gaps (Gray 1995).
In general, PAR was shown to increase according to gap size (Gray
1995). In this light survey, percent transmissions of red light, far red light, blue
light, and R/FR ratios were shown to increase as gap diameters increased.
154
Patterns in the horizontal distribution of color in forest gaps are complex. In
general, axes expected to receive greater percent PAR also received greater
transmissions in red, far red, and blue light. Because these measurements were
taken in large canopy openings with little to no vegetation left standing, this is
not altogether unexpected. Indeed, any variations in distribution patterns could
be attributed to few sources of interference in the downward path of light in
these gaps: snags, stumps, shrubs, and bushes. However, the distribution of
R/FR ratios in these gaps showed some unique patterns. In 50 m gaps, ratios
were lower at the center and edges of the openings. The smallest gaps (20 m
in diameter), showed higher ratios along the south and west axes, where shade
endured longest. Along the east to west axis, the 30 m gaps behaved similarly.
Along the north to south axis, 30 m gaps showed an opposite pattern; ratios
were higher in the north-south transect. In general, these patterns agreed with
the shading patterns observed in gaps, but variations in the spatial environment
might have generated some variation from the expected results.
Blue light has been shown to play a role in the inhibition of seedling
germination (Tanno 1983) and inhibition of seedling elongation (Morgan 1981;
Obrenovic 1992) in some species. Regulation of synthesis of glutamine
synthetase (GS), a regulatory enzyme in the assimilation of ammonia, in species
of Pinus have been shown to be affected by exposure to blue light (Elmlinger et
al. 1994). The vertical profile in canopy gaps showed that blue light, relative to
other wavelengths, was found to be most prevalent near gap floors in 20 m and
155
30 m gaps measured. Based on this observation, the relationship of seedlings
and blue light in canopy gaps were examined more closely.
Vertical attenuation in a forest gap has been assumed to follow Beer's law
that assumes a homogeneous light path (Koslowski etal. 1991). Researchers
have referred to canopy light environments as photohomeostatic (Larcher 1995).
The results of this study showed that light in a forest gap passed along a
heterogeneous path, resulting in greater attenuation rates as light nears the
forest floor. Gap stereogeography and solar radiation patterns interact to define
light patterns reaching openings in forest canopy. Some heterogeny of plant
canopies result from the complex distribution of plant biomass throughout the
forest stand. In forest gaps at northern latitudes, contributions to heterogeny
might be greatly affected by the structure of the stand of trees surrounding the
forest gap.
Successful establishment and growth of seedlings of dominant species in
H. J. Andrews Experimental Forest light gaps were strongly related to changes
in spectral light patterns along axes in canopy gaps. In many cases, greater
seedling numbers were located in the center of gaps, regardless of size. This
would suggest that areas of greater light intensity played some role in seedling
establishment. However, this study found strong associations between the
distribution of colors along gap axes and seedling establishment. In smaller
gaps, all species were affected by ratios of R/FR light, but some unique
relationships were found on different axes. For example, in 30 m diameter gaps,
156
Douglas-fir seedlings were significantly associated with percent transmissions in
blue and red wavelengths on the south axis, where greater shading occurred.
Douglas-fir seedling establishment was affected by transmissions in blue, red,
and far red light on the east axes, also a shaded region of the gap. Likewise,
the east axis had greater associations between red, far red, and blue
transmissions and the successful establishment of western hemlock. Gray
(1995) discussed temperature effects on the establishment of western hemlock;
seedling establishment is prohibited by greater soil temperatures because of
high direct solar radiation in gaps. In addition to temperatures, distribution of
color along axes might strongly affect patterns in western hemlock establishment
(R2 > 0.50). Interestingly, western redcedar showed a preference for blue and
red light transmissions along the south axis only.
In 50 m gaps, Douglas-fir was predominantly found along the west axis,
highly significantly associated with changes in light transmissions along this
axis. No associations were detected for western redcedar in larger gaps.
However, western hemlock was associated with light changes along the cardinal
axes in larger gaps.
Denslow (1980) discussed how distribution of resources can differ
between forest gaps of different shapes and sizes. This study has corroborated
to some extent the suggestion that partitioning of light could occur in conifer
forest gaps. Species distributions along axes in different gaps as well as unique
distributions within individual gaps was demonstrated in H. J. Andrews
157
Experimental Forest.
Germination of seedlings can be dependent on blue and R/FR ratios in
forest gaps, and likely these ratios played a role in the observed patterns of
seedling distribution. Also, species' reported predilection for shade habitat was
supported by the observed distributions of dominant species seedlings surveyed
in H. J. Andrews gaps.
It is important to acknowledge that patterns in seedling regeneration
result from years of exposure to heterogeneous environmental variables, and a
single snapshot in time of light distribution cannot approach a comprehensive
examination of the importance of color in seedling establishment and growth.
The data from varied light environments found in the tropical cloud forest
have indicated that color might be an important physical factor controlling
seedling development and forest regeneration processes. Transmissions
peaked at sites where sunflecks occurred at the time of measurement, but in
general, most percent transmission values were extremely low. Hence, those
species found in this forest must have unique adaptations to survive in this light-
limited forest.
Two plots were surveyed in a montane cloud forest. The light gap was at
the bottom of two steeply sloping hillsides; hence, both tropical forest canopies
sampled were adjacent to a forest light gap. Plot A was permanently established
on the west side of this light gap, and plot B was established on the east side of
the gap, and was greater in elevation by a few meters. Plot A showed greater
158
transmissions in red, far red, and blue light, and greater R/FR ratios than plot B.
Density of plants was not quantified, but physical movements during the light
sampling was more restricted by the vegetation in plot B. The species
composition differed between plots, as well. Trees in excess of 20 m were
common in plot A. In plot B, brambles and shrubs were common in the lower
canopy and might have influenced horizontal light measurements at the 1 m
level.
Time restrictions did not allow for a light intensity survey of the plots, but
shading appeared greater in plot B than plot A. Transmission values in plot B
support this subjective observation.
Color distribution was very heterogeneous, even at very low
transmissions (< 0.05% in plot A; < 0.04% in plot B). One would assume higher
transmissions would radiate to adjacent areas from where maximum
transmissions occurred. However, this generally was not the case. Areas of
greater transmission were dispersed randomly throughout the sampling plots,
with one exception. R/FR ratios in plot A were uniformly greater toward the east
end of the east to west axis. This pattern was attributed to the proximity of the
light gap to this side of plot A and the steepness of the slope along which these
measurements were made, relative to the rest of plot A. And, in general,
transmissions were greater in this area of plot A for red light but not for far red or
blue light transmissions.
It has become apparent that the assumption of an exponential attenuation
159
of vertical light in forest systems has been too simplistic, light environments in
forest systems are more complex, and are more stratified than previously
understood. Attenuation of light became greater with increased depth in the
canopy, resulting in an extremely reduced light habitat near the forest floor.
Seed germination and seedling physiology of species in this forest is dependent
on these changing spatial and temporal patterns of light (Foster and Janson
1985; Kennedy and Swaine 1992; Forget 1992a, £>; Hammond and Brown 1995).
Sunflecks have been shown to often provide the majority of solar energy to light-
limited tropical forests (Chazdon et al. 1996).
In La Mucuy, light transmissions were distributed uniformly throughout the
6.6 m vertical profile of plant canopy in plot A, except for light at sites along the
cardinal axes that showed some transmissions were greater higher up in the
plant canopy. At two sites in plot A, far red light transmissions were higher near
the forest floor than at 6.6 m in the overstory. In plot B, light transmissions were
typically higher up in the canopy and lower near the forest floor for all
wavelengths assessed.
In future work, an assessment of how this variability in the vertical
distribution of color in tropical systems is related to the distribution of prolific
epiphytic species in the plant overstory would be most interesting. Also, this
information can be used to show how species that distribute biomass up in the
plant canopy use light by correlating leaf orientation patterns and leaf area ratios
by species functional characteristics, such as shade-tolerance or shade-
160
intolerance. Close attention to taxonomic relatedness is necessary to optimize
the comparative value of studies conducted by different researchers, and in
different locals.
In order for plants to adapt to light environments, i.e., via selection
pressure, light regimes would have to be predictable. In tropical montane
forests, low light intensities are a predictable variable. However, species have
been shown to be able to acclimate rapidly to brief and unpredictable
occurrences of increased light by sunflecks through small openings in the forest
canopy (Chazdon et ai. 1996). Also, shade-tolerant species, when released
from light suppression, quickly respond by increasing growth rates to optimize
light gap opportunities. This study documents the distribution of color in a
tropical montane cloud forest, but is only a snap-shot of the spatial light
environment that varies temporally as well as spatially. To make improved
assessments in future studies, it would be better to measure light readings
averaged over a full photoperiod and from simultaneous readings from sensors
arranged in a plot distribution both beneath tree canopy and in a canopy gap.
The following conclusions are based upon the findings of the light
surveys. No attempt was made to analytically compare the results of the two
surveys; however, several generalizations can be made regarding the
distribution and effect of color in these two different light environments.
1. The distribution of spectral light in the temperate montane forest gaps
differed relative to the size of the gaps.
161
2. Areas in the gaps receiving more shade tended to show patterns in the
distribution of spectra in a gap, e.g., gap edges versus gap
centers.
