Changes In Stream Amphibian Populations Following Large Fires In Idaho


David S. Pilliod and P. Stephen Corn
Aldo Leopold Wilderness Research Institute, 790 E Beckwith Ave., Missoula, MT 59807, Phone: (406) 542-3256; FAX: (406) 542-4196; Email: dpilliod@fs.fed.us

ABSTRACT:

Information on the influence of forest fires on stream amphibian populations is lacking. This paper presents some of the preliminary results from a multi-year study that is investigating the effects of prescribed and wildland fire on stream communities in Idaho, Montana, and Oregon. We compare amphibian densities and biomass and stream habitat conditions in 7 streams flowing through watersheds that burned at varying intensities in the summer of 2000 to 6 streams in nearby unburned forests in central Idaho(fires absent for 50-70 yrs). Streams were sampled at low-flow from late June through September 2001 and 2002. Amphibians and habitat conditions were measured in 30 randomly located 1-m “belts” along a 1 km section of each stream. Tadpoles of the Rocky Mountain tailed frog (Ascaphus montanus) were found in all streams, but densities and biomass were lower in burned streams compared to unburned streams. Spatial variability of tailed frog tadpole densities, as measured by the coefficient of variation within a stream, appeared to be increasing in burned streams relative to unburned streams. We suspect that tailed frog tadpole distributions within streams are changing in response to altered habitat conditions after fire. Preliminary habitat data indicate that streams in burned watersheds have less cover, greater daily fluctuations in water temperature (i.e., higher daily maximums and lower daily minimums), greater fine sediment, and higher levels of nutrients than streams in unburned watersheds. Increased light, nutrients, and temperature may result in increased stream productivity and have long-term positive effects tailed frog populations. We will continue to monitor these populations over time.