Arctic Climate Impact Assessment ACIA 20002004 wwwaciauafedu

In 2000, the Arctic Climate Impact Assessment (ACIA) started. It is a collaborative project of the Arctic Council (CAFF and AMAP) and the International Arctic Science Committee (IASC). The goal of ACIA is to evaluate and synthesize knowledge on climate variability, climate change, and increased ultraviolet (UV) radiation and their consequences. The aim is to provide useful and reliable information to the governments, organizations, and peoples of the Arctic on policy options to meet such changes.

ACIA will examine possible future impacts on the environment and its living resources, on human health, and on buildings, roads and other infrastructure. Such an assessment is expected to lead to the development of fundamental and useful information for the nations of the Arctic region, their economy, resources, and peoples. Within the major, peer-reviewed ACIA scientific volumes published in 2004, there are three ecosystem chapters; a terrestrial, a freshwater, and a marine chapter. Each chapter deals explicitly with current biodiversity in the Arctic, including recent changes documented by indigenous knowledge, and the likely impacts of changes in climate and UV-B radiation. It seems likely that biodiversity in terms of number of species will increase in response to warming, but that some Arctic specialist species will be lost. Species will relocate as they did during past climate changes.

Millennium Ecosystem Assessment (MA) (2000-2005) (www.millenniumassessment.org)

In 2000, the Millennium Ecosystem Assessment (MA) board established a working group to provide the framework and criteria for selecting assessments at multiple scales and to make recommendations to the board for the component assessments. The MA is a "multiscale" assessment and the overall assessment will include component assessments undertaken at several different geographic scales, ranging from individual villages to the globe. The process has been designed so that the findings at any given scale are informed by the assessment components undertaken at other scales.

A diversity of ecosystem types and problems are addressed in this process, including the polar regions.

The MA will, among other things, contribute to:

• Enhanced public awareness of the impacts of ecosystem change on human well-being and the steps needed to address these impacts.

• Improved international and global cooperation in ecosystem management.

A focus of the MA is "ecosystem services," and biodiversity is an important component of these. The studies are ongoing.

Scandinavian/North European Network of Terrestrial Field Sites (SCANNET) (20012004) (www.scannet.nu)

In February 2001, the Scandinavian/North European Network of Terrestrial Field Sites (SCANNET) was formally inaugurated. SCANNET is a network of field site leaders, research station managers, and user groups in the North Atlantic Region that are collaborating to improve comparative observations and access to information on environmental change in the North. SCANNET partners provide stability for research and facilitate long-term observations in terrestrial and freshwater systems. One of the science topics that SCANNET is working with is biodiversity. The working group is led by Turku University (Finland) and documents the variations in trends of biodiversity among the sites.

The main aims are to:

• Explore the range of biodiversity information available at different spatial scales across the field stations/sites within SCANNET.

• Identify major gaps in the North European biodiversity knowledge.

• Develop comparable and standardized monitoring protocols to detect biodiversity responses to environmental changes over northernmost Europe.

The final results from this work are published on the network's web site.

The Circum-Arctic Terrestrial Biodiversity Initiative—Causes and Consequences of Changing Biodiversity in Arctic and Alpine Terrestrial Ecosystems (IASC CAT B) (2002- ) (www.iasc.no)

The Circum-Arctic Terrestrial Biodiversity Initiative (CAT B) was launched in 2002 as an IASC project. The broad goal of this program is to quantify and understand the role of biodiversity in Arctic and alpine ecosystems, and to evaluate both actual and potential threats to biodiversity.

The overarching goal is to understand the causes and consequences of changes in biodiversity in the Arctic (in the terrestrial realm). This program will address the key science issues outlined below through the formation of a multinational, circum-Arctic, integrated, and standardized research network. The project will aim to:

• identify relevant drivers of change across contrasting regional/local settings;

• develop monitoring strategies;

• conduct a variety of intra- and intersite experiments and meta-analyses;

• predict the potential impact of change on biodiversity and ecosystem function;

• predict the potential impact of changes in biodiversity on ecosystem function and feedback processes to further change;

• provide products to user groups such as global change modelers, the remote sensing research community, educators, industry and local communities, conservation organizations, and planners.

