Abstract:
The vegetation and soils in many arctic tundra regions are influenced by the distribution of nonsorted circles, unique patterned-ground features that dot the well-vegetated tundra landscape. They are flat to dome-shaped, bare soil patches 0.5 to 3 m across and lack a border of stones. Localized soil disturbance due to cryogenic processes creates unusual micro-environments with unique plant communities, slow soil development and deep active layers. The contrast between barren nonsorted circles and the well-vegetated stable tundra provides an ideal opportunity to examine the complex linkages among vegetation, soil and disturbance through cryogenic processes, offering insight into how the tundra system operates. The central goal of this thesis is to understand the complex linkages of the nonsorted-circle system along a natural climate gradient on the North Slope in the Alaskan arctic tundra at different scales, ranging from plot level to regional changes. This thesis examines the interactions among vegetation, soil and cryogenic regime by treating the nonsorted circles within the stable tundra as a single complex system. The thesis presents a formal description and analysis of the plant communities on and off nonsorted circles along the climatic gradient using Braun-Blanquet classification approach. The thesis also studies the physical effects of vegetation, soil organic mat and snow cover on the microclimate of nonsorted circles and the stable tundra along the same climate gradient. The influence of vegetation on cryogenic processes is examined experimentally by manipulating the plant canopy on nonsorted circles. When compared to the stable tundra, nonsorted circles have minimal vegetation cover, resulting in warm soil temperatures and deep thaw depths in summer and allowing for increased ice-lens formation during freeze-up. The resulting frost heave and needle-ice formation at the soil surface maintain the bare surfaces of the circles through soil disturbance. Cryogenic processes dominate the system at the northern sites, while the warmer climate towards the south allows for thick vegetation mats on and off the nonsorted circles, suppressing cryogenic processes. The strength of the interactions among vegetation, soil and cryogenic regime may change under a warming arctic climate, possibly leading to the local disappearance of nonsorted circles.
