Epsilon Archive for Student Projects

Abstract

Birch (Betula pendula Roth in this study) is a widespread broadleaf species in the Swedish
forests. Different birds, saproxylic insects, understorey vascular plants and mycorrhizal fungi
are dependent on birch and birch deadwood. The mixture of birch and Norway spruce (Picea
abies (L.) Karst) in forest stands has been long discussed due to their ecological compatibility
and ecosystem services.
In this study, initial data from five different experimental forest stands with planted birch
and Norway spruce has been used to simulate the stands until the final felling for management
alternatives with varying thinnings and species proportions. The stands had a group mixture of
Norway spruce and birch. The basal area development and diameter growth of birch have been
compared between treatments. The simulated birch deadwood over time and the net present
values of the stands for varying management alternatives have been compared respectively as
a biodiversity indicator and economic indicator.
The stands have been simulated with six different management alternatives with one
thinning where 10%, 20%, 30%, 40%, 50% and 60% of birch proportion after thinning has been
maintained. An unthinned alternative has been simulated as control. No significant loss in
productivity (total basal area of birch and Norway spruce) and the economic outcome has been
observed in the stands with an increasing proportion of birch. The basal area of birch was the
highest in the alternatives with 50% and 60% of birch and was the lowest in the alternatives
with 10% and 20% of birch. The post-thinning increase in the basal area of birch has been
observed. Due to the thinning response, the basal area of birch in the alternative with 40% of
birch had no significant difference from the basal area of birch in the alternatives with 50% and
60% of birch.
The diameter growth of birch was significantly higher in the thinning alternatives when birch
was thinned and with increasing thinning intensity (at 10% and 20% of birch proportion), the
diameter development of birch was the highest. Therefore, thinning favoured the birch diameter
growth. birch deadwood supply significantly increased when birch proportion was higher (40-
60%).
The net present values for different treatments with varying birch proportions in this study
did not show any significant decrease with the increasing birch proportion. Overall productivity
in the stands was not lost with increasing birch proportion in the stand and the revenues earned
were profitable. The birch deadwood in the stands with a higher initial proportion of birch was
significantly higher. Thus, based on the results from this study, maintaining a higher proportion
of birch as a group mixture (> 10%, as required by FSC) in the stands as well as trying out
mixtures with birch proportions between 30- 40% can be recommended which will allow
increasing the natural value of the forests without losing production and economic value of the
forests.