Initial vegetative response to alternative thinning treatments in second growth Douglas-fir stands of the central Oregon Cascades

The Young Stand Thinning and Diversity Study was initiated to examine ecosystem level effects of alternative silvicultural systems on forest health and productivity. Typical "commercial thin", "heavy thin", and "light thin with gaps" treatments were implemented with uncut control in four 30-50 year old "second growth" Douglas-fir stands in central Oregon. Our objective was to determine immediate vegetative response to these thinning regimes.

In the first year following treatment, several aspects of stand character were evaluated. Differences in overall plant community structure were observed; results are comparable to other research following disturbance (Crouch 1985, Dyrness 1973). Herb, low shrub and tall shrub cover was highest in control plots with several significant differences between treatments. Bryophyte cover was strongly affected with a nearly linear decline in relation to overstory cover reductions. Tree regeneration was approximately uniform throughout the treatments, except in the smallest classes of hardwood seedlings. Species diversity imitated trends from other disturbances, e.g. fire (Franklin and Dyrness 1973) and clearcutting (Crouch 1985, Dyrness 1973). Colonizing weeds were present in thinned sites yielding a slightly higher value of species richness.

Natural cycles of disturbance and succession produce the diversity of late-successional forests necessary for many plant and animal habitats (Ruggiero et al. 1991). Stand thinning is comparable to natural disturbance in many ways. Our long-term goal is to determine which and to what extent these management strategies will resemble natural forest disturbance and succession, accelerating the return of old growth characteristics in younger managed stands.