3. In the tropical montane forest, horizontally-distributed light
transmissions under a forest canopy are very low, generally < 1 %.
This suggests that cloud forests are extremely light limited.
4. The horizontal distribution of light in the tropical cloud forest site was
generally uniform.
5. The vertical distribution of light spectra in the conifer-forest gaps site
showed greater blue light near the forest floor, relative to other
wavelengths examined.
6. Vertical extinction coefficients in a conifer forest differed for each
unique 5 m slice of the forest gap; attenuation of light in forest
gaps might not follow Beer's law.
7. Vertical extinction of light in a tropical forest differed for each unique
0.6 m slice of the forest overstory; also, Beer's law of exponential
attenuation of light in tropical forest canopies might not apply.
8. Vertical distribution of light spectra are most likely affected by the
geometry of adjacent stands of trees surrounding the gaps; in H. J.
Andrews Experimental Forest, south-standing trees affected
shading in gaps surveyed (Gray 1995).
9. Vertical distribution of light spectra in tropical canopies showed
162
variations in patterns; percent transmission of some wavelengths
were greater higher in the forest canopy.
10. Future work should take into account temporal variations in light a
well as spatial patterns.
APPENDIX
TABLES OF RESULTS FROM LINEAR REGRESSION
ANALYSIS OF SEEDLING DATA AND
CANOPY GAP LIGHT
1 6 4
II }g JS
^.se §> 0 •S."- o J2
^ ( I ) O q S -X o o ^ te d » -g •O I v LU a £ . r j i-« >- C CO CO Ofl) (OQ.U. o £ -g CO -p ^ " « £ i S o g « o • £ = 2 I -s d w S S . w > W T3 (B > « w <D -a xr z £ a: o>ca $ Q) 0 00 :§ + jfi g <5 H "S ° W w JO c « II O « 5 M v - o ~ ra l ^ v § > § & m « ® w a) -JS £,-§ ® « S g 2> o -e .a > * •— F > IS •* "o = C (0 r-TJ .. 0 U3 . J= « I - l ~ a -" .2 > " M UJ
<D +Z O J>» X *** S « m " E H -P cb 3 ? S i : E h- c r ^ jc «r c
<T E c
<0 «(M £
~oj E CD w
cc CC
q:
cr
co: in: oo: o>: in: xr; co; d j o j
o : m: o>: oo:
i^: CM: r^: h-:
in: o : CM: h-: co: o : oo: o : in: co: h-: Is-:
r^: in: oo: IS - : CM: co: co: o>: co: CM: M : M :
o : oo:
o : o : o : o ; o ; o ; o; o ;
in: h»: TT: CO: CM: O : co: o : o j o'j
o : a co: ^t: ^ CM: M : IT co: CM: C o'j o'j c
M <o O: T-; oo: o j o'i d :
co O: o :
o in; o : d :
^ CM CD: in: oo*. CM: CM:
o : o : o'i o : o'i
o>: m-. Is-: O: co
oo: m: co: t - : O; O: o'i o l o'i
O: o :
in CM oo
h-: o : i^:
Is- co cN cm o>: IT
O: oc O: CM: ^
o : o : o : o : c
a> co t- :
in: o : o'i
o CM: o :
a> CM: co:
o : o :
in ^ co h- o o
CM: o : o i o : • •
0>: 0>; cO* oo: m: co: t - : xf, co: h-'i d: T-'i
1: 1: :
m; CM:
O) oo ^ c» CO: CM: co: d i
CM H - ^ T-: in* IT o : O: c d : o'i c
r - o T - ; o> o> o> co oo oo CM CO o CO O> CO T-h-: co CM: CM: r^: O: CO: O: m: co: O: oo: O: O: O: T—. o : R - : o : CM: O: O: • - : T-;: T - ; o : C o i o : o'i o i o i o'i o i o'i o i o'i o'i o'i d : o'i o'i c
in: o : m: CM: IS-: co: o : h-: o : O: o : o : co: CM: ^r: M o>: in: o>: h*: oo: o : m: oo: o>: co: o : CM: o : in: ir *<ti r ~ \ oo : f ^ : c o : <%ti r * - : CM; i n : CM: OO: CO: o : c o : CM; C
o j o | o i o | o | o j o | o | o j o ; d j o j o j o j o j c
r*- co T*"; o ^ co CM o) o o o o m co co d O ; O : co: M ; co: R^: oo: O : O ; CM* OO; M ; o>: Ic. oo: O : O : T - ; CM: R- : T-J oo: m: O : -R-: R-»: o : oc O : co: o : Q : R^: o : -R-#: Q : CM: O : O : H - : O : CM: XT o i o i o i o i o : o i o i o i o i o i o i o i o i o i d i c
• • • • «f • • • • • «f • • • • «* • • • • • • • • • «J • • •• • • • • • • «jf • • • • • •• • • • y • • • • • f * • • • • * • • • • "f * • • * • f • * • * • *f • • * * * *1* * coj T- I T-| CM! co! r^l o>| CM! K coj oo; ooj a>\ cr co: o>: o ; O; m: CM: CM: xr co*. oo CO: co cr co: CM: : i^S oo: O: oo: co: xr: co: o>: o : m: c\ r-'i xr• o'i r-'i xf! xfi cM'i o'i o i CM! CM! iri! CM! o ! d i c
mj co! r^; co« oo! c»i h-; •-« t-| mj co! coj o>! coj coj cc r^: io: o ; m: oo: m; in: o>; oo; co-, m; ^ CM! T - : CO! C ^ i CM: ^ ^ ^ 1 0 ' *"1 co: co: r*»: oo: cc o'i o'i o'i o'i d : o'i o'i o'i o'i o'i o'i o'i r^i o'i o'i c
JC o c J > cc
®j ®! ®! ®j l i l l 3 \ - d -oi -oi -o! *zJi vd a ! a -2: 2: 2: 2: ° - 5 o>S a>: a>: o: Dt: UL: U-: LL m; OQ; m; m; ts; ig; aq K-. cc; a:; u.; a;: eel a
T-i co: h-i coi «t: oi xri cm' *-i coi mi r>-co: co*. CM: r-: r—. co: N: n csi: r-: co: co: o: cm: t-: in: co: m: hs co: o>: m: m: co: oo: h»: co: m: o>: t-: coc r*»: a>: m: cm: oj o| o'i o| oj oi o| o o| d| o; oi
co: co: oo: cl CM: r* t-: c> in: c
o; o; c H oo- «ni CM: CM: oi oi mi oi o: CM: ooi io: O: CM: o>: CM: o*. co: r- t—, o; CM: o>: xj- o CM: CO: co: O: O: cos CM: O: co: O: o: O: o: t-: o: O: co: t- o: o: O: CM: o'l di oi o'i oi oi o: o": d oi oi oi oi
co co: co: oi
co! cd cr l : oc O: IT o'i c
Oi *t\ Oi CM* Q; ^i f-l ClJ T-i N; xl"i 0>; coi ID* r H o> ^ •- co; co h- oo o>: ir>: o>: co: cc mi CM: «>: oo: co: CO: t-: o: CO: co: o: xr: cr
cm! oi coi *-! o'i oi c <: : cm: : :
t-: o: o: CM: T-I o: to: cot i; I; i ; »; I; I; ; |/); I;
co co to cm io co a> H o o> m o cm m: u-h- o cm o>: o: t- CDs cm o <*•: CM: co: t-: cc co: f: CO: O: CO: T: *0: h»: CO: *: u>: CM: CO: O: cn oi o'i o'i T i oi o'i o'i d o'i o'i *-'! oi oi -'i c
r : co: CM: m:
in: o: o>: oo: a>: co: r: 1-: o: h-:
oo: o: r : o>: h-: o: oo: oo: cm: in: an
h-: in: o: o; o; oj o; o; o* o; o;
oa cm: oo: oo: mc o: in: cm: co: cot co: co: cm: co: iq a*: m: co: d oj o; oj oj
co: co: o>: r-: c o: cr ^i c
o'i o'i c
CD o i : O: co: o: o: o'i
0>| o! oi
co-co: CM: O: oo o> oo: o:
o: o: CO; T-; in: o: o: o: di oi
as H cm cm co h- co cc CO: Is-. CO: •«-: co- CO: oc hs ca t-j o: h-: co: m; cm: cc co: Q o: o: O: o: co: o: u o'i d o'i o'i o'i o'i o'i o'i c
co CO: rx
oo o oo: CM co O:
tj-:
o> co: oo: coi cm:
M ooi CM: CO: t-J s: coi irii •: i • ;
CO m,« o'i co: co:
^ oo r : co m: cm T~: CO: CO: o>: mt o>: oo: CM: CO: r-? h-*i csi: co: cot r-: »j w): :
oo co r . o> o o>: oc o'i v-i
in; oo: f"-: i -i oi mi ooi coi coi coi a> crjl co: oo; o>: xf; -rti co: co: ^ h- co! co cm cm t-in: m: r: oq: oo: cq: cq: cm co: co: r : co: m: ^ co: co*: <*! cd: coi co! coi o'i ci coi coi r 'i d: mi c
s i sr1: x1: s1: =*. -j- —i —i: —b —i: —b —i: —b n a: 0.: 0.: a.; Q-: Q.: £L- O: 0. 0. CL O. 0L- CLi g X I Xj X: X: x; Xj x: U x: X: X: X: X: X: I H H H- H K H H H R R R R R R R H —I; —J; —I; —1 _J: _ii _JS
166
§
8
Si
8
<0
O) CO
§
8
"S " 8
s
167
S " s
= * ^ . 2 § > o
« 8 § o t
O C V ^ ££ CO W >- c OT ~
£ a, (5 0. U.
