Management of land and water
- Human impacts on the biodiversity of the Arctic
Changes in both land and water use influence biodiversity in the Arctic. This is different to the situation in most of the more southern biomes where changes in land use predominate. In the Arctic, the limited expansion of forestry and agriculture is likely to be restricted to particularly productive environments, although there is greater potential for aquaculture in the Arctic.
In the Arctic, the original change in land use might not be obvious and impacts may be progressive and long-lasting. Thus the gradual increase in grazing pressure, particularly by sheep, has resulted in the loss of sward diversity and eventual soil erosion. This was probably a contributory factor in the extinction of agricultural colonies in Greenland between AD 1350 and 1450. In Iceland, “desert” with unstable and eroding soils resulted from a combination of removal of the 25% forest cover and the introduction of sheep since settlement in the 9th century. Soil rehabilitation is now a priority, but is a long, slow process. Establishment of long-term grass swards has had some success, and planting birch (Betula pubescens) and native willows (Salix lanata and S. phylicifolia) is proving a successful conservation measure, using mycorrhizal inocula, for re-establishing species and habitat diversity of grasslands, shrublands, and woodlands that were lost through overgrazing although non-native species can cause problems.
Draining of peatlands, and other wetlands including marshes and salt marshes, has been widely undertaken to bring the land into productive use, mainly for forestry but to a limited extent also for agriculture. In general there is an inverse correlation between the extent of drainage and northerliness. Data for relatively small areas are not available, but national data are presented in Table 10.5. The index, P, gives an indication of how much of the national peatland has been drained, which in the most northerly areas is relatively small. Drainage has a major impact on biodiversity. Invariably most of the species characteristic of the wetland are lost, except where small populations survive in drainage ditches. The newly created habitats are more prone to invasion by non-native species, and soil erosion may become more problematic. Migratory bird species may lose nesting places, and the land cannot retain as much water as before and so runoff increases during and immediately after storms. Drainage therefore has a major effect on the functioning of ecosystems, as well as encouraging biodiversity loss, usually for very limited economic gains at a time when climate change is likely to increase both the risk and rate of desertification in the Arctic. Biodiversity conservation in the Arctic should recognize the importance of wetlands as functional ecosystems with their full biodiversity complement.
Overgrazing on the tundra can be severe; the subject has been reviewed by Hallanaro and Usher. In Finland, there were around 120,000 reindeer at the start of the 20th century. This increased to around 420,000 animals by 1990, but subsequently declined to around 290,000 animals by 2000. The effects of overgrazing are clearly shown wherever areas of countryside are fenced off. Figure 10.8 shows an area of Norwegian Finnmark where the density of reindeer trebled between 1950 and 1989. Overgrazing eliminates ground cover by shrubs and dwarf shrubs, as well as reducing the cover of herbs, grasses, and lichens. A more detailed analysis of the area where this photograph was taken is shown in Fig. 10.9. Over the 23 years from 1973 to 1996, the area changed from one having around a sixth of the land being moderately to heavily grazed (with the remainder being slightly grazed), to one having around two-thirds being overgrazed, a little under a third being moderately to heavily grazed, and only a small proportion (probably less than 5%) being slightly grazed.
The long-term effects of overgrazing are unknown, but if it results in the elimination of key species, such as shrubs, the recovery of the overgrazed ecosystems will be very slow. If all the key plant species remain in the community, even at very low densities, and are able to re-grow and set seed after the grazing pressure is lifted, then recovery could be faster. Two factors are important – the intensity of the grazing pressure and the period of time over which it occurs. Experimental exclosures have shown that, once grazing pressure by large herbivores is lifted, the regrowth of shrubs and tree species can be remarkable. Outside the fence, willows are reduced to small plants, of no more than a couple of centimeters high and with a few horizontal branches of up to 20 cm. These plants have few leaves and generally do not flower. Inside the fence the willows grow to at least 40 cm high, and are full of flowers with abundant seed set (Fig. 10.10). It is unknown how long these dwarf, overgrazed plants can both survive and retain the ability to re-grow after the grazing pressure is reduced. There have been no studies on the associated invertebrate fauna of these willows. So, it also unknown whether the phytophagous insects and mites are able to survive such a “bottleneck” in the willow population, or for how long they can survive these restricted conditions.
Although the vascular plants are the most obvious, it is the lichen component of arctic habitats that can be most affected by overgrazing. In areas with reindeer husbandry, the lichen cover has generally thinned on the winter grazing grounds. In the most severely impacted areas the lichens have been almost completely grazed out of the plant communities, or have been trampled, exposing bare ground which is then subject to erosion. Lichens, which are capable of surviving the harshest of environmental conditions, are frequently the most important photosynthetically active organisms in tundra ecosystems. Albeit slow-growing, many lichen species only thrive at low temperatures, and there is concern that if climate change results in a reduction in the number of lichen species or individuals, there could be a massive release of CO2 to the atmosphere. The combination of very low growth rates, overgrazing by domesticated or wild mammals and birds, and climate change indicates that large areas of the Arctic are susceptible to huge habitat changes in the future. Potentially, the lichen cover could be replaced by bare ground, with the risk of erosion by wind and running water, or by species that are currently not native to the Arctic.
