Structural changes in two virgin boreal forest stands in central Sweden over 72 years

Abstract

Structural changes were analysed in two virgin forest stands by comparing tree data collected in 1922 and 1994. One stand was dominated by pine (Pinus sylvestris L.), while the other was a mixed pine and spruce (Picea abies (L.) Karst.) stand. Between 1922 and 1994, the standing volume of living trees increased by 46% in the pine stand and by 71% in the mixed stand, while the volume of dead trees increased by 126% and 87%, respectively. The proportion of spruce increased at the expense of pine and deciduous tree species in both stands. The density of conifer seedlings fell by 90% between the two dates, and diameter distributions changed considerably as a result of changed regeneration conditions and differing mortality rates of different size classes. The data suggest that a reversed J‐shaped diameter distribution of spruce could be a temporary phenomenon rather than a stable long‐term characteristic. The structural changes found, which seem to be characteristic of many protected forests, appear to be due to the absence of fire disturbance. It is questionable, therefore, that the policy of fire prevention is consistent with the major aims of nature conservation programmes.