Japanese stilt grass (Microstegium vimineum), a nonnative invasive grass, provides alternative habitat for native frogs in a suburban forest

by Christopher Nagy^1,2, Seth Aschen¹, Rod Christie¹, and Mark Weckel^1,2

¹Mianus River Gorge Preserve, 167 Mianus River Road, Bedford, NY 10506

²American Museum of Natural History, Central Park West, New York, NY 10024

Abstract

Japanese stilt grass (Microstegium vimineum) is an invasive grass in the eastern and midwestern United States. It tolerates a wide range of light and moisture conditions and has readily replaced native herbaceous vegetation in many areas. Despite its detrimental effects, Japanese stilt grass does provide some benefit, serving as habitat for ground amphibians such as frogs and toads (anurans) in areas where populations of white-tailed deer (Odocoileus virginianus) have depleted native herbaceous cover. We investigated relative abundances of common anuran species both inside and outside of a stilt grass invasion front in a Northeastern mixed hardwood forest. We used pitfall trap arrays to sample anuran species during the summers of 2006 and 2007 and we captured four species: wood frog (Rana sylvatica); pickerel frog (Lithobates palustris); spring peeper (Pseudacris crucifer); and American toad (Bufo americanus). We captured more individuals from each of these species in stilt grass plots. Too few spring peepers were captured for analysis, so we modeled the captures of the three remaining species—wood frog, pickerel frog, and American toad—with negative binomial regression against stilt grass presence/absence, soil moisture, soil temperature, and relative humidity. We compared models containing these parameters using AIC (Akaike's Information Criterion), a common information criterion used in model selection. All three species selected stilt grass plots, but appeared to do so for different reasons. Pickerel and wood frogs seemed to select primarily areas of high soil moisture, which was consistently greater in stilt grass plots. American toads selected stilt grass areas and areas of high humidity, though humidity did not vary according to stilt grass presence or absence. For all three species, stilt grass seemed to provide habitat value beyond any causal or correlative relationship with microclimate. These results suggest that some invasive species of herbaceous cover provide alternative habitat for native wildlife in degraded communities. Managers need to consider the effect on wildlife when considering removal of invasives, particularly when there is little native habitat and when removal would be destructive.

Keywords: Japanese stilt grass (Microstegium vimineum), wood frog (Rana sylvatica), pickerel frog (Lithobates palustris), American toad (Bufo americanus), invasive species management, Mianus River Gorge.