Short-Term Response of Forest Birds to Experimental Clearcut Edges (Respuestas a Corto Plazo de las Aves de Bosque a Bordes Creados Experimentalmente por Tala Rasa) Author(s): Marc-André Villard, Fiona K. A. Schmiegelow and M. Kurtis Trzcinski Reviewed work(s): Source: The Auk, Vol. 124, No. 3 (Jul., 2007), pp. 828-840 Published by: University of California Press on behalf of the American Ornithologists' Union Stable URL: http://www.jstor.org/stable/25150340 . Accessed: 28/01/2013 08:25 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. . University of California Press and American Ornithologists' Union are collaborating with JSTOR to digitize, preserve and extend access to The Auk. http://www.jstor.org This content downloaded on Mon, 28 Jan 2013 08:25:02 AM All use subject to JSTOR Terms and Conditions
14
Embed
Short-Term Response of Forest Birds to Experimental ...web.umoncton.ca/umcm-conservation/files/umcm-conservation/wf/w… · Short-Term Response of Forest Birds to Experimental Clearcut
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
Short-Term Response of Forest Birds to Experimental Clearcut Edges (Respuestas a Corto Plazode las Aves de Bosque a Bordes Creados Experimentalmente por Tala Rasa)Author(s): Marc-André Villard, Fiona K. A. Schmiegelow and M. Kurtis TrzcinskiReviewed work(s):Source: The Auk, Vol. 124, No. 3 (Jul., 2007), pp. 828-840Published by: University of California Press on behalf of the American Ornithologists' UnionStable URL: http://www.jstor.org/stable/25150340 .
Accessed: 28/01/2013 08:25
Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jsp
.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact [email protected].
.
University of California Press and American Ornithologists' Union are collaborating with JSTOR to digitize,preserve and extend access to The Auk.
http://www.jstor.org
This content downloaded on Mon, 28 Jan 2013 08:25:02 AMAll use subject to JSTOR Terms and Conditions
SHORT-TERM RESPONSE OF FOREST BIRDS TO EXPERIMENTAL CLEARCUT EDGES
Marc-Andre Villard,1'4 Fiona K. A. Schmiegelow,2 and M. Kurtis Trzcinski3
^Canada Research Chair in Landscape Conservation, Departement de biologie, Universite de Moncton, Moncton,
New Brunswick E1A 3E9, Canada;
2Department of Renewable Resources, University of Alberta, Edmonton, Alberta T6G 2H1, Canada; and
department of Biology, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada
Abstract. ?Numerous studies have addressed the potential consequences of
increasing the density of edges through human activities, but most have docu
mented responses to existing edges. Here, we monitored the response of seven
forest bird species to experimentally created edges around five plots (10 ha, n = 3;
25 ha, n = 2) in the boreal mixed-wood forest of Alberta, Canada. We also mapped
bird detections in six control plots (10 ha, n = 5; 25 ha, n =
1). The focal species were Least Flycatcher (Empidonax minimus), Red-eyed Vireo (Vireo olivaceus),
Yellow-rumped Warbler (Dendroica coronata), Black-throated Green Warbler (D.
virens), Ovenbird (Seiurus aurocapilla), Mourning Warbler (Oporornis Philadelphia), and White-throated Sparrow (Zonotrichia albicollis). In the two breeding
seasons
following experimental clearcutting, we
quantified birds' responses to edges in
the absence of substantial edge-induced changes in vegetation by comparing the
distribution of detections between treatment and control plots. We predicted that
forest-edge specialists would be attracted to edges, forest-interior specialists would
avoid them, and interior-edge generalists would show a neutral response. None of
these predictions was consistently supported among plots and years, except in the
Mourning Warbler. However, none of the significant responses was the opposite of predictions. We also predicted that postharvest colonization of treated plots
would mainly involve forest-edge specialists, whereas most local extinctions
would involve forest-interior specialists. Only the colonization of 10-ha fragments followed the predicted pattern. The relatively neutral response to forest edges we
observed suggests that, in general, boreal forest birds do not respond to the edge
itself or to proximate cues of edge proximity. Rather, significant responses may be
delayed until edge-to-interior gradients in vegetation are established. Received 30
March 2005, accepted 14 July 2006.
