Snag decomposition following stand-replacing wildfires alters wildlife habitat use and surface woody fuels through time

High-severity wildfires create pulses of snags that serve a variety of functions as they decompose over time. Snag-related benefits (and hazards) are often linked to specific decomposition stages, but snag decomposition rates and pathways are not well understood in many forest types. We examined temporal patterns of snag decomposition, wildlife cavity creation, and surface woody fuel dynamics in dry coniferous forests of the interior Pacific Northwest region of North America by sampling 159 forest stands within a 39-year chronosequence of stand-replacing wildfires in dry coniferous forests dominated by ponderosa pine and Douglas-fir. We found that most snags broke or fell during the first 15 years after wildfire; small-diameter snags mostly broke off at or near ground level, while many large-diameter snags initially broke off above a height of 2 m and then remained standing for an extended period. Ponderosa pine and lodgepole pine snags fell earlier than Douglas-fir and true fir snags of comparable diameter classes. Wildlife cavities were most common in stands surveyed 8–20 years after fire and in snags with broken tops but were not limited to large diameter snags. Cavity snag diameters ranged from 17 to 98 cm, with 64% of cavity snags having diameters between 30 and 60 cm and 22% of cavity snags having diameters >60 cm. Surface woody fuels increased as snags broke and fell, reaching maximum levels in all size classes 15–20 years after fire. The percentage of large diameter rotten woody fuels increased steadily beginning about 15 years after fire, with implications for fuel management and subsequent wildfire behavior and severity. Our study supports the proposition that fire-killed snags represent a transient resource pulse in which the relative contribution of snags to different ecological functions varies with snag diameter, species, time since fire, and landscape position.