Predicting crown sizes and diameter distributions of tanoak, Pacific madrone, and giant chinkapin sprout clumps

Crown size and stem diameters were measured on a total of 908 sprout clumps of tanoak (Lithocarpus densiflorus), Pacific madrone (Arbutus menziesii), and giant chinkapin (Castanopsis chrysophylla). The clumps, age 1 to 16 years, were located at 23 sites in southwestern Oregon and 20 sites in northwestern California. Regression equattons were developed for predicting individual-clump crown size and stem-diameter distributions of dominant sprouts from the 2 total basal area (dm at 1.37 m) in stems of the parent ree (PBA) and number of growtng seasons ince burning (AGE). Variables of PBA, AGE, and species incombination accounted for over 75% of the total variation in hardwood crown width and height and for 62% of the variation in sprout number. Variables describing site characteristics and competing vegetation abundance did not explain more than 2% of additional variation in hardwood crown stze or sprout diameter distribution. On the basis of the Kolmogorov-Smirnoff test (c• = 0.05), the Weibull function adequately described the reverse J-shaped istribution of stem diameters for individual sprout clumps. The goodness of fit for each of the predictive models for tanoak and madrone was verified with independent data. West. J. Appl. For. 7(4):103-108. Evergreen species, such as tanoak (Lithocarpus densifiorus), Pacific madNote: Paper 2748 of the Forest Research Laboratory, Oregon State University, Corvallis, OR. Financial support for this research was provided by the USDI Bureau of Land Management and the USDA Forest Service under the auspices of the Southwest Oregon Forestry Intensified Research (FIR) program (grant no. PNW-85-422). Additional funding was provided by USFS Timber Management, Washington Office, San Francisco, CA. rone (Arbutus menziesii), and giant chinkapin (Castanopsis chrysophylla), are the dominant hardwood trees in southwestern Oregon and northwestern California. After a disturbance, such as cutting or burning, these species sprout vigorously from subterranean burIs (McDonald and Tappeiner 1990, McKee 1990, Tappeiner et al. 1990). Tanoak and madrone compete vigorously with associated Douglas-fir seedlings, limiting their growth (Hughes et al. 1990, Harrington et al. 1991a) and probably their survival. On the positive side, these hardwoods provide habitat and mast or berries for a variety of wildlife (McDonald and Tappeiner 1990, McKee 1990, Tappeiner et al. 1990). Effective management of pure hardwood or mixed hardwood/conifer stands in this region requires two types of quantitative information: (1) equations that predict size of hardwood crowns through the period of crown closure of the stand are needed to forecast expected levels of hardwood competition for associated conifer seedlings; and (2) computer simulators developed to predict growth and yield of stands in this region, such as ORGANON, require a listing of individual tree sizes for both conifer and hardwood components at an age when dominant stems can be identified (Hester et al. 1989). Thus, equations are needed to predict the number and size of dominant stems produced by individual hardwood clumps at various times since sprouting. The objective of this study was to develop equations that predict crown size and stem-diameter distributions of individual sprout clumps of tanoak, madrone, and chinkapin. Crown development of 1to 6-year-old sprout clumps of tanoak and madrone has been related to the size of the parent tree from which the clump originated (Tappeiner et al. 1984). In order to predict the size of a hardwood crown and the size distribution of its dominant stems up to the time of crown closure, we supplemented the data of Tappeiner et al. (1984) to include a broader range of hardwood ages (1 to 16 years) and a wider variety of sites throughout southwestern Oregon and northwestern California.