We studied the course of primary succession following deglaciation and the convergence/divergence of plant community development with respect to topographic factors at Koryto Glacier Valley on Kamchatka's Pacific coast. Vegetation changes over an ∼270-yr-old chronosequence were related to concurrent changes in substrate and soil properties. Ordination analyses showed that substrate texture and topography are the most important environmental factors influencing the course of succession. About 25 yrs after surface deglaciation, belowground stagnant ice melts, and moraine consolidation causes the successional communities to diverge. Species-poor communities, dominated by alder and grasses (Alnus fruticosa, Calamagrostis purpurea), occurred on the fine-grained substrate of moraine crests, while species-rich communities, dominated by legumes and forbs (Oxytropis kamtschatica, Saxifraga species), developed on the coarse-grained substrate of moraine flanks, and in depressions communities dominated by willows and sedges (Salix arctica, Juncus beringensis) developed. In depressions and plains adjacent to the ridges, succession toward Alnus stands is hindered by late-melting snow and flooding. Plant-species richness peaked at the 80-yr-old moraine, but thereafter decreased as the rapid growth of Alnus led to dense stands that dominated resources and inhibited colonization and growth of earlier, as well as later, successional species. Mat-forming capacity, high litter production, an extensive root system, and snow-pressure tolerance enable A. fruticosa to maintain dominance without replacement by Betula ermanii. This potential climax species remains scattered on rock terraces and elevated locations above the valley basin where it escapes snow avalanches and accumulation, a factor responsible for the inversion of vegetation zones in this maritime region.
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Vol. 40 • No. 2