Bird response to disturbance varies with forest productivity in the northwestern United States |
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Authors: | David B McWethy Andrew J Hansen Jake P Verschuyl |
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Institution: | (1) Ecology Department, Montana State University, P.O. Box 173460, Bozeman, MT 59717, USA;(2) NCASI Western Wildlife Program, P.O. Box 1259, Anacortes, WA 98221, USA |
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Abstract: | Huston’s Dynamic Equilibrium Hypothesis predicts that the response of biodiversity to disturbance varies with productivity.
Because disturbance is thought to break competitive advantage of dominant species in productive ecosystems, species richness
is predicted to increase with disturbance frequency in productive systems. Recovery of plant biomass following disturbance
is also predicted to be faster in productive systems. Here we provide the first test of Huston’s hypothesis in the context
of setting harvest rates in managed forests for achieving biodiversity objectives. We examined predictions relating to vegetation
and bird response to disturbance and succession in productive and less productive forests in western Oregon and Washington,
USA. We found that measurements of understory cover and shrub diversity were higher in young, productive stands than less
productive stands of similar age. Later-seral forests in productive environments (mean age = 67 years) had less variable and
more complete canopy closure than similar-age forests in less favorable settings. At the stand scale, bird abundance and richness
decreased with canopy closure in highly productive forests whereas bird abundance and richness increased with canopy closure
in less productive forests. At the landscape scale, bird abundance and richness within stands increased with increasing levels
of disturbance in the surrounding landscape within highly productive forests, whereas bird abundance and richness decreased
with increasing disturbance in the surrounding landscape within less productive forests. Our results indicate that bird response
to disturbance varies across levels of productivity and suggest that bird species abundance and associated species richness
will be maximized through relatively more frequent disturbance in highly productive systems. |
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