Nutrient and biomass removals from a red spruce--balsam fir whole-tree harvest

A mechanized whole-tree harvest was conducted on a watershed in central Maine dominated by Picearubens Sarg. and Abiesbalsamea (L.) Mill. The harvest removal and redistribution of biomass, nitrogen, phosphorus, calcium, magnesium, and potassium were estimated and evaluated with respect to estimates of site nutrient reserves. Regression equations were developed to estimate the nutrient contents and ovendry weight of the aboveground components of the Picearubens and Abiesbalsamea. Unit area estimates of nutrient and biomass removals were based on the application of the regression equations to a tally of all trees on twelve 0.04-ha square plots. Unit area estimates were made of exchangeable and total nutrients contained in the forest floor and glacial till above a hardpan. The harvest removed 90% of the biomass, 91 % of the nitrogen, phosphorus, potassium, and calcium, and 90% of the magnesium in the above-stump portions of the forest. These removals were from two to four times the amount of nutrients that would have been removed by a bole-only harvest, while increasing biomass removals by 1.4 times. The nutrients removed by the harvest were between 0.1 and 5% of the total soil reserves. Nutrient removals are evaluated in the context of three commonly used evaluation approaches: static comparisons of nutrient pools, nutrient input-output budgets, and computer simulation.