Primary Succession in the Aralkum

Abstract

The dry seafloor of the Aral Sea is a new surface, where terrestrial plants (including seed banks) and animals have not existed before. It is now actively populated by organisms. The formation of plant communities, soils, a new groundwater level, aquifers, and all components and processes of ecosystems is occurring more or less simultaneously. It is a typical primary succession. The succession on the dry seafloor has continued for the last 50 years. The distribution and dynamics of the vegetation and ecosystems were surveyed along transects. On average, the succession on loamy stands can be described by two to four stages, and on sandy soils by three to five stages. The existence of a distinct stage is a consequence of the ecological conditions and stability, and thus might range between 2 and 30 years. The succession on the sands in the starting phase is caused by exogenous factors. The replacement of the Salicornia and Suaeda phases by annual psammophytes is caused by exogenous factors. The further process of the succession after the settlement of Stipagrostis pennata is endogenous and is caused by biological mechanisms (speed of the dispersal of the annual and perennial species, their ability to establish themselves on the open sand surface). The succession on the loamy soils is mainly caused by exogenous factors. The Aralkum vegetation is very dynamic in composition. This leads to unexpected combinations and interrelationships. There are many examples of rapid changes of unique plant communities and ecosystems with unique composition by various species from the psammophytic, halophytic and hygrophytic units.