EARLY SURVIVAL AND HEIGHT GROWTH OF DOUGLAS-FIR AND LODGEPOLE PINE-SEEDLINGS AND VARIATIONS IN SITE FACTORS FOLLOWING TREATMENT OF LOGGING RESIDUES

Logging residues were broadcast burned, piled and burned, removed, or left in place after clearcutting in a high-elevation subalpine fir (Abies lasiocarpa (Hook.) Nutt.)-lodgepole pine (Pinus contorta Dougl. ex Loud.) forest in north-central Washington. Survival, height growth and foliar nutrient content of planted Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) and lodgepole pine seedlings, variations in soil factors (nutrients, temperature, moisture, and compaction), and air temperature were compared for four residue treatments. First- and second-year survival of seedlings planted with a power auger was similar for all residue treatments. During the first growing season, little height growth occurred, and height growth was similar for all residue treatments, probably because of transplant shock. Second-year height growth increased greatly, with the most growth occurring on the burned treatments and the least occurring on the slash-left treatment. Levels of foliar nutrients generally were similar for all residue treatments for both species at the end of the second growing season, but in Douglas-fir, the highest levels of nitrogen (N), sulfur (S), calcium (Ca), and magnesium (Mg) occurred in the pile-burned treatments. Extractable soil nutrients initially increased with both burn treatments, but returned to levels similar to those in other treatments and the surrounding forest soil within 3 years. Twenty-seven percent of Douglas-fir seedlings and 31 percent of lodgepole pine seedlings had terminal shoots or whole tops that had been chewed off during the first year in the slash-left treatment. No damage occurred in the other treatments. Seasonal trends of air and soil temperature were similar for all residue treatments, but during summer, highest afternoon air temperatures occurred in the slash-left treatment. Soil temperature (at 20 cm) in the slash-left treatment during summer remained at 10-degrees-C compared to 14.5-degrees-C in the other treatments. Soil moisture levels remained high throughout the growing season. These results indicate that for the type of high-elevation forest studied, broadcast burning of residues resulted in the best performance of planted seedlings for the first 2 years after residue treatment.