Browsing by Author "Niittynen, Pekka"

Soil moisture regulates a wide range of ecosystem processes at high latitude ecosystems. Soil moisture and temperature control carbon cycle in arctic soils and therefore had impacts on many climate change feedback loops. Arctic-alpine vegetation is adapted for cold and often dry or water saturated soil conditions though the adaptations are species specific. Therefore the aim of this study is to examine how soil conditions, especially moisture, affect on species fine scale distributions in low energy ecosystems. The data contains 21 study grids and holds 378 study plots (1 m2 each) in total. The data is collected during three summers in 2011-2013 at Saana massif in northwestern Finland. Vascular plant, moss and lichen species are sampled from all plots. Soil moisture and temperature are measured in situ, pH is determined from soil samples at a laboratory and radiation is calculated based on the fine scale topography. NMDS-ordination and nominal GBM-models are carried out to study how the explanatory variables affect on species composition. Species richness and diversity are examined by comparing GLM, GAM, and GBM models with the base variables to models which soil moisture is added as a fourth explanatory variable. The same two variable combinations are used to model distributions of individual species in biomod2 platform. Soil moisture and pH were the most effective variables that control vascular plant species composition. Soil moisture was alone the most important variable for mosses but none of the variables showed importance over others in case of lichens. Vascular plant and moss species richness increased with increasing soil moisture. Lichens showed an opposed trend. The community evenness is highest in moist habitats excluding lichens that showed the highest evenness in the driest end of the moisture gradient. Including soil moisture as an explanatory variable into the models improved the predictions of species distribution models in every species group. Vascular plants, mosses, forbs and decidious dwarf shrubs responded positively to soil moisture. Lichens had mostly negative and evergreen dwarf shrubs mostly unimodal response curves towards soil moisture. Soil moisture was the single most important variable in species distribution models but there was a lot of variation between the individual species. Soil moisture is the most important environmental variable that controls species distributions and vegetation characteristics at fine scale in the arctic-alpine environment. The moist habitats maintain the highest vascular plant and moss species pools and are therefore the most important ones for diversity on landscape level. Lichens are distributed more randomly and variables used in this study failed to model lichens as accurately as the other species groups. Most of the lichen species favored dry and acidic soil conditions but results could be due to low competition through low productivity, not direct effects on lichens survival. The individual species vary strongly in their responses to the environmental variables but the different growth forms appears to react quite similarly towards the explanatory variables. This research supports the idea of environmental heterogenity as an important factor for species distributions and confirms the need for local and fine scale studies. According to results of this study soil moisture should be included in species distribution models when predicting climate change effects on the arctic-alpine vegetation.