Juvenile growth depending on canopy density and silvicultural treatment in naturally regenerated Norway spruce stands: first results of a weeding trial in the lowland of northwestern Germany

摘要

In the Lower Saxony Forest District of Sellhorn a weeding experiment was carried out in 1999 on a collective of fast growing spruce in a dense spruce natural rejuvenation stand. Three tending strategies, (self-differentiation, selective clearing, reduction of the amount of trees) under three canopy densities (100%, 70%, 50%) governed by the size of the basal area, were compared. In contrast to height increment, which depended almost entirely on the canopy density, a distinct increase in diameter could be achieved by early site enlargement. This effect was heightened by increasing the amount of available light. Stability of the individual trees was far inferior in the self-differentiating areas of the natural regeneration plot. The effects of weeding on branch strength has so far been tolerable, the amount of green knots was considerably higher and self-pruning was noticeably slower compared to that in the untreated rejuvenation areas. It was evident that under the prevailing site and silvicultural conditions, with a dense, continually accruing spruce regeneration plot, the self-differentiating ability largely independent of canopy density, is very limited. After a critical appraisal of all tested parameters, it would appear that early tree number reduction is a useful method of achieving a satisfactory increment of growth and stability.