Structural traits of woody plants and geomorphological conditions to the vegetation recovery at Ksudach caldera (Southern Kamchatka) since the explosive eruption in 1907

This study considers the restoration of the plant cover destroyed by a catastrophic volcano eruption in the south of Kamchatka Peninsula (the Ksudach caldera, Shtyubel cone), with a particular attention to the role of woody plants. It aims to qualitatively estimate (at a qualitative level) the rate of the primary succession development depending on the microrelief and the modern relief-forming processes. The vegetation recovery in the caldera after the Shtyubel cone eruption 109 years ago proceeds slowly and irregularly. It proceeds most slowly on a thick tephra mantle continuously disturbed by water and wind erosion, lahars, debris flows, landslides, etc. Such conditions are most typical of the western part of the caldera dominated by pumice fields with occasional patches of pioneer herbs and dwarf shrubs. Alpine tundra communities with gradually expanding patches of shrub alder develop in the southern, eastern and northeastern parts of the Ksudach caldera. Since 1997 the area of the shrub alder communities has increased by 1.9 times, while the alpine tundra — by 1.3 times only. The woody plants (dwarf shrubs and prostrate shrubs) are of particular importance in the process of the vegetation recovery on pumice fields. We suggest that the bark thickness of woody plants is an integrated indicator, which may serve for estimating the state of ecosystem in the course of the primary succession development on juvenile sediments. The extremely inhospitable environments cause changes in physiological processes in the plant body and in its bark in particular. The results show that woody plants have a “thin” bark and develop some structural-functional arrangements for keeping bark tissues at their minimum. So, the woody plant structure and the rate of changes in plant communities are under control of the geomorphic conditions and primarily — of physicochemical features of the pyroclastic cover.