Do Shade and Shrubs Enhance Natural Regeneration of Douglas-Fir in South-Central Idaho?

Abstract

Abstract Shade duration and shrub composition in microsites with naturally regenerated Douglas-fir seedlings (Pseudotsuga menziesii var. glauca) were compared to randomly located control plots without seedlings in hot, dry group selection cuts in the southernmost Boise National Forest. Shade duration was estimated using a sighting device which allowed quantification of the degrees of the sun's arc intercepted by timber, shrubs, or other obstructions. Measurements were standardized for the median date for summer high temperatures. Seedlings received more whole-day (P<0.001) and afternoon (P<0.001) shade than control plots, and seedlings on southern exposures received more shade than those on other aspects. Seedling plots had more shrub cover than control plots (P<0.007). However, of nine shrub species examined, only buckbrush exhibited a significantly positive association with seedlings. Soil surface temperatures under buckbrush were reduced more than under other species, and unshaded surfaces remained above 50°C for extended time periods. These results suggest that natural regeneration of Douglas-fir may be enhanced by harvest practices and site preparation methods which provide shade during critical stages of germination and early seedling establishment. West. J. Appl. For. 10(1):24-28.