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Aims: The relative importance of species within an ecosystem shows spatio‐temporal variability related to both the terrain features and numerous rapidly changing factors. Accordingly, functional and species patterns may show some level of persistence, or, due to various disturbances, fluctuations. Communities with high species richness were found to maintain a higher degree of stability than species‐poor or perturbed vegetations; however, diversity and its stability may be spatio‐temporally variable. Based on these considerations, our aim was to assess the responses of a sandy pasture, both species‐wise and at the community level, to the relatively invariant habitat, and to the more rapidly changing environmental conditions. Location: Hungary. Methods: We surveyed the vegetation in an area of about 1 ha by means of high‐resolution spatio‐temporal sampling: we recorded the surface aerial cover (%) of the plant species during 15 campaigns covering spring, summer and autumn aspects for seven years (2013–2019) in 80 × 60 m grids. The biological activity of the ecosystem (above‐ground biomass, soil respiration) was also followed up together with the environmental limiting factors. Results: During the study period, which was characterized by significant warming, the grassland showed a balanced physiological performance with year‐to‐year variability. Fluctuating differentiation of the plant species with different environmental optima along with the terrain attributes was assumed to be responsible for this balanced physiological performance. Although community‐level diversity remained stable, some species favoring cooler, wetter positions disappeared. Conclusions: Terrain features of the study area within 1.5 m or less elevation differences created considerably heterogeneous conditions for a high number (114) of plant species with different ecological needs to co‐occur. The stability of the diversity was found to show terrain relatedness, that is spatial as well as temporal patterns compared to the null model of spatio‐temporal independence, and the ecosystem functions followed these patterns. [ABSTRACT FROM AUTHOR]

Questions (i) Which species dominate mid-successional old-fields in Hungary? How does the identity of these species relate to local (patch-scale) diversity and to the progress of succession? (ii) Which species have the strongest negative impact on diversity in spontaneous old-field succession and what generalizations are possible about traits of these species? (iii) Are these species dominant or subordinate components in mature target communities? (iv) Do native or alien species have stronger effects on the diversity and progress of succession? Location Abandoned agricultural fields (abandoned croplands, orchards and vineyards) at various locations throughout Hungary. Methods Vegetation patterns on 112 old-fields, in 25 sites varying in soil and climatic conditions, topography, landscape contexts and land-use histories were sampled. Most old-fields had appropriate seed sources in the immediate vicinity, i.e. natural or semi-natural grasslands (meadows steppes, closed and open sand steppes) as source and target habitats. Age of abandoned fields ranged from 1 to 69 yr, but most sites were between 15 and 60 yr. The cover of vascular plant species (%) was estimated in 2 × 2-m plots. Relationships between diversity, progress of succession (similarity to target communities) and identity of dominants were tested. Results A small portion of successional dominants (eight species) had strong negative impacts on diversity. These species belonged to Poaceae, Asteraceae and Fabaceae. Most of these species were wind-pollinated, and capable of lateral vegetative spread. Dominant species varied in size and had, on average, a low requirement for N but a high requirement for light. With one exception, Solidago gigantea, they were native to the Hungarian flora. Significant differences were found among the impact of successional dominants when dominant species were grouped according to their original role (dominants or subordinates) in natural communities. The overall effect of species identity was also significant. Bothriochloa ischaemum was identified as the species with the strongest negative effect on species diversity. Conclusions Our results suggest that mid-successional dominant species differ in their impact on diversity and progress of succession. Mid-successional plots dominated by alien species, or by native species that were originally subordinate in natural communities, regenerate less successfully and may temporarily arrest succession. Therefore, early colonization of native dominants should be enhanced with restoration measures. [ABSTRACT FROM AUTHOR]