Terry V. Callaghan1, Andrei A. Velichko2*, Olga K. Borisova3 1 Sheffield Centre for Arctic Ecology, Univ. Sheffield, UK; Abisko Research Station, Sweden; e-mail: [email protected] 2* Institute of Geography RAS, Moscow; e-mail: [email protected] (Corresponding author) 3 Institute of Geography RAS, Moscow; e-mail: [email protected] GEOGRAPHY TUNDRA IN A CHANGING CLIMATE 4 ABSTRACT northern forest gives way to sparse forest Both palaeogeographical reconstructions with patches of the tundra, then, to patches and general circulation models indicate of forest in the tundra, and, finally, to the open that global warming is especially strongly tundra. Within the tundra/forest ecotone, manifested in high latitudes. Under a 2°С «the northern border of the forest», i.e., the increase in mean global temperature, almost extent to which tree species penetrate to the the entire modern tundra zone would north, can be traced. Currently, the northern become potentially suitable for tree growth. forest tree line is between 51°N (in eastern Nevertheless, palaeobotanic data cannot be Canada) and 84°N (in Greenland). In some applied directly to estimating vegetation regions, the tundra is only a narrow band of response to the global warming expected land (30–150 km) between the Arctic Ocean in the 21st century, as they characterize a coast and the closed boreal forests. In these quasi-equilibrium state of ecosystems, which regions, the Arctic ecosystems are particularly takes several centuries to be achieved. Low vulnerable to expansion of woody vegetation migration rates of trees, damage caused by under anthropogenic warming. Latitudinal fires and insects, processes of soil drying or patterns in the spread of the tundra are paludification, and influence of herbivorous influenced by altitudinal zonation, therefore, animals and human activities may slow down in mountain areas of the south part of the considerably forest spread in tundra. Climate forest/tundra ecotone, there is a complete warming will probably cause a decline in the transition from the northern boreal forest at populations of Arctic species and expansion low elevations to the tundra and screes in of ranges of some southern animal species the upper mountain zone. into the Arctic. Global warming, detected qualitatively KEY WORDS: tundra, polar ecosystems, initially, began in northern Siberia and global warming, northern tree line shifts northeastern North America in the 1960s. Since then, the permafrost temperature INTRODUCTION has risen by 2–4°C in northwestern North America and by 0.6–0.7°C in Siberia In this article, the term “tundra” is used in [Anisimov et al., 2002] causing intensification its broadest sense to refer to the type of of thermokarst processes and disturbances vegetation and ecosystems that occupy of soil cover. Under these conditions, the an area north of dense boreal forest. tundra transitioned from a carbon reservoir Clear boundary between these types of to a carbon source [Oechel et al., 1993]. vegetation does not exist; they are linked by Increased rate of decomposition of peat and mutual gradual transition (ecotone) where, growth of lake area caused a sharp increase in the direction from south to north, closed in methane emissions [Zavarzin, Kudeyarov, ggi311.inddi311.indd 4 117.08.20117.08.2011 111:53:141:53:14 2006; Christensen et al., 2004 and others]. productivity, and lesser participation of Studies of possible changes in the tundra tree species in vegetation composition. vegetation due to human-caused warming However, as in any other zone, in the most include the evaluation of the characteristic favorable sheltered habitats, there may be an time lag of vegetation response to this extrazonal community, for example, a plant warming and, in particular, the analysis of population whose main range lies far to the migration rates of tree species. south [Matveyeva, Chernov, 2000]. GEOGRAPHY Although the current Arctic climate is Biodiversity in the Arctic is rather low: it has 5 warmer than at any other time in the last about 3% and 2% of the global flora and 400 years [Chapin et al., 2005], in the tundra, fauna, respectively [Callaghan et al., 2005, there are still some populations of plants, Matveyeva, Chernov, 2000]. Nevertheless, such as patches of sparse forest that are some groups of plants (mosses, lichens, relics of even warmer Holocene Optimum horsetails) in the tundra are very diverse. conditions. Modern meridional gradients Other groups of species (e.g., large in the Arctic climate are significant. For mammals) are very poorly represented example, the average July temperature and here: after the extinction of the Pleistocene the annual precipitation range from 10– fauna at the end of the glacial epoch and 12°C and 250 mm in the southern part of the beginning of the Holocene, the tundra the tundra to 1.5°C and 45 mm in its far has been inhabited by only two species north, respectively [Callaghan et al., 2005]. of large carnivores and 2 species of large The growing season determined by the herbivores [FAUNMAP Working Group, 1996]. temperature and duration of the snow cover, In the tundra, there are over 1.800 species of varies from 3.5 to 1.5 months. In the tundra vascular plants, 4000 species of spore-bearing zone, there is continuous permafrost with plants, 75 species of terrestrial mammals, 240 a 40–80 cm deep, on average, seasonally species of birds, 3,200 species of insects, and thawed layer increasing from north to south. 