™ £ tf <o £ <o II § £ E S o 8 n c
5 «p —. o £ "E <o co
O) Q) O) <2 CD
= f 5 5 5 7 •O > (rt W_ CD g > ^ = £ 0 : W CCL 5 a) 0
in: i a o : co: co: m : ~ " cm: m: "<t". u>: co: r^: ~<i: int ~ ~ o>: o>:
M in: co: o : o f o ; o : o ; o ; o ; o ; o o ; o ; o ;
co: m : co: Is- ! co: co : cm; co! o : d i
r - : co cm : oo xj-: cm oo: o o" j d
cm cm co: o :
o co m ; 00; co: o : t-: o : o : o :
00 oo CM: O ; co: f^: o : o : 0 1 d i
o in H K o : m: t-: o :
• • •• o : o :
Tf COi T- o T-| O) in: h - xf; r^« o ; co: co • xr: t - co: CM: co: CM: cm : co: a o : o : O : CM: O : o i at o i o'i o i o ! o i
t - o> h* co o : Is-o : m
"£ o 0
1
o co: m :
xt| CO: m :
T-* xt; co:
T—• ' * • co-
T"; T-; co:
CO m i xf:
o O : co:
CM: Is-: £
ci
CO m
^ i
CM m ; O :
co O : o>:
s ! xf;
CD co : o :
h- | T— J xf :
o in CO
"£ o 0
1
t | * i in: 1:
r*; co;
r^i i ;
xfi T—: 1:
h-'i o : A r-i i;
in: •;
^•i m :
• ti
a j
d i o i i •
d
o O : i ! :
: : j i i i : : : ! :
"S. xr: o i xf; o>:
i^: CMi cm! T—; r^:
co| o>: m :
o | wo-rn:
m CM:
5 i in;
co: o j o>; co:
m j
o>:
CO j in q ;
oo j co : co :
oo xt-xr
a3 T-
co: cm: cm*: CM- r^i cm! coi cr* T-: oi! cm! ^*i * • : CMi o 1 a3
T-
co O) c
a> 0 CO
q :
c 0 0
1 o
Q.
8 <D
CM: CM: h-: co: co: co: co: K ^r: co: co: o ; o'i o j
»• * • * «|« * * m • • • • • « «| •> (
CO; coi CM: ^ «n o>: o : ^r: o : o : o :
d : o i o ' i
i n o> co: o>: m O : O : CMi coi r-*i * - : *: CM:
O : co: cm: co:
h-: Cf>: oo: oo: co: co: xr: m :
o ; o ; o ; • • • a|* • • m m • • • • • i
CM xf: o : o i
O) co,* CM: coi co:
00 o cm h-: O : m: t - : o : 0 1 d i
co* O ; CO; ^f: O : co: coi o i co: cm:
t-: co: O o>: co co: oo: coc r^i o : *r2 o'i o ; oc
in- cm! H in; in- r -T-: T-: oj? O : rtl Q d i d i d
co t - H o>: cm oos in: oo: O csii d i CNt in: ^r: «nt
• : c >: •:
0>: h-: oo: co: o>: co: h-: h-:
co: co: : co: cm: h-: m : xf: xr: xr: r^: o :
m : o • - : o o>: xr oo: o
o : o ; o j o : o : o : o
K o i T- : o i t—• T-: O: o: o"! o i
m co i n in o> h» ! o>: t~: o : O : O : m :
xr CM co CM o : co o : i n
0 : 0 : 0 : 0 : 0
x#- o CM CM o i h- i d i d i T |
co- o i O) • co; cp: : r » o>: ^ t : d i coi "r- i co: : : co: : :
00 co co • co o>: xr
t ! w *
r : i 2 i 5 i 3 : *5i ^ 1 H ^t! H <*>: o>j m | co • a> \ * -co: <2: 2;: 3 : co; in ; oo; co: o . CM: co o cm o> 00 CM: in: O : xf: o>;, o : 00; t-j 09 cq: m: o>; o>: h - : cq i N : N : xfi coi coi coi r - i o i co f^i CMi r-'i co i r - i o*
: : r - : r»: : : r - : cm: : : •*—: r - : : : t- : »
I
I CO
CO
1
CO CD
o 0) 04
CO
a): 3 :
CQ; J ! § ; §1 1 1 1 i l • § •§! "si "si a : I m i m l 5 j fej fej j j i jgj a? a:; a q a s K j
: : : H : IL| UJ »• s " ' 5 * ' '
* i « u . P
&
Z j Wj UJj 2 ; CO: UJ: ^ (0; Uij z j CO j 111 1 $
•4, -J : -J | J -J j - j ! - j l -»! J - j l - J i -j": -J:' —J! _ l ! _ i
a g f i s a g a a f ? f i f s f i a i < i i < i i £
168
.SPcCL , 3 oc
"2 "Slit «5
5 . 2 1 • ^
i i v S i
s > i ^ § u: CD to . CD ® £ (B w "
* » S § " 8
g a | " a
•® 2 c S 2 g> (u O ) (0 (0 ~ *5 w oo" "S % - • - o £ »
« : JJ{: X - ^ "coi ^ S : "Jg: g : J;: -g: J-: cr -is: CM: O : t-: co: O : •-: -rn: CM: O : •-: jZi O : O : V • •« *• •• W « •• •« •• W • •• *» W > •» •« o : o : o : o : o : O : o : O : o : O : o : o : o : o : o : c _ ( ; . : c : - - . .. -n
O
c cc c
E
o C3
co: oo: -K: cm:
? i s i c : o «
co rt\ "SS <o -g o
E : <Pi c : o :
coi
l i S | o : r^: c : cm:
co: co:
JS: coi t-: co: *2:: o : co: x : •• •• o >
o : o ; c ;
i 4*
coi coj <ai o>; tg:
m : co: 4S: co: o : g : • i •• W *
o : o : c :
o j coj co* m : co -tt
° i -Si o : o : o :
: •: c :
m : ^r: cm: in: o>: o : o : o :
d | o i
o> i -a> o O): u>: co: l^-: •• M
o : o :
co o> in; T-* cm: O :
*» *«
O: o: cm:
oo: co: o>: tg: «*•: Si <°\ E i o ; c :
co* <5i coi tsi
8 I o : c :
coj coj
8 | l i o*. o :
O : O : o : co: o : -r-: o : o : o : -s: **: co: ^ in: t-: r^: £>i co: l^: &
° : ° i E i ^ i 0 4 i ^ o i o j o j c j o i o j C
• " f
o j o j cm: o h»: o>: ^r: co:
o i o'i
^ i i^i CO;
cq: O :
oo: o i co: :
CM: a>:
I-: -tti coi o>: ir J 5 r». o> c *« u • •» •» >: o : cm: co:
• • • • • • « ! » • • •»« !« mi
co; o>: oo: co; co: co: co co cm *-• co| co cm m i a m i 00: Is-: q>: -g; co: CM: oo -g: co: o> o oo cm cc -S: T-: m : & co: CM: m : iS: O : t- ; co: S i <<tl xr n n ! "* « **'• rti %>i; m ; g » •« •« *» y • •* M •: w » o : o : t-: o : o : r-: o : c : •: : : c : •: : : c :
r-: o : t-: o : o : o :
Z j (0: ail z i coj UJj $ ! z i co! uji z i (0; Uii §
HI: LLJ: Lii: Lii: IDi UJ: LU: UJ: llH ill: UJi UJi UJi ml UJi a S i S : S j S i S i S j S i S i S S i S i S i S : S i S : 2 CO- CO! CO: CO: COi COi COi COi COi COi COi COi COi COi COi cc CL: &»: 0-i Q-: Q-i 0-i Qui 0-: Q-i GL! Q-i CLi Q-i Q-; a
-r-: o>: CM o t- t- ^ H m: CM CO i- o>: o>: Cs O: CM: CO: O: t-: CO: Ot CM: CO: O: O: O: c> o": o: o'i o'i oi O: oi o'i d o'i O: oi o": oi oi c
"<T: O: XT*: O); O: T-J CM: O: O oo: CO: CO: CO: M: IR in: o: o: xf: N-: co: o>: o co: co: Is-: co: o>: cc co: Y-: o>: o>: o>: co: in: oo: cot o: o: oo: in: oo: o>: a co: o: r: m: co: o: in: m: ^ o: m: m: co: co: a>\ oj oj oj oj oj dj oj oj dj oj oj dj dj oj oj c xtf coj T-; o| CM: in| co! mi <£>; h»! co! a>\ co! co! o Is-N; co: CM: co: co: v; t-» co. co: co; r-; t-: o>: O: *• CM: o>: co: m: CM: m: CO: m: o O: h-: in: xf: CM: O:
cq: O: O: r-» O: O: Is-: O: O: t-: O: c o! oi d: oi oi o'i o'i oi d di di oi di o'i oi c CO; XT' G> CO: *0 H C*j CO CM CO CM If in: r-: CM: CM: CO: O: t-: CM CM: CO: xf: CO: o cc O: co: O: CM: O: m: O: t-: ot O: O: r-: r -: CO: O: c oi o'i o'i o'i o'i o>i o'i o'i d m'i di o'i o'i di oi cn
