The structure of advanced virgin forests in Finland

Abstract

The study deals with the structure of advanced virgin forests in Finland based on the national forest inventory carried out in the 1920's. At that time, virgin forests covered 2/3 of the forested area of Finland. Stand structure was described in terms of the d.b.h. distribution. The study material consisting of 10 x 50 m sample plots was grouped according to geographical region, site type and the age class of the overstorey. A stand was classified to be advanced if the age of the overstorey was at least half of the currently applied rotation age and if the stem volume exceeded 40 m³/nectare. About 60% of all virgin forests (i.e. 932 sample plots) were classified to be advanced. In the 1920's. the majority of advanced virgin forests were mixed stands with an all‐sized structure. Trees of small diameter prevailed and the stem number diminished rather steadily with increasing d.b.h. Even‐sized stands with a d.b.h. range of 15 or 20 cm and a normally distributed diameter frequency accounted for only 10 sample plots (i.e. about one percent). The stand structures described in this study can be used as models when developing so‐called natural silvicultural regimes. This concept includes methods for maintaining and developing the growing stock as a mixed stand all‐sized in structure.