Key words: edge effects, field experiment, forest landscape, forest management,
Tambien mapeamos las detecciones de las aves en seis parcelas control (10 ha,
n = 5; 25 ha, n =
1). Las especies focales fueron Empidonax minimus, Vireo olivaceus,
Dendroica coronata, D. virens, Seiurus aurocapilla, Oporornis Philadelphia y Zonotrichia
albicollis. En dos epocas reproductivas subsecuentes a los cortes experimentales, cuantificamos las respuestas de las aves a los bordes en ausencia de cambios
substanciales en la vegetacion inducidos por el borde, comparando la distribucion
de detecciones entre las parcelas control y de tratamiento. Predijimos que las
especies especialistas de borde serian atraidas a los bordes, que las especies de
interior de bosque los evitarian y que las especies generalistas de interior y de
borde tendrian una respuesta neutra. Ninguna de estas predicciones se
cumplio sistematicamente entre parcelas y anos, excepto para O. Philadelphia. Sin embargo,
ninguna de las respuestas significativas fue opuesta a las predicciones. Tambien
predijimos que la colonizacion post-cosecha de las parcelas de tratamiento
involucraria principalmente a
especies especialistas de borde, mientras que la
mayoria de las extinciones locales involucraria a especies especialistas de interior
de bosque. Solo la colonizacion de fragmentos de 10 ha siguio el patron predicho. La respuesta relativamente neutra a los bordes de bosque que observamos sugiere
que, en general, las aves de los bosques boreales no responden al borde en si ni a
sehales directas de la proximidad del borde. Las respuestas significativas podrian ocurrir mas tarde, una vez que los gradientes en la vegetacion desde el interior del
bosque hacia los bordes se hayan establecido.
Habitat edges influence the distribution of
many bird species: some cluster their territories
along edges, whereas others tend to avoid them
(Kroodsma 1984, Lanyon and Thompson 1986, Noss 1991, McCollin 1998, Renfrew et al. 2005).
Compared with the number of forest-edge "spe
cialists," relatively few species have been shown
to actively avoid forest edges (Baker et al. 2002), and even fewer exhibit consistent edge avoid
ance across studies (McCollin 1998, Villard
1998). It is critical to determine whether this lack of consistency is real, or whether it reflects
the lack of a general conceptual framework to
properly analyze, interpret, and compare pat terns in edge response (Ries et al. 2004).
Among the variety of mechanisms that
may explain significant positive or negative
responses to forest edges by woodland birds,
we distinguish three types: "access," "proxi
mate cues," and "ultimate cues." First, spe cies may be attracted toward edges because
they facilitate access to resources in adjacent
patches (Lanyon and Thompson 1986, McCollin
1998, Ries and Sisk 2004). Second, species may respond to proximate environmental cues
found near edges, such as
particular vegetation structures (McCollin 1998, Imbeau et al. 2003),
microclimatic conditions (Chen et al. 1999),
edge-related variations in food abundance
(Burke and Nol 1998, Ibarzabal and Desrochers
2004), or perhaps the presence of interspecific
competitors (Bollinger and Gavin 2004) or cer tain nest predators (Winter et al. 2000, Chalfoun
et al. 2002, Ibarzabal and Desrochers 2004,
Morton 2005). Third, ultimate effects of edges on
reproductive success may promote dispersal either away from or toward edges (e.g., Foppen and Reijnen 1994, Bollinger and Gavin 2004).
Thus, birds may respond either to proximate cues (the forest edge itself or conditions associ
ated with edge habitat) or to ultimate cues (e.g.,
edge effects on vital rates). When proximity to
an edge has consequences on individual fit
ness, an ability to use proximate cues would
represent a major advantage for individuals
possessing it.
To date, most studies investigating the spa tial response of forest birds to edges have been conducted in sites with pre-existing edges (e.g.,
Hansson 1983, Kroodsma 1984, Noss 1991,
Germaine et al. 1997, Flaspohler et al. 2001,
Manolis et al. 2002). In such cases, responses to proximate cues from the vegetation may be
more difficult to distinguish from responses to other proximate cues (microclimate, abun
dance of food, or nest predators), because the
This content downloaded on Mon, 28 Jan 2013 08:25:02 AMAll use subject to JSTOR Terms and Conditions
830 VlLLARD, SCHMIEGELOW, AND TrZCINSKI [Auk, Vol. 124
influence of the vegetation is difficult to control
(but see Kristan et al. 2003). However, edge-to interior gradients in forest vegetation
are not as
strongly developed in the first years following clearcut harvesting (Harper and Macdonald
2002), providing opportunities to reduce con
founding effects.