: •: <: : CM: »: •: : : : :
CM! oj Oi\ coj CM! O! T-j CM: «>; T-j xfj o| coj co! a>j c oo; CM: co: o>: o>; o>: o>: CM: o. o>: CM t- oo CM c O: m: o>: Is-: O: t-: co: oo: r-t hs o>: oo: O: co: oc o'i T-'i os "i o'i csi: o'i TF: at T-*! o'i rti o'i o'i o'i ^
"*V ••"V ••••I" ""V **-*T ••••r •"•V •"•T ^i 0>; O; o j T-; Is-: o j CO; co; xt; CO; o> CO in* m; xf; CO; r^: h-: h»: xf; xf: CM: Si in: try. O: O: CM: h-: o: Si o: co: oi o'i o'i ini o'i o'i
N £ n *
o
r-j co! o i
CO; o>: co: O): cm: co:
cm o>: cm: CD: o i
co; h-: m: cm: m: cm: io: in: o j o |
o | coj T"! f ! CO: I*-: o : O: o i o'i
•••V -•••T *
K 0>; CO; CO; o>; T—• xf; xf; oi O; o: in: o'i o'i co'i
CO| CM; T-j CMi H CO; CM| in[ ml r-j coj CO CO: CO; h-; O: O); CO; COs t-; CO; CO; rt: CM: O: r-; m: o>; co: m; o m: t-; co: m; m; t-; O; in: CO: O: m: cot O; in; CO;
O): CM: co: CM: t-; t-; h-; o : h*: xr: o : o : in: o : O: cm: ox i*-: o : cm: co: cm: J**-: o : m: xr: o : xt: ^ o : o : «*: in: m: o : xr; m: co: o ; ^t: in o : o : xr: in: o; o j o j o j o'i o; o j o; de oi oi di o;
§ i CO; in* O; T-| t-; O; CO? CM; O; T-j h»; 1 _ ; CO; CO; CO; <*t; IO; CO: CN| f**-; CO; t-« t-; CO: CO: O: o>: CO: CO: O: co CM: CM: O: CO: O: CM: o>: O: o: t-; o>: r-\ o l^: o>: i-; o: o: o": o'i o: o'i o'i oi oi dc o'i o'i o'i o'i
^ co co t - N. o> co • - xr o O) T- ^ m O -f- CM; xf: T-: ^ CM CO; CO: t- co! T-: co: m; o>; O: co: co t-: O: co: O:
T-j H oj o>j H ooj CM; ooj coj CM? coj coj h»j d)j •" O: tj-; o: m*. CO: t-: o): ia CM: t : O) in <*t\ in; cr CO: O: O: co*. l : o: Cj oo: CO;. O: O: co: f-;, c o': di oi o'i o'i o'i o! di o'i o: di oi oi oi c
r|i —j! -J: —ji -J: Ji -J: >J: «i ^ ^ ,<! .< Pi g pi ps g g fg i<j j< j<i j<i j<i S 8 21 2 ; 8 8 2'= 8 2 S 8 8 ° o o M *~i M H: Hj H: h-{ H H: h-j Hj H; K: I—:
^ c S - a S j c c s? "o = . <D -Q CZ (0 «•— E g s ~ i » •= -n ° ^
c ® w £ £ j3 (0 £ D> 3 ^ ^ E - -D 11 -
S d z 2* 00 TJ W < ^ 1 E • o o t I S 2 ® H . 2
0)
r". w oj *- == P i f £
g ° c | i « 8 E .2 § " „ tn ^ ^ a> w Jr *— •—• $ <D W w. "?t w 1 1 1 $ S o | •? I o> g £ . # 1 2 § 1 E |2 jc 3= o c ^ 5 ±£ ++ *i= C O .2 ^ V) r CD CO <5 i s S i : : £ & » j : S e g o>:5 g II c
I S - : co: oo: in: o>: o>: T"! in: CM: o : IS-: o : CM: o : Oj o i d ; o j oj • • • • » • ....4- "4" *—f o | T-i coi coj co: coi co: r-: t—; CM: oo: m: CM: oo: ^r. o : o'i » o j o j
—*T* • — r o i o>\ t—; oi o co: o i T"! oo: co: yr-i O: o i ^ri d : d i
O o o h-O o>: in CO: CO co: o>: co: CM o i coi
T—: o i
oo: CM: CM: o : Si co;
^ i 1 : o i Oj o i o j —4-••••4* —•4
ooi o>i CO: in: Is-: xf: CM: co: CM: o : co: o j o j o j —4. ""V ooi o>i o>; "*•! Is-: co:
m: co: o i ail
L ; o'j
CM: l -: CM: Oj oj
col xf; oo: io: cv oi
o>! JN: Is-: o:
O: l^: t—: co:
oo: m: o: CM: h»: Tf: o: CM:
Tf:
o j o; .............. oi co; in: oo:
CM: oi oi
r-i ml Si CM: O: : o l o l
CD; A>; "r-j T—; CO: OO!
ml oi t—• T—r I
*o: a>:
LL-j
§?! z l
LLI; LLIj 111 Xi Xi X CO: CO:
O: co: oo:
Oj S i
co:
o>! o>:
co:
o>:
iO; CM: io:
oo oo: co:
to:
co: in: on CM:
o>:
cc 1 or a
c c
a cc CN
a xl CN
o>: oo: I S - : co:
*o O: co:
O:
co: r-: co:
oo oo: CM: co:
tnj
co:
c cc h-a
cn c c c
r-c
CM co: o>:
CM:
a cc c
# |
•D; Q> Qi
T3j <D: •D;
Q> Qi Q:;
£ i LL:
QT; LL; ac\
oc li.
UJ: Xi CO-
CO: Ui:
U L S : X i CO;
\L 2 CC h
175
£ ii &<CL„ "V
"S a.
c Q. jr .« 1 1 8 .. E J2°ui ? H.£ v 2 j= S ^ I ^ S ! » « S OT £ •+•* in w
« ii § 2> "S 3 o | «0£ ™ £ '£ s 2 O) 0 O) {g (0 iE -c *55 o, co = * - - II
o; o; o; o; o; o; o; o; o; oj o; oj oj R^I ^T\ §S.I | * J CM| ooj r-J oo[ *-| oo| coj ioj mj to co: O : O ; ^T: CM: co: oo: co: T : co* I^-: r : t-: o>: CM: CM: VO; oo: <*-: r : CM: co: oo: in: o: o: o: CM: CM: O : R - : CM: o: CM:
•• •• •» •• •• •• •• •» •• «I *• •• o: O : O : O : O : O : O : O : O : O : O : O : O :
h-co: c CM: OC co: a oj c
00; t-T- : c ®i g oi C
CM o R - o>: oi co oo; T-; co; co; o>: d m r : o oj co: CM: co: *n: ^ o>: m: oo; o: i : ^R-: cr m: co: o: o>: CM: O: ^ o>: co: o: m: o: oo: ic h»: o>: o: o: T-: o>: o: CM: o: o: o: CD: o: o: t: CM: CM: C
CO; D> CO M O T - CO CO CO; CO; O O co CM oo in in O co: co: M ; oo: R^: oo CM od r : xr: oo: in: m: CM: co: o: i : r : yti co: co: co: a • l »i «i <i •« *t •« «« H *t *t •* •« •» ••
co: CM: O : m: CM: R^: XR: T - : CO: CO; m: o: o: o: H«
a co CD
o> c aj % co
tn
I
CO a> c5 (0
zj (Oj Ui: $1 zi CO: Ujl Z: C0j Uil Zj (0j III; §
- I I - J ! - J ! - J ! - J ! _J! _J! _J I _JI _J! _J I _ I ! _J! _ I ! _J! _ <: <: <: J<: <: <: <i <• <i <\ <\ <\ < r : r : r : r-: r~: r~: r*: r~: r~: I -: h: hi H H H I-
H : O : ft! RT: N : RT: A : A ; RS: N : R \ I A « A * A * A - R si gj Si gi gj & s ei g Pi Pi Pi P| pi s t—: H: I—: H: I—: h
176
# i I S3
= c O) h-
t O) W HI CO S Si ~ 2 u-(0 (D O W ^ £ £ 9 °- E ® II ° (d c
co| CM! O: •-! CM: co| <r-\ co| io| coi CM! m| CM! o o r- T- o m o o o h- o o o> r~i q: CM: o: o: O: o: O: O: O: O: oi r-: O: o: oi o'i oi oi oi oi oi oi oi di oi di oi
Oi\ it h- cc o: c O: c oi c N; r ^ C\ O: c oi c
> w • • « m mm mm » « • • • • • • • • • • • • • m mmw^ mm •• m + wQtmmmmmifm*
co| ^t| CM| col o>| ai\ o>| io| o>| *t\ <«•: Is-; r^| o| io| a co: O: oo: CM t-i co; in- t-: CO ^ co CM o>: cc O: t-: o: o: t-: O: t-: O : O: t-« O: -r-: O: *• oi oi oi di oi oi oi oi oi oi oi oi oj oj oi c
h-: 00: co: <*: oo: <*: co: WO: T-: <<*; CM: O : o; oj oi 0 co o oo: R^: CM CM: TNI o: o: CM: 01 oi oi OO| ' t j T-j co: ^ co O: CO; p: oi t-j oi
