Landform-vegetation units in karstic depressions (dolines) evaluated by indicator plant species and Ellenberg indicator values

Abstract

In this study, the objects of research were circular and concave karstic depressions, called sinkholes or dolines. All these negative topographic anomalies were previously recognized as safe havens for cool-adapted species on karstic plateaus. However, the high geodiversity of doline landforms on karst plateaus does not ensure that all dolines are really safe havens that should be considered for conservation status. We propose the use of indicator species to identify different dolines' “sections” and their overall types to identify dolines with high conservation value for cool-adapted species. We aimed to divide dolines into landform-vegetation units (LVU) according to basic geomorphic characteristics and indicator plant species. We carried out intensive sampling of vegetation plots (n = 286) across 10 dolines of different geomorphology ranging from 20 m to 100 m in diameter and from 2 m to 20 m in depth. Each doline was classified into a maximum of four LVUs: bottom, lower slope, upper slope and top. Vascular plants were used as a proxy for ecosystem biodiversity and indicator of ecological conditions. The diversity of vascular plant communities was sampled along N–S transects from one side of the doline over the bottom to the other side. Geodiversity parameters of individual dolines were calculated using a high-resolution digital elevation model (LiDAR / Light Detection And Ranging) and their significance was established by permutation test in CCA (Canonical Correlation Analysis). The floristic gradient was established by the first axis of PCoA (Principal Coordinates Analysis) and shows the species turn-over along the trajectory. Discrete plant communities were determined by TWINSPAN (Two-Way Indicator Species ANnalysis) classification. Based on this analysis, transects were disintegrated into four LVUs. Communities within LVUs were compared by Ellenberg indicator values and according to habitat preference of species. The indicator (also termed diagnostic) plant species were calculated by fidelity measure and related to ecological conditions along transects. We found that all four LVUs appear only in dolines that are at least 13.5 m deep and those can serve as a good safe haven for cool-adapted species in foreseen climatic change. We also confirmed that doline depth is the most important factors influencing the plant community composition. The results can be directly transformed to other karst regions (karst plateaus) with the same zonal vegetation, but calibration is needed in case of their application in other areas.