Lilles, Erica

Forest ecosystems and the ecological services they provide are complex and dynamic. Disturbance and successional processes impact habitat for animals such as caribou (Rangifer tarandus caribou Gmelin 1788, Banfield 1961, 1974) and moose (Alces alces L.). The forested winter habitat of the Tweedsmuir-Entiako caribou herd has been significantly affected by recent disturbance. In order to evaluate the mid- and long-term consequences for habitat, we require an understanding of how habitat attributes change as stand structure changes over time. I developed a framework to link a stand dynamics model (SORTIE-ND), via linker functions, to three ecosystem elements relevant to caribou populations: terrestrial forage lichen, moose forage, and vertical cover. I first used SORTIE-ND to model stand structure dynamics following mountain pine beetle (Dendroctonus ponderosae Hopkins) attack and clearcut harvesting. I developed linker functions and refined them with empirical data. These functions were applied to stand structure output from SORTIE-ND to project the response of habitat to the disturbance agents. I addressed three questions: 1. What is the influence of edaphic site on the provision of elements of caribou habitat over time? 2. What is the influence of stand type on the provision of elements of caribou habitat over time? 3. How do recovery trajectories of caribou habitat elements differ in response to disturbances such as mountain pine beetle and clearcut harvest? I found that site and stand type interacted to influence the suitability of terrestrial lichen, moose forage and vertical cover. Poor productivity sites were most favourable for terrestrial forage lichen. Higher productivity stands and broadleaf stands provided the greatest suitability for moose shrubs. Both mountain pine beetle attack and clearcut harvest improved stand suitability for lichen and moose browse though for different sites and stand types. Interestingly, I found that severe mountain pine beetle attack resulted in conditions that favoured forage lichen for longer than clearcuts. Clearcuts resulted in conditions that were more suitable than mountain pine beetle attack for winter forage for moose. When operating on landscapes with caribou winter habitat, forest managers should consider disturbance history, the distribution of sites and stand types, silviculture systems and the future desired state of ecosystem services. The SORTIE-ND modelling framework could be used to support the evaluation of alternative management decisions in caribou winter habitat including alternative silviculture strategies. This approach could also provide stand- and site-specific trajectories of the recovery of caribou habitat that could be applied to habitat supply models.

At a long-term experimental trial in northern British Columbia, Canada, I analysed the impact of varying amounts of timber retention: 0% (clearcut), 40%, 70%, 100% (unharvested) on CWD volume, decay class, and inputs from windthrow over 27 years. I used attributes (diameter, length, decay class, and height above the ground) known to be favourable to marten to create an index for assessing the impact of harvesting intensity on CWD habitat features. I then used airborne laser scanning (ALS) to predict CWD volume, habitat value, and piece attributes over the landscape. Stands with 70% retention had CWD attributes that resulted in CWD habitat features similar to unharvested stands. Clearcuts contained pieces that were smaller, more decayed, and closer to the ground, which contributed less valuable habitat, compared to stands with higher retention. Windthrown trees were the majority of CWD inputs and volume change was positively related to percent retention.