Terry Callaghan and Margareta Johansson

See also Climate: Research Programs; Conservation; Global Warming

Further Reading

Bliss L.C., O.W. Heal & J.J. Moore (editors), Tundra Ecosystems: A Comparative Analyses, Cambridge and New York: Cambridge University Press, 1981 Chapin III, F.S. & C. Körner (editors), Arctic and Alpine Biodiversity: Patterns, Causes and Ecosystem Consequences, Berlin: Springer, 1985 Cornelissen, H et al., "Global change and arctic ecosystems: is lichen decline a function of increases in vascular plant biomass?" Journal of Ecology, 89 (2001): 984-994 CAFF (Conservation of Arctic Fauna and Flora), Arctic Flora and Fauna: Status and Conservation, Helsinki: Edita, 2001 Matveyeva, N. & Y. Chernov, "Biodiversity of terrestrial ecosystems." In The Arctic Environment, People, Policy, edited by M. Nuttall &T.V. Callaghan (editors), Amsterdam: Harwood Academic Publishers, 2000, pp. 233-274 Nellemann, C et al., GLOBIO, Global methodology for mapping human impacts on the biosphere, UNEP/DENA/ TR.01-3, 2001

Sakshaug, E. & J. Walsh, "Marine biology: biomass productivity distributions and their variability in the Barents and Bering Seas." In The Arctic Environment, People, Policy, edited by M. Nuttall & T.V. Callaghan, Amsterdam: Harwood Academic Publishers, 2000, pp. 163-198 Vincent, W.F. & J. Hobbie, "Ecology of Arctic lakes and rivers." In:The Arctic Environment, People, Policy, edited by M. Nuttall & T.V. Callaghan (editors), Amsterdam: Harwood Academic Publishers, 2000, pp. 197-232

BIOGEOCHEMISTRY

V.I. Vernadsky first used the term "biogeochemistry" as a scientific discipline in 1926 in the context of a subdiscipline of geochemistry, which at that time had been an established research field for almost a century. Vernadsky recognized the importance of biological processes for certain geochemical reactions, but it is only in recent years that researchers have found that it is virtually impossible to study geochemical processes at the surface of the Earth without studying biogeo-chemistry. Researchers now know that biota affects almost all geochemical reactions at the surface of the Earth.

Biogeochemistry textbooks usually introduce and subdivide the Earth surface system as the atmosphere (gaseous envelope surrounding the planet extending 500 km above the Earth's surface), the lithosphere (the outer region of the solid Earth extending to a depth of about 100 km), the hydrosphere (the part of Earth that contains water in liquid, vapor, and frozen form), and the biota (life itself, that sequesters carbon and nutrients from the other spheres). The real thrust in the study of biogeochemistry, however, is the cycling of matter between these different spheres. The biogeo-chemical cycles have become a research subject of increasing importance in recent decades due to their pivotal role for the understanding of how Earth will respond to major anthropogenic impacts such as greenhouse gas emissions, acidification, and land-use changes.

The major global biogeochemical cycles include the global water cycle, the carbon cycle, the global cycles of nitrogen and phosphorus, and the global sulfur cycle. The global water cycle includes the everlasting importance of water in transport and transformations of matter in nature. The water cycle interacts with most other global biogeochemical cycles on the surface of the Earth.

The global carbon cycle is driven by the fundamental ability of photosynthetic organisms to capture energy from the sun in organic compounds that in turn act as substrate for the whole of the biosphere as well as a provider of oxygen to the atmosphere (see Carbon Cycling). Of special relevance to the Arctic is the significant uptake of atmospheric carbon dioxide in the cold surface waters of the Arctic Ocean and surrounding oceans. This is an important biogeochemical process that "helps" mankind, consuming some of the extra carbon dioxide we add to the atmosphere through the burning of fossil fuels. Other examples of biogeochemical processes associated with carbon cycling in the Arctic are found in the terrestrial environments. Here there are large carbon stores in the soils, and it is estimated that about 30% of the global soil organic carbon is stored in northern boreal and Arctic soils. This represents a significant past global atmospheric carbon sink, and biogeochemical studies are currently focusing on studying the stability of this sink functioning in a changing climate. There is evidence from northern Alaska that the tundra may be susceptible to change from a sink to a source of atmospheric carbon dioxide as a response to an initial warming. Whether this may lead to a sustained loss of soil organic carbon to the atmosphere is still uncertain and a matter of intense biogeochemical research. Further important carbon-associated processes in the Arctic include the anaerobic (oxygen-free) biogeochemical transformations of carbon in wet tundra environments. These lead to the formation, and emission to the atmosphere, of a range of different reduced compounds, including the important greenhouse gas methane. Wet tundra and northern wetlands are significant atmospheric sources of methane, and much attention in Arctic terrestrial biogeochemical studies has focused on understanding the controls on such trace gas emissions to the atmosphere.

