Trends in plant species-wise abundances with parallel maintenance of community-level diversity in a Hungarian sandy pasture

The relative importance or the abundance of plant species in ecosystems shows large spatio-temporal variability due to habitat- and species-related factors. What is more, in Hungary, climate change is accompanied by an increased probability of droughts and heat waves with further consequences on community attributes both in time and space.

The finely undulating (no more than 1.5 m elevation differences within the study site) surface in our sandy grassland study site was formed through the combined effects of wind, water erosion, and drought, and resulted in uneven soil nutrient and water distributions. We surveyed the vegetation of an ~ 1 ha area along 15 campaigns covering spring, summer, and autumn aspects for 7 years in 80 × 60 m grids where the surface cover of plant species within 78 patches of 0.5 × 0.5 m quadrates was recorded. The large spatial and temporal dataset (n=78 × 15=1170 quadrates with an overall species number of 114) enabled us to follow both species-wise (abundances) and community-level (e.g., diversity) patterns along with different terrain attributes for years.

During the study period, the grassland functioned as a carbon sink with a balanced physiological performance with year-to-year variability. The yearly sum of precipitation was very variable without any statistically significant change since the establishment of the study station (2002); however, significant warming was observable since then.

Within the study area, vegetation differentiation was detectable along with the terrain attributes. This vegetation differentiation was temporally variable following the patterns of how species with different environmental requirements split available places/resources through time. At hotter, dryer, more elevated positions, and more on the ridges, we could differentiate a larger ratio and diversity of a group of species favoring such conditions, while another group was more abundant in areas with opposite conditions. The presence of such different species groups and functional types within this relatively small area with a slight surface undulation may have been responsible for the observed balanced physiological performance of the grassland. However, although the diversity of the community as a whole didn’t change significantly during the study period, one of the ecological group diversities, that of species favoring cooler, wetter positions, decreased. So, not only temporal variability but also trend-like shifts were observable in the vegetation composition through time, and the stability of the diversity was found to show a terrain-related pattern.