Altitudinal changes in composition and structure of mountain-temperate vegetation: a case study from the Western Carpathians

Changes in composition and structure of plant communities in relation to the soil and snow cover variation were analyzed along an altitudinal transect (1150-1750 m) from the mountain-temperate forests to a woody shrub community and alpine meadows on Mt Velky Gapel', Slovakia. The soils below the treeline (similar to1510 m) had a more developed organic layer above the mineral substratum. Generally, soil depth decreased as the altitude increased, although the maximum values were recognized at a middle altitude in a beech stand. Snow was redistributed by westerly winds from the ridgeline down to the upper forest margin. Mean snow depth decreased with altitude up to almost snow-free sites around the summit. In the 48 plots at 16 sites we recorded 118 taxa including 6 tree, 7 shrub, 18 grass, 42 herb, 5 fern, 25 moss and 15 lichen species. The species diversity showed no distinct relationship to altitude but declined with canopy consolidation. The TWINSPAN floristic classification distinguished five groups of community types characterised by different dominants, and a further three clusters of samples from transition zones. Horizontal compositional heterogeneity increased in areas where trees were aggregated and tree basal area was smaller. Vegetation composition became more patchy at open-canopy Acer pseudoplatanus-Abies alba mixed forest at 1150 m, in Picea abies forest limit similar to1470 m, and in Pinus mugo krummholz at 1590 m. Species turnover of the entire transect was 6.1 half-changes as estimated by DCA. Despite this heterogeneity, none of the 15 elevational bands had significant aggregation of species' limits. Vegetation varied continuously, with individual species overlapping in transition zones delimited by dominant taxa. The coincident aggregation of up-slope and down-slope boundaries was found at a belt 1430-1510 m. This discrete ecotone corresponds to a shift from the closed coniferous forest to P. mugo krummholz. The second inherent up-slope boundary aggregation indicated the P. mugo krummholz - alpine meadow vegetation transition at similar to1700 m. Spatial analysis (K-function) of eight forest plots (0.12 ha each) showed that at lower elevation, adult trees of the broad-leaf forest were closer to a random arrangement while at higher elevation, trees of evergreen coniferous stands became aggregated toward the forest limit with the highest intensity from 2 to 4 m. Altitudinal gradient and related factors explained 35% of the variance in vegetation data. Canonical correspondence analysis also showed that main vegetation changes above the treeline area were associated with the topographic pattern of pine shrubs and snow cover.