Forest Investment Account (FIA) - Forest Science Program
FIA Project Y051053

    Implications of landscape composition and pattern in managed sub-boreal forests
Contributing Authors: Steventon, J. Douglas; Bergerud, Wendy A.; Ott, Peter K.
Imprint: B.C. : Bulkley Valley Centre, 2005
Subject: Forest Investment Account (FIA), Sustainable Forestry, British Columbia, Martens, Squirrels
Series: Forest Investment Account (FIA) - Forest Science Program
A combination of simulation modelling and field study of selected species is being used to examine conservation implications of timber harvest rate and pattern. Emphasis is on assessing alternate harvest strategies in response to the mountain pine beetle (Dendroctonus ponderosae) in the Nadina Forest District. A 100-year time frame was chosen to get a sense of whether short-term management decisions have mid- to long-term implications. The study focus is on species that are generally associated with mid- to late-seral forest, and are space constrained (have defined home-ranges) and thus are potentially sensitive to habitat arrangement at that home-range scale (termed habitat dilution or density). Model verification and replicated simulations are ongoing, and formal peer review yet to be done. Thus results should be considered interim and potentially subject to revision. There was no consistent, strong difference in simulations comparing a clumped harvesting strategy and a dispersed harvesting strategy. However, clumped harvesting showed some marginal benefit especially for large home-range size species (200+ hectares). The influence of landscape pattern on the number of potential home-ranges was affected by species plasticity in expanding to encompass sufficient habitat (tolerance of habitat dilution), and the habitat weighting given young to mid-seral forest (degree of mature forest specialization). More investigation, across a wider range of parameterization, is required to further test these initial results. A pilot study to field test the habitat dilution effect was conducted using live-trapping for marten (Martes americana) and northern flying squirrel (Glaucomys sabrinus). These were chosen as representing greatly different home-range scales (200 vs. 10 hectares for females), are both reasonably abundant, and have been the subject of local radio-telemetry based studies to support model development. Hypothetical home-ranges were delineated using the simulation model and 14, 200-ha marten-scale sample sites chosen representing varying levels of habitat dilution (mostly representing increasing area of young, harvested forest). Within each marten-scale sample site there were 16, 12 ha squirrel-scale sample sites. Only squirrel-scale sites with mature forest were sampled, and all trap locations were in mature forest habitat. The idea was to assess the effect of the surrounding area on otherwise suitable sites. 1 In total 135 squirrel-scale sites were sampled. Flying squirrels were captured at 23 sites, for a total of 32 captures. There were no captures from June until mid August, reflecting poor detection probability during summer. Estimated detection probability increased exponentially into the fall. There was some evidence of a modest positive effect of habitat dilution at the scale of the 12-ha squirrel sample units. We speculate that such an effect, if real, could occur from lower predator occurrence in fragmented habitat, or from packing effects. There were only 2 marten-scale sites with a marten capture (3 total captures), precluding any analysis for that species. Results to-date support, or at least do not refute, a clumped harvesting strategy as being appropriate in response to the mountain pine beetle outbreak. The next phase of the project will include an examination of the feasibility of an adaptive management and effectiveness monitoring strategy at landscape unit and TSA scales.
Doug Steventon.
Related projects:  FSP_Y062053

Extension Note 74

Updated August 16, 2010 

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