Bird–habitat relationships in jack pine boreal forests

Abstract

We made counts of 42 bird species at 217 points in 44 jack pine Pinus banksiana stands in the boreal region of north-central Saskatchewan, Canada because of concerns about the impact of forestry on avian biodiversity. Using multivariate analyses we describe the main patterns of bird species abundance and composition in relation to local habitat variables. According to canonical correspondence analysis (CCA), 17 of 43 explanatory variables accounted for significant variation in the bird species matrix: stand age, tamarack Larix laricina canopy cover, percentage shrub Alnus glutinosa, canopy closure (6–30%), percentage herbs, maximum canopy height, percentage shrub Alnus viridis, percentage moss, percentage shrub Betula nana, minimum and mean shrub height, percentage litter, white birch Betula papyrifera canopy cover, white spruce Picea glauca canopy cover, mean canopy height, canopy closure (71–100%), and zero shrub canopy closure. Habitat and stand identity (clustering of sites within stands) explained 55.5% of the total variation; 16.3% was unique to habitat alone (29.4% of the total variance explained — TVE) and 17.2% (31.0% TVE) was shared with stand identity. Stand identity accounted for 22.0% (39.6% TVE) of the variation. Neotropical migrants associated with “overmature” mixed-wood stands included Cape May Dendroica tigrina, bay-breasted D. castanea and Tennessee Vermivora peregrina warblers. Conversely, orange-crowned V. celata, palm D. palmarum, and Nashville V. ruficapilla warblers were found in young stands. The presence of several Neotropical migrants was associated with mixed-wood attributes (ovenbird Seiurus aurocapillus with aspen, red-eyed vireo Vireo olivaceus with shrub alder, and Swainson’s thrush Catharus ustulatus with canopy white birch). Jack pine stands older than commercial rotation age must be maintained in a managed landscape because their bird communities differ from younger stands. Because of the limited avian diversity in pure jack pine stands, sufficient mixed-wood stands must be regenerated to sustain populations of characteristic bird species. We recommend that jack pine mixed-woods be managed using shelterwood or selective cuts, and that rotation age of some stands be increased. Without the extensive fires necessary for regeneration, cutting patterns at the landscape level should approximate natural disturbance patches both in size and frequency of disturbance.