Recovery Plan for the Northern Spotted Owl - DRAFT
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Recovery Plan for the Northern Spotted Owl - DRAFT

Recovery Plan for the Northern Spotted Owl - DRAFT Recovery Plan for the Northern Spotted Owl - DRAFT

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10.07.2015 Views

year intervals (Appendix F). With the reduction of fire during the last 6 to 10decades, forests have become quite dense and multistoried, primarily from theinvasion of more shade-tolerant grand fir, Douglas-fir, and Englemann spruce.Lack of fire likely has resulted in better owl habitat.Insects and diseases are of major concern in many of these forests. Defoliatorsand bark beetles are common, as are root diseases (Annillaria, Phelllnus and H.annosuni). Insects and diseases probably have increased as shade-tolerantconifers invaded after fire suppression (Appendix F). These forests frequentlyhave been managed by individual tree selection with the goal of salvaginglarger dead or diseased trees. This practice, along with fire exclusion, hascontributed to today's mixed species, multistoried stands. Fire hazard is highdue to the dry climate, fuels from dead trees, and the multistory structure(Appendix F).III. Stand Development andManagementThe studies and models discussed here were designed to understand andpredict the effects of thinning and regulating stand density on forest standgrowth, development, and yield. They were not designed specifically to determinehow to provide owl habitat. For example, they do not provide informationon snag production from mortality of larger trees or the development of largelimbs or cavities which may be used as nest sites. Nevertheless, these studiesare valuable background for developing silvicultural systems to provide habitat.They show that tree size and stand structure can be regulated by carefulmanagement of stand density. There are growth models, applicable to theforests used by owls, which can be used to predict trends in stand development,tree size, crown cover, mortality, and other factors. Background informationand techniques are available that can be applied to stands of variousages, structures, species composition, and sites to grow stands for owl habitat.There is a large body of literature on stand growth and development dating toEurope in the 19th Century (Assmann 1970) and it includes many studies inNorth America. However, we will discuss only the information developed fromstudies in forests within the range of the northern spotted owl.A. Stand Manipulation and ThinningNumerous studies have shown that regulation of stand density affects individualtree and stand characteristics such as crown length and width, branchand stem size, leaf area index, vigor, and wind stability. Effects are apparentin young and old stands. Reukema (1975) summarized information fromreplicated spacing studies, established 50 years earlier at Wind River ExperimentalForest. On these dry sites, high stocking reduced height and diametergrowth rates and resulted in stands of poor vigor. Eversole (1955) recognizedthese trends when the stands were 25 years old, and there was no reversal oftrends in height and diameter growth rates during the intervening 25 years.496The most thorough study on the effects of management on young Douglas-fir isthe regionwide "levels of growing stock study" (Marshall 1990, Curtis andMarshall 1986, Williamson and Curtis 1984, Tappeiner et al. 1982). The studyis being conducted on five study sites with each of nine treatments replicatedthree times at each site. Treatments range from no thinning to intensivethinning, with only about 50 trees per acre remaining at age 40 years. Thisstudy shows that in stands on a wide range of site productivity, frequent

thinning has altered substantially stand structure and tree growth. Forexample, after 25 years at the Hoskins, Oregon, study site, diameter distributions,crown length, wood volume, and basal area growth were altered bythinning (Marshall 1990). The average diameter of the stands, especially thenumbers of trees in the larger size classes, increased following thinning (FigureG. 5). For example, after heavy thinning, diameters ranged from 16 to 24inches; after light thinning they ranged from about 4 to 20 inches. The crownsize of individual trees and understory development increased as thinningintensity increased (Figure G.6). Understory biomass increased from about 9pounds per acre in unthinned plots to more than 6,300 pounds per acre withheavy thinning. The trends and actual values for diameter (Figure G.7) andother parameters at the other sites were quite similar to those at the Hoskins,Oregon, study site (Curtis and Marshall 1986).Thinning regimes can be flexible and Douglas-fir stands can respond equallywell to different intensities and timing of thinnings (Reukema 1972). Stands38 years old were thinned: a) lightly (12 percent volume removed) at 3-yearNumber oftrees per acre50Light40 thinning(treatment 7)30 _ j \ Heavy30 - / w \ No thinning(treatment 1)20 40100D060 - o thinning(treatment 9)80-40-20-00 1 0 20 30Diameter class (inches)Figure G.5. Number of trees per acre by diameter class at age 45 years; 20 years afterthinning. Hoskins, Oregon, level of growing stock study (Marshall 1990).497

thinning has altered substantially stand structure and tree growth. Forexample, after 25 years at <strong>the</strong> Hoskins, Oregon, study site, diameter distributions,crown length, wood volume, and basal area growth were altered bythinning (Marshall 1990). The average diameter of <strong>the</strong> stands, especially <strong>the</strong>numbers of trees in <strong>the</strong> larger size classes, increased following thinning (FigureG. 5). For example, after heavy thinning, diameters ranged from 16 to 24inches; after light thinning <strong>the</strong>y ranged from about 4 to 20 inches. The crownsize of individual trees and understory development increased as thinningintensity increased (Figure G.6). Understory biomass increased from about 9pounds per acre in unthinned plots to more than 6,300 pounds per acre withheavy thinning. The trends and actual values <strong>for</strong> diameter (Figure G.7) ando<strong>the</strong>r parameters at <strong>the</strong> o<strong>the</strong>r sites were quite similar to those at <strong>the</strong> Hoskins,Oregon, study site (Curtis and Marshall 1986).Thinning regimes can be flexible and Douglas-fir stands can respond equallywell to different intensities and timing of thinnings (Reukema 1972). Stands38 years old were thinned: a) lightly (12 percent volume removed) at 3-yearNumber oftrees per acre50Light40 thinning(treatment 7)30 _ j \ Heavy30 - / w \ No thinning(treatment 1)20 40100D060 - o thinning(treatment 9)80-40-20-00 1 0 20 30Diameter class (inches)Figure G.5. Number of trees per acre by diameter class at age 45 years; 20 years afterthinning. Hoskins, Oregon, level of growing stock study (Marshall 1990).497

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