Succession in Marginal Arctic Environments

Abstract

In a broad sense the entire Arctic might be considered a “marginal” environment. Polar deserts and semideserts are marginal for establishment of vascular plants sensu stricto. In extreme polar habitats some populations of plants are not fully self-sustaining. These may not produce viable seed and depend on propagules dispersed from more favorable habitats, which may be quite remote. These marginal populations rarely progress beyond the initial invasion phase of succession. The second phase, stand formation and build-up of a critical standing crop which would lead to habitat improvement and finally to replacement of pioneer species, rarely occurs. Rather, the colonizers have been historically subjected to repetitive additional constraints such as short-term climatic variations, and unfavorable summer weather patterns, which result in meager progress and low survival rates. Instead of a progressive succession we often find evidence of slow advancement, holding position, retardation, retrogression, and reinvasion. In marginal habitats, the progress of succession can be defined as a function of the biological driving forces which are intrinsic to the invading and establishing species, and the environmental resistances which represent a sum of the adverse factors hindering the success of species establishment. Theoretically, the progress of revegetation and directional change in the plant community can be measured as a successional half-time, i.e., time required to achieve the mid-point of development expected in a particular habitat situation. In marginal habitats, this half-time can be measured on a time scale of millennia and may be virtually infinite.