Browsing by Author "Kainulainen, Heli"

Arctic shrubification means that woody plants will disperse to new, beforehand treeless areas due to changes in environments. Shrubification happens with the increase of number of individuals or size of individual plants as well as when plants disperse to new areas above or north of their current limits. Shrubification alters arctic environments and affects other species in the area. In northern Fennoscandian ecotone of forest and tundra the most common tree species are mountain birch, juniper, goat willow, rowan, aspen and pine. Local environmental variables and climate determine the distribution of these tree species. With changing climate the potential distribution of these species will also change. These changes can be predicted with species distribution modelling and using different climate scenarios. The current distribution of tree species as well as the heights of mountain birch were examined in the study area of Rastigaisa, Northern Norway. With distribution data and data from environmental variables a model based on ecological theory was constructed. Models explaining the current distribution of tree species were constructed using two different modelling techniques (GAM, GBM). These models were used to create predictions of probability of potential distribution for climate in 2040-2069 using three different climate change scenarios (RCP2.6, RCP4.5, RCP8.5). These predictions were binarized to enable studying of the area of potential distribution and the altitude of potential distribution. Same methods were used to create a model that predicts the height of mountain birch that were used to create models of mountain birch height change in different climate change scenarios. The most important environmental variables for the studied species were mean summer temperature and insolation as well as soil moisture. Slope and surface deposit type weren’t as important, but still affected the predicted distributions of species. The models predicted the current distribution of tree species rather well, even if there were some differences between observed altitude and predicted altitude. In all climate change scenarios the areas and altitudes of potential distributions of mountain birch, goat willow, rowan and pine grew remarkably compared to the present predicted distribution. The height of mountain birch also grew on all scenarios. The area and altitude of potential distribution of aspen grew in all scenarios, but there were differences of how much between models and scenarios. The altitude of potential distribution of juniper changes upwards so that the minimum and maximum altitude both moved. At the same time different models gave different results on the change of area of potential distribution so that in the GAM-model the potential distribution area of juniper gets drastically smaller. The results of this study are similar to the results in earlier studies about species distribution changes. It is likely that there will be shrubification in the study area when climate will warm up in the future. To get more accurate results in the future it would be important to take biotic interactions into account as well as survey the are more closely.