N- T- CO O CO CM CO CM CM O 1- CO Cd CO: *n: in: o>: CM: co co co Is- m CM it co: t-: m: o>: O: co: O: Is-: O; t-: C t-: o: o: CM: CM: o: o: CM: CM: CM: O: O: c o: o: o: o: o: o: o: o: o: o: c v- oo o co t-j co co o co h- m XF: T-: CM: CM: O; co«. co: co; CM H- CO: cc O: O: r : O: p: p: co: oi O: Is-: O: co: c o'i o'i o'i oi oi oi oi o'i oi t- : di o'i c
O; iO; O: co; co.» co; co.- co; co co m co h- oo H o>: O: h-: o>: oo; in; O; co.* CM: coi coi t-j r^j ooi ^ CM: Is-: ^r: CM: oo: in*, m; CM: o>: <*•; m: oo: xr:
cd: a>:
3 : 2l
co; ml I "-! "•! iSi
(Z: <£\
on- a
IL: U. aii a
z j coi iLij z j coi ui; z i <oj uii z! <oi ui; §
tU: UJ; 111: UJ: UJ: UJi UJi Ui: Ui! HI I UI! UI: uj: UI! Ui- U Si S: 5i s; 5: 5i Si 5i Si Si 5: Si 5! Si S: S Wi OT: »: CO: Wi Wj CO; CO; »• C0| CO; CO- {oi COi COi CC CL; a.: 0.: 0.: Q-i Q_: a.: (L; 0.: CL: Q_: Q_: a.- Q-! Q-i a
17 7
#"i C o U) _ <0 .2 co o ^ (0
® ™ z " 0 6
*- ® in *-« £ « S <o — -1-" — s u. Si i* jr co -Jo e x § °- "p
(0 c ™ « v S o f S ? - & ® "E ® S "5
§ ^ | s s - » " =5 Hs t ! CO CM O) II §, O « II s ° ^ s t c
"S £ .<2 g f cr « ® — *= ® § " % > .2" !> ~ V a # 5 8 « £ . « To > J jS + 9 « . £ E i ° "S » c 3 ° V 4= ? W S " "S ® « « B I <2 fc (1)
.12 o | i C
m 5) ® w 0)
S . S i 2
_ E 2 1 ° 05 -+-» 0) >» 4+ E 8 i f u 3 g £ w e l l » CjQ = j I p S g i
• i l i s - E j «*-» O •• r r C i2 a o § E c a> w </> o 4B o »- S w S 1o <o ^ m ® r fl) k •2 ™ ra.S> ® 8 -O £ J2 " E = £ £ § ¥ = f s s l l l ficoi ® 8 & k g 2 - 1 ? =
. 5 c C w
xj of <o •— aJ ^ i3* w. +- +5 c
o * ° . a) c ° = c c £ o CN S . 2 8 « 5 0 H5 -JI w
ffi; 22; 91 SS; fcl 2 ; r*i JQj _ CO* Tf* O* T"' CO* ur>; o i col o | o i xfi K-l d coi xH CM: o i
O: xr: O; O: O: t- : q o : O: t-: co: t-: o : o : O: O: o : O: O: ae O: o : O: r—. o : o i o'i o i o : o i o'i o i d o'i d i d i d i o i
xtf a rti cr o : t-o i c
o> cm co t - r - cm T-l c\| cm co cm o>| o> co H h-: O: T-; O: CO; O: o os o> o o io o ^ cq: p : O: p : O: o : O: o r-: o : O: m: O: o o i o i o'i o i o i o'i d i d d i o i o i o i o'i o'i c
co; CM: <N: T-. m : |v-: cm H N o co H t - oo co cq xf; CM: O: l^: CO; oo: o>: ca CO: co o>: O: CO: r^: r-cm: ^ti r^: CM: m; r**: csi io: xr: h-: t-: xf: T-: IT o i o i o i o'i o i o'i o'i o'i d o i o'i o'i o'i o'i o'i c
<D 0
1 o O
co: co; o : o°: o'i
co: u>: an
cm: h«-; oo; co:
o'i • — • J t
coj io| CM: CM: " ~ !
O: O: o i
io o i o :
o ;
O: o :
oo: t—: 0>: ^r: o'i
H Si!
co: co: io: cm: cm; o>: o>:
CM: io: CQ xf: io: OX co: o>: cot r^: «o: ca
o : co: co: o»;
co: h-: io: h-;
o ; o ; o ; o ; o o ; o ; o ;
CM: r -: o>: o>: o : co: ^r:
o |
o o O: O: O: o :
co- Oi Oi IO; CO; *1 O: Q O: o : o
o co; O: o :
t*i o j o :
o : o : o : o : o ; o : o : o o : o ;
—1 a>\ coj coi o : co: O: O: o'i o'i
coi O: o i
io; O: O:
•••r ....y —•1-"••T ioj T-! O:
o | K O:
io; O: O:
o i CM: xt:
o'i o'i o i o'i
o i co* N t—; O; T-; O: O: Oi Oi o i d
to •O: co: o i
co! T-! O: o'i
••"V coi coi o to: xf: o : <Dl co: o i r-i d i
CM: xi a>: io: o : o>: cc xr; cm; c o ; o'i c
•••••J 4— CM; H C| x-: o> r-co: xf; c> o : o : o'i o i cj
H cn xr: cr
2ti S : £°: ^ *-! <*>: o>l *+\ coj coj c xt: o : O: co: i^: CM: io; co: t-; cm: h* o> xr oo io c xr; CM: p ; xf; CO: O: p : l^: xjj p« p ; r^; csj: CM: o i C •-i coi CM: xti r^\ xfi cMi xf'i rA coi oi: xri o i coi x-i cr
-J: -J; -J: _J: _i: _i: _J: _i _i: _J: _j: I: k i: a.; q.: a.; o.; a a . ql cl; d j cl; a.; cl; a.; a.; a.; i E S Ei S ? ! E: S ? ! 2 .Xj I | x i X; X| X; 3 H h H h H J—: h~: H: I—• Kj H I - : H H H
a>: co: o>: xf: co: co: o : o : o : ° ! ° i ^ i o i o j o'j
r"i CM: co* co; O: CM: O: co: r^: co: co: O: o i o i o":
CM; * - : o>: h*: o>: xf; O : O : CM: d i o ! o i
co: h-: CM: xf: co: t - ; co: CM: t— ; o : O: t - j o : o : o : t - :
xf: i o : 10: CM: r^: o : io: m: o : o : co: o>: o : o : o : oo:
co: co: CM co: xf: i t oo: co: c: oo: a
o ; o ; o : o ; o ; o ; o ; o ; o ; o j c
oof coi r*-i i^-i ^ i ooj o | o | cr co,* U): t - j o : • - : co: c oo: CM: o>: O: O: oo: c cm: «*•: CM: o : o : o : c
o i o'i o : d : o : o'i d : o i o i o : c
Si csi: O: CO: CO: co: t - : cm: co: co: t - :
.T............ r - j t - | N; CO CM: T - T- : o>: O: O: CO:
o i o i d i
o oo io xi": T-: oo: r - : o : O: oo: uii o'i d i o i
r - t - c\ m- O; cv o : o i c o i t™i c
t - co io cm co m oo o co t - co o co o o> a in\ t - j co; i ^ : o>: CM: o co xr : o CD; o i O : o>: o>: a oo: co: co: m: o : oo: oo: oo: O : io: oo: m: x f : CM: c\ xf: d i o i o i co'i d i o ' i o i CM*i t^: o i o i m": T^i o ' i i -
(0 O)
££
<D O
o a
n
c JS <D > CO
<n
to o o
co
in: on i o>:
5>i ^ i o i o i
co: O): in: h-: co: co: co: cm: oo: cm; o : co: o j o i o j
co: xt: in: oo: o j
m: oo: t - : o>: o : O: o>: t - : x r : cm: co: in: co: t - : o>: r - i co: oo: o : cm: x f : t - : o : h - : o>: t - : o : cm:
co: oo: cs o i CMi a oo: t - : jv
o : o ; o : o ; o ; o ; o ; o ; o ;
co oo o>: CMi t - : in: O: o : d i o'i
t - m T-: CM: xf: xf; o i co'i
0 O 1 -CM t - h-CO: r - : o : o : CM: o : 01 o i o'i
t - ; xf; t - j co: col t - : t - : co: T-: o'i o i o i
co co cm xi- o o r^ t - : <o: t - : m; O : m : m ; t - ; O : i^: xf; o : O : t - ; O : CO: o : o : cm: o : o : x - ; cm: o : o'i o i d i o'i o'i d i o'i o'i
co: *oi coi o ! t-5 coi m; r - ; xfr: xt; o>; m; O: CO: u); xf: o : O: O: CM: O: in: CMi o i o i d i o i o i d i o'i
co co cv CM: io: cc o : O: c o : t - : c o i o'i c
o x- x| i -: co: c\ m: xt; cr d i c
coi T"i o>: ooj coi r -: oo: co: co; t - ; co: xf: a>; oo: coi ini co: co'i ini
CO o : xf CM O CM T-r**: oo; co: ooi co xf: oo: cq: co: coi xfi io! r^i co:
co oo r -: co; co: o>:
o co oc — — CC
c\ T - i S i t - : |s-: o : cc
1 ! I ! s i §i a ! s i | i "gi ui 2 ! £ i £ m j mj mi s ; w; fej a:; oc\ d£| K j a
U_: U.
