Low-centered Polygons Research Articles

Tundra Fire Effects on Soils and Three Plant Communities Along a Hill-Slope Gradient in the Seward Peninsula, Alaska

During summer 1977, wildfires burned extensive areas of low arctic tundra in the Seward Peninsula, Alaska. The present study was initiated in July 1978 to determine the effects of these fires on tundra soils and vegetation. Nine 10 m × 1 m permanent belt transects were established at regular intervals along the topographic gradient of a burned hill-slope in the central Seward Peninsula near Imuruk Lake. Soil characteristics and plant species density and cover were determined in each of the 90 1-m² plots on this slope during July of both 1978 and 1979. Soils and vegetation had been quantitatively sampled on this slope in 1973, thereby providing pre-fire comparisons; a sedge tussock-shrub tundra community with mud circles occupied the poorly drained footslope and a birch and ericaceous shrub tundra community with elongate turf-banked frost boils had developed on the moderately well-drained backslope. The broad, poorly-drained summit of this slope was occupied by sedge-shrub tundra with low-centered polygons. The severity of burning in July 1977 varied along this slope with moderate to heavy burning of the birch and ericaceous shrub tundra and light to moderate burning of the sedge tussock-shrub tundra and sedge-shrub tundra communities. Post-fire (1978 and 1979) changes in plant cover, species composition and soil thaw depths are shown to vary with position on the slope and burning severity. The relationship of these changes to natural succession in the absence of fire is discussed.

A new Clitocybe from the Alaskan Arctic

A new species of Clitocybe is described from the Alaskan Arctic. This agaric grows on low-center polygon rims, high-center polygons, and on beach ridges. Drawings of microscopic features and macrophotographs are included.

Nitrogen Fixation in Arctic Coastal Tundra in Relation to Vegetation and Micro-Relief

A study to estimate nitrogen fixation input in arctic coastal tundra was carried out using the acetylene reduction assay. Areal estimation was attempted by high intensity sampling over a limited area of tundra containing both high-centred and low-centred polygons with their corresponding variations in micro-vegetation. The highest average rates of acetylene reduction were obtained from cores in damp interpolygonal troughs (10.50 µmoles ethylene/m²-hr) where mats of the blue-green alga Nostoc were abundant. Wet moss-algal associations in hydric meadows showed high nitrogenase activity (average 6.86 µmoles ethylene/m²-hr) and dry high-centred polygons were comparatively inactive (2.80 µmoles ethylene/m²-hr). The lichens Peltigera sp. and Stereocaulon sp. were the most active nitrogen fixers in the drier tundra. Nitrogen fixation increased with rising temperature with a measured Q10 for Nostoc commune of 3.7.

Tundra Relief Features near Point Barrow, Alaska

Topography of this area results from erosion and mass wasting of a permafrost terrain, low temperature processes such as thermal expansion and contraction of frozen ground, surface uplift caused by accumulation of, and subsistence resulting from thaw of ground ice. High- and low-centered polygons, ice-wedge troughs, ice-core mounds and thaw basins are features in this region; genetic relations between these are discussed.