In-stream habitat predicts salamander occupancy and abundance better than landscape-scale factors within exurban watersheds in a global diversity hotspot

Abstract

The southern Appalachian Mountains have experienced rapid human population growth rates since the 1980s. Land used practices are shifting from rural to residential. The majority of development has been low density, and is often near biologically diverse areas such as National Forests and National Parks. The long-term effects of urbanization in the southeastern Appalachian Mountains are not clearly understood and even less is known with respect to stream salamander response to urbanization. In order to determine the temporal influence of exurban housing on southern Appalachian streams we sampled 27 first-and second-order streams in watersheds containing exurban developments ranging in age from four to forty-four years, along with eight forested streams, over the course of two summers. We sought to determine if the relative age of an exurban development related to occupancy and abundance of southern Appalachian stream salamanders. Age of exurban development and other watershed scale variables were not top predictors of salamander assemblages, while local site variables such as salinity and undercut banks predicted the abundance of several species of salamander. Our results suggest local habitat improvements can be used to better conserve salamanders and stream ecosystems in an increasingly urbanized region.

Multiple drivers, scales, and interactions influence southern Appalachian stream salamander occupancy

“…For example, studies examining effects of urban land use on stream salamander abundance from a single region disagree on whether changes in catchment forest cover or local riparian forest cover are the most important predictor of declines (Willson and Dorcas , Price et al. ) though recent studies suggest that riparian forest is most important across ecoregions (Surasinghe and Baldwin , Weaver and Barrett ). Additional disagreement exists in whether land‐use legacies impact current distributions (Surasinghe and Baldwin , Weaver and Barrett ).…”

“…) though recent studies suggest that riparian forest is most important across ecoregions (Surasinghe and Baldwin , Weaver and Barrett ). Additional disagreement exists in whether land‐use legacies impact current distributions (Surasinghe and Baldwin , Weaver and Barrett ). Moreover, many of these aforementioned studies did not measure other reach‐level parameters that may have contributed to declines.…”

“…To date, few studies have addressed the interactions of multiple types of land-use change or the combined effects of environmental changes from reach to catchment scale on stream amphibians (Fig. 1;Sweeten andFord 2016, Weaver andBarrett 2017). Most previous studies of streamassociated amphibian abundance focused on regionally significant land uses such as commercial timber harvest in the Pacific Northwest (Welsh and Hodgson 2008, Kroll et al 2010, urban development in the Piedmont (Barrett et al 2010, Price et al 2012, or coal mining in central Appalachia (Price et al 2016, Sweeten andFord 2016).…”

“…While studies of scale-dependent land-use effects collectively suggest that stream-dwelling amphibians are most sensitive to reach-level sedimentation and catchment-level loss of forests (Welsh and Olliver 1998, Crawford and Semlitsch 2007, disagreement exists regarding the relative influence of these factors on population declines or distribution changes (e.g., Kroll et al 2008, Welsh andHodgson 2008). For example, studies examining effects of urban land use on stream salamander abundance from a single region disagree on whether changes in catchment forest cover or local riparian forest cover are the most important predictor of declines Dorcas 2003, Price et al 2011) though recent studies suggest that riparian forest is most important across ecoregions Baldwin 2015, Weaver andBarrett 2017). Additional disagreement exists in whether land-use legacies impact current distributions Baldwin 2014, Weaver andBarrett 2017).…”

Should landscape variation in population status be assessed with individual‐ or population‐level indicators?

“…We selected 6 factors to characterize sites: forest cover, elevation, aspect (northness and eastness), slope, and stream drainage area (Wilkins and Peterson 2000, Dodd and Dorazio 2004, Gould et al 2017, Cecala et al 2018, Gould and Peterman 2021). Although stream amphibians are sensitive to watershed forest loss (Crawford and Semlitsch 2008, Peterman et al 2011), variation in occupancy exists even among streams with high watershed forest cover (Cecala et al 2018, Weaver and Barrett 2018). Elevation is known to affect salamander body size and surface activity (Caruso et al 2014, Connette et al 2015, McEntire and Maerz 2019).…”