Recovery Plan for the Northern Spotted Owl - DRAFT

area, structure, ages, location; need for fire protection and fuel breaks: diseaseand insect populations: access, and other uses. When thinning stands, forexample, activities probably should be spread over time and space to avoidhaving large contiguous areas of temporarily open canopy, and to avoid nestingowls. Similarly, treatments such as prescribed burning to reduce fire hazardshould be scheduled with regard to stand structure, owl use, fuel concentrations,fire control strategies, and other considerations.A. Stand Structure and Owl HabitatOwl habitat as used in this report is defined as the stand structures that owlsuse for nesting. This type of habitat is apparently the most critical for survivaland recovery of owls. The structure has been quantified (see Appendix B) bystudies in which tree diameter and heights as well as snags, logs, and othervegetation were inventoried in stands used for nesting. The structures ofstands used for nesting are consistently multistoried with many small treesand fewer large trees per area (Figure G. 1). They are typically mixed specieswith two or more age classes which have developed following one or moredisturbances such as light fire, windthrow, and root diseases. Species in theoverstory are generally redwood, ponderosa pine, sugar pine, western hemlock,and Douglas-fir, while the understory may include western hemlock, westernred cedar, white fir, tanoak, bigleaf maple, and Douglas-fir on dry sites. Thereare often large dead trees and logs on the forest floor. The structures resemblethose of old-growth stands (Spies and Franklin 1991).B. Producing Stand Structure for NorthernSpotted OwlsActual examples of thinning show that reducing the density of overstory treesallows space for trees to produce large crowns and stems, and for trees andshrubs to be established in the understory (Figures G.2 and G.3). If stocking isnot controlled, dense stands may develop (Figure G.4), and it would take manyyears for these stands to produce owl habitat.The following key points emerge from the review of stand development historyand literature (11 and 111) and from developing silviculture prescriptions (IV):1. Disturbances of various sizes and intensities are a natural part of longtermforest stand development.2. Many stands within the range of the owl are growing at high densities(many trees per area). Thinning these stands will increase growth rates,sizes of crowns, and diameters of remaining trees.3. Mortality caused by suppression and crowding among trees is not likelyto provide large snags or logs on the forest floor because only the smallertrees die. Thinning of stands will shift the size of a tree that dies fromdisease, insect, fire, and other causes, to large sizes.4. To provide large snags and logs on the forest floor in young (30 to 80+years) conifer stands, it often may be necessary to kill some of the largertrees in the stand. This is particularly true for stands regenerated afterharvesting or reforestation following a fire.5. Development of a multistoried stand from single-story conifer standsgenerally will require thinning, small openings in the canopy, or someother disturbance to reduce overstory density. If a dense layer of shrubsis present, disturbance or control of this layer likely will be required toestablish conifers or hardwoods which can form the additional layers.6. Young stands (10 to 80+ years) on productive sites develop quite rapidly.486