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Scientifica Acta 2, No. 2, 65 – 69 (2008)
Experimental Ecology and Geobotany
Multi-scale investigations of alpine vascular plant species in
theSan Juan Mountains of Colorado, USA GLORIA target region
Julie CrawfordDipartimento di Ecologia del Territorio,
Università di Pavia, Via S. Epifanio, 14, 27100 Pavia,
[email protected]
The Global Observation Research Initiative in Alpine
Environments (GLORIA) is an internationally co-ordinated long-term
observation project that assesses and predicts vascular plant
diversity change due toaccelerating climate change. There are
currently 40 GLORIA target regions worldwide; the San Juan
Moun-tain target region (SJM) of southwestern Colorado, USA is one
of these. This study uses the baseline datacollected at SJM for
immediate interpretation of current vegetation composition,
abundance, richness, anddiversity at different spatial and
taxonomic scales. It employs a wide range of multivariate
techniques usinga continuum of distance coefficients to isolate the
relative importance of species composition and speciesabundance on
the SJM summits.
1 Introduction
Climate affects vegetation composition and distribution both
directly (e.g. temperature) and indirectly (e.g.soil moisture).
Human-induced global climate change is a well-documented fact. In
recent decades, thewestern mountains of the United States have
experienced some of the largest temperature increases in thenation,
resulting in reduction in stream and spring flow, increase in
evaporation and evapotranspiration,increase in wildfire severity,
and outbreaks of tree pathogens [16, 17, 24]. It is estimated that
with continu-ation of current emissions releases, this pattern will
continue and the west may have increases of over 8˚Fby 2100 [17].
This increase would significantly impact snow pack, stream flow,
and land surface drying.The documented 2-3 degree increase in
temperature in the western mountains over the last 30 years
hasalready led to species moving to higher elevations [5, 7, 14].
This movement of vegetation upslope hasbeen seen worldwide [6, 8,
9, 18, 19, 20].
The Global Observation Research Initiative in Alpine
Environments (GLORIA) is an internationallycoordinated long-term
observation project that uses alpine plant and temperature data to
assess and pre-dict biodiversity change due to accelerating climate
change. Data collection follows a rigorous protocoldeveloped by the
international GLORIA program (www.gloria.ac.at). Currently,
worldwide, there are 40active GLORIA target regions, 12 in set-up,
and 17 planned. In the summer of 2006, The Mountain
StudiesInstitute of Silverton, Colorado set up the fifth GLORIA
target region in the United States in the San JuanMountains of
southwestern Colorado (SJM) (Figure 1). Four summits ranging in
elevation from 3,717.0meter (12,195 feet) to 4,234.9 meter (13,894
feet) in the Lake City Caldera were chosen based on GLO-RIA summit
selection criteria [21]. In this study, the SJM data are used as a
contemporary investigationinto alpine plant species in relation to
scale. As scale is recognized to be important in ecology [25],
andmulti-scale studies are better able to investigate the many
abiotic and biotic factors that influence and helpexplain
vegetation richness, association, pattern, and distribution [10,
27, 28], this study investigates fourlevels of spatial scale and
two levels of taxonomic scale.
1.1 Methods
Field data collection and data input strictly followed the
GLORIA Field Manual – Multi-Summit Approach[21]. Low impact
monitoring plots were installed on each of the four summits using a
specific observation
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66 Scientifica Acta 2, No. 2 (2008)
Fig. 1: GLORIA target region set up in the San Juan Mountains of
southwestern Colorado, USA.
protocol. Sampling design included four upper and four lower
summit area section plots and a series of 1x 1 meter plots per each
aspect of each summit. Plots of varying size allowed for a
comparison of spatialscale. In total, plot areas follow: sixteen
10-meter summit area sections = ∼ 6,000 square meters,
sixteen5-meter summit area sections = ∼2,500 square meters, and of
both the sixteen 2 x 2 meter plots and sixty-four 1 x 1 meter plots
= 64 square meters each. Two taxonomic scales, species and family,
were alsoinvestigated. Multivariate analyses follow the work of M.
