Effects of prescribed fire on a Sierra Nevada (California, USA) stream and its riparian zone

Concerns about the effects of fire on ecologically sensitive habitats have limited the use of prescribed fire in the management of forest riparian areas. Using a beyond-BACI (Before-After-Control-Impact) experimental design, we examined the effects of a 26-ha prescribed fire that burned upland and riparian areas of a first-order watershed, and compared this to five unburned sites examined from 1 to 7 years pre-fire and 1 year post-fire. We monitored pre- and post-fire riparian vegetation, large woody debris, sediment, water chemistry, periphyton, and benthic macroinvertebrates. The prescribed fire in the riparian zone was patchy in terms of intensity, consumption, and severity; it consumed 79% of the pre-fire fuel in the riparian zone, 34% of the total surface fuel, and 90% of the total ground fuel. The prescribed fire significantly reduced percent cover of surface vegetation and plant taxa richness in comparison to unburned sites but not plant diversity (Simpson's D). Community composition of understory riparian vegetation changed post-fire, most likely as a result of the reduction in taxa richness and cover. Riparian tree mortality (>11.5 cm DBH) was only 4.4% post-fire. Similarly, there was no post-fire change in large woody debris volume and recruitment, or fine sediment in pools (V*). Post-fire, there were increases in some water chemistry parameters (SO4−, total P, Ca2+, and Mg2+) and a decrease in periphyton biomass; however, these changes were short-term, and recovery occurred in ≤1 year. Macroinvertebrate community composition but not density, richness, or diversity was affected 10-19 d post-fire; composition recovered within 1 year. The trends observed in this study examining multiple abiotic and biotic parameters suggest that this prescribed fire either had no or short-lasting (≤1 year) impacts on Dark Canyon Creek and its riparian zone. The limited observed impacts are at least partially a result of the small portion (<20%) of the watershed area burned, moderate topography, the low- to moderate-severity of the fire, and the relatively low precipitation (and thus, stream flow) that occurred post-fire.