Edge influence on the old-growth forest indicator lichen Alectoria sarmentosa in natural ecotones.

摘要

Question: Is the pendulous epiphytic indicator lichen Alectoria sarmentosa influenced by proximity to forest edge in natural old-growth forests? Location: Large (28400 ha), naturally heterogeneous boreal landscape in northern Sweden dominated by old-growth Picea abies forest in a matrix of open wetland. Methods: The abundance of A. sarmentosa and forest structure were quantified in ten edge-interior transects (0-100 m) at southern to western forest edges. Four 10 m x 50 m plots were sampled along each transect. Mass of A. sarmentosa in the lower canopy (0-5 m) of P. abies was estimated from maximum thallus length. Results: The maximum length of A. sarmentosa was four times lower, and the lichen mass 16 times lower, at the forest edge compared to the forest interior. Lichen mass showed a monotonic decrease from the interior to the edge. Mean distance of edge influence was 58 m for lichen mass, and extended longer into the forest than changes in stand structural variables. The response of A. sarmentosa to edges is a result of a combination of changes in microclimate and substrate availability. Conclusions: The indicator species A. sarmentosa is strongly affected by proximity to forest edge in natural old-growth forests. Edge influence is thus important in controlling the abundance of this group of pendulous lichens in natural forest ecosystems. Distance of edge influence was longer in natural wetland-forest ecotones than previously reported for fragmented forests; this was probably due to higher lichen abundance and lower site productivity in the study area. Understanding lichen response to natural landscape structure may help us to improve conditions for epiphytes in managed forests..