Determination of forest communities on the basis of small plots (microplots) within the geomorphologically diverse landscape of the Kras plateau (Italy, Slovenia)

Abstract

The article deals with forest communities that develop on small surfaces on steep gradients of the geomorphologically diverse landscape of the Kras plateau. They appear in small depressions called dolines, where a steep gradient of ecological conditions appears over a small spatial scale. We tried to detect the turnover of forest communities on this small scale and steep gradient with small plots (microplots) of 4 ​m² arranged in a continuous transect. We sampled only the ground layer and estimated the cover of each vascular plant species. The main problem was that we could not sample vegetation plots in standard sizes, which would allow a standard classification procedure. We built an expert system based on all of the relevant standard vegetation plots from the region and applied this system on a microplot matrix. We classified one third of microplots in this way, but the remainder were classified by semi-supervised k-means clustering. We thus established 8 communities that appear in dolines and compared their characteristics and ecological conditions by Ellenberg indicator values. Our results show that oak-hornbeam forests can be found in the bottom of dolines. Towards the bottom of deeper dolines, mesophilous ravine forests dominated by sycamore on rocky places, and sessile oak forests on deeper soils appear. On lower slopes, thermophilous ravine forests dominated by limes appear on rocky places. Upper slopes are dominated by Turkey oak, hophornbeam-pubescent oak forests and shrub formations. Turkey oak forests can be found on rather deeper soils than hophornbeam-pubescent oak forests. At the top, hophornbeam-pubescent oak forests can be found that build the zonal vegetation of the region. On rock walls vegetation of rock crevices can be found. The high biodiversity of the region supports the idea that diverse karstic features might have the potential for formation of refugia in future foreseen climate change, related to the potential of karstic relief to create diverse climatic conditions.