The abundance of nitrogen and phosphorus controls many biogeochemical components and are often key determinants of ecosystem, functioning. Arctic ecosystems both terrestrial and marine, are generally nutrient poor, and nitrogen in particular is the limiting factor for ecosystem productivity. Carbon cycling can therefore rarely be studied in the Arctic without considering the biogeochemical transformations of nitrogen and phosphorus as well. Many ecological and biogeochemical studies in the Arctic have hence worked with factorial experimental manipulations of nitrogen, phosphorus, and other nutrients in various combinations to better understand the complex interactions between element cycling and climate that controls the productivity of ecosystems.

A prerequisite for understanding how human changes to biogeochemical cycling on Earth may affect climate in the future is a thorough understanding of how climate changes have been connected to natural biogeochemical cycling in the past. Here the Arctic contributes with a very important tool in that permafrost, ice sheets, and lake and ocean sediments keep records of past variations in the atmospheric concentrations of trace gases and other atmospheric constituents (see Ice Core Record). The study of ice core records, in particular, has become crucial for the understanding of global biogeochemical cycling and how it interacts with the physical climate system.

Torben R. Christensen

See also Carbon Cycling; Global Change Effects; Global Warming; Ice Core Record

Further Reading

Butcher, S.B. et al. (editors), Global Biogeochemical Cycles,

London: Academic Press, 1992 Reynolds, J.F. & J.D. Tenhunen (editors), Landscape Function and Disturbance in Arctic Tundra, Berlin: Springer, 1996 Schlesinger, W.H., Biogeochemistry: An Analysis of Global

Change, San Diego: Academic Press, 1997 Schultze, E.D. et al. (editors), Global Biogeochemical Cycles in the Climate System, San Diego: Academic Press, 2001

BIRCH FORESTS

Birches (Betula spp.) are widely distributed throughout the temperate and boreal forests of the Northern Hemisphere. The capacity to withstand low winter temperatures, lengthy snow cover, and cold summers allows tree-sized birches to reach the latitudinal and altitudinal limit of tree growth, in certain places extending beyond the treeline of coniferous species. Dominance of natural birch forests at the Arctic tree-line is restricted to the cool and oceanic climates of northeastern and northwestern Eurasia, but birches also form the alpine treeline around steppe districts of the Eurasian interior. Since they are light-demanding species, the ability to maintain themselves as climax forests must be viewed in the light of delimited competition with shade-tolerant species in these treeline areas. Elsewhere, birches are common as pioneer trees in secondary forests, but generally give way to shade-tolerant species at late-successional stages.

In the northwestern periphery of Europe, downy birch (Betula pubescens) forms the most extensive areas of pure birch forests. The northernmost occurrences appear to rest on shelters from cold and drying winds, but inadequate growing-season temperatures also prevent downy birches from reaching tree size at their northwestern extremities. Downy birch cannot withstand summer drought, and its distribution limit in southern Europe corresponds to an average July rainfall of 50 mm. Toward east, the distribution limit of downy birch relates to a mean January temperature of -30°C. The corresponding species in northeastern Eurasia, stone birch (B. erminii), is also associated with the cool and damp summer climate of northern coastal areas. It has been found to withstand winter temperatures down to -47°C, but does not form forests in areas with permafrost and warm summers. Both downy birch and stone birch are relatively persistent to the harsh and strong winds near Arctic oceans. The great majority of stone birches are found at the Kamchatka Peninsula, with similar extents of birch forests only present in northern Fennoscandia.

Birches are able to grow in a wide range of soils, including those very acidic and nutrient-poor sites near alpine and Arctic treelines. They vary considerably in structure and species associations, depending on local climatic and soil conditions. On base-poor soils in tim-berline areas of northwestern Europe, the subspecies, mountain birch (B. pubescens spp. Czerepanovii), occurs as small, crooked, and multistemmed (poly-cormic) trees. These open and scrublike forests are rather simple communities, often with ericaceous dwarf shrubs, willow shrubs (Salix spp.), junipers (Juniperus communis), and dwarf birches (Betula nana) as the only accompanying woody plants. On the driest and poorest soils in northeastern Fennoscandia, reindeer lichens (Cladonia spp.) dominate the forest floor together with crowberry (Empetrum nigrum coll.), cowberry (Vaccinium vitis-idaea), heather (Calluna vulgaris), and dwarf birches. Lichen-rich communities are typical of continental climates with low precipitation and thin snow cover. As precipitation and snowfall increase west of the Scandinavian mountain range, mosses (e.g., Hylocomium splendens, Pleurozium schreberi) replace reindeer lichens in the ground vegetation, and species such as bilberry (Vaccinium myrtillis) and dwarf cornel (Cornus suecica) become more prevalent. Also wavy hair-grass (Deschampsia flexuosa) sometimes dominates the forest floor in mountain birch forests, often due to grazing by livestock and semidomestic reindeer.