Here, we measured the short-term response of forest bird species to experimentally cre
ated clearcut edges. We mapped bird territories
during the breeding season preceding clearcut
harvesting of the forest adjacent to our study
plots, and during the two subsequent breeding seasons. Seven species
were common enough
among plots and years to be included in the
analyses: Least Flycatcher, Red-eyed Vireo,
Yellow-rumped Warbler, Black-throated Green
Warbler, Ovenbird, Mourning Warbler, and
White-throated Sparrow (see Table 1 for scien
tific names). Collectively, these species represent a wide range of nesting and foraging strategies
(ground, shrub, and canopy nesters; ground for
agers, foliage gleaners, and aerial insectivores). We also examined population turnovers (local
extinctions and colonizations) for all other song bird species present in the study plots.
We tested the following predictions: after
clearcutting, (1) species classified as forest-inte
rior specialists would establish territories farther
from actual forest edges than from control-plot
boundaries, (2) species considered to be forest
edge specialists would defend territories located
closer to clearcut edges, whereas (3) territory location in relation to clearcut edges
or control
plot boundaries would not differ significantly for
interior-edge generalists. Finally, we
predicted that (4) in treatment plots, most postharvest col
onization events would involve forest-edge spe
cialists, and that most local extinctions would be
detected among forest-interior specialists. Ries
and Sisk (2004) pointed out that such a priori pre dictions should be made only when information
on habitat quality and resource distribution is
available for both sides of the edge. In the study area, only one of the seven species considered,
the White-throated Sparrow, is known to nest
and forage in recent clearcuts (Hannah 2001).
Experimental edges were sharp immediately
postharvest, with scattered shrubby patches and woody debris left in clearcuts. Therefore,
it is safe to assume that clearcuts represented nonhabitat for six of the seven species examined
during the present study. Preference or avoidance of forest edges by
certain species has important conservation
implications (Ries et al. 2004). For example, these phenomena would strongly influence the
amount and quality of habitat available for a par ticular species in a given landscape. Although
edge avoidance is routinely assumed by authors
Table 1. Comparison of predicted and observed responses of seven passerine bird species to
experimental clearcut edges in the first two years postharvest (see text for details).
Predicted Observed Observed
Species response (10-ha plots, P) (25-ha plots: R, P / F, P)
Least Flycatcher Neutral No data Yr 1: At (0.002) / N (0.90)
(Empidonax minimus) Yr 2: At (0.001) / N (0.22)
Red-eyed Vireo Avoidance Yr 1: N (0.94) Yr 1: N (0.27) / Av (0.076)
(Vireo olivaceus) Yr 2: N (0.33) Yr 2: N (0.42) / N (0.36)
Yellow-rumped Warbler Avoidance Yr 1: N (0.47) Yr 1: N (0.25) / N (0.51)
(Dendroica coronata) Yr 2: N (0.18) Yr 2: N (0.67) / N (0.78) Black-throated Green Warbler Avoidance No data Yr 1: Av (0.033) / N (0.63)
(D. virens) Yr 2: Av (0.055) / N (0.13) Ovenbird Avoidance Yr 1: N (0.17) Yr 1: N (0.11) / N (0.86)
(Seiurus aurocapilla) Yr 2: N (0.19) Yr 2: Insufficient data
Mourning Warbler Neutral Yr 1: N (0.29) Yr 1: N (0.44) / N (0.98)
(Oporornis Philadelphia) Yr 2: N (0.62) Yr 2: N (0.22) / N (0.24) White-throated Sparrow Attraction Yr 1: N (0.61) Yr 1: N (0.59) / N (0.37)
(Zonotrichia albicollis)_Yr 2: N (0.79)_Yr 2: N (0.68) / N (0.86) Note that there are two pairwise comparisons per year among 25-ha plots. Responses consistent with predictions are in bold.
See text for details on study design. Abbreviations: R = riparian fragment, F =
upland fragment, N = neutral, At = attraction,
Av = avoidance.
