Natural Regeneration of Douglas-Fir (\u3cem\u3ePseudotsuga Menziesii\u3c/em\u3e Var. \u3cem\u3eGlauca\u3c/em\u3e) in Southcentral Idaho Clearcuts: Effects of Shrubs and Shade on Seedling Establishment

Limited natural regeneration of Douglas-fir (Pseudotsuga menziesii var. glauca) exists on clearcut sites in the southern Boise National Forest. In this study I measured 20 neighborhood characteristics of 340 naturally-regenerated seedlings and 235 randomly-selected plots on nine study sites. stepwise logistic regression analysis indicated that only one of those variables, shade, explained a substantial amount of the variation in seedling presence. Path analysis was used to illustrate the interrelationships between the four variables retained in the logistic regression model. Other variables provide information useful for forester managers interested in improving natural regeneration. Ceanothus velutinus, for example, appears to improve natural regeneration of Douglas-fir in the study area. To test the conclusion that shade is important for seedling survival I conducted a field experiment in which 110 newly-planted 2-0 Douglas-fir seedlings were shaded with standard shade cards; 110 seedlings served as un shaded controls. Shaded seedlings had significantly greater first-season survival than control seedlings. In addition, control seedling survival was higher on western aspects than on southwestern aspects