Title: Northwest Forest Plan—the first 15 years (1994–2008): status and trends of northern spotted owl populations and habitats
Author: Davis, Raymond J.; Dugger, Katie M.; Mohoric, Shawne; Evers, Louisa; Aney, William C.
Source: Gen. Tech. Rep. PNW-GTR-850. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 147 p
Station ID: GTR-PNW-850
Description: This is the second in a series of periodic monitoring reports on northern spotted owl (Strix occidentalis caurina) population and habitat trends on federally administered lands since implementation of the Northwest Forest Plan in 1994.
Here we summarize results from a population analysis that included data from longterm demographic studies during 1985–2008. This data was analyzed separately by study area, and also in a meta-analysis across all study areas to assess temporal and spatial patterns in fecundity, apparent survival, recruitment, and annual rates of population change. Estimated rates of annual population decline ranged from 0.4 to 7.1 percent across federal study areas (weighted average of 2.8 percent). Covariates for barred owls (Strix varia), weather, climate, habitat, and reproductive success were analyzed and had varying degrees of association with owl demographic parameters. We now have more evidence that increasing numbers of barred owls and loss of nesting/roosting habitat contributed to demographic declines in some study areas.
We also summarize results from a habitat analysis that used the above data in conjunction with remotely sensed data from 1994 to 2007 to develop “habitat suitability” models and habitat maps. These maps were used to quantify the amount and distribution of owl habitats. We also report on causes of habitat change during this period. On federal lands, nesting/roosting habitat declined by 3.4 percent rangewide, with some physiographic provinces experiencing losses of 10 percent. Dispersal habitat increased by 5.2 percent, but dispersal-capable landscapes declined by 1 percent.
Wildfire remains the leading cause of habitat loss. We developed a rangewide “wildfire suitability” model and map to illuminate the portions of the owl’s range where suitable nesting/roosting habitat overlaps with landscapes suitable for the occurrence of large wildfires.
Barred owls and management of owl habitat in fire-prone areas continue to be topics for future monitoring, research, and management consideration.
Keywords: Northwest Forest Plan, effectiveness monitoring, northern spotted owl, geographic information system, owl habitat, habitat suitability, wildfire suitability, demographic study, remote sensing, predictive model, habitat model.
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Davis, Raymond J.; Dugger, Katie M.; Mohoric, Shawne; Evers, Louisa; Aney, William C. 2011. Northwest Forest Plan—the first 15 years (1994–2008): status and trends of northern spotted owl populations and habitats. Gen. Tech. Rep. PNW-GTR-850. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 147 p.