z j coi uj; 5 i z i wi mi $ i z i coi u i ! $ i z i coi uii §
UJ: UJ: uj; UJ: UI: UJ; uj: uj; UJ; UJ: UJ: UJ; UI: UI: UJ: U X : X : X : X : X : X : X i X i X : X : X i X i X : X i X i I C0 CO CO W <0 CO: CO; CO; CO; CO; CO; CO; CO; CO; CO; V. H : H-; I - : I - : H i l - i t- i H-: l - i I - : t - i I - : H i h
179
. ® OC. 09
£ £ ^ C V c «j .2 (go _ </> JS co c « Oh-t <D 3 3 o>z 5 o
o>° m
2 ® •= " (0 £ Ul UJ .. — +•* — « IX. s " s L 55 <a-o a. g
• so m «= I 8 * g 8 •§ ® = - ~ S"£ • g-o « r ~ £ ® T3 >" c XI Q. £ ® o P
5 s £ S i £ 8 j 2
I 2 « s £ s; c ®
o ;3-2
! ? § * - i § ° ? 1 » S
-- a> "S = -g >r ^ "SS uj C II ^ W « Q ^ A) - -C (A ® 4,! r J2 ^ ® W W -c -S ® 1? ts 8 » o 2 £ " 2 E 5 c ° ( 5 « $ ^ l - H - § £
*- $£ •£ 21 O W - f j ^ r +* O C O r C ® QLO C £ C « (n 'a g 5 o ^ *X £ & CO 8 s i | N ^ ^ C7> ™ > **?*• 2 £ -s> £ w § - 0- 0) tf> I— (O •2 ? "S « tr »
ffim-S 8 8 a :
<2 £ 2 .8 £ 1 _ O T3 C « 2 of w - ai -r? ±s "W >» . p
lO: O) CO o CO o in: r^: m; cm: O: •t •• »« o: o: o:
T-! Oi T-j cm in o t-: CM: CM:
co: O): hs h-: o: rx t-: t-: cm: o: co: o : o: t-j o: o j o'i oj o'|
oo* h»; co- co-o>: o>: co: CM: T": t-; o>; CM: CM: T-: x-: d i o i ol o i
CO: CO; oo cm t- t-4 -*-• O: O: co: ^t:
t-: o: CD: rt: o: co: o: o : o i o ;
•«*4 4-cm! mi T-; OO: h-: oo: cm: t-:
• • •• o: o :
CM t-io CM O: o :
io: O: r »: ul ^t: in: cm: r-co: o>: co: Is-o>: i*"*: r-i ^ d ; o j o j c
O; T-j 00; CN Oj co: o>: cr O: o: o>: o o: o : o : c o i o i o i c
o>i ooj T-j d cm.* CM: m: a t—; T-j *ti o
i -: o>; O; O: K; CM; o>: CO: t*: co m oo r -i oo H CM: CO: ^t: o>: o>: oo: l^: t- ; co: m; •-• o i co o i - : oo: CM: CO: CO: ^r: CM: oo: co: h-: CO: in: a •» 'i •• •• _* i •# •» i •» •» •# •» •« >( in: O: •*-: co: t-: t-: co: t-: t—: : m: cm: o :
cm: t-j oo: o>: cm: m: m: cm: • i •• ° : Of
"—4 4 co- mj oo: r-: in: o: o: o i o i
o h-h-:
-J; O: co:
•—•I *•-coj o j T-; o>: t-: o : cd: a»i
co: o>: r^: r*»: co: m: r^: CM: co: o : h*:
2 : Si o : o: co: o>: co:
Oj Oj Of o: o ; •i i t >: o j ooj »: oo; in
co: co: O: o: o: o i o i d i
s i r^i cm! 0 coi O: co: O: O : 01 o'i
co: CM: O: t-: co: m: co: co: in: ° i ^ o>: o'i oj Oj —4 f* 4' a>i r-; cd co: o
O: O : t-: o: o : o'i ol o i
h-: O): O: h-: xr: T-: co: o>: ^r: cm: o :
r -: oo: h-in: co: ^ ^r: o co: r-: cr
o i o : o i o< o ; c •—4 4 •••—4-in* coj CMj m i*. in: CM: cm: O: t~: o : o'i d i o i
T-i coi oo: cf O: o>: cr o: o: c •• o: o : c
1 ^ oo o>
•-; xf: o: #-*: *-%: —c: o: o : o:
o>; o i r - :
i n i n ; O :
m ; O :
oo; N ; O :
00 co: CD:
oil T-;
"M"; oo o :
i n * h - i r - :
o o>: CM:
«?] o ' i o i o j o i o i o j r ^ i t •
—-4- •—4- • • •4 - 4*
: i
• — 4 - —•4- . . . -4 co j CO; O):
o j co : o>:
co j
S j T-; CO: CM:
i n j CM: m :
oo j co: i n ;
l ^ i o o :
co j CO t- j
CM; o i i r-:
cd: o ' i H o i : d j o i T-:
r-i t—:
co; ^ Is-i r
O T) co: ^ cm5 c
O) c JE 0 > CO
CO 3
CO Q>
o
(0
*•+ : +• : +f ; "Oi T3; •oi a>: Oi Q): Q i £L\ Ql\
tti CC: a:; a LL-: U-: IL: U
IJL: U-i
z j col ui; § : z i to; uj; 5 : zs coi ui; z j w| uij 5
-Ji ^ -J < : < : < i < i < i <1 < i < i ^ t t : Hi Hi Hi Hi Hi Hi Hi Hi Oi Oi Oi Oi Oi Oi p j p j Oi ^ r-: r—: r—: r-: I—: r-:
< : <C' < : <t H K Hi Hi Hi Hi h O: O: p i p i p : Oj C
- J—; |-H: Hi H: Hi
LITERATURE CITED
Ackerly, D.D. 1996. Canopy Structure and dynamics: Integration of growth processes in tropical pioneer trees. In S. S. Mulkey, R. L. Chazdon, and A. P. Smith, editors. Tropical Forest Plant Ecophysiology. Chapman and Hall, New York, N. Y.
Ackerly, D. D., and F. A. Bazzaz. 1995. Seedling crown orientation and interception of diffuse radiation in tropical forest gaps. Ecology 76(4): 1134-1146.
Alvarez-Buylla, E. R., and R. Garcia-Barrios. 1991. Seed and forest dynamics: A theoretical framework and an example from the neotropics. The American Naturalist 137(2): 133-154.
Anderson, Margaret C. 1966. Some problems of simple characterization of the light climate in plant communities. In R. Bainbridge, G. C. Evan, and 0. Rackham, editors. Light as an Ecological Factor. John Wiley and Sons, Inc., New York, N.Y.
Aphalo, P. J., D. Gibson, and A. H. Di Benedetto. 1991. Responses of growth, photosynthesis, and leaf conductance to white light irradiance and end-of-day red and far-red pulses in Fuchsia magellanica Lam. New Phytologist 117:461-471.
Ballare, C. L., R. A. Sanchez, A. L. Scopel, J. J. Casal, and C. M. Ghersa. 1987. Early detection of neighbor plants by phytochrome perception of spectral changes in reflected light. Plant, Cell, and Environment 10: 551-557.
Ballare, C. L.,A. L. Scopel, R., and A. Sanchez. 1990. Far-red radiation reflected from adjacent leaves: An early signal of competition in plant canopies. Science 247: 329-332.
. 1991. On the opportunity cost of the photosynthate invested in stem elongation reactions mediated by phytochrome. Oecologia 86: 561-567.
181
Baraldi, R., G. Cristoferi, O. Facini, and B. Lercari. 1992. The effect of light quality in Prunus cerasus. I. Photoreceptors involved in internode elongation and leaf expansion in juvenile plants. Photochemistry and Photobiology 56(4): 541-544.
Barrett, D. R., and J. E. D. Fox. 1994. Early growth of Santalum album in relation to shade. Australian Journal of Botany. 42: 83-93.
Battles, J. J., T. J. Fahey, and E. M. B. Harney. 1995. Spatial patterning in the canopy gap regime of a subalpine Abies-Picea forest in the northeastern United States. Journal of Vegetation Science 6: 807-814.
Battles, J. J., J. G. Dushoff, and T. J. Fahey. 1996. Line intersect sampling of forest canopy gaps. Forest Science 42(2): 131 -138.
Battles, J. J., and T. J. Fahey. 1996. Spruce decline as a disturbance event in the subalpine forests of the northeastern United States. Canadian Journal of Forest Research 26: 408-421.
Begonia, G. B., and R. J. Aldrich. 1990. Changes in endogenous growth regulator levels and branching responses of soybean to light quality altered by velvetleaf (Abutilon theophrasti Medik.). Biotronics 19: 7-18.
