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Developing animal-habitat models for management of high-elevation forests Huggard, David John

Abstract

I examined ways to develop better models relating animals to habitat features, forest harvest types and edges, using data on spruce grouse (Falcipennis canadensis) and small mammals (masked shrews, Sorex cinereus; montane shrews, Sorex monticolus; and southern redbacked voles, Clethrionomys gapped). The work was part of the multidisciplinary Sicamous Creek Silviculture Systems project in high-elevation Engelmann spruce-subalpine fir forest in southern British Columbia. Spruce grouse in winter selected knolls and areas with dense, small and short trees, dense canopy cover, and exposed rock. Grouse avoided forest within 5- 10 m of cutblock edges. Occurrence of grouse in forests near open wetlands increased with increasing predicted habitat quality, but declined within 10-20m of the opening. Removing 33% of timber volume with openings of 0.1, 1, or 10 ha reduced occurrence of grouse by a similar amount; uniform partial cutting reduced their occurrence by 69%. Habitat relationships were less evident for small mammals collected in pitfall traps. As a preliminary step in model development, I elaborated techniques that partition environmental and spatial variation in abundance to include variation due to habitat types, habitat elements, and shared variation, and also estimated measurement error. Unexplained variation was high, and equalled expected measurement error in half the cases. Relationships with habitat elements were confounded to varying degrees by habitat type differences and spatial patterns. The elaborated technique is useful to characterize variation observed in habitat relationship studies, and to guide further study and interpretations of results. I compared classification and regression trees (CART) and neural networks (NN) to linear additive models. The more complex NN and CART habitat models fit data better than linear additive models, but had equal or poorer predictive abilities with data from independent sites. The fit of a model and its predictive ability were unrelated across 14 data sets and the 3 techniques. However, CART and NN modelling have heuristic benefits, suggesting non-linear and contingent relationships for future study. I summarized effects of harvest types on small mammals using likelihood functions to facilitate applied interpretations and a Bayesian combination with literature estimates. Sorex cinereus and immature red-backed voles declined in clearcuts by 26 - 57%, while uniform partial cutting had smaller negative or positive effects. Sorex monticolus increased slightly in both harvest types. Edge response varied for the 3 small mammal species. The shrews showed weak positive associations with shrub, herb, or forest floor cover. Red-backed voles showed stronger positive, interacting relationships with canopy, shrub cover and coarse woody debris. Management implications are presented for maintaining spruce grouse and small mammal habitats.

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