Fallen Trees Host Wildlife for Many Decades
Subalpine fir and interior spruce trees can serve as wildlife habitat for 100 years or more after they die. Fallen logs become more useful to wildlife as their decay progresses from classes 1 to 3. During this period, logs contain enough structural integrity to provide small concealed spaces for rodents and birds, yet become soft enough for excavating spaces.
Once a log collapses into the ground, reaching decay class 4, its role as wildlife habitat declines. In wet, cold portions of the Sub-boreal Spruce biogeoclimatic zone forest northeast of Prince George in central British Columbia, spruce usually reaches class 4 around 60 years, and up to 148 years, after dying. Subalpine fir logs in class 4 typically died 70 to 110 years earlier.
In the old forests sampled, spruce snags usually stand less than 20 years before falling. Fir snags often stand over 20 years, with 74 years the oldest measured. The length of time a log has lain on the ground has greater bearing on its decay class than the time since death.
S. Craig DeLong, Lori D. Daniels, Ben Heemskerk and Ken Olaf Storaunet. 2005. Temporal development of decaying log habitats in wet spruce-fir stands in east-central British Columbia. Canadian Journal of Forest Research. 35(12): 2841-2850.