On base-rich soils in the coastal lowlands, birches grow as tall trees with single and straight trunks. Apart from birches, other species are usually admixed in the tree layer such as rowan (Sorbus aucuparia), aspen (Populus tremula), gray alder (Alnus incana), bird cherry (Prunuspadus), and tall willows (Salix spp.). In river valleys and fjords in northern Norway, meadow birch forests are particularly luxuriant, with tall herbs and ferns flourishing in the undergrowth. Globeflowers (Trollius europaeus), wood's cranes-bill (Geranium sylvaticum), meadowsweet (Filipendula ulmaria), monkshood (Aconitum lococtonum), alpine blue sow-thistle (Cicerbita alpina), lady-fern (Athyrium filix-femina), and ostrich fern (Matteuccia struthiopteris) are characteristic species in the ground vegetation. Low herbs and ferns such as beech fern (Phegopteris connectilis), violets (Viola spp.), and stone bramble (Rubus saxatilis) are also widespread in meadow birch forests, but dwarf shrubs, mosses, and lichens are less frequent.

In mountainous oceanic areas along the Norwegian coastline and on the North Atlantic islands (Scotland, Iceland, and southwestern Greenland), dwarf shrubs and grasses dominate the undergrowth. Occasionally other tree species such as rowan occur, whereas hazel (Corylus avellana) and silver birch (Betula pendula) are often intermingled with downy birches in northwestern Scotland. Vegetation is extensively modified by grazing, reflected in a high abundance of grasses such as wavy hair-grass, mat-grass (Nardus stricta), or common bent (Agrostis capillaris). In Iceland, bog bilberry (Vaccinium uliginosum) is widespread together with other dwarf shrubs, whereas wood's cranes-bill and stone bramble are common on richer sites. In the far northwest of Scotland, open woodlands prevail with heather, bracken (Pteridium aquilinium), and purple-moor grass (Molinia caerulea) as characteristic species in the undergrowth. On richer soils the following herbs are common: primroses (Primula vulgaris), wood sage (Teucrium scorodonia), bluebells (Hyacinthoides nonscripta), wood-sorrel (Oxalis ace-tosella), and wood anemone (Anemone nemorosa).

In Kamchatka, stone birch forests occupy large areas between the alluvial meadows in river valleys, and the dwarf pine and alder thickets (Pinus pumila, Alnus maximowiczii) on mountain slopes. The forests are open and parklike with trees looking more like oaks rather than white birches. The mild and very humid climate, and the fertile volcanic soils, favor the dense and tall undergrowth of herbaceous plants, resembling coastal birch forests in northern Norway.

The most conspicuous tall herb is meadowsweet (Filipendula kamtschatica) reaching 3-4 meters at full size, but other species such as cranesbill (Geranium erinathum), meadow rue (Thalictrum kemense), fire weed (Epilobium augustifolium), and horsetails (Equisetum hiemale) are also prevalent. Small trees of willows (Salix hultenii) as well as shrubs of mountain ash (Sorbus sambucifolia) and honeysuckle (Lonicera chamissonis) are among the most common woody plants in the birch forests. In certain subalpine zones in northeastern Eurasia, stone birches extend into the Pinus pumila thickets, in which they exhibit a poly-cormic form with several stems sprouting from the same base. These forests are vicarious to the timber-line forests in northwestern Europe, with Vaccinium-Empetrum heaths as the dominating undergrowth.

Vera Helene Hausner

See also Treeline

Further Reading

Atkinson, Mark D., "Betula Pendula Roth (B. Verrucosa Ehrh.) and Betula Pubescens Ehrh." Journal of Ecology, 80 (1992): 837-870

Fredskild, Bent & S0ren 0dum (editors), "The Greenland Mountain Birch Zone, Southwest Greenland." Meddelelser om Gr0nland, Bioscience, 33 (1990): 1-80 Hamet-Ahti, Leena, "Zonation of the Mountain Birch Forests in Northernmost Fennoscandia." Annales Botanicae Fennicae Vanamo, 34 (1963): 1-127 Hulten, Eric "The plant cover of Southern Kamchatka." Arkiv for Botanik (Ser. 2), 7 (1971): 181-257 Hunt, David (editor), Betula—Proceedings of the IDS Betula Symposium, October 2-4, 1992, International Dendrology Society, 1992, pp. 1-111 Wielgolaski, Frans E. (editor), Nordic Mountain Birch Ecosystems. Man and the Biosphere Series, Volume 27, London: The Parthenon Publishing Group, 2001

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