Climate change is expected to produce faster and greater changes in high-latitude regions, because it is likely to be amplified by alterations in albedo, atmospheric composition and permafrost. Terrestrial ecosystems in polar regions are strongly regulated by temperature and precipitation; they are less affected by human activities and will likely show the strongest signal-to-noise ratio. In the context of the International Geosphere-Biosphere Program (IGBP), the Global Change and Terrestrial Ecosystems (GCTE) research programme for the Arctic provides a useful scheme for studies pertaining to the prediction of the effects of climate change on terrestrial ecosystems. The primary aim of GCTE is to understand and model the effects of primary ecosystem processes such as the exchange of energy, water and trace gases with the atmosphere, element cycling and storage, and biomass accumulation or loss. Through intensive studies in key biomes along biogeochemical transects, the programme aims to model changes in species distribution and composition, and consequent changes in ecosystem function, in order to predict patterns of change in ecosystem composition and structure. Arctic research over the past 20 years has shown that climatic change has produced a change in the function of terrestrial ecosystems, which are now net sources of CO2 to the atmosphere (Oechel and Vourlitis 1996). This change is thought to be transient, but there is no evidence as to how long it will last. Moreover, the results of simulations based on climate-change scenarios are mixed with regard to whether C sequestration will increase or decrease within the next two decades. Plant productivity seems rather unresponsive to the observed warming, and the expected northward migration of vegetation will probably occur in the long term, in contrast with the relatively instantaneous response of soil microor-ganisms.According to Oechel and Vourlitis (1996), despite the development of the GCTE programme, we are still far from being able to predict the response of Arctic ecosystems to climate change. They maintain that much of this ignorance stems from the multivariate nature of natural systems, and the multitude of interactions and feedback which are difficult to define through field observations, experimentation, or even modelling approaches.
Antarctic terrestrial ecosystems have poorly organised communities whose dynamics are controlled by rather simple biological interactions and cybernetic feedback processes. The desert environment of Antarctic ice-free areas is strongly affected by changes in water availability, which in turn affects soil processes, hydrology and biogeochemistry, plant productivity, survival, and colonisation processes. Any reduction in ice cover will probably result in the exposure of new substrata, enhanced mechanical and chemical weathering of rocks, and increased rates of soil formation. There is therefore a need for continuous, improved instrumental monitoring of the physico-chemical and biological characteristics of periglacial areas in order to understand and model the effects of global change on water, permafrost, soil, and primary ecosystem processes. Monitoring should include remote sensing and in-situ measurements, mapping the extent of vegetation, and biological characterisation at community and population levels (both floristically and faunistically) to detect changes in community structure and extent, and possible biological invasions. Although Antarctic terrestrial ecosystems are rather "simple", the results of studies within the framework of the GCTE indicate that it is difficult to predict their response to climate and environmental changes. Research will be necessarily speculative, as predictions will be based on extrapolation of environmental and biogeographical data, palaeobiogeographical reconstructions, ecosystem modelling and ecophysiology (Adamson and Adamson 1992; Hansom and Gordon 1998). Although a short-term effect of warming and ice melting in maritime Antarctica is an increase in new uncolonised grounds, it cannot be excluded that enhanced snowfalls will reduce habitats for terrestrial and freshwater organisms in the future and/or in other Antarctic regions. The potential impact of exotic immigrant species may be overstated.
As discussed by Walton et al. (1997), some aspects of research on Antarctic ice-free landscapes cannot be ignored, for example, logistic costs and potential environmental impact, the paucity of long-term environmental data for many locations, the high sensitivity to climatic forcing, which may make it difficult to distinguish long-term trends from interannual variability, and the presence of many generalist species which may provide a buffer against change. The impact of logistic support to research activities and tourism could confuse the signals of global climate change and those of long-range transport of persistent pollutants. On the other hand, there is no doubt that global-change research in Antarctica will help identify environmental management options, and suitable approaches to minimise the impact of human activity and to ensure long-term protection and conservation of freshwater and terrestrial ecosystems.
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