Negligible impacts of biomass removal on Douglas-fir growth 29 years after outplanting in the northern Rocky Mountains

To investigate the long-term impacts of biomass harvesting on site productivity, we remeasured trees in the 1974 Forest Residues Utilization Research and Development Program at Coram Experimental Forest in western Montana. Three levels (high, medium, and low) of biomass removal intensity combined with broadcast burning treatment were assigned after clearcut in western larch (Larix occidentalis Nutt.) stands in 1974. From 1976 to 79, twenty five 2 + 0 bare root seedlings of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) were consecutively planted in rows. In 2013, tree height, dbh (diameter at breast height), foliar N and C concentrations were measured. From cross-sectional sapwood area, growth efficiency (the ratio of 5-year-basal area increment to total leaf area) was calculated. Previous measurements from 1980, 1987, 1992, and 2001 were used for dbh and height growth analyses. At this site, none of the response variables were affected by biomass removal level. Only seedling planting year contributed significantly to affect tree mean height, dbh, volume. Growth efficiency was not affected by any treatment. These results indicate no apparent effect of biomass removal on site productivity for the range of biomass harvest levels performed.