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

Abstract

Over 80% of amphibian species that are declining are forest dependent. Forestry practices are a major cause of forest alterations globally, and it is well documented that clearcutting can contribute to amphibian declines. However, there might be adverse effects of forestry practices other than clearcutting. For example, planting overstory trees in rows (plantations) can change groundcover microhabitats and soil moisture levels, but the effects of this common practice on amphibian populations are not well studied. We compared the impacts of common intensive pine plantation operations to naturally regenerated pine forests on the desiccation, movement rates, behavior, and survival of >900 juvenile southern toads (Anaxyrus terrestris). Pine plantations had significantly more accumulation of conifer needles and less exposed soil, herbaceous groundcover, broadleaf litter, and soil moisture than natural pine forests despite the greater canopy cover at plantations. Litter cover explained 85% of groundcover microhabitat variance among forest types and predicted minimum soil moisture levels. When toads were held in small outdoor enclosures that constrained microhabitat selection, 24‐h desiccation rates and 72‐h mortality were significantly greater in pine plantation than in naturally regenerated pine forest because of lower soil moisture, especially during low rainfall periods. In large outdoor pens where juvenile amphibians could select microhabitats, movement was strongly directed down slope and increased with precipitation. However, initial speeds were positively associated with pine density, likely because toads were trying to evacuate from the drier high‐pine‐density areas. High‐intensity silviculture practices that eliminate herbaceous or vegetative groundcover, such as roller chopping and scalping, increase amphibian desiccation because planted conifers dry the upper soil layer. Our study highlights the importance of prioritizing lower intensity silviculture practices or lower pine densities to retain groundcover microhabitat that serves as amphibian refugia from dry conditions that are predicted to increase in frequency with climate change.

Influence of landscape and vegetation characteristics on herpetofaunal assemblages in Gulf Coastal Plain pine forests

“…Further work is needed to understand herpetofaunal population dynamics in working forests, as evidenced by the relatively low occupancy estimates we saw for many species and by the variation in responses shown by herpetofauna to specific effects of forest management activities in other studies (Rothermel and Luhring 2005, Todd and Andrews 2008, Haggerty et al 2019. Low occupancy estimates are a common feature of many reptile and amphibian species (Guzy et al 2019, Zipkin et al 2020), but it can be difficult to discern if low estimates are due to sampling methodology, interspecific interactions, unincorporated landscape variables, or naturally sparse populations.…”

Habitat selection by a threatened desert amphibian

“…We propose that even in the absence of water, features created by monsoon flows reduce the potential for desiccation and may provide important habitat for Chiricahua leopard frogs. Similarly, the understory composition of Florida pine plantations mediates the response of amphibians to drying, with Southern toads ( Anaxyrus terrestris ) experiencing greater desiccation risk in areas with less herbaceous groundcover and moving through more densely covered areas when available (Haggerty et al., 2019). Low‐lying cover could also provide some protection from predation.…”

How plants affect amphibian populations

“…Haggerty et al . (2019b) also found that amphibian desiccation was higher within intensive pine plantations compared to naturally regenerated stands, despite greater canopy cover. Historical disturbance may also cause long‐standing changes in ground‐layer structure and function that negatively impact amphibian populations (Burrow et al ., 2021).…”

“…There have been relatively few attempts to demonstrate that vegetation drives the associated responses of amphibian species. Reduced groundcover vegetation in densely planted forest plantations in the southeastern USA has been linked to decreased amphibian larval occupancy and increased desiccation‐related mortality of juvenile amphibians (Haggerty, Crisman & Rohr, 2019a,b). Burrow, Crawford & Maerz (2021) also found that persistent reduced groundcover associated with historical agricultural use decreased juvenile frog survival in the presence of predatory ants.…”