2.500 species of fungi [Callaghan et al., 2005, Biological activity is mainly concentrated in Matveyeva, Chernov, 2000]. Some species of the annual thawed layer; the nutrients are animals and plants (e.g., reindeer, lemmings, poorly available to plants because of the cotton grass) are particularly numerous and extremely slow decomposition of organic widespread, and are typical of the Arctic. matter caused by various factors, including Trophic relationships in the tundra zone are low soil temperature. The Arctic ecosystems relatively simple with short food chain. In the have very low biological productivity. Arctic, about 3.8 million people reside, the Nevertheless, the continued existence of native population comprising 8% [Chapin an imbalance between the rates of carbon et al., 2005]. fixation and heterotrophic respiration led to a significant accumulation of carbon in the Plant and animal species, living in the Arctic Arctic soils that contain about 12% of the now, have characteristics that, in the past, global reserves of the soil carbon [McGuire enabled them to overcome a variety of et al., 2007]. natural “filters” [Körner, 1995], whereas the more southern species did not pass this Points of view of researchers on the filter, or have not yet reached the Arctic in classification of vegetation in the tundra their distribution. In general, the adaptation and its geographic distribution are quite of arctic plants and animals to the modern different. Assuming the broad definition harsh climate led to their specific responses to of the tundra used herein, its total extent warming and the invasion of more southerly is about 7.5 million km2 [Bliss, Matveyeva, species. The Arctic species are mostly long- 1992]. Within the tundra, from south to lived, slow growing, and have low and north, in general, there is a reduction in plant irregular reproduction rates [Callaghan et height, storied structure, and vegetation al., 2005]. ggi311.inddi311.indd 5 117.08.20117.08.2011 111:53:141:53:14 This article is largely based on the analysis of averaging about 40 m for 1° temperature material collected during the preparation of increase [Callaghan et al., 2005]. It was the section of Chapter 4 of the Report of the primarily due to warming of the mid-20th Working Group II IPCC in 2007, dedicated to century and to some changes in land use. the tundra ecosystems [Fischlin et al., 2007]. At the same time, in some regions of northern RECENT AND ONGOING CHANGES Eurasia, the forest boundary moved south GEOGRAPHY IN THE FUNCTIONING OF SPECIES due to progressive paludification [Crawford 6 AND ECOSYSTEMS IN THE TUNDRA ZONE et al., 2003; Hinzman et al., 2005]. At the same time, within the area from Archangelsk to Basic conditions for the functioning of the Chukotka, tundra-like landscapes emerged arctic ecosystems (climate, ultraviolet radiation, in the area of about 470 km2 because of degree of pollution, and socio-economic factors) human disturbance, i.e., logging and forest- are subject to constant changes [Callaghan tundra scorching [Vlassova, 2002]. Thus, in et al., 2005, Chapin et al., 2005]. Below, we the Arkhangelsk region and Komi Republic, shall mainly focus on transformations of the tundra border zone is now 40–100 km ecosystems in the tundra zone under the further to the south than shown by earlier influence of climate change that occurred in mapping. Numerous factors controlling the the past or is anticipated. location of the northern forest boundary include winter snowiness, because, among Observations indicate a gradual increase in other factors, the snow cover protects the the role of shrubs and trees in the tundra young shoots of trees from being eaten by zone. Thus, repeated aerial photography moose and reindeer [Cairns, Moen, 2004]. In showed that the role of shrubs in tundra cases where the forest boundary shifted to vegetation in northern Alaska has increased the north in response to the current global at 140 out of 200 sample plots [Sturm et al., warming, such shifts should be considered in 2001]. This trend is confirmed by satellite the context of the processes that developed images analysis for a larger territory. Birch throughout the Holocene, because in many forests in a region of northern Norway have locations, the modern forest boundary increased from 2.400 km2 in 1961 to over is in more southerly position than in the 3.500 km2 in 2000, and woody biomass Holocene Climatic Optimum.