Impact of forestry practices at a landscape scale on the dynamics of amphibian populations

Abstract

Forest loss is a primary cause of worldwide amphibian decline. Timber harvesting in the United States has caused dramatic changes in quality and extent of forest ecosystems, and intensive forest management still occurs. Although numerous studies have documented substantial reductions in amphibian densities related to timber harvest, subsequent extinctions are rare. To better understand the population dynamics that have allowed so many amphibian species to persist in the face of widespread forest disturbance, we developed spatially explicit metapopulation models for four forest-dependent amphibian species (Lithobates sylvaticus, Ambystoma opacum, A. talpoideum, and A. maculatum) that incorporated demographic and habitat selection data derived from experiments conducted as part of the Land Use Effects on Amphibian Populations Project (LEAP). We projected local and landscape-scale population persistence under 108 different forestry practice scenarios, varying treatment (partial cut, clear-cut with coarse woody debris [CWD] removed, and clearcut with CWD retained), cut patch size (1, 10, or 50 ha), total area cut (10, 20, or 30%), and initial amphibian population size (5, 50, or 500 adult females per local breeding population). Under these scenarios, landscape-scale extinction was highly unlikely, occurring in < 1% of model runs and for only 2 of the 4 species, because landscape-scale populations were able to persist via dispersal even despite frequent local extinctions. Yet for all species, population sizes were reduced to -50% in all clear-cut scenarios, regardless of the size of harvested patches. These findings suggest that debate over timber harvesting on pool-breeding amphibian populations in the United States should focus not on questions of landscape-scale extinction but on the ecological consequences of dramatic reductions in amphibian biomass, including changes in trophic interactions, nutrient cycling, and energy transfer. Additionally, we conclude that amphibian declines and extinctions are far more likely to occur as a result of permanent habitat loss resulting from development than from the temporary degradation of habitat caused by current forestry practices.

Tamm review: Terrestrial vertebrate biodiversity and intensive forest management in the U.S.

“…Similarly, female size, fecundity, and age classes of plethodontid salamanders did not differ among varying amounts of canopy removal in the Appalachian Mountains of Virginia and West Virgina (Knapp et al 2003). Although salamander numbers generally decline immediately following timber harvest, extirpations from harvested sites are rare (Tilghman et al 2012, Harper et al 2015).…”

Amphibian sensitivity to habitat modification is associated with population trends and species traits

“…One possible explanation for a direct effect of larval habitat on SHM is that terrestrial breeders often depend on forest resources for reproduction, such as moist leaf litter for oviposition (Wells, 2007); in some systems, stream-breeding amphibians also depend on forested stream reaches for population persistence (Becker, Fonseca, Haddad, Batista, & Prado, 2007), suggesting they may rely on relatively unaltered, low-order streams. In contrast, populations of pond breeders appear to be more likely to persist in altered habitats such as pastures and clear cuts (Harper, Patrick, & Gibbs, 2015;Neckel-Oliveira & Gascon, 2006). Interestingly, egg laying with larval development in lentic habitats is an ancestral reproductive mode that persisted through the last mass extinction at the end-Cretaceous, and lineages with terrestrial development [e.g., Craugastoridae] have evolved multiple times from this ancestral mode (Gomez-Mestre, Pyron, & Wiens, 2012;Wells, 2007;Wiens, 2007).…”

Effects of forestry‐driven changes to groundcover and soil moisture on amphibian desiccation, dispersal, and survival

“…, Harper et al. ), and could increase amphibian persistence in planted forests by influencing desiccation risk (Rittenhouse et al. , Rohr and Palmer ) or behavior (Harpole and Haas ).…”

“…While it is well documented that intensive timber harvest can cause rapid amphibian declines (Tilghman et al 2012), the pre-harvest phase of plantation is unnaturally dense for decades and can more gradually change groundcover biotic and abiotic conditions, but their effects on amphibian populations are less studied (Means andMeans 2005, Hansen et al 2013). Moreover, the retention of forest groundcover microhabitat can mediate the negative impacts of canopy removal on amphibian biomass (Todd and Rothermel 2006, Patrick et al 2008, Popescu et al 2012, Harper et al 2015, and could increase amphibian persistence in planted forests by influencing desiccation risk (Rittenhouse et al 2008, Rohr andPalmer 2013) or behavior (Harpole and Haas 1999). Previous work has also suggested amphibian behavioral avoidance of inhospitable habitat created by forestry practices as one contributor to biodiversity loss (Semlitsch et al 2008, Popescu andHunter 2011).…”