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Understanding plant-plant interactions is essential in planning and implementing effective grassland management strategies. Positive and negative interactions generally co-occur in plant communities and the net effect of these interactions may depend on the disturbance regime, including grazing. Shrubs can act as biotic refuges by physically protecting neighbouring plants from herbivores. As a result, we would expect that in pastures the diversity and flowering success of plants is higher in the close vicinity of shrubs compared to the open vegetation. Nevertheless, we can also assume a competitive trade-off cost for plants that grow together with shrubs. In this study, we assessed the small-scale effects of dwarf shrubs (30–40 cm in diameter) on species density and flowering success. Specifically, we considered three types of microsites: (i) shrub interior, (ii) edge of shrub, and (iii) open pasture (more than 2 meters away from the shrub). We surveyed these three types of microsites using 10 × 10 cm sized plots both in grazed and ungrazed meadow steppe, in central Hungary. The highest species density was found at the edge of shrubs, both in grazed and ungrazed vegetation. Meanwhile, species density did not differ significantly between shrub interiors and the open pasture. However, in grazed vegetation, species flowering success was significantly higher in shrub interiors and edges than in the open pasture; no significant trend was observed for this measure in ungrazed vegetation. In contrast to previous studies, we did not detect a competitive effect of small-sized shrubs on plants in ungrazed vegetation. Our results indicate that small-sized shrubs protect other plants from herbivores and that the edge effect plays an important role for the maintenance of small-scale species diversity in pastures. Overall, our results underline the beneficial effect of biotic refuges in pastures and we suggest that retaining a sparse population of small-sized native shrubs is advantageous from a conservation point of view.
Steppes used to cover large areas of Hungary, but most of this vegetation has since been destroyed. In Central Hungary, some patches have survived on ridges in wet meadows. These habitat complexes face profound land use changes and their optimal management regime is uncertain. We identified seven annually mown steppe and wet meadow types according to their grazing regime and history and aimed to answer the following questions: (1) Does grazing have beneficial effects on mown steppes and wet meadows? (2) Should the presently homogeneous management of neighbouring steppes and wet meadows be maintained? (3) Is annual mowing sufficient in assisting the recovery of steppes and wet meadows on former croplands?
We selected three localities for each of the seven vegetation types and sampled them with 50 quadrats (50 × 50 cm) in each locality, making a total of 1,050 quadrats. Vascular plant diversity relations were evaluated using the total number of species per habitat type (species richness) and the average number of species per quadrat (microsite diversity). The effect of grazing and history on microsite diversity was tested with linear mixed-effect models. We used Redundancy Analysis to disentangle the role of grazing intensity and management history on species composition. Plant species were then sorted into functional groups, and the proportions of these groups were used to evaluate community structure.
Our results indicate that mowing alone cannot maintain as high a diversity as the combination of the two land use types, thus grazing should be introduced to non-grazed areas. Steppes, however, were found more sensitive to the intensity of grazing than wet meadows. Under heavy grazing, no increased microsite diversity was detected in the steppes and the proportion of disturbance indicators tended to increase. In contrast, the same grazing intensity resulted in only positive effects in wet meadows. Thus, uniform land use on adjacent steppes and wet meadows is not recommended but intensive grazing should be stopped on steppes. Secondary steppes were less diverse than primary ones and their community structure was also poorer, whereas wet meadows had a better regeneration potential. Thus, mowing alone is an incomplete tool to restore the plant diversity of secondary steppes; they should also be grazed and/or should be supported by other active interventions.