Bjorkman, 0., and S. B. Powles. 1981. Leaf movement in the shade species Oxalis oregana. I. Response to light level and light quality. Light Level and Light quality Year Book - Carnegie Institute of Washington, Annual Report of the Director, Department of Plant Biology. 80: 59-62.
Bormann, F. H., and G. E. Likens. 1979. Pattern and process in a forested ecosystem. Springer-Verlag, New York, N. Y.
Briggs, W. R., and M. lino. 1983. Blue-light-absorbing photoreceptors in plants. Philosophical Transactions of the Royal Society of London Series B, Biological Sciences 303: 347-359.
Brokaw, N. V. I. 1985 a. Gap-phase regeneration in a tropical forest. Ecology 66(3): 682-687.
• 1985 b. Treefalls, regrowth, and community structure in tropical forests. In S. T. A. Pickett and P. S. White, editors. The ecology of natural disturbance and patch dynamics. Academic Press, Inc. New York, N. Y.
182
Brown, N. D., and T. C. Whitmore. 1992. Do dipterocarp seedlings really partition tropical rain forest gaps? Philosophical Transactions of the Royal Society of London Series B, Biological Sciences 335(1275): 369-378.
Canham, C. D. 1989. Different responses to gaps among shade-tolerant tree species. Ecology 70(3): 548-550.
Casal, J. J., R. A. Sanchez, and D. Gibson. 1990. The significance of changes in the red/far-red ratio, associated with either neighbour plants or twilight, for tillering in Lolium multiflorum Lam. New Phytologist 116: 565-572.
Chazdon, R. L., R. W. Pearcy, D. W. Lee, and N. Fletcher. 1996. Photosynthetic responses of tropical forest plants to contrasting light environments. In S. S. Mulkey, R. L. Chazdon, and A. P. Smith, editors. Tropical Forest Plant Ecophysiology. Chapman and Hall, New York, N. Y.
Clark, D. B., D. A. Clark, and P. M. Rich. 1993. Comparative analysis of microhabitat utilization by saplings of nine tree species in neotropical rain forest. Biotropica 25(4): 397-407.
Collingborne, R. H. 1966. General principles of radiation meteorology. In R. Bainbridge, G. C. Evans and 0. Rackham, editors. Light as an Ecological Factor. John Wiley and Sons, Inc., New York, N.Y.
Collins, S. L., S. M. Glenn, and D. J. Gibson. 1995. Experimental analysis of intermediate disturbance and initial floristic composition: Decoupling cause and effect. Ecology 76(2): 486-492.
Connell, J. H. 1978. Diversity in tropical rain forests and coral reefs. Science (Washington D. C.) 199:1302-1310.
Cornelissen, J. H. C. 1993. Aboveground morphology of shade-tolerant Castanopsis fargesii saplings in response to light environment. International Journal of Plant Sciences 154(4): 481-495.
Davis, M. H., and S. R. Simmons. 1994. Far-red light reflected from neighboring vegetation promotes shoot elongation and accelerates flowering in spring barley plants. Plant, Cell, and Environment 17: 829-836.
Denslow, J. S. 1980. Gap partitioning among tropical rainforest trees. Biotropica 12(suppl.): 47-55.
183
Elmlinger, M. W., C. Bolle, A. Batschauer, R. Oelmuller, and H. Mohr. 1994. Coaction of blue light and light absorbed by phytochrome in control of glutamine synthetase gene expression in Scots pine (Pinus sylvestris L.) seedlings. Planta 192: 189-194.
Endler, J. A. 1993. The color of light in forests and its implications. Ecological Monographs 63(1): 1-27.
Environmental Systems Research Institute, Inc. 1994. Arc/Info, Version 7. Redlands, CA
Evans, G. Clifford. 1966. Study of woodland light climates. In R. Bainbridge, G. C. Evans and O. Rackham, editors. Light as an Ecological Factor. John Wiley and Sons, Inc., New York, N.Y.
Floyd, B. W., J. W. Burley, and R. D. Noble. 1978. Foliar development effects on forest floor light quality. Forest Science 24: 445-451.
Forget, P-M. 1992 a. Regeneration ecology of Eperua grandiflora (Caesalpiniaceae), a large-seeded tree in French Guiana. Biotropica 24(2 a): 146-156.
. 1992 b. Seed removal and seed fate in Gustavia superba (Lecythidaceae). Biotropica 24(3): 408-414.
Fosket, D. E. 1994. Plant Growth and Development: A Molecular Approach. Academic Press, Inc. Australia.
Foster, S. A., and C. H. Janson. 1985. The relationship between seed size and establishment conditions in tropical woody plants. Ecology 66(3): 773-780.
Franco, M. 1986. The influence of neighbours on the growth of modular organisms with an example from trees. Philosophical Transactions of the Royal Society of London Series B, Biological Sciences. 313: 209-225.
Frankland, B., and R. J. Letendre. 1978. Phytochrome and effects of shading on growth of woodland plants. Photochemistry and Photobiology 27: 223-230.
Franklin, J. F. 1963. Natural regeneration of Douglas-fir and associated species using clear-cutting systems in the Oregon Cascades. U. S. Department of Agriculture. General Technical Report PNW-3.
184
Freyman, S. 1968. Spectral distribution of light in forests of the Douglas-fir zone of southern British Columbia. Canadian Journal of Plant Science 48: 326-328.
Gray, A. N. 1995. Tree seedling establishment on heterogenous microsites in Douglas-fir forest canopy gaps. Ph. D. Dissertation, Oregon State University, Corvallis, OR.
Grime, J. P. 1981. Plant strategies in shade. In H. Smith, editor. Plants and the daylight spectrum. Academic Press. New York, N. Y.
Hammond, D. S., and V. K. Brown. 1995. Seed size of woody plants in relation to disturbance, dispersal, soil type in wet neotropical forests. Ecology 76(8): 2544-2561.
Hendry, G. A. F. 1993. Plant pigments. In P. J. Lea and R. C. Leegood, editors. Plant biochemistry and molecular biology. John Wiley and Sons. New York, N. Y.
Hirose, T., and M. J. A. Werger. 1995. Canopy structure and photon flux partitioning among species in a herbaceous plant community. Ecology 76(2): 466-474.
Holmes, M. G. 1981. Spectral distribution of radiation within plant canopies. In H. Smith, editor. Plants in the daylight spectrum. Academic Press, New York, N. Y.
Holmes, M. G., and H. Smith. 1977. The function of phytochrome in the natural environment. I. Characterization of daylight for studies in photomorphogenesis and photoperiodism. Photochemistry and Photobiology 25: 533-538.
Jans, L., L. Poorter, R. S. A. R. van Rompaey, and F. Bongers. 1993. Gaps and forest zones in tropical moist forest in Ivory coast. Biotropica 25(3): 258-269.
Jensen, J. R. 1996. Introductory digital image processing. A remote sensing perspective. Prentice-Hall Publishing, Upper Saddle River, N. J.
Kasperbauer, M. J. 1988. Phytochrome involvement in regulation of the photosynthetic apparatus and plant adaptation. Plant Physiology and Biochemistry 26(4): 519-524.
185
Kay, S. A., B. Keith, K. Shinozaki, M. L. Chye, and N. H. Chua. 1989. The rice phytochrome gene: Structure, autoregulated expression, and binding of GT-1 to a conserved site in the 5' upstream region. Plant Cell 1(3): 351-360.
Kelly, L. G. 1967. Handbook of numerical methods and applications. Addison-Wesley, Reading, Massachusetts, pp. 48-51.
Kennedy, D. N., and M. D. Swaine. 1992. Germination and growth of colonizing species in artificial gaps of different sizes in dipterocarp rain forest. Philosophical Transactions of the Royal Society of London Series B, Biological Sciences 335(1275): 357-366.
Koslowski, T. T., P. J. Kramer, and S. G. Pallardy. 1991. The physiological ecology of woody plants. Academic Press, Inc. New York, N. Y.
Lamprecht, H. 1954. Estudios selvicuturales en los bosques del valle de La Mucuy, cerca de Merida. Universidad de Los Andes, Facultad de Ingenieria Forestal.
Larcher, W. 1995. Physiological plant ecology, 3rd edition. Springer-Verlag, New York, N. Y.
Lee, D. W. 1987. The spectral distribution of radiation in two neotropical rainforests. Biotropica 19(2): 161-166.
Lee, D. W., K. Baskaran, M. Mansor, H. Mohamad, and S. K. Yap. 1996. Irradiance and spectral quality affect Asian tropical rain forest tree seedling development. Ecology 77(2): 568-580.
Levin, S. A., and R. T. Paine. 1974. Disturbance, patch formation, and community structure. Procedures of the National Academy of Sciences. 71: 2744-2747.
Loiselle, B. A., E. Ribbens, and 0. Vargas. 1996. Spatial and temporal variation of seed rain in a tropical lowland wet forest. Biotropica 28(1): 82-95.
Lowman, M. D., and M. Moffett. 1993. The ecology of tropical rain forest canopies. Trends in Ecology and Evolution. 8(3): 104-107.
Mancinelli, A. L. 1989. Interaction between cryptochrome and phytochrome in higher plant photomorphogenesis. American Journal of Botany 76(1): 143-154.
