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Vulnerability of European reindeer husbandry to global change

Vulnerability of European reindeer husbandry to global change

Around one million reindeer are grazed in northern Europe, on an area of about three quarters of a million square kilometres. These reindeer are managed principally by indigenous northern peoples - mainly Sámi, Komi and Nenets - and form an important part of their economic and cultural identities. The presence of large numbers of large mammals has a significant effect on the distribution and type of vegetation north of the treeline, and it is important to understand the influence of reindeer before attempting to interpret any changes that may be occurring in the pattern of vegetation.

Diagram as described adjacent

Organisation of reindeer husbandry within Europe. Grey areas are designated reindeer-herding areas. The red and blue lines indicate two levels of political/administrative subdivision. White areas are also used for herding but are not allocated to specific herding organisations.

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Mean present-day density of reindeer, interpolated onto the 55-km modelling grid employed by the BALANCE project.

As part of the BALANCE project, we are investigating the vulnerability of European reindeer husbandry to global change in the period to 2080. Socioeconomic and political factors are dominant, and are considered in the component of this project led by Dr Piers Vitebsky, but environmental factors are also significant. Of these, the most important is the distribution of vegetation. We model the reindeer density as a linear function of the biomass in 10 different 'plant functional types' (PFTs). These PFT biomasses are generated by our colleagues in the BALANCE project. By regionalising our linear model (using different sets of coefficients for each of the countries: Norway, Sweden, Finland and Russia), we can explain 76% of the variance in the current-day reindeer density on the basis of vegetation distribution. We are thus reasonably confident in using the predicted vegetation distributions for 2080 to estimate the likely reindeer density then. Our results suggest a reduction in total numbers of reindeer of between 8 and 23%, primarily as a result of increasing tree cover.

Diagram as described adjacent Diagram as described adjacent

Dominant PFT in 1990 (left) and 2080 (right). Dark green = boreal needle-leaf evergreen (e.g. spruce, pine); light green = shade-intolerant deciduous broadleaf trees (e.g. downy birch); yellow = tall deciduous shrubs (e.g. birch, willow); buff = tall evergreen shrubs (e.g. juniper); purple = graminoid and forb tundra; red = grassland.

We consider other environmental factors. Temperatures are predicted to increase, and since reindeer are adapted to low temperatures this has potentially a negative impact. In practice, it appears that only the projected increase in summer temperatures is likely to have a significant effect. Summer increases of up to 5 degrees are predicted to occur in the far north east of the region, increasing heat stress.

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Predicted summer maximum temperatures in 2080, and (right) increase in summer maximum temperature from 1990 to 2080. (Data calculated by BALANCE project colleagues)

In summer, major rivers present obstacles to the passage of reindeer, while in winter these rivers are frozen and can be crossed easily. Thus the duration of the freezing period is a factor. In most parts of the region, this is predicted to decrease by 0.5-1 months. The impact is likely to be most significant in regions where herding territories are dissected by major rivers. In general, this means the far eastern part of the region.

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Duration of the frozen period, in months, in 1990 and 2080.

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Rivers large enough to be uncrossable by reindeer, mapped onto the distribution of herding territories. (Note: only rivers within the geographical definition of Europe, i.e west of the Ural watershed, have been calculated.) The most significant dissection of territories occurs in the far east of the region, caused by the Pechora-Usa river system, although some dissection also occurs on the Kola Peninsula (Tuloma and Voron'ya rivers).

Deep snow cover renders the underlying vegetation inaccessible, or accessible only at considerable cost in energy expenditure. The frequency of deep-snow events is predicted to decrease in virtually all parts of the study region in which reindeer herding takes place, although there are some increases in the far north east of the region.

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Predicted increase (blue) or decrease (red) in the frequency of deep-snow events. (Based on data supplied by BALANCE project colleagues.)

A particularly dangerous snow-related phenomenon is refreezing, when some of the snow melts and then refreezes to form a layer of ice. If the layer is too thick it can be impossible for reindeer to break through it to the vegetation below, and unless supplementary fodder is provided many animals can die. Events of this severity occur every few decades. The phenomenon is called гололёд (gololyod ≈ 'hungry ice') by reindeer herders in Russia. It has been modelled by BALANCE project colleagues at the University of Utrecht. Trends in the maximum value of the 'refreezing index' for a particular month, averaged over ten years, vary spatially and month by month. In October, the trend in reindeer-herding areas is generally towards lower maximum values of the index, while in November it is generally towards higher values. In other winter months there is no discernable trend. Probably the November trends are more significant.

Diagram as described adjacent Diagram as described adjacent

Difference in 10-year mean maximum refreezing index between 2080 and 1990. Left: October; right: November. Red indicates decreasing value of the mean maximum index, while blue indicates increasing value. The calculations are not accurate for coastal pixels.