Where do the treeless tundra areas of northern highlands fit in the global biome system: toward an ecologically natural subdivision of the tundra biome.

Risto Virtanen,Bernt Johansen,Lauri Oksanen,Jukka Käyhkö,Johan Olofsson,Hans Tømmervik,Juval Cohen,Tarja Oksanen,Jouni Pulliainen,Bruce C Forbes

doi:10.1002/ece3.1837

Abstract

According to some treatises, arctic and alpine sub-biomes are ecologically similar, whereas others find them highly dissimilar. Most peculiarly, large areas of northern tundra highlands fall outside of the two recent subdivisions of the tundra biome. We seek an ecologically natural resolution to this long-standing and far-reaching problem. We studied broad-scale patterns in climate and vegetation along the gradient from Siberian tundra via northernmost Fennoscandia to the alpine habitats of European middle-latitude mountains, as well as explored those patterns within Fennoscandian tundra based on climate-vegetation patterns obtained from a fine-scale vegetation map. Our analyses reveal that ecologically meaningful January-February snow and thermal conditions differ between different types of tundra. High precipitation and mild winter temperatures prevail on middle-latitude mountains, low precipitation and usually cold winters prevail on high-latitude tundra, and Scandinavian mountains show intermediate conditions. Similarly, heath-like plant communities differ clearly between middle latitude mountains (alpine) and high-latitude tundra vegetation, including its altitudinal extension on Scandinavian mountains. Conversely, high abundance of snowbeds and large differences in the composition of dwarf shrub heaths distinguish the Scandinavian mountain tundra from its counterparts in Russia and the north Fennoscandian inland. The European tundra areas fall into three ecologically rather homogeneous categories: the arctic tundra, the oroarctic tundra of northern heights and mountains, and the genuinely alpine tundra of middle-latitude mountains. Attempts to divide the tundra into two sub-biomes have resulted in major discrepancies and confusions, as the oroarctic areas are included in the arctic tundra in some biogeographic maps and in the alpine tundra in others. Our analyses based on climate and vegetation criteria thus seem to resolve the long-standing biome delimitation problem, help in consistent characterization of research sites, and create a basis for further biogeographic and ecological research in global tundra environments.

Highlights

The treeless tundra biome, characterized by low summer temperatures (Ko€ppen 1900; Ko€rner and Paulsen 2004; Ko€rner 2007), consists of arctic and alpine subbiomes (Bliss 1956; Billings 1973; Gabriel and Talbot 1984)
We studied broad-scale patterns in climate and vegetation along the gradient from Siberian tundra via northernmost Fennoscandia to the alpine habitats of European middle-latitude mountains, as well as explored those patterns within Fennoscandian tundra based on climate–vegetation patterns obtained from a fine-scale vegetation map
Altitudinal extensions of the tundra are routinely regarded as integral parts of the circumpolar arctic; the alpine sub-biome is restricted to middlelatitude mountains (Brown and Gibson 1983; Olson et al 2001; see Sonesson et al 1975; Bliss 1981)

Summary

Introduction

The treeless tundra biome, characterized by low summer temperatures (Ko€ppen 1900; Ko€rner and Paulsen 2004; Ko€rner 2007), consists of arctic and alpine subbiomes (Bliss 1956; Billings 1973; Gabriel and Talbot 1984). Altitudinal extensions of the tundra are routinely regarded as integral parts of the circumpolar arctic; the alpine sub-biome is restricted to middlelatitude mountains (Brown and Gibson 1983; Olson et al 2001; see Sonesson et al 1975; Bliss 1981). In contrast to Olson et al (2001), Ko€rner et al (2011) include all “rugged” tundra areas (with local altitudinal differences exceeding 200 m) in the alpine sub-biome, regardless of latitude or of absolute altitudes. They motivate their focus on topography by pointing out that many specific features of altitudinal zones or belts, which distinguish them from corresponding latitudinal zones, are caused by relative rather than absolute altitudes. Several authors (e.g., Elvebakk et al 1999; Moen 1999; Sjo€rs 1999; Walker et al 2005) use strictly the polar tree line (tree line at altitude zero) as the southern limit of the arctic, and regard all altitudinal extensions of the tundra as parts of the alpine sub-biome

Objectives

Methods

Results

Discussion

Conclusion