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AVIAN DENSITY AS A FUNCTION OF FOREST AGE AND FOREST TYPE IN ALBERTA

BAM estimated densities for 73 avian species in relation to forest age classes for each leading tree species (“forest type”) in the boreal region of Alberta. The results are shown graphically by species under the RESULTS section. The Alberta Forest Songbird Information System (AFSIS) for each species may be downloaded from that species’ page, and includes the 95% confidence intervals for each estimate in each forest age and type category.

The AFSIS database presents the state of knowledge about how boreal songbirds respond to five forest habitat types (deciduous, pine, upland spruce, lowland spruce, and mixed wood) and eight forest age classes (0-20, 21-40, 41-60, 61-80, 81-100, 101-120, 121-140 and >140 years). Densities were calculated in each of five Alberta Land Use Zones that intersect the boreal/hemiboreal region. (Click here to see a map showing the different land use zones in Alberta,) Future analyses will develop similar relationships outside Alberta.

The avian densities (male birds per hectare) were estimated using avian and vegetation data from the Boreal Avian Modelling Project, the Breeding Bird Survey, and the Alberta Biodiversity Monitoring Institute (ABMI). Methods to compute density and correct count data for nuisance variables rely on the methods described under Avian Data Analysis.

Forest age and dominant forest type within 150 metres of each avian point count location were computed from Alberta Vegetation Inventory data. Of the more than 50,000 available point counts, information about leading tree species and forest age were available for 38,572. The remaining point counts were not included in models to predict bird density but were are used elsewhere to evaluate the major vegetation type where each species was located.

AFSIS models assumed consistent patterns of habitat use by a species across different land use regions of Alberta. In other words, this assumes that birds respond to forest age in the Lower Peace region in the same way they respond to forest age in the Lower Athabasca. Density in the same forest type and age class will differ between regions but the relative way birds respond to age and leading species (forest type) is assumed to be the same. Insufficient data currently exist to compute an interaction term between forest age, forest type, and spatial location that would allow for differential habitat selection by a species in different places.

These results are being used as scientific inputs to the Alberta Land Use Framework and other land use planning exercises to understand how change in forest age and type will influence birds. These types of land use scenario models will aid in the development of regional management plans that balance sustained economic growth against other social and environmental goals (http://landuse.alberta.ca/).