J. Anderson [1, 2, 3, 4].
1.1.1 Results
There were a total of 97 vascular plant species from 28 families
found within the plots of SJM. Thisrichness value is ranked 16th
among the current target regions worldwide. Thirty-five of the 97
totalspecies are considered alpine obligates [11, 26] and are most
threatened by global climate change. SJMspecies with a more arctic
distribution are also greatly threatened, and those species at
their southern limitof distribution are at risk of local extinction
[14]. Two alpine obligates that are endemic to Colorado,
Drabastreptobrachia and Penstemon hallii, are at risk of total
extinction. Twenty-two of the 97 total plant speciesobserved on the
four alpine summits of SJM are considered subalpine or lower
elevation species [11, 26].This suggests the effects of climate
change over recent decades are already in progress, that is,
species aremoving up in elevation. The lowest elevation summits of
SJM are at greatest risk of loosing their alpinecharacter due to
encroachment of lower elevation species. Plant diversity may
actually increase over time,however, species composition is
expected to change in the future.
In general, species richness and diversity were greater with
increased plot area (Figure 2). This followsa well-documented rule
in ecology that more area equals more habitats (and microhabitats)
available forcolonization and greater species richness (e.g.
species-area curves; [15, 23]). Alpine environments containa great
number of microhabitats created by such factors as contrasting
exposure and variable snow coverand substrates. In SJM, the
measured abiotic factors of percent cover of scree and litter, as
well as overallplot area were the most important factors
influencing vegetation composition and abundance. Other studieshave
shown that alpine plant species richness is tied with slope aspect;
south and east aspects having highestrichness [6, 13, 22]. With a
sample size of just four summits within SJM, there was only a trend
that southand east slopes were more floristically rich. Overall,
the highest summit was least floristically rich andhad the highest
cover of scree, the second highest summit had the highest species
richness and a variety of
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Scientifica Acta 2, No. 2 (2008) 67
Fig. 2: Species richness and diversity plotted with symbols
proportionate to the plot area, San Juan Mountain GLORIAtarget
region, Colorado, USA.
Fig. 3: Species richness in the 2 x 2 meter, 5- and 10- meter
summit area section plots by summit and aspect, San JuanMountain
GLORIA target region, Colorado, USA. Plots from left to right:
lowest to highest in elevation.
microhabitats, and the two lowest summits had intermediate
richness levels and more gentle slopes withless scree (Figure 3).
This illustrates that habitat, not elevation, has greatest
influence on the alpine plantsof SJM.
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68 Scientifica Acta 2, No. 2 (2008)
The aggregation of finer taxonomic scales into coarser scales
distorts data by underestimating speciesrichness [12]. Here, the
highest richness on any one peak was 47 species. To further dilute
this to thenumber of families represented by these 47 species, 18,
made the results less strong. Richness by specieswas much greater
and more irregular than richness by family, though similar trends
occurred for bothtaxonomic scales. Beta diversity, the measure of
differences in species across the four summits, variedby spatial
scale, but was similar for both taxonomic scales. At larger spatial
scales, when looking atcomposition only, beta diversity was
greatest in the highest summits; when looking at abundance
only,beta diversity was greatest on the lowest summits. In both
instances, the opposite was true of the smallestspatial scale.
Because the choice of dissimilarity measure has important
implications for interpreting test results andobserved patterns, a
continuum of distance coefficients were used in most multivariate
analyses. Theintermediate spatial scale, the smallest taxonomic
scale, and the distribution measures of Jaccard and Man-hattan
proved to be the best at finding differences in the dataset of SJM.
Due to the variety of habitats andplant species found at SJM,
multiple spatial scales were necessary to capture the full extent
of the alpinevegetation of SJM.
Acknowledgements Special thanks go to my family and friends, Dr.
John Wood, Dr. Graziano Rossi, Dr. KorenNydick and the Mountain
Studies Institute, the American Alpine Club, the Colorado Mountain
Club Foundation, andthe Conservation Biology Wilderness Research
Class of Truman State University. In memory of GN and Shan.
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© 2008 Università degli Studi di Pavia