Evidence of continued effects from timber harvesting on lotic amphibians in redwood forests of northwestern California

We compared species richness and relative abundance of stream-associated amphibians in late-seral redwood forests with those in mid-seral, second-growth forests to examine the continued (as opposed to immediate) effects of timber harvest on amphibian populations. Lacking pre-harvest data on amphibian abundances for streams in the second-growth stands, we assumed that nearby tributaries transecting late-seral stands with similar topography and flora harbored similar numbers of animals as second-growth stands prior to harvest. The study was conducted in two blocks (ca. 160 km apart) with three matched-pairs of streams per block. The mid-seral forests (treatment, n = 6) ranged from 37 to 60 years post-harvest; the late-seral forests (control, n = 6) consisted of unharvested stands. We conducted nocturnal visual encounter surveys to sample for amphibians in spring, summer, and fall, for 2 years, with three repeated visits per season. Environmental factors, including water temperature, air temperature, and fine sediment loads were also recorded. Results indicated that amphibian species richness and relative abundances of lotic amphibians were significantly greater in the late-seral forest streams compared with streams transecting mid-seral forests. Water and air temperatures were similar in both forest types, but streams in mid-seral forests had greater amounts of fine sediments compared with the streams in the late-seral forests.