Vegetation composition and shrub extent on the Yukon coast, Canada, are strongly linked to ice-wedge polygon degradation

Abstract

Changing environmental and geomorphological conditions are resulting in vegetation change in ice-wedge polygons in Arctic tundra. However, we do not yet know how microscale vegetation patterns relate to individual environmental and geomorphological parameters. This work aims at examining these relations in polygonal terrain. We analysed composition and cover of vascular plant taxa and surface height, active layer depth, soil temperature, carbon and nitrogen content, pH and electrical conductivity in four polygon mires located on the Yukon coast. We found that vascular plant species composition and cover correlates best with relative surface height. Ridges of low-centred polygons and raised centres of high-centred polygons support the growth of mesic and wetland species (e.g., Betula glandulosa, Salix pulchra, S. reticulata, Rubus chamaemorus, various ericaceous dwarf shrubs, Eriophorum vaginatum, Poa arctica). Wetland and aquatic plant species (e.g., E. angustifolium, Carex aquatilis, C. chordorrhiza, Pedicularis sudetica) grow in low-lying centres of polygons and in troughs between polygons. We also found a relationship between vascular plant species composition and substrate characteristics such as pH, electrical conductivity and total organic carbon, although the individual influence of these parameters could not be determined because of their correlation with relative surface height. Our findings stress the regulatory role of microtopography and substrate in vegetation dynamics of polygonal terrain. Ongoing warming in this region will lead to changes to polygonal terrain through permafrost degradation and subsequent conversion of low-centred into high-centred polygons. Our results indicate that shrubs, particularly Betula glandulosa and heath species, have the potential to expand most.

Keywords

• Ice-wedge polygon mires
• western Canadian Arctic
• modern vegetation
• microtopography
• permafrost.