Impact of shrub canopies on understorey vegetation in western Eurasian tundra

Abstract

Question: How does the composition and species richness of understorey vegetation associate with changing abundance of deciduous shrub canopies? What are the species‐specific associations between shrubs and understorey plants? Location: Tundra habitats along an over 1000‐km long range, spanning from NW Fennoscandia to the Yamal Peninsula in northwest Russia. Methods: The data from 758 vegetation sample plots from 12 sites comprised cover estimates of all plant species, including bryophytes and lichens, and canopy height of deciduous shrubs. The relationships between shrub volume and cover of plant groups and species richness of vegetation were investigated. In addition, species‐specific associations between understorey species and shrub volume were analysed. Results: Shrub abundance was shown to be associated with the composition of understorey vegetation, and the association patterns were consistent across the study sites. Increased forb cover was positively associated with shrub volume, whereas bryophyte, lichen, dwarf shrub and graminoid cover decreased in association with increasing volume of deciduous shrubs. The total species richness of vegetation declined with increasing shrub volume. Conclusions: The results suggest that an increase of shrubs – due to climatic warming or a decrease in grazing pressure – is likely to have strong effects on plant–plant interactions and lead to a decrease in the diversity of understorey vegetation.

The Response of Alpine Salix Shrubs to Long-Term Browsing Varies with Elevation and Herbivore Density

“…Furthermore, the height to stem diameter ratio was greater in the absence of sheep, and lowest at high sheep density, which implies that height growth may be more limited than radial growth by browsing. This supports the premise that interspecific competition, most likely from fast growing herb species that are highly selected by sheep in low alpine habitats (Evju et al, 2009), limits Salix growth in the absence of sheep: Indeed, cover of understory herbs has been linked to Salix shrub volume (Pajunen et al, 2011). Other recent work has also highlighted that herbivore density can affect the elevational distribution of plant communities (Speed et al, 2012).…”

“…(den Herder et al, 2008), as well as mountain hare (Lepus timidus) (Ehrich et al, 2012), moose (Alces alces), and other Cervidae and domestic sheep (Mob+k et al, 2009). Specific understory vegetation is also associated with canopy-forming wil-584 / ARCTIC, ANTARCTIC, AND ALPINE RESEARCH ᭧ 2013 Regents of the University of Colorado 1523-0430/6 $7.00 lows (Pajunen et al, 2011). Salix shrubs are highly selected by browsing herbivores (Kitti et al, 2009;Tape et al, 2010) and therefore would be expected to be more strongly affected by herbivore densities than other less preferred species (Gill, 2006).…”

Plant co-existence patterns and High-Arctic vegetation composition in three common plant communities in north-east Greenland

“…Plant co-existence and eventual establishment within the dominant vegetation are governed by many factors, including both external factors*e.g., availability of airborne seeds (Klanderud & Totland 2007)*and factors modulated by the species already present (Pajunen et al 2011), which may also affect microhabitat characteristics* e.g., the accumulation of allelopathic substances or the structure of the canopy of the dominant species, which has important effects on the availability of light to plants growing below (Shevtsova et al 1995;Totland & Esaete 2002), or on the provision of moisture, shelter and nutrients. Viable seed rain would be expected to decrease with increasing altitude (Thompson 1978).…”

“…The dynamic balance between variations in the resource and abiotic stresses on plants is important because this balance is expected to determine the nature of plantÁplant interactions (Lortie et al 2004) and thus control the plant co-existence patterns. The distinct role of contrasting life forms of plants and of individual species in relation to co-existence patterns in Arctic environments remains poorly explored (Pajunen et al 2011), although this issue is crucial to understand potential changes of vegetation under varying abiotic stress regimes.…”

“…This is related to the retreat of sea ice and increased precipitation in northern Greenland (Stendel et al 2008). The marked effect of climate change on organisms (e.g., Post et al 2009;Callaghan, Tweedie et al 2011) and on ecosystem functioning (e.g., Euskirchen et al 2006;Lara et al 2012;Myers-Smith et al 2011) in the Arctic and the consequences of these effects at a larger scale have led to an increasing importance of understanding climateÁ ecosystem interactions in northern latitudes, particularly as not all ecosystems have responded as expected to climate change (Callaghan, Tweedie et al 2011;. Snow cover and length of the growing season are crucial factors determining the characteristics and functioning of plant communities occurring in deglaciated areas in the Arctic (Evans et al 1989;Elberling et al 2008;.…”