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Silviculture, Growth and Production of Sitka Spruce - Preliminary Results from the Ecouves Experimental Scheme.

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The Ecouves experimental scheme, which was set up in 1966, is designed to compare six repeated silvicultural treatments, divided into three complete, but fairly different blocks in terms of fertility. This article presents the results obtained from the analysis of successive inventories from 1974 to 1988. Overall production by volume obeys the same function of the dominant height, whatever the fertility and the silvicultural treatment in compliance, hence, with Eichhorn's law. Somewhat lower production is however noticeable in the treatment that includes the most extensive thinning. Volumes predicted using this relation are lower than those obtained using the relation established for Brittany. Total production per basal area as a function of the dominant height follows the same pattern whatever the silvicultural treatment, but levels are slightly different depending on the block. Fertility and thinning stimulate girth growth of growing stock (250 per hectare) and of dominant trees. Thinning, in contrast to site fertility, has no influence on height growth. Removal of small understorey stems during a thinning operation involving 250 growing stock trees had no influence on their growth either. Intensive, early thinning decreases the risk of windthrows by producing stockier trees and accelerating their maturity. Less densely populated stands together with higher fertility foster thicker growth layers. Low-density treatment on favourable sites can lead to growth rings that overshoot the upper limit (10 mm) allowed for structural wood. This risk has yet to be quantified.

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