10-YEAR DEVELOPMENT OF DOUGLAS-FIR AND ASSOCIATED VEGETATION AFTER DIFFERENT SITE PREPARATION ON COAST RANGE CLEARCUTS

Side-by-side comparisons were made in an operational-sized, replicated experiment, installed in 1980-81 on four areas in the Coast Ranges of Oregon, to determine the effects of six methods of site preparation o n the subsequent survival and growth of Douglas-fir (Pseudotsuga menzi esii (Mirb.) France) and associated vegetation. A decade later, tree s urvival, total height, and stem caliper were significantly greater aft er site preparation by broadcast burning, slashing and burning, sprayi ng Tordon 101 and burning, or aerial spraying of glyphosate than for m anually spot-clearing vegetation at planting time, or no site preparat ion, and the differences were still increasing. Protecting seedlings f rom animals, primarily mountain beaver (Aplodontia rufa), with plastic mesh tubing resulted in 13 percent higher survival; and protected tre es averaged 6 percent taller, 9 percent larger in stem diameter, and 4 9 percent more in volume than unprotected trees at 10 years. Protectio n improved seedling performance in every site-preparation treatment. S ite preparation by burning reduced total cover the most, from 50 to 5 percent or less. Vegetation recovery in all treatments was rapid; orig inal levels were exceeded by midsummer 1981, the first posttreatment g rowing season. Total cover on spot-cleared areas almost equaled that o n unprepared areas by 1982 but not until 1985 or later on burned or sp rayed areas. Herbaceous vegetation was a much higher proportion of tot al cover for 5 years after burning or spraying than after spot-clearin g or no site preparation, but eventually all areas were dominated by w oody vegetation. Removal of the overstory by logging fostered diversit y among dominant plant species and initiated successional trends in al l areas. Site preparation caused large differences in the frequency of occurrence and surface area dominated by individual species but only minor increases in the total number of species. Dynamics of individual species or groups are shown by the frequency, cover, and average heig ht of their dominance in each treatment over time. Site preparation by burning or spraying and protection from foraging animals were require d to obtain more than minimum tree stocking and growth, even in moist coastal conditions. The study results are most specific to the salmonb erry (Rubus spectabilis Pursh) brush type but certainly have wider app licability throughout the Coast Ranges and beyond wherever a heavy cov er of competing vegetation develops rapidly and populations of foragin g mammals are high.