Decay Dynamics Of Coarsewood Habitat In Old-growth Spruce and Pine Stands in the Rocky Mountain Foothills
Department of Geography, University of British Columbia, Vancouver
This thesis presents research on the decay dynamics of coarsewood wildlife habitat in the foothills of the Rocky Mountains, west-central Alberta. The study sites were located in permanent sample plots in five Picea glauca and five Pinus contorta old-growth stands. I combined field sampling, dendrochronology, and permanent sample plot data to characterize snags and logs. I used a functional classification scheme to assess the potential wildlife habitat value of snags and logs. The study had two main objectives: (1) to quantify the magnitude of error in dendrochronological work on decayed wood and (2) to assess the accumulation and persistence of snags and logs and their potential functions as wildlife habitat.
I used permanent plot data to verify the accuracy of year-of-death esti- mates obtained by crossdating snags and logs. I obtained YOD estimates from 71 snags and 54 logs. Most YOD dates occurred within the observed interval of death dates from the permanent plot data (54%-80%, grouped by species and coarsewood type) and most remaining dates preceded the in- terval of death. Overall, the magnitude of error in YOD estimates increased with time since death.
I located 322 snags and 405 logs. Mean densities were 403 snags/ha and 506 logs/ha. Snags and logs in intermediate decay classes were the mostcommon, and I hypothesize that most snags reach decay class 4 or 5, rot at the base and fall over, rather than decaying completely in situ. Coarsewood persisted for many decades after death: estimated time since death of the oldest snag and log was 180 and 175 years, respectively. Time since death varied significantly across decay class, but the range of YOD dates in each decay class was so broad that decay class was not a reliable indicator of approximate time since death. Most observations of habitat functions were limited to one of five functional types. Less than 1% of snags and 4% of logs provided four or more habitat functions.
Given the longevity of coarsewood in these stands, management plans must take a long-term view in order to maintain levels of coarsewood that are within the natural range of variability.