Epsilon Archive for Student Projects

Abstract

Mixed forests will harbour other ecosystem services than a planted coniferous
monoculture. This study used early results from a long-term experiment to examine
if different precommercial thinning treatments can be used to increase diversity in
planted stands of Norway spruce (Picea abies) mixed with high densities of natural
regeneration of birch (Betula spp.).
Precommercial thinning treatments are standard in the Swedish even-aged clear-cut
silvicultural system and are used to shape the future commercial thinning stand.
Three different precommercial thinning strategies were applied as treatments in
planted stands of Norway spruce (Picea abies). Used selection strategies were I)
spruce monoculture with an even diameter distribution and the largest stems, II)
mixed stand with an uneven diameter distribution and only the largest 1/8 of stems,
combined with the smallest trees and III) mixed stand an even diameter distribution
and the largest stems. The treatments were tested with densities of 1200 and 1500
stems hectare-1 after treatment. Investigated parameters after treatment were
quadratic mean diameter, diameter distribution, mixed species ratio and the
development over two years after treatment.
The experiment was established on two sites with three blocks on each site.
Precommercial thinning was performed in 0.08-hectare sized plots with a buffer
zone of 5 m. All trees within the treatment plot were measured directly after
precommercial thinning and two years after treatment, as a part of a long-term
experiment. Measurements were taken by cross-calipering all trees at 1.3 m and
registering tree species. Sample trees were selected from the whole diameter
distribution and used for height measurements.
Results showed that increased stand diversity could be created through a mixed
species strategy in precommercial thinning. The diameter and height distributions
were largely unaffected by treatment. Planted spruce had a larger diameter than the
naturally regenerated birches, which were more slender and less dominant. Overall,
the results were in line with previous studies in southern Sweden. The study was
concluded with practical applications and suggestions for future research.