Research

Land Forms and Vegetation

Overview:

Several land form and vegetation types occurring within the region.

-Thaw Lake Plain: numerous thaw lakes, drained lake basins, and expanses of low centered, ice-wedged polygons. Vegetation: aquatic and wet tundra species including pendant grass, aquatic sedges, cottongrass, and a few herbaceous plants and mosses.

-Hilly Coastal Plain: gently rolling hills and poorly developed ice-wedge polygons. Vegetation: several varieties of willows and herbaceous plants.

-Foothills: hills separated by drainage channels giving the hills a "ribbed" appearance. Vegetation: sedge tussocks, dwarf shrub willow, birch, and alders. Height and density of these plants are dependent upon the protection given by the surrounding slopes. (Some willows may reach six feet, while dwarf shrubs on the coastal plain may rarely exceed a few inches.)

-River Flood Plains: barren deltas, braided river channels, and the terraces and alluvial deposits associated with old river channels. Vegetation: alpine tundra.

Flora:

“Due to the extreme cold, short growing season and nutrient-poor soils, Arctic vegetation is extremely fragile. Plant communities scarred by bulldozer tracks, oil spills and other human activities can take decades to recover.”

Source: http://oz.plymouth.edu/~lts/conservation/Ecosystems/northslope.html

Vegetation on the arctic tundra is highly diverse.  The shrub tundras are dominated by deciduous vascular plants.  Slightly warmer soil temperatures, deeper thaw, and more rapid N mineralization associated with the high water flow rate in water track and river bar localities cause denser canopies and higher total foliar N. 

The differences in canopy structure between the graminoid-dominated wetland tundras and the mixed tussock tundra communities are probably related to drainage characteristics and their effects on nutrient availability

The highly heterogeneous nature of the heath sites is probably determined by their different degrees of exposure on ridge and hill tops.  Microtopography affects the growth and structure of heath, with sheltered hollows causing denser vegetation and ridge tops causing sparse canopies. (Shaver et al., 1996)

(Source: Williams, M.; Rastetter, E. Vegetation characteristics and primary productivity along an arctic tarnsect: implication for scaling-up.  Journal of Ecology 1999 87: 885-898.)

Photosynthesis and Respiration in Mosses and Lichens

Roles of bryophytes and lichens:

“Bryophytes and lichens constitute a large part of the total biomass of present-day tundras, and in Rangifer distribution areas the latter are an important part of the food web.  They are important in the structure and function of the ecosystems because of their effects as insulators and filters.  Their insulating properties is partly form increased reflectance and partly from the numerous air pore space when dry.”  à soil under bryophyte and lichen mats tends to be cold and moist.

-          affect nutrient cycling of the ecosystem by intercepting aerial deposition and leaching from dripping aboveground vascular plant parts(Cowles, 1984; Rosswall and Granhall, 1980)

-          subsequently released upon the decomposition of tissues(exceedingly slow process largely due ot the chemical composition)

-          lichens with cyanobacterial symbionts and bryophytes with cyanobacterial associations provide the main input of nitrogen into the ecosystem(Alexander et al., 1978; Baselier et al., 1978,; Kallio, 1975)

-          lichens, and to lesser extent bryophytes, have also been shown to inhibit growth of neighboring vascular plants and thus further reduce ecosystem productivity

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Photosynthesis and Respiration

General pattern

“There is a great deal of similarity in the CO2 exchange patterns of bryophytes and lichens(Longton, 1992). Both have simple structures and little control over water loss.  They are metabolically active when wet; short respiratory burst is sometimes experience  when they are demoistened after desiccation during which internal activity Is quickly resumed.  As they dry out, they first increase their net CO2 exchange rate, reach a maximum net cO2 exchange rate at intermediate water contents, and then with further drying they decrease their activity, which eventually ceases.  Any further change in moisture regimes will affect their distribution patterns and hence the cryptogamic species composition of arctic vegetation.  ((relation to the change in water supply as a result of drilling and ice-road building activities??))  Arctic bryophytes show lower rates of photosynthesis under ideal short-term conditions than do their subarctic, temperate, and tropical conspecifics(Oechel and Sveinbjornsson, 1978; Sveinbjornsson, 1980), whereas the present authors have found similar rates in congeneric arctic and tropical lichens(unpublished data) and Lechowicz(1982) found no latitudinal differences in maximum photosynthetic rates among lichen species.

Arctic bryophytes and lichens exhibit distinct temperature optima, which are lower than those of temperate conspecifics and congenerics(Lechowicz, 1982; Sveinbjornsson and Oechel, 1980), and they are able to photosynthesize at lower temperatures than can temperate ones.”

(Source: OECHEL, W.C., CALLAGHAN, T., GILMANOV, T., HOLTEN, J.I., MAXWELL, B.,MOLAU, U., SVEINBJORNSSON, B., Global Change and Arctic Terrestrial Ecosystems P. 114-115)

Summary:

In order to understand the ANWR ecosystem, it is also necessary to investigate the energy and nutrient cycles.  The carbon balance of the ecosystem have been highly influenced by global climate changes and CO2 content changes.  The arctic contains 11% of the world’s organic matter pool, and within the arctic tundra ecosystems, there are both carbon sinks and carbon sources.  Vegetation changes in the Alaskan tussock tundra over the past decade has brought about important feedbacks on the region’s biogeochemical cycles, through altered rates of carbon and energy exchange between biosphere and atmosphere.  Modeling analysis suggests that the source/sink strength of tundra depends on changes in photosynthesis that result from the partitioning of nitrogen between vegetation and soils, and on changes in soil moisture, which affect soil respiration rates.  All of these factors may be affected by machine and human activity in the region and disturbances in the permafrost.

Nutrient cycling and fertilization studies in arctic ecosystems show that plant growth is strongly limited by nutrient availability.  Such activity depends highly on decomposition, nitrogen mineralization, phosphorous availability, and controls on carbon and nutrient cycles, which in turn depend on temperature, moisture, decomposability of litter inputs, depth of thaw etc.

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