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Fig. 6.5 Time series of the difference in ice extent in March (maximum) and September (minimum) from the mean values for 1979—2005. Based on a least-squares linear regression, the rates of decrease in March and September were 2% per decade and 7% per decade, respectively. Recent data from March 2006 are also shown and represent a new record minimum for the period of observation. (Reproduced with permission from Richter-Menge et al., 2006.)

questions concerning the long-term survival of arctic vegetation. Will climatic warming lead to a new flourishing of arctic plants, or will the unaccustomed heat cause extensive destruction and loss of biodiversity in an ancient cold-adapted flora?

Much of the High Arctic, particularly in Eurasia, can be described as coastal (Fig. 6.2) and consequently the timing of the summer retreat of the sea ice has a strong influence on plant development. Recent years have seen a distinct trend for an earlier retreat of sea ice (Fig. 6.5) and one particular response noted at Hornsund in Spitsbergen has been remarkable coastal floral displays by the early flowering purple saxifrage (Saxífraga oppositifolia; Fig. 6.6).

Fig. 6.6 A vegetation response to climatic warming at high latitudes. Vigorous early summer flowering display of coastal populations of the purple saxifrage (Saxifraga oppositifolia) in recent years at Hornsund, Spitsbergen (77° N) appears to be related to an early retreat of sea ice.

Fig. 6.7 Trends of gross primary production (Pg) as interpreted from NDVI satellite measurements (see Section 5.2.1) in the tundra regions versus boreal forest areas. The dotted lines represent linear trends of the plotted parameters. Both areas have shown a general increase in air temperature (Ta), but with a drop in temperature following the Pinatubo eruption in 1992. Although both areas have warmed since the eruption and Pg initially recovered in both areas, Pg has tended to increase in the tundra since 1997, whereas Pg declined in the forested areas. (Reproduced with permission from Goetz et al., 2005.)

Fig. 6.7 Trends of gross primary production (Pg) as interpreted from NDVI satellite measurements (see Section 5.2.1) in the tundra regions versus boreal forest areas. The dotted lines represent linear trends of the plotted parameters. Both areas have shown a general increase in air temperature (Ta), but with a drop in temperature following the Pinatubo eruption in 1992. Although both areas have warmed since the eruption and Pg initially recovered in both areas, Pg has tended to increase in the tundra since 1997, whereas Pg declined in the forested areas. (Reproduced with permission from Goetz et al., 2005.)

A time series analyses of a 22-year record of satellite observations in which the Arctic is defined somewhat widely in terms of latitude (60-90° N) and not by vegetation (as in this discussion) has shown that only about 15% of the extended region displays significant positive trends, of which just over half involved temperature-related increases in growing season length and photosynthetic intensity, mostly in the tundra (Fig. 6.7). Trees growing north of 60° N in this study (Goetz et al., 2005) and described as arctic forest, in areas not affected by fire were found to have suffered a decline in photo-synthetic activity possibly due to drought as there was no noticeable change in growing season length.

In relation to the true tundra (the treeless Arctic) these satellite observations confirm some of the effects already noticed by arctic dwellers particularly in the Low Arctic. Willows and alders have been noted as growing taller, with thicker stem diameters and producing more branches, particularly along shorelines. Indigenous human communities have also reported increases in vegetation, particularly grasses and shrubs - stating that there is grass growing in places where there used to be only gravel. Further north, on Banks Island, in the western Canadian Arctic, it has been observed that the musk oxen are staying in one place for longer periods of time, which is taken as additional evidence that vegetation is richer. Arctic sorrel (Oxyria digyna) is described as coming out earlier in the spring, with noticeably bigger, fresher, and greener leaves (Callaghan, et al. 2005). However, negative effects are also reported. In northern Finland, marshy areas are said to be drying out. Sami reindeer herders in Utsjoki (northern Finland 70° N) have observed that berries such as the bog whortleberry (Vaccinium uliginosum) have almost disappeared in some areas. Other berry-bearing species such as cloudberry (Rubus chamaemorus) and cowberry or lingonberry (Vaccinium vitis-idaea) have been noted to be suffering adverse effects as a result of high temperatures early in the year followed by inadequate moisture. Declining cloudberry production has been noted over the last 30 years (Callaghan et al, 2005).

In arctic Alaska, air temperatures have warmed 0.5 °C per decade for the past 30 years and over this same period shrub abundance has increased. It has been suggested (Sturm et al., 2005) that winter biological processes are contributing to this conversion through a positive feedback that involves the snow-holding capacity of shrubs, and the insulating properties of snow. It is suggested that hardy microbes profit from higher winter soil temperatures, due to the snow trapping of the shrubs providing great soil insulation. The resulting increase in microbial activity increases plant-available nitrogen which then stimulates more shrub growth and yet more snow trapping.

Physically adverse effects can arise from high temperatures which bring about the melting of surface snow and ice thus exposing unstable slopes and screes. Climatically, the rain belts in Russia are moving north increasing the flow of Asian rivers into the Russian Arctic Ocean (Richter-Menge et al., 2006); this together with melting of the permafrost is in danger of destroying large areas of tundra. With the melting of the permafrost layer, the risks of flooding and erosion from increased river flow in spring will cause large-scale erosion in the Russian Arctic, and in areas where there has been nuclear weapon experimentation and related activities in Soviet times there is a real danger of releasing of radioactive isotopes into the Arctic Ocean (for review see Crawford, 1997b).

Fig. 6.8 Juxtaposition of contrasting habitats on the Brogger Peninsula, Spitsbergen (79° N). Note the dry beach ridges and gravel screes that alternate with the dark-coloured mires and greener patches of bog growing in the effluent from the Morebreen bird cliffs.

The question therefore remains: is the Arctic a fragile ecosystem, which will suffer major perturbation should climatic warming continue or has it a hidden biological resilience to change and disturbance that is not yet fully understood? The lack of uniformity of response is not surprising. The tundra contains a multitude of habitats both at large- and small-scale levels. In the latter, different microhabitats, which are likely to vary in their response to climatic warming, are often found in close juxtaposition to each other. Dry gravel ridges may suffer from drought while only a few metres away cold wet shores that harbour a large part of the arctic flora may in fact be growing better and flowering more profusely as a result of the earlier retreat of the sea ice (Figs. 6.6, 6.8).

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