Do northern spotted owls use harvested areas?

Abstract

The 2011 Revised Recovery Plan for the northern spotted owl (Strix occidentalis caurina) declared that active forest management is compatible and consistent with recovery goals. The plan indicated that ecologically motivated silvicultural treatments should improve stand conditions, promote forest resiliency, and develop late-successional structural complexity over the long term. Yet most biologists believe that intensive, even-aged silvicultural systems (i.e., clearcut, seed-tree, or shelterwood regeneration methods) degrade habitat for northern spotted owls. Only for the coastal redwood forests of California is it broadly accepted that small-patch clearcut harvest units interspersed within a landscape containing significant large stands of large, old trees can provide adequate habitat. Spotted owls prey upon ground-dwelling prey, such as dusky-footed woodrats (Neotoma fuscipes), in these situations, primarily along edges of 6–30year old clearcuts that contain dense patches of shrubs and hardwoods as well as woody debris. Demographic pressures presumably cause surplus prey to emigrate into adjacent older stands with sparse understories, where they may be more vulnerable to predation by spotted owls. During 5 radio-telemetry studies in both the Klamath and Coastal Redwood Physiographic Provinces, we detected and observed northern spotted owls foraging as far as 600m from forests within harvest-created hardwood/shrub patches that contained scattered conifers and snags. Preferential use of such areas occurred in winter, especially in patches with conifer basal area of 9–18m2/ha that were outside of dense nesting areas. In areas where ground-dwelling small mammals comprise a significant proportion of the owl’s prey base, we hypothesize that use of young harvest units with retained conifers may contribute to spotted owl conservation. Such treatments may promote greater prey biomass, which could assist females to attain a high plane of nutrition prior to nesting. This hypothesis should be tested and refined via adaptive management experiments.