This content downloaded on Mon, 28 Jan 2013 08:25:02 AMAll use subject to JSTOR Terms and Conditions
Fig. 1. Map of study area, 200 km north of Edmonton, Alberta. Calling Lake occupies the north
east corner. Plot codes refer to controls (C), upland fragments (F), and riparian (lakeshore) frag ments (R). Smaller plots are 10 ha in size and larger ones 25 ha.
This content downloaded on Mon, 28 Jan 2013 08:25:02 AMAll use subject to JSTOR Terms and Conditions
836 Villard, Schmiegelow, and Trzcinski [Auk, Vol. 124
significantly when comparing 10-ha plots and
controls for both forest-interior specialists and
forest-edge specialists (G test, Gad]
= 9.77, P =
0.021), whereas the difference between 40-ha
plots and controls was not significant (P =
0.20). As predicted, most colonization events in frag ments involved forest-edge specialists (Fig. 5), but this was evident only in 10-ha fragments, where species turnover was greatest. There
were relatively few local extinctions, either in
fragments or controls, and the proportions of
forest-interior and forest-edge specialists going
locally extinct were similar. Interestingly, the
most striking pattern was the large proportion of colonization events in control plots involv
ing forest-interior specialists. These paralleled a
sharp increase in overall abundance in these
sites in the second year following harvest
(Schmiegelow and Hannon 1999).
Discussion
In spite of the diverse life histories of the seven
species considered, the dominant pat tern was one of neutral short-term response to
clearcut edges, especially in the smaller frag ments (10 ha). Neutral responses were predicted
in only two of those seven species. At the level
of species assemblages, the predicted influx
of forest-edge specialists was observed in 10
ha fragments, but numerous colonizations by
20 j-1
18 10-ha fragments H
16 El 40-ha fragments I 14 Controls r?i
8 12 I I 10 I
Is ^ I
1 1 LE(I) LE(E) C(l) C(E)
Fig. 5. Number of local extinctions (LE) and
colonizations (C) recorded in the study plots over the first two years following experimen tal clearcut harvesting. Data are
grouped by habitat-use category (I
= forest-interior special
ists, E = forest-edge specialists).
forest-interior specialists were also observed in
control plots. This latter result mirrors patterns in overall abundance, where total numbers of
individuals detected by point counts in the control plots increased significantly in the sec
ond year following harvest (see Schmiegelow et al. 1997, Schmiegelow and Harmon 1999). By contrast, overall number of individuals detected
in the treatment areas remained stable, despite
apparent colonization by forest-edge special ists (F. K. A. Schmiegelow unpubl. data). Thus,
experimental harvesting resulted in shifts in bird distribution across the study area in the first two
years postharvest (see Schmiegelow et al. 1997),
but these shifts were not reflected in predicted short-term responses by individual species on
the basis of existing edge-response classifica
tions. However, none of the patterns observed
was the opposite of predictions (i.e., avoidance
instead of attraction or vice versa). Therefore,
one could attribute the low predictive success
of the edge-response classification we tested to
alternative factors, such as low statistical power
(Murcia 1995). Nevertheless, to our knowl
edge, the present study is among the few field
experiments measuring forest birds7 response to
edges that feature spatial and temporal controls
and, at the 10-ha scale, replication. How can we
interpret these results? Four
types of explanation come to mind: (1) environ
mental conditions in our study region
or study sites are
atypical, (2) our results reflect a lack of
sensitivity in our approach to the measurement
of species' responses or low statistical power,
(3) existing classifications of bird species with
regards to their response to edges are invalid,
or (4) many boreal bird species do not or cannot
use proximate cues to detect edge habitat.
Disturbance regime and response to forest
edge.?As noted above, the study area is
characterized by an active fire regime, and
large-scale anthropogenic disturbance (for
estry, exploration for oil and gas) is recent.
Hence, one could hypothesize that forest
bird populations of north-central Alberta
are relatively unresponsive to the treatment
because they have evolved in a fine-grained,
highly dynamic landscape (Mutch 1970, Perera et al. 2004) where habitat edges dominate "natural" landscape mosaics. Longer-term
monitoring of responses at a regional scale is
necessary to determine whether newly created
anthropogenic edges elicit stronger responses
This content downloaded on Mon, 28 Jan 2013 08:25:02 AMAll use subject to JSTOR Terms and Conditions