CROWN DENSITY OF SPRUCE TREES RELATED TO NEEDLE BIOMASS

Several monitoring programmes for the 'new forest damage' in Europe are based on visual assessment of crown density. In this report crown density is related to measured crown characteristics. The material comprised 100 old and 25 young Norway spruce trees visually assessed by crown density relative to a fully-foliaged tree. All branches were recorded by diameter class, and branch weight, needle weight, needle retention and shoot length, were measured in a sample of about 8%. Crown density increased with increasing number of living branches per tree, especially in the lower branch diameter classes, and with increasing needle weight per branch. The ratio of needle dry-weight to branch basal area was curvilinearly related to crown density. In combination these effects implied that the visual assessment of slightly defoliated trees tended to underestimate the actual reduction in foliage biomass. Stem sapwood area and needle biomass were to some extent, but not completely mutually adjusted. Crown density increased with increasing needle retention and shoot length, but less pronouncedly so than with needle biomass.