Shrew response to variable woody debris retention: Implications for sustainable forest bioenergy

Abstract

Shrews are integral components of forest food webs and may rely on downed woody debris to provide microhabitats that satisfy high moisture and metabolic requirements. However, woody biomass harvests glean downed woody debris to use as a bioenergy feedstock. Biomass Harvesting Guidelines (BHGs) provide guidance on the amount and distribution of downed woody debris retained after harvest to ensure ecological sustainability of woody biomass harvesting and limit detrimental effects on wildlife. However, the success of Biomass Harvesting Guidelines at reaching sustainability goals, including conservation of wildlife habitat, has not been tested in an operational setting. Thus, we compared shrew captures among six woody biomass harvesting treatments in pine plantations in North Carolina, USA from April to August 2011–2014 (n=4) and Georgia, USA from April to August 2011–2013 (n=4). Treatments included: (1) woody biomass harvest with no BHGs; (2) 15% retention with woody biomass dispersed; (3) 15% retention with woody biomass clustered; (4) 30% retention with woody biomass dispersed; (5) 30% retention with woody biomass clustered; and (6) no woody biomass harvested. We sampled shrews with drift fence arrays and compared relative abundance of shrews among treatments using analysis of variance. Additionally, we used general linear regression models to evaluate the influence of downed woody debris volume and vegetation structure on shrew capture success at each drift fence for species with >100 captures/state/year. In 53,690 trap nights, we had 1,712 shrew captures representing three species, Cryptotis parva, Blarina carolinensis, and Sorex longirostris. We did not detect consistent differences in shrew relative abundance among woody biomass harvest treatments, but relative abundance of all species increased over time as vegetation became established. In North Carolina, total shrew capture success was negatively related to volume of downed woody debris within 50m of the drift fence array (P=0.05) in 2013 and positively related to bare groundcover in 2013 (P=0.02) and 2014 (P<0.01). In Georgia, total shrew capture success was negatively related to herbaceous groundcover (P<0.01) and leaf litter groundcover (P=0.02) and positively related to woody vegetation groundcover (P<0.01) and vertical vegetation structure (P=0.03) in 2013. Our results suggest that shrews in our study area were associated more with vegetation characteristics than downed woody debris and that woody biomass harvests may have little influence on shrew abundances in the southeastern United States Coastal Plain.