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[20]. 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[22][23] 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[24].
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[25]. 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[26].
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[27] (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[28].
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[29].
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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