Forest Succession and Amphibian Migrations: Implications for Landscape Connectivity

Conservation of forest-dependent amphibians is dependent on finding a balance between timber management and species’ habitat requirements. Accurate predictions of the response of amphibian communities to disturbance rely on a good understanding of the scales at which ecological processes affect distribution and abundance through space and time. I investigated the response of 14 species to four different forestry treatments (partial harvest, clearcut with coarse woody debris [CWD] removed, clearcut with CWD retained, and uncut control) over a six-year period, using 2.1-ha experimental treatments. Forest amphibians showed a strong negative response to complete canopy removal at a broad spatial scale, but site-specific variation in the use of forestry treatments was the norm at a finer scale. Four forest-dependent species showed substantial declines in abundance beginning at 2 – 3 years post-disturbance. Avoidance of clearcuts by forest species and site-specific patterns of habitat use were maintained throughout the study. 2 Incipient vegetative succession and retaining CWD did not mitigate the effects of clearcutting; I found only a modest positive effect of succession on habitat use by emigrating juvenile wood frogs (Lithobates sylvaticus). I studied the permeability to juvenile wood frogs movements of four forestry treatments (recent clearcut, mature forest, 11-year-old conifers, and 20-year-old natural regeneration). I conducted experimental releases in 50 x 3 m terrestrial enclosures built in each treatment. Recent clearcuts and young coniferous stands were significant barriers to movements, and were three times less permeable to movement compared to the mature forest and 20-year-old regeneration. In addition, I found that juvenile wood frogs reared in semi-matural conditions did not show inherited directionality upon emergence, rely on proximate cues for orientation, and avoided forested wetland cues. Vegetative succession in young stands (5-6-year-old) mitigated the effects of clearcutting on microclimate, but juvenile wood frogs strongly avoided these stands. Thus, microclimate cannot be used as a sole parameter to predict potential habitat use by amphibians. Closed-canopy habitat was preferred by all terrestrial life stages of forest amphibians. A viable forest management strategy is to plan for spatially and temporally-structured harvests that retain canopy between high-quality breeding sites, and avoid clearcutting and conversion to conifer plantations.