|Abstract or Summary
- Snags, standing dead trees, are used by many species of wildlife. Despite the importance of snags their basic ecology remains unknown.
Some forest management practices eliminate snags from the forest with a concomitant effect upon snag-dependent wildlife. My objective was to describe the density, spatial distribution, and physical character of snags in seral. stands of Douglas-fir Pseudotsuga men%iesii (Mirb.) Franco in the Oregon Coast Range. I sampled 33 stands in Western Oregon. Natural and managed
Douglas-fir stands and riparian stands were sampled in general age classes of 10, 35, 70, 100 and 2OO+ years. Three of these Douglas-fir stands were research Permanent Sample Plots (PSP). I described snags in relation to changing vegetation (forest sucussion) and the decay process of snags (snag succession). On the PSPs I used linear regression and discriminant analysis to examine the relationships 1) between age of snags (the time since tree death) and their
physical characteristics, and 2) between past use of snags by woodpeckers and the physical characteristics of snags (Appendix II). I used data and equations from the PSPs for an1ysis of snags in the remaining 30
stands of the Coast Range Sample (CR5).
Populations of snags are dynamic. As the forest ages the rate of production of snags decreases, and consequently, the density of snags decreases from 77.0 to 7.4 per acre in natural stands of Age Classes 35 and 200+, respectively. In these same natural stands, respectively, the mean dbh of snags increased from 5.3 to 28.3 inches. Douglas-fir snags compose >80 percent of total snag densities in each forest age
class. The spatial distributions of snags were random (61 percent), aggregated (31 percent) or regular (8 percent) in natural stands of Douglas-fir. Individual snags are dynamic. The physical characteristics of
snags change with age and decay. The changes in physical characteristics of snags are correlated significantly with snag age (P<0.00l); however, the aging and decaying of snags are correlated imprecisely. Larger snags stand longer; some of the largest Douglas-fir snags 614 inches dbh) stand longer than 200 years. The densities (standing crops) of snags in seral stands of Douglas-fir are the interactive products of rates of production and survival of snags. Generally standing crops of snags are composed of few young (8ound) and old (highly decayed) snags and more middle-aged
snags (partially decayed). Riparian stands had lower densities of snags than natural stands of Douglas-fir. Only riparian forests had notable densities of red alder Alnus rubra Bong snags. The densities of snags in managed stands of Age Classes 3S, 70, 100, and 10 were significantly less than the snag densities in natural stands of Age Classes 35, 70, 100, and 200+, respectively (x2=30.3,
23.1, 7.8, 7.0; P<0.01). In this study the kinds of snags in natural and managed stands were similar. Clearcutting of natural stands of Douglas-fir, however, eliminated large, sound snags. The effect that forest management has upon populations of snags is
a function of the intensity of management. Even though stands sampled in this study were not intensively managed, populations of snags had their numbers reduced and compositions altered. The conversion of old
stands to young stands by clearcutting had the most detrimential effect upon populations of snags. The reduction or elimination of snags through management will result in the reduction or elimination of
snag-dependent wildlife in Douglas-fir forests. To maintain snag-dependent wildlife the snag resource must be maintained through careful management. Suggestions for snag management are given in Appendix III.