Biomass growth and element uptake by young trembling aspen in relation to site treatments in Northern Ontario, Canada

A second-growth boreal mixedwood, consisting mainly of trembling aspen and balsam fir, with white spruce, balsam poplar and white birch admixed, defoliated in part by spruce budworm was harvested in late autumn 1992 by conventional cut-and-skid, whole-tree logging. Four blocks, subdivided into 10-m 6 10-m plots, separated by buffer strips, were laid out. The objective of the study was to compare the efficacy and environmental implications of screefing (i.e. organic layer removal) versus high-speed mixing (using a prototype forestry rototiller), both applied in strips and across whole plots, versus no treatment (cut control) in terms of regrowth biomass production and nutrient uptake. All plots were quickly occupied by a verdant herbaceous regrowth and, depending upon treatment, hardwood shoots. Screefing generally increased numbers of hardwood shoots-relative to the control, whereas mixing generally reduced numbers. Above-ground standing crops including tree and non-tree species by the middle of 1997 ranged from 9500 kg ha(-1) on cut control plots to 4400 kg ha(-1) on whole-area mixed plots. Nutrient contents in the aboveground vegetation varied commensurately, ranging up to 91 kg ha(-1) for N, I I for P, 79 for K, 94 for Ca, 18 for Mg and 8 for S. Leafy matter recovery on the most responsive treatment (harvest with no further site preparation) was ca. 70% complete within five years and the N, P, K, Ca, Mg, and S contents therein had reached or almost reached the same levels as the precut stand. This implies that nutrient cycling largely resumes within five years of harvest. Crown Copyright (C) 2003 Published by Elsevier Science Ltd. All rights reserved.