Biomass and nutrients in Great Lakes – St. Lawrence forest species: implications for whole-tree and conventional harvest

Abstract

Total aboveground biomass and nutrient contents were measured in a mixed conifer and hardwood stand in Ontario. Removal of woody stems > 9 cm dbh (conventional harvest) yielded 138 000 kg/ha; removal of essentially all aboveground woody material (whole-tree harvest) yielded an additional 52 000 kg/ha, a 38% increase. Whole-tree harvest increased N removal by 191 kg/ha (132%). Logging slash on the conventional harvest plot added 163 kg N/ha to the forest floor. Nutrients within various biomass components of seven tree species were compared. Pinusresinosa Ait., the dominant conifer, produced the greatest amount of biomass per unit mass of nutrient, combining low nutrient concentrations with a high proportion of biomass in stem wood. Populustremuloides Michx., the dominant hardwood, had high proportions of cation-rich bark but had a lower whole-tree N concentration than most other species. High nutrient contents in Abiesbalsamea (L.) (Mill.) and Piceaglauca (Moench) Voss were related to large amounts of fine branches and foliage. Compared with the dominants, shade-tolerant species had less differences in nutrient concentrations between small and large diameter portions of stems and branches, suggesting a limited capacity for retranslocation. Abiesbalsamea was particularly poor at conserving K. A conventional harvest often leaves small diameter stems of species (Abiesbalsamea, Acerrubrum L.) that accumulate large amounts of nutrients and that may be poorly adapted to low throughfall cation inputs and high light intensities following overstory removal. Replacement of stands of Pinus spp. by Populus spp. represents a less efficient use of site nutrient capital in that the latter species produce less biomass per unit nutrient retained in permanent aboveground tissues. Whole-tree harvesting on nutrient-poor sites in the Great Lakes – St. Lawrence forest may lead to establishment of aspen stands of low productivity.