Recovery Plan for the Northern Spotted Owl - DRAFT

Spotted owl use of young, managed timberlands: The significance of theowl's relationship to old-growth forests (sensu Old-growth Definition TaskGroup 1986) is obvious: old-growth forests are declining rapidly throughoutthe owl's range as a result of logging (Thomas et al. 1990, USDI 1990). Ifnorthern spotted owls are ecologically dependent (Ruggiero et al. 1988) on oldgrowthor mature forests, then continued logging of their habitat will lead tothe probable extinction of the population (Thomas et al. 1990, USDI 1990).However, Forsman et al. (1977), Forsman (1988b), and Hays et al. (1989)reported spotted owls occupying young, managed stands at lower densitiesthan in old-growth stands. A managed stand is defined in a broad context,that is, managed stands in which cutting of trees has occurred. This clarificationis necessary because there are no examples of forests in which logging orsilviculture has occurred where the response of owls is documented experimentally.Further, Forsman (1980), Solis (1983), Forsman et al. (1984),LaHaye (1988), Chavez-Leon (1989), Solis and Gutifrrez (1990), and Sisco(1990) describe habitat used by northern spotted owls in both old-growth andmature stands. Their descriptions of mature forest structure used by spottedowls is similar to the structure of uneven-aged managed forests in northwesternCalifornia (Appendix B). Thus, it is not surprising that spotted owls arebeing observed in younger managed timberlands throughout the distribution ofthe subspecies (Diller 1989, Irwin et al. 1989b, 1989c, Kerns 1989, Pious1989). There is hierarchy of information needed to assess and understandthese observations of owls in managed forests. In order of increasing importance,these classes of information are 1) presence of individuals, 2) presenceof pairs, 3) density, 4) variation in reproduction, 5) survival schedules, 6)dispersal patterns, 6) ratio of internal to external recruitment, and 7) populationstability. The structure and proportions of habitats used by owls relativeto available habitats are also necessary to evaluate the observations. Finally,future harvest patterns must be known and must accommodate owl needs inorder to predict the effects of the logging activities on the birds inhabiting thesemanaged timberlands.On one side, this habitat variation argues that spotted owls are not habitatspecialists. On the other side, it suggests that spotted owls show adaptiveresponses to regional variation in environmental conditions. Regional variationin habitat selection by owls does not indicate that they will respond positivelyto any human-induced habitat changes in one part of their range that lead tohabitat conditions similar to those used by owls in other parts of their range.An additional problem in assessing variation in habitat use is the lack of aconsistent definition of vegetation seral stage classification (see Table F 1 inThomas et al. 1990). Terms such as "old-growth, mature, young age,unmanaged, managed, second-growth" are defined in the literature usingdifferent parameters and criteria. This impedes rather than facilitates communicationamong interested persons.Owls in managed forests within the California Klamath and California Coastprovinces usually occupy stands with high structural diversity, high canopyclosure, and either large-diameter trees or residual old trees (Appendix B).These stands are usually more than 60 years old after partial logging events ofthe past (Thomas et al. 1990). For example, stands in the redwood region ofthe California Coast province described by Kerns (1989) have a structuresimilar to unmanaged (i.e., not previously logged) mature stands occupied byowls in a nearby national forest (Solis and Gutierrez 1990). Apparently, thefast growth of redwood trees, presence of understory hardwood trees, and theremnant old trees within the stands facilitate rapid structural development ofthese coastal forests. Critical aspects yet to be estimated in previously harvestedforests are the survival, recruitment, dispersal, and reproductive patternsof these birds relative to conspecific populations in unlogged forests.21