Browsing by Subject "tundra"

Reindeer herding and climate change are causing notable changes in tundra ecosystems. In this thesis, I examine the impacts of summer reindeer grazing and climate change on Fennoscandian tundra moss and lichen communities at Mt. Saana, North-Western Finnish Lapland. The research questions are whether there have been temporal changes in moss and lichen communities over three decades, if the changes are consistent under different grazing pressures, and if the changes reflect recent climate change. The study is based on permanent plots and long-term time series data from 1990 to 2023 at intervals of about ten years. The results indicate significant correlations between reindeer grazing and moss and lichen abundances and an indication of climate change affecting the vegetation composition. Heavy grazing pressure during summer reduced moss and lichen abundances, particularly affecting lichens, while mosses benefit from moderate grazing pressure. During the study period, mosses had overall increased, while lichens had decreased. A slight recovery of lichens was observed between 2010 and 2023. At Kilpisjärvi, mean temperatures have increased significantly over the study period, affecting vegetation growth conditions. The increase in moss abundance could be related to the warmer temperatures and the lichen dynamics to changes in snow cover, warm winter events and increased competition from vascular plants. The temporal changes are also possible due to variations in grazing pressure. Overall, the findings emphasize the significant effects caused by reindeer grazing and climate change in tundra vegetation. Thus, the effects of reindeer grazing and climate change should be considered simultaneously when studying the changes in vegetation composition in tundra environments.

In the process of decomposition soil carbon is transformed into CO2 by microbial respiration, which makes decomposition a key process for understanding carbon cycling an releases of CO2. Since the northern permafrost regions contain half of all belowground carbon and the tundra regions are expected to be markedly affected by climate warming, it is of particular interest to understand how warming will affect decomposition in the tundra. Decomposition is however influenced by many factors, from climatic factors such as temperature and precipitation to the belowground organisms inhabiting the soils and the aboveground system dictating the litter that falls to the ground and is decomposed. Further, grazing has been shown to oppose some of the effects of warming on tundra. In this thesis I analyzed data collected from two long-term field experiments, one in Kilpisjärvi (NW Finland) and the other close to Kangerlussuaq Fjord (SW Greenland), both using fencing for manipulation of grazing regime and open-top chambers for artificial warming. My aim was to not only investigate how warming and grazing affect decomposition, but also to understand whether the magnitude of changes in decomposition can be explained by changes in plant community traits and soil characteristics. I found that in contrast to my hypothesis, warming decreased decomposition in Kangerlussuaq, where the soil was drier and contained less carbon than in Kilpisjärvi. I found no effects of grazing on decomposition, plant community traits nor soil characteristics in neither of the study locations. Neither did I find any consistent associations between changes in decomposition and changes in plant community traits, indicating that the effect of litter quality on decomposition is minor in these areas likely rather limited by climate. I found an association for increased decomposition when plant community C:N ratio and C:P ratio increased as a response to warming, but only in Kilpisjärvi, and since increased plant community C:N and C:P ratios are linked to resistant litter this positive effect is unlikely driven by enhanced litter quality. However, I did find a positive relationship between increased root biomass and increased decomposition as a response to warming that was consistent across areas and grazing regimes, indicating that warming can boost decomposition in different tundra habitats by promoting root growth.