Abstract:
Edge effects resulting from forest fragmentation are likely to alter the distributions and
interactions of resident species. I evaluated changes in species composition, species
turnover, and relative abundance of ground arthropods across replicated transects
extending from regenerating clearcuts into old-growth Douglas-fir forests. Arthropods
were collected from 3-August to 14-September in 1997 and 23-May 1998 to 31-July
1998 using pitfall traps. Pitfall traps were positioned at 75 m (in the clearcut), -25, 0
(forest edge), 50, 100 and 200 m into the forest in 1997. In 1998, traps were repositioned
at 25, 0, 25, 50 ,lOO, and 200 m into the forest. Changes in species composition and
relative abundance were compared using non-metric multidimensional scaling ordination.
Two-hundred, five species representing 24,178 individuals were collected. Edge effects
on species composition and relative abundance were apparent up to 100 m into old-growth
forests. Species were characterized as edge-phobic (interior forest associates),
edge-philic, edge-insensitive or as edge-input (clearcut associates). The majority of
species were characterized as either edge-phobic or edge-input species. Seasonal patterns
in activity are also reported. To further address the impacts of edges on community structure, changes in species abundance of predator taxa across the edge-forest gradient
were compared to four models of resource partitioning. Observed patterns of species
abundance did not differ across the edge-forest gradients and were consistent with a
model of random assortment (or non-equilibrium) where an individual predator species
utilizes resources independently of other predators. This pattern was consistent whether
species abundance was expressed as numerical abundance or biomass. This study
suggests that edge effects resulting from forest fragmentation alter species composition
and may negatively affect interior forest species. Furthermore, although species
composition changes across forest edges, this study suggests that resource partitioning by
a trophic group such as predators remains unaffected by forest edges.
