Wood volume yield and stand structure in Norway spruce understorey depending on birch shelterwood density

Wood volume yield and stand structure were investigated for Norway spruce u nderstorey growing at 1500 trees ha-l under birch shelters of two different densities, 300 and 600 trees ha(-1), and Norway spruce growing without she lter, in a field trial in the boreal coniferous forest, 56 years after the establishment of the stand and 19 years after establishment of the trial. Wood volume yield in sheltered spruce (mean annual increments of 1.87 and 1 .78 m(3) ha(-1) year(-1) under the dense and sparse shelterwoods, respectiv ely) was significantly lower than that of unsheltered spruce (mean annual i ncrement 2.43 m3 ha(-1) year(-1)). The loss in wood volume yield for shelte red spruce was more than compensated for by the additional wood volume yiel d in the shelterwoods (mean annual increments 3.26 and 1.88 m(3) ha(-1) yea r(-1) for the dense and sparse shelterwood respectively). Shelterwood density did not produce any significant differences in inequali ty of the understorey stands, measured as skewness and the Gini coefficient for the wood volume distributions. This implies that two-sided competition for nutrients and water was more significant than competition for light. Immediately after trial establishment, trees in the no shelterwood treatmen t (i.e. where all overstory trees had been removed) showed a marked increas e in diameter growth. Over time, the growth rate of unsheltered Norway spru ce was reduced to a level comparable to that of sheltered spruce. The diffe rence in average diameter has persisted during the trial period. There was no similar effect on height growth, resulting in an increased slenderness i ndex (h/d) with increased shelterwood density for the understorey trees. (C ) 1999 Elsevier Science B.V. All rights reserved.