Gone with the wind: Effects of a tornado blowdown on the small mammal assemblage inhabiting eastern deciduous forest in western Pennsylvania
Tornados are common natural weather phenomena which highly influence ecosystem structure and function. In eastern deciduous forests, tornados often cause a substantial amount of physical damage, which greatly decreases the spatial heterogeneity of the forest. A tornado struck the area of Ligonier, PA on 1 June 2012, creating a path of severe canopy damage about 8 miles long and affecting about 90 acres of forest. Forest blowdowns substantially increase the amount of course woody debris, which creates refugia for small mammals. Following the tornado, experimental forest management for each blowdown area was initiated which included salvage logging, no salvage logging, and control (unaffected forest). Our objective was to examine impacts of a tornadic blowdown and subsequent forest management on the small mammal assemblage in the eastern deciduous forest. In Nov 2013, we established an extensive small mammal live-trapping grid across both forest treatments and control forest, with trapping occurring seasonally (spring, summer, and fall). Traps were baited with rolled oats and custom-made baitballs. Small mammals were ear-tagged, and data collected included trap station, species, sex, age class, body mass, body condition, and reproductive condition.
The small mammal assemblage was composed mainly of Peromyscus leucopus, Clethrionomys gapperi, and Blarina brevicauda. Six other species were trapped less frequently, including Sorex cinereus, Sorex hoyi, Glaucomys volans, Tamias striatus, Napaeozapus insignus, and Microtus pennsylvanicus. Trapping success rate was >30% for each trapping session. Overall, more small mammals were found in the blowdown area than expected. Seasonally, small mammals were more likely to be found in the blowdown area in the fall (61%), but less likely in the spring (36%). Small mammals in the blowdown area were found to have lower body masses and skewed sex ratios compared to those in control areas. For P.leucopus, the most commonly caught small mammal in our study, all juveniles were caught in the salvaged treatment area. In spring/summer, no reproductive activity was seen in the salvage treatment, while non-salvage and control treatments had normal reproductive activity. Age, sex, and body mass differences of the two most frequently trapped small mammals were seen in salvage treatment compared to the other treatments. Although these mammals all strongly prefer forested habitat, the added complexity of the ground cover seems to make the non-salvaged blowdown area one of opportunity for small mammals willing to occupy it.