Changes in Tree Growth, Biomass and Vegetation Over a 13-Year Period in the Swedish Sub-Arctic

Abstract

This study was conducted in the Swedish subArctic, near Abisko, in order to assess the direction and scale of possible vegetation changes in the alpine-birch forest ecotone. We have re-surveyed shrub, tree and vegetation data at 549 plots grouped into 61 clusters. The plots were originally surveyed in 1997 and re-surveyed in 2010. Our study is unique for the area as we have quantitatively estimated a 19% increase in tree biomass mainly within the existing birch forest. We also found significant increases in the cover of two vegetation types-''birch forest-heath with mosses'' and ''meadow with low herbs'', while the cover of snowbed vegetation decreased significantly. The vegetation changes might be caused by climate, herbivory and past human impact but irrespective of the causes, the observed transition of the vegetation will have substantial effects on the mountain ecosystems.

Changes Versus Homeostasis in Alpine and Sub-Alpine Vegetation Over Three Decades in the Sub-Arctic

“…Although we cannot generalise from one forest site, we are not surprised to reveal decreased species richness at the forest site since the tree and shrub cover have increased considerably over the last three decades, changing light regimes and competition which may affect the composition and richness of the ground-vegetation (e.g. Callaghan et al 2002;Wielgolaski 2005;Walker et al 2006;Hedenås et al 2011).…”

“…The most pronounced vegetation shift supported both by warming experiments (Walker et al 2006) and observations over the last few decades, is an increased cover, biomass and upward movement of deciduous trees and shrubs (Kullman 2002;Van Bogaert et al 2010;Hallinger et al 2010;Hedenås et al 2011;Rundqvist et al 2011). Warming experiments also suggest that graminoids will generally increase in abundance (Walker et al 2006).…”

“…As a consequence, shifts in species distributions and plant community composition in Arctic and sub-Arctic regions are expected, and some changes have already been observed (e.g. ACIA 2005; Tape et al 2006;Bhatt et al 2010;Hedenås et al 2011;Rundqvist et al 2011;Callaghan et al 2011a).…”

Modelling Tundra Vegetation Response to Recent Arctic Warming

“…The underlying mechanism in the model is an increase in light attenuation, favouring taller plants to the detriment of the ground vegetation they shade. Shrub expansion and densification has been reported in numerous studies and related to recent warming trends (Kullman 2002;Jia et al 2003;Tømmervik et al 2004;Tape et al 2006;Hedenås et al 2011;Rundqvist et al 2011). A popular hypothesis is that increased microbial activity in warmer soils enhances the availability of nutrients, particularly nitrogen, and that this lends a competitive advantage to shrubs relative to other types of tundra plants (Chapin et al 1995;Tape et al 2006).…”

“…Changes in Arctic plant communities may already be taking place in response to warming over recent decades. Important lines of evidence include positive trends in surface greenness and photosynthetic activity inferred from satellite data (Tucker et al 2001;Bunn and Goetz 2006;Bhatt et al 2010;Beck and Goetz 2011), advancement of elevational and latitudinal treelines (Sonesson and Hoogesteger 1983;Kullman 2002;Harsch et al 2009;Van Bogaert et al 2010, 2011, and an increased cover, abundance and stature of shrubs in tundra areas (Kullman 2002;Jia et al 2003;Tømmervik et al 2004;Tape et al 2006;Hedenås et al 2011;Rundqvist et al 2011). Despite numerous local exceptions, the weight of evidence from observational studies suggests that, in general, Arctic vegetation is responding to rising temperatures through increases in productivity, density, cover and stature of vegetation and, in many areas, an increase in woody biomass and the representation of trees and shrubs (Post et al 2009;Callaghan et al 2011;Elmendorf et al 2012).…”