Browsing by Author "Suvanto, Susanne"

Climate change is predicted to cause changes in vegetation productivity and biomass in northern areas. Understanding the factors affecting biomass helps us to estimate the future changes in plant communities and the amount of carbon stored in vegetation. In this thesis I examine the effects of soil properties (soil moisture, temperature, pH and calcium), geomorphological processes and topography on the small scale variation of aboveground vascular biomass. I also compare two biomass variables: the dry weight of a biomass sample and the vegetation volume. The data was collected during summer 2011 on the northern slopes of fell Saana, north western Finland. Modeling was done with generalized linear models (GLM) and also with generalized estimation equations (GEE) since they are able to take spatial autocorrelation into account. Variation partitioning was used to find out the single and combined effects of variable groups (soil, geomorphology and topography). The connections between the most common plant species and the biomass variables were also studied. Soil properties have a stronger impact on both biomass variables. Soil group alone explains 7 % of variation in the dry weight of biomass and 20 % of variation in vegetation volume. Geomorphology explains 4,7 % of variation in the biomass dry weight and 14,5 % in vegetation volume. Topography has the least effect on the biomass variables (2,2 % and 2,0 %). The combined effects of groups are also relatively strong, e.g. the combined effects of geomorphology and topography explain 9,7 % of variation in vegetation volume. Models with vegetation volume as a response variable were able to explain more of the variation (unexplained variation 48,7 %) than models of biomass dry weight (67,1 %). Also the relative importance of the variable groups differed for the two biomass variables, e.g. the soil group affected vegetation more than biomass dry weight. Both biomass variables correlated strongly with the two species with the largest coverage on the study site, crowberry (Empetrum nigrum ssp. hermaphroditum) and dwarf birch (Betula nana). The correlation of crowberry with vegetation volume was stronger than with biomass dry weight. Even though the models explain only about half of the variation, results suggest that soil properties and geomorphological processes have a clear impact on vegetation biomass. The impact of topography is strongly linked to other variable groups. A large amount of the unexplained variation and the importance of the combined effects of variable groups are due to the complexity of the factors controlling vegetation biomass. This makes it more complicated to predict the future changes of vegetation biomass. Changes will depend on how rising temperatures and increasing rainfall will affect not only soil properties and geomorphology but also all the factors that are behind the unexplained variation of biomass in the models.