Initial movements of a dispersing amphibian in response to partial harvesting in the acadian forest of Maine, USA

Abstract

Maintaining amphibian populations in managed forests requires a balance between timber extraction and retaining functional connectivity for animals that use multiple vegetation types to satisfy habitat requirements, particularly where extensive harvesting may increase fragmentation. Quantifying dispersal patterns in response to harvest, especially across high-contrast edges adjacent to unlogged forest, is critical for evaluating the effects of harvest configuration on amphibians. We tested the initial postmetamorphic orientation of juvenile wood frogs (Lithobates sylvaticus) at edges in harvests (31-60% retention standwide) in the Acadian forest of Maine, USA, during the period when juveniles emigrate from breeding pools. We released juveniles (n = 621) in 10-m diameter arena enclosures spanning edges. Frog movement in uncut controls (~70-75% canopy) was contrasted with movement in the following: harvester trails (0% retention) running parallel to edges of uncut forest; perpendicular harvester trails; or residual strips of partially cut matrix-forest (~30% retention) between trails. We observed a nonsignificant trend for higher proportions of individuals entering control forests versus harvests (χ12 = 2.504, P = 0.113) and a stronger trend for movements into control forests versus perpendicular-oriented trails (52:35 for forest versus treatment; χ12 = 3.322, P = 0.068). The biological relevance of such patterns warrants further consideration. Juveniles may enter partial harvests at rates similar to those for intact forest, but quantifying the effects of harvest configuration on movement patterns, residency times, and ultimately survival is necessary to determine whether these harvests represent sink habitats.