Optimizing the structure and management of uneven-sized stands of Finland.

摘要

In Finland, uneven-sized forest management is gradually becoming an acceptable practice. At the moment, there are no silvicultural instructions for the management of uneven-sized forests, although there is willingness among forest owners to adopt this practice. This study optimized the steady-state structure and management of uneven-sized Scots pine and Norway spruce stands, so as to help develop management instructions. The post-thinning diameter distribution of the uneven-sized stand was optimized with 20-year cutting cycle when aiming at maximal economic profitability. Spruce stand optimizations were done for fertile and medium sites and pine stand optimizations for medium and poor sites. The optimal post-thinning distributions had a truncated reverse J shape, the frequencies of all trees larger than 18-20 cm being zero. This shape means that all log-sized trees have to be removed at 20-year intervals when economic profitability is maximized. When sawlog production was maximized, the largest retained trees were 25-30 cm in diameter at breast height (d.b.h.). The optimal diameter distributions of pine stands were clearly more uniform than spruce distributions, i.e. the preponderance of small trees was less pronounced in pine. With 2 per cent discounting rate, the optimal post-thinning basal area of trees larger than 5 cm d.b.h. was 11-12 m2 ha-1 for fertile spruce stands and 4-9 m2 ha-1 for pine stands and spruce stands of medium fertility. Uneven-sized management was found to be more profitable than even-aged management; even-aged management was more profitable only in spruce stands on fertile sites in southern Finland with low discounting rate (1 per cent). Increasing discounting rate and decreasing site productivity improved the relative performance of uneven-sized management.