Browsing by Author "Lahtinen, Tuulia"

Finland has a relatively small amount of mixed forests in comparison to monoculture forests. Mixed forests can provide opportunities to improve and increase different ecosystem services. Regardless of the several studies conducted in Nordic countries around the mixed species forests, on-going and up-to-date research is still greatly needed. The most common mixed species forests in Finland have a mixture of spruce and birch or pine and spruce. The main objective of this study was to examine the growth dynamics and the present state of single storied, young commercial spruce-birch (Picea abies, Betula pendula, Betula pubescens) mixture stands, where juvenile stand management practices have been done. The data gathering was conducted in southern Finland from 10 different stands which all had two 500 square meter area plots. This project is part of SEKAVA-programme led by Luonnonvarakeskus (Natural Resources Institute Finland). The stand level data was first analyzed and described with Excel program. The first hypothesis assumed that in these forests silver birch was naturally regenerated to site after planted spruce. The second hypothesis was that spruce and silver birch have been growing height in phase for the last 4 years. It was established that the silver birch was approximately only one year younger on stump height than spruce. The height difference of dominant sample trees between spruce and silver birch was only 1,4 meters. The data also showed how within the last four years the height growth of spruce and birch has been very different. The spruce could have up to 10 cm bigger annual height growth in comparison to the height growth of the silver birch. These measurements were taken as the average annual growth from the past 4 years. The tree level data was modelled with R studio -program to observe the factors affecting the tree growth. During the data analysis, it was established that Chapman-Richards model was more suitable for the needs of the research than the generalized mixed model. The Root Mean Square Error (RMSE) for Chapman-Richards model for spruce model was 26,3 % and 9,1 % for birch model. The annual height increment of the tree level was modelled by a linear mixed model. The RMSE for linear mixed spruce model was 14,4 % and 19,3 % for the birch model. These models showed how the nutrition levels of the ground work as a contributing factor of the diameter growth for both spruce and birch. Additionally, spruce trees had the better annual height growth the longer the tree was, and the lower the crownline was. Birch trees had also the better annual height growth the longer the tree was. The research was able to conclude that spruce trees had the strongest annual height increment when aged 20 years while the growth of birch trees started to slow down when reaching the age of 20 years. Based on the research data, silver birch grows notably better than downy birch in a mixed forest of birch and spruce trees. The models used in this research were specifically built to support this thesis and therefore are not exactly transferable for other studies.