Forests provide shelter during the coldest months of the year, and some of the mammals that feed on the tundra in summer migrate to the forests in winter. Pressure on herbaceous ground vegetation, especially on the lichens, can be severe. This is likely to be more of a problem in managed forests where the trees are grown closer together, less light reaches the forest floor, and the herbaceous and lichen layer is thus sparser. Overgrazing of the forest floor vegetation, including the young regeneration of tree species, is a problem in some areas and a potential problem in all other areas. Overgrazing, however, may not just result from agricultural and forestry land use; it may also result from successful conservation practices. For example, the population of the lesser snow goose (Chen caerulescens) in northern Canada rose from 2.6 million in 1990 to 6 million in 2000 as a result of protection. In summer, the geese feed intensively on the extensive coastal salt marshes (of western Hudson Bay), but large areas are now overgrazed, the salinity of the marshes is increasing, and vegetation has deteriorated. These examples demonstrate the potential fragility of ecosystems in which the food web is dominated by a few key species – a situation not uncommon in the Arctic.
The introduction of species into species-poor northern ecosystems is a disturbance which can have major impacts on the existing flora and fauna. The impact of introduced foxes and rats on seabird populations on arctic islands is particularly strong. A similar situation also occurs when new species are introduced into isolated freshwater ecosystems or when conditions change within a lake. For example, opossum shrimps (Mysis relicta) were introduced into dammed lakes in the mountains of Sweden and Norway by electric companies to enhance prey for burbot (Lota lota) and brown trout (Salmo trutta). Unexpectedly, the shrimps ate the zooplankton that was a food source for Arctic char (Salvelinus alpinus) and whitefish (Coregonus lavaretus), leading to an overall decline in fish production. Arctic char provide many interesting insights into arctic species. The resident population in Thingvallavatn, Iceland, was isolated from the sea 9600 years ago by a volcanic eruption, and became trapped within the lake. There are now four distinct forms that, although closely related genetically, are very different with respect to morphology, habitat, and diet. The Arctic has been described as a “theatre of evolution” as the few resident species capitalize on those resources that are not contested by other species. This encourages genetic diversification, a feature that is strongly shown by the Arctic char, a genetically diverse species and the only freshwater fish inhabiting high-arctic waters.
The subtle and sensitive interactions within food webs are illustrated by an experiment at Toolik Lake LTER (Long Term Ecological Research) site in Alaska. Lake trout (Salvelinus namaycush) play a key role controlling populations of zooplankton (Daphnia spp.), snails (Lymnaea elodes), and slimy sculpin (Cottus cognatus). To test the hypothesis that predation by lake trout controls populations of slimy sculpin, all large trout were removed from the lake. Instead of freeing slimy sculpin from predation, the population of burbot rapidly expanded and burbot became an effective predator, restricting slimy sculpin to rocky littoral habitats, and allowing the density of its prey, chironomid larvae, to remain high. This is an example of changes in “topdown” control of populations by predators, contrasting with “bottom-up” control in which lower trophic levels are affected by changes in nutrient or contaminant loading (see also Chapter 8).
Disturbance resulting from management in marine ecosystems has not been widely studied, other than by observing the impacts of trawling on seabed fauna and habitats (Figs. 10.6 and 10.7) and preliminary consideration of the potential impacts of invasive species through aquaculture, ballast water, and warming. Impacts of trawling are not particularly apparent in shallow waters where sediments are soft and organisms are adapted to living in habitats that are repeatedly disturbed by wave action. In deeper waters, undisturbed by storms and tides, large structural biota have developed, such as corals and sponges, and which provide habitats for other organisms. These relatively long-lived, physically fragile communities are particularly vulnerable to disturbance and are not adapted to cope with mechanical damage or the deposition of sediment disturbed by trawls.
Fish farming also affects marine ecosystems. This can be local due to the deposition of unused food and fish feces on the seabed or lake floor near the cages in which the fish are farmed. Such deposits are poor substrates for many marine organisms, and bacterial mats frequently develop. There can also be polluting effects over wider areas due to the use of veterinary products. Over a wider area still, escaped fish can interbreed with native fish stocks, thereby having a genetic effect. Thus, commercial fishing and fish farming can have adverse effects on arctic biodiversity. Sustainable management practices may be difficult to develop, but their introduction and implementation are essential if the fishery industries are to persist into the future.
There is a particular need to assess the potential problems faced by migratory fauna. The challenges met by migratory species are illustrated by the incredible dispersion of shorebirds to wintering grounds in all continents (Fig. 10.4). Recent evidence on waders from the East Atlantic flyway compares the population trends in seven long-distance migrant species that breed in the high Arctic with 14 species that have relatively short migrations from their breeding grounds in the subarctic. The long-distance migrants all show recent population declines and are very dependent on the Wadden Sea on the Netherlands coast as a stopover feeding ground. The waders with shorter migrations are much less dependent on the Wadden Sea and show stable or increasing populations. The emerging hypothesis is that waders with long migrations are critically dependent on key stopover sites for rapid refueling. For the Wadden Sea, although the extent available has not changed, the quality of resources available has declined through expansion of shellfish fisheries. There is evidence of a similar impact on migratory waders at two other sites. In Delaware Bay, a critical spring staging area in eastern North America, the impact is again due to over-exploitation of food resources by people. Similarly, the requirements of people and waders are in conflict in South Korea where a 33 km seawall at Saemangeum has resulted in the loss of 40,000 hectares of estuarine tidal flats and shallows. This site is the most important staging area on the East Asian Australasian Flyway, hosting at least 2 million waders of 36 species during their northward migration. At least 25,000 people are also dependent on this wetland system.
Thus, there are many forms of physical and biological disturbance in the Arctic (as well as in southern regions used by arctic species during migration). Such disturbances arise directly or indirectly from human intervention and the management of land and water. Although deliberate intervention can generate unexpected consequences, there is no doubt that conservation management is essential if the biodiversity of the Arctic is to be protected. In particular, implementation of international agreements, such as the Convention on the Conservation of Migratory Species of Wild Animals (also known as the Bonn Convention) and the Ramsar Convention on Wetlands, is increasingly urgent as a means to protect wetland and coastal areas.
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