1976: National Forest Management Act
Among other requirements, the National Forest Management Act of 1976 required the Forest Service to “maintain viable populations of existing native and desired non-native vertebrate species in the planning area.” A viable population was defined in the regulations as “one which has the estimated numbers and distribution of reproductive individuals to insure its continued existence is well distributed in the planning area.” This regulation clearly emphasized both the number and distribution of reproductive individuals in the population, and it clarified the goal to “insure.... continued existence” of a population.
In the effort to analyze the viability of the northern spotted owl population in the Pacific Northwest, scientists worked to predict the necessary amount and distribution of suitable habitat over time, estimate the ability of habitat to support breeding pairs of owls, and analyze genetic and demographic risks to the owls. The purpose of the analyses was to understand the implications of alternatives on northern spotted owls for the first planning period (ten to fifteen years) and to further assess the likelihood that owl populations would persist up to specified periods in the future.
The decline in the amount of habitat and the increase in fragmentation made the owl more vulnerable to extinction.Three major threats to owl population viability included the variability of birth and death rates through time, loss of genetic variation, and random catastrophes.
USDA Forest Service.“Draft Supplement to the Environmental Impact Statement for an Amendment to the Pacific Northwest Regional Guide: Volume 1, Spotted Owl Guidelines." USDA Forest Service, Pacific Northwest Region, 1986.
Northwest Regional Guide: Volume 1, Spotted Owl Guidelines.” USDA Forest Service, Pacific Northwest Region, 1986.