Epsilon Archive for Student Projects

Abstract

Recently more and more attention is paid to the quality of thinning operations and not only
thinning efficiency. In order to produce a valuable final crop at the end of the rotation period
injuries to the residual stand should be avoided. Thinnings of low quality may not favor the
growth of the remaining trees and the timber value at final fellings may be diminished. Wounds
imposed in thinning operations are most often reported to deteriorate the timber quality by the
incidence of stain or wood decay.
The study aimed at investigating the relationship between thinning damages and stand
characteristics such as basal area after thinning, dominant height, age at breast height, spacing
and tree species. Strip-road width, distance between strip roads and forwarder types were also
included. The study is based on an inventory project carried out at SCA Skog AB in northern
Sweden. Damage levels in relation to stand parameters were measured in 100 randomly chosen
thinned stands in five forest districts. Data collection was based on circular sample plots.
The average level of damaged trees was 5,8 %. Large variation in the number of damaged trees
was found among all stands measured. No clear pattern with regard to respective forest districts
could be seen. In regression analysis the group of stands dominated by Norway spruce or
lodgepole pine were found to be positively correlated with the damage levels. Thinning during
the winter period, i.e. December-March were found to be negatively correlated with the damage
levels. Spacing after thinning was nearly-significant and also negatively correlated with the
number of damaged trees. The analysis of damaged trees showed that trees with stem damages as
the dominant damage type amounted to 55,7 % while trees with butt damages as the dominant
damage type amouted to 44,3 %. Additionally, 61,1 % of the damaged trees were found within 5
m from the strip-road edge.
An overview of the litterature concerning thinning damages was done in relation to the obtained
results. Additionally, possible improvements towards the reduction of thinning damages were
discussed.