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Numerous environmental factors are confirmed to have significant influence on the habitat choice of invertebrates and thus on the assemblage structure. In dry, sandy grasslands the vegetation cover and height are assumed to be the most important factors in shaping the distribution of spiders and true bugs. The present study was carried out at a natural sand dune area in the Kiskunság region of the Hungarian Great Plain. Two adjacent sand dunes and the dune valley between them were sampled using a transect consisting of pitfall traps. The traps were arranged in 4 parallel transects, running from the sand dune top through the dune valley to the adjacent sand dune. Each row consisted of 40 traps, three meters apart. The effect of microhabitat parameters on the species richness and abundance of invertebrate assemblages were tested with linear regressions with forward selection procedure. A total number of 1447 spider and 1580 true-bug individuals of 58 and 55 species were collected, respectively. The mean number of spider species along the transects was 10.5 ± 3.7 and 9.8 ± 3.0 for true bugs. Although our data did not show a significant effect of the plant species number on species richness and abundance of the two studied taxa along this gradient, the results of the canonical correspondence analysis and the Mantel test emphasized the importance of the total coverage and vegetation composition on the distribution of invertebrate species. The correspondence analysis and the multivariate ANOVA revealed different spider and true-bug assemblages on the two slopes (multivariate ANOVA: Araneae: F = 3.609, P <0.001, Heteroptera: F = 5.248, P <0.001), possibly due to the more dense and diverse vegetation on the north facing slope, which is presumably brought about by the different insolation and moisture conditions of the slopes.
Scale-dependency is one of the well-known features of ecological boundaries. Unfortunately, there are relatively few case studies analysing boundaries of different scales. Moreover, properties of moving split window (MSW) technique, a method potentially suitable for examining boundaries at several spatial scales, are not fully understood. In this study, we used artificial data sets to test the capacities and limitations of the MSW method. We also applied field data from the Mecsek Mts (Hungary) (611 m a.s.l.) in order to reveal possible boundaries at different scales and to contribute to the knowledge on vegetation pattern of mountain areas. We found that one should apply several window-widths when using MSW, since this is the only way to detect and differentiate between boundaries of different scales. Our study revealed the vegetation pattern of Mt Tubes: there is a series of continuously intergrading mesic communities on the northern slope, while the southern slope is occupied by a mosaic of different xeric communities. In this pattern, boundaries of two different scales have been identified. We conclude that MSW could effectively be used in similar mountain regions to analyse herb layer vegetation patterns and boundaries.
Moderating effects of trees on the environment in their immediate proximity are considered an important force in structuring plant communities, especially in harsh environments. In the semi-arid regions of the middle Carpathian Basin, such facilitative influences are expected to become crucial for the survival of several plant species, given the current warming and drying tendencies. We used 20 × 20 m plots to analyze whether grassland species adapted to mesic conditions penetrate forest patches, where they are able to survive. Using transects and the moving split window analysis, we also investigated how far the positive effects of the forest patches extend into grasslands, and whether this enables the existence of a steppe community that cannot tolerate extreme dry conditions and unfavorable soils. We found that beside forest-related species, forest patches hosted large numbers of grassland-related species. Among them, plants of closed steppe grasslands were the most numerous, which usually cannot tolerate the harsh conditions of open sandy grasslands, and are often confined to areas with better water and soil conditions. Our results showed that there is a 5–8 m wide closed steppe zone around the forest patches. Some species that are not able to survive in open xeric sandy grasslands are restricted to this zone. Unfortunately, while considerable attention is paid to the research, protection and restoration of sandy grasslands, forest patches are usually neglected. Our results emphasize that the establishment of individual trees and groups of trees should be actively promoted, because they have considerable nature conservation benefits by supporing closed steppe species.
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