Small mammal diversity and abundance in Douglas fir old growth forests

Small mammal diversity and abundance was compared between two Douglas fir (Pseudotsuqa menziesii) old growth stands, which differed in structural complexity.The study was conducted in the Hyalite drainage of the Gallatin National Forest, 35 kilometers south of Bozeman, Montana, in the Lick Creek and History Rock Creek drainages.The forest stands were similar in elevation, slope, precipitation, tree species composition and ages of trees, but differed in soil types and aspects.They differed significantly in the amount of downed woody debris, and downed logs 7.6 cm and greater in diameter.The two stands were not significantly different in the number of canopy layers, mean ground vegetation heights, and duff depths.Small mammals were live-trapped and after 7,200 trap-nights, 508 animals were captured a total of 1,105 times.Significantly more total animals were trapped in the more complex forest, History Rock.There were significantly more red-backed voles (Clethrionomys gapperi) in the History Rock stand, and significantly more deer mice (Peromvscus maniculatus) in the simpler stand, Lick Creek.The Shannon Diversity Index was applied to these trapping results, and the Lick Creek stand ranked significantly greater in species diversity than did the History Rock site, in spite of the greater number of individuals and species in History Rock.Significantly greater numbers of snowshoe hare (Lepus americanus) pellets were found in the History Rock stand, but no significant differences were found in numbers of red squirrels ( Tamiasciurus hudsonicus) or northern pocket gophers (Thomomvs talppides) between the two stands.