186
McCormac, A. C., G. C. Whitelam, M.T. Boylan, P. H. Quail, and H. Smith. 1992. Contrasting responses of etiolated and light-adapted seedlings to red-far red ratio - A comparison of wild-type, mutant and transgenic plants has revealed different functions of members of the phytochrome family. Journal of Plant Physiology 140(6): 707-714.
McNellis, T. W., and X-W Deng. 1995. Light control of seedling morphogenetic pattern. The Plant Cell 7:1749-1761.
Messier, C., and P. Bellefleur. 1988. Light quantity and quality on the forest floor of pioneer and climax stages in a birch - beech - sugar maple stand. Canadian Journal of Forest Research. 18: 615-622.
Mitchell, P. L., and F. I. Woodward. 1988. Responses of three woodland herbs to reduced photosynthetically active radiation and low red to far-red ratio in shade. Journal of Ecology 76: 807-825.
Mohr, H., and H. Drumm-Herrel. 1983. Coaction between phytochrome and blue/UV light in anthocyanin synthesis in seedlings. Physiologia Plantarum 58: 408-414.
Morgan, D. C. 1981. Shadelight quality effects on plant growth. In H. Smith, editor. Plants and the daylight spectrum. Academic Press. New York, N. Y.
Obrenovic, S. 1992. Blue light perception by plants. Journal of Photochemistry and Photobiology B: Biology 14:146-150.
Oliver, C. C., and Larson, B. C. 1996. Forest stand dynamics, updated edition. John Wiley and Sons, Inc. New York, N. Y.
Popma, J., F. Bongers, and J. M. del Castillo. 1988. Patterns in the vertical structure of the tropical lowland rain forest of Los Tuxtlas, Mexico. Vegetatio 74: 81-91.
Raven, J. A. 1983. Do plant photoreceptors act at the membrane level? Philosophical Transactions. Royal Society of London. Series B. Biological Sciences 303: 403-417.
Robinson, N. J., A. H. Shirsat, and J. A. Gatehouse. 1993. Regulation of gene expression. In P. J. Lea and R. C. Leegood, editors. Plant biochemistry and molecular biology. John Wiley and Sons. New York, N. Y.
187
Rokich, D. P., and D. T. Bell. 1995. Light quality and intensity effects on the germination of species from the Jarrah (Eucalyptus marginata) forest of western Australia. Australian Journal of Botany 43: 169-179.
Runkle, J. R. 1982. Patterns of disturbance in some old-growth mesic forests of eastern North America. Ecology 63:1533-1546.
. 1985 Disturbance regimes in temperate forests. In S. T. A. Pickett and P. S. White, editors. The ecology of natural disturbance and patch dynamics. Academic Press, New York, N. Y.
Runkle, J. R., and T. C. Yetter. 1987. Treefalls revisited: gap dynamics in the southern Appalachians. Ecology 68: 417-424.
Russell, G., P. G. Jarvis, and J. L. Monteith. 1989. Absorption of radiation by canopies and stand growth In Russell, G., B. Marshall, and P. G. Jarvis, editors. Plant canopies: Their growth, form and function. Cambridge University Press, New York, N. Y.
Salisbury, F. B., and C. W. Ross. 1985. Plant physiology, 3rd edition. Wadsworth Publishing Company. Belmont, CA.
SAS Institute, Inc. 1990. SAS, Version 6. Cary, N. C.
Schwartz, A., and D. Koller. 1978. Phototropic response to vectorial light in leaves of Lavatera cretica L. Plant Physiology 61: 924-928.
Shugart, H. H. 1987. Dynamic ecosystem consequences of tree birth and death patterns. A set of computer models predicts long-term behavior of forests. Bioscience 37(8): 596-602.
Shugart, H. H., and D. L. Urban. 1989. II. Factors affecting the relative abundances of forest tree species. In P. J. Grubb and J. B. Whittaker, editors. Toward a more exact ecology. Blackwell Scientific Publications, Oxford, England.
Silen, R. R. 1960. Lethal surface temperatures and their interpretation for Douglas-fir. Ph. D. Dissertation, Oregon State University, Corvallis, OR.
Smith, A., K. P. Hogan, and J. R. Idol. 1992. Spatial and temporal patterns of light and canopy structure in a lowland moist forest. Biotropica 24(4): 503-511.
188
Smith, H. 1983. The natural radiation environment: Limitations on the biology of photoreceptors. Phytochrome as a case study. Symposia of the Society for Experimental Biology 36:1-18.
. 1984. Introduction. In H. Smith and M. G. Holmes, editors. Techniques in photomorphogenesis. Biological Technique Series. Academic Press, New York, N. Y.
Smith, H., J. J. Casal.andG. M. Jackson. 1990. Reflection signals and the perception by phytochrome of the proximity of neighboring vegetation. Plant, Cell, and Environment 13: 73-78.
Smith, T. M., and M. Huston. 1989. A theory of the spatial and temporal dynamics of plant communities. Vegetatio 83(1-2): 49-69.
Spies, T. A., and J. F. Franklin. 1989. Gap characteristics and vegetation response in coniferous forests of the Pacific northwest. Ecology 70(3): 543-545.
. 1991. U. S. Department of Agriculture. General Technical Report PNW-GTR-285.
Spies, T. A., J. F. Franklin, and M. Klopsch. 1990. Canopy gaps in Douglas-fir forests of the Cascade mountains. Canadian Journal of Forest Research 20: 649-658.
Steege, H. Ter., C. Bokdam, M. Boland, J. Dobbelsteen, and I. Verburg. 1994. The effects of man made gaps on germination, early survival, and morphology of Chlorocardium rodiei seedlings in Guyana. Journal of Tropical Ecology. 10:245-260.
Strauss-Debenedetti, S., and F. A. Bazzaz. 1996. Photosynthetic characteristics of tropical trees along successional gradients. In S. S. Mulkey, R. L. Chazdon, and A. P. Smith, editors. Tropical Forest Plant Ecophysiology. Chapman and Hall, New York, N. Y.
Swaine, M. D., and T. C. Whitmore. 1988. On the definition of ecological species groups in tropical rain forests. Vegetatio 75: 81-86.
Taiz, L., and E. Zeiger. 1991. Plant physiology. The Benjamin/Cummings Publishing Company, Inc., Redwood City, CA.
189
Tanno, N. 1983. Blue light induced inhibition of seed germination: The necessity of the fruit coats for the blue light response. Physiologia Plantarum 58: 18-20.
Terborgh, J. 1992. Maintenance of diversity in tropical forests. Biotropica 24(2 b): 283-292.
Terborgh, J., R. B. Foster, and P. Nufiez V. 1996. Tropical tree communities: A test of the nonequilibrium hypothesis. Ecology 77(2): 561-567.
Thomas, B. 1981. Specific effects of blue light on plant growth and development. In H. Smith, editor. Plants and the daylight spectrum. Academic Press. New York, N. Y.
Thompson, W. A., P. E. Kriedemann, and I. E. Craig. 1992 a. Photosynthetic response to light and nutrients in sun-tolerant and shade-tolerant rainforest trees. I. Growth, leaf anatomy, and nutrient content. Australian Journal of Plant Physiology. 19:1-18.
Thompson, W. A., L. -K. Huang, and P. E. Kriedemann. 1992 b. Photosynthetic response to light and nutrients in sun-tolerant and shade-tolerant rainforest trees. II. Leaf gas exchange and component processes of phtosynthesis. Australian Journal of Plant Physiology. 19:19-42
Uhl, C., and K. Clark, N. Dezzeo, and P. Maquirino. 1988. Vegetation dynamics in Amazonian treefall gaps. Ecology 69: 751-763
Vandermeer, J., D. Boucher, I. Perfecto, and I. G. de la Cerda. 1996. A theory of disturbance and species diversity: Evidence from Nicaragua after hurricane Joan. Biotropica 28(4 a): 600-613.
Vezina, P. E., and D. W. K. Boulter. 1966. The spectral composition of near ultraviolet and visible radiation beneath forest canopies. Canadian Journal of Forest Research 44:1267-1284.
Vince-Prue, D. 1983. The perception of light-dark transitions. Philosophical Transactions. Royal Society of London. Series B. Biological Sciences 303: 523-536.
Watt, A. S. 1947. Pattern and process in the plant community. Journal of Ecology 35: 1-22.
190
White, P. S., and S. T. A. Pickett. 1985. Natural disturbance and patch dynamics: An introduction. In S. T. A. Pickett and P. S. White, editors. The ecology of natural disturbance and patch dynamics. Academic Press, Inc. New York, N. Y.
Whitmore, T. C. 1989. Canopy gaps and the two major groups of trees. Ecology 70(3): 536-538.
Woodward, F. 1.1989. From ecosystems to genes: The importance of shade tolerance. Trends in Ecology and Evolution 3(4): 111-115.
Yavitt, J. B., J. J. Battles, G. E. Lang, and D. H. Knight. 1995. The canopy gap regime in a secondary Neotropical forest in Panama. Journal of Tropical Ecology. 11:391-402.
Zar, J. H. 1984. Biostatistical Analysis, 2nd edition. Prentice-Hall, Inc. Englewood Cliffs, N. J.
Zeiger, E., S. M. Assmann, and H. Meidner. 1983. The photobiology of Paphiopedilum stomata: Opening under blue but not red light. Photochemistry and Photobiology 38(5): 627-630.