Fuel treatment effects on snags and coarse woody debris in a Sierra Nevada mixed conifer forest

Abstract

Snags and coarse woody debris are important elements of the structure and function of mixed conifer forests in the Sierra Nevada. In this paper, we report on the impacts of several replicated fuel treatments including, prescribed fire, commercial thinning (crown thinning and thinning from below) followed by rotary mastication of understory trees, mechanical followed by prescribed fire, and control, on snag and CWD quantity and structure. Post-treatment, the density of snags greater than 15 cm DBH in decay class 1 significantly increased in fire only and mechanical plus fire treatments compared with mechanical only and control treatments. Snag volumes (m 3 ha −1) were not significantly different between treatments for all decay classes. CWD (density, percent cover, volume) in decay classes 1 and 2 was not significantly altered by any treatment when aggregated across all diameter classes. Volume of CWD in decay class 3 was significantly reduced in the fire only treatment when compared to controls. Density and volume of CWD in class 4 was significantly reduced in mechanical plus fire and fire only treatments when compared with the controls and mechanical only treatments. Retention of large CWD levels may benefit some wildlife species short-term but increases in fire hazards and increased difficulties in fire control are the negative consequence. High overall fuel loads also increase the probability of snag and CWD consumption when an area inevitably burns. The influences of altering snag and CWD characteristics should be analyzed in the context of long-term forest management goals, including the reintroduction of fire as an ecosystem process and creation of forest structures that can incorporate wildfire without tree mortality outside a desired range.