1Questions: (1) Which species dominate mid-successional old-fields in Hungary? How does 2 the identity of these species relate to local (patch-scale) diversity and to the progress of 3 succession? (2) Which species have the strongest negative impact on diversity in spontaneous 4 old-field succession and what generalizations are possible about the traits of these species? 5 (3) Are these species dominant or subordinate components in mature target communities? (4) 6 Do native or alien species have stronger effects on the diversity and progress of succession? 7Location: Abandoned agricultural fields (abandoned croplands, orchards and vineyards) at 8 various locations scattered throughout Hungary. 9Methods: Vegetation patterns on 112 old-fields, in 25 sites varying in soils and climatic 10 conditions, topography, landscape contexts and land use histories were sampled. Most old-11 fields had appropriate seed sources in the immediate vicinity, i.e. natural or semi-natural 12 grasslands (meadows steppes, closed and open sand steppes) as source and target habitats. 13The age of abandoned fields ranged from 1 to 69 years, but most sites were between 15 and 14 60 years. The cover of vascular plant species (in %) was estimated in 2 m x 2 m plots. 15Relationships between diversity, the progress of succession (similarity to target communities) 16 and the identity of dominants were tested. 17Results: A small portion of successional dominants (eight species) had strong negative 18 impacts on diversity. These species belonged to Poaceae, Asteraceae and Fabaceae families. 19Most of these species were wind pollinated, and capable of lateral vegetative spread. 20 Dominant species varied in size and had, on average, low requirements for nitrogen but a 21 high requirement for light. With one exception, Solidago gigantea, they were native to the 22

Questions How does the spatial configuration of sampling units influence recorded plant species richness values at small spatial scales? What are the consequences of these findings for sampling methodology and rarefaction analyses? Location Six semi‐natural grasslands in Western Eurasia (France, Germany, Bulgaria, Hungary, Italy, Turkey). Methods In each site we established six blocks of 40 cm × 280 cm, subdivided into 5 cm × 5 cm micro‐quadrats, on which we recorded vascular plant species presence with the rooted (all sites) and shoot (four sites) presence method. Data of these micro‐quadrats were then combined to achieve larger sampling units of 0.01, 0.04 and 0.16 m² grain size with six different spatial configurations (square, 4:1 rectangle, 16:1 rectangle, three variants of discontiguous randomly placed micro‐quadrats). The effect of the spatial configurations on species richness was quantified as relative richness compared to the mean richness of the square of the same surface area. Results Square sampling units had significantly lower species richness than other spatial configurations in all countries. For 4:1 and 16:1 rectangles, the increase of rooted richness was on average about 2% and 8%, respectively. In contrast, the average richness increase for discontiguous configurations was 7%, 17% and 40%. In general, increases were higher with shoot presence than with rooted presence. Overall, the patterns of richness increase were highly consistent across six countries, three grain sizes and two recording methods. Conclusions Our findings suggest that the shape of sampling units has negligible effects on species richness values when the length–width ratio is up to 4:1, and the effects remain small even for more elongated contiguous configurations. In contrast, results from discontiguous sampling units are not directly comparable with those of contiguous sampling units, and are strongly confounded by spatial extent. This is particularly problematic for rarefaction studies where spatial extent is often not controlled for. We suggest that the concept of effective area is a useful tool to report effects of spatial configuration on richness values, and introduce species–extent relationships (SERs) to describe richness increases of different spatial configurations of sampling units.

Spatial patterns of ecosystem processes constitute significant sources of uncertainty in greenhouse gas flux estimations partly because the patterns are temporally dynamic. The aim of this study was to describe temporal variability in the spatial patterns of grassland CO 2 and N 2 O flux under varying environmental conditions and to assess effects of the grassland management (grazing and mowing) on flux patterns. We made spatially explicit measurements of variables including soil respiration, aboveground biomass, N 2 O flux, soil water content, and soil temperature during a four-year study in the vegetation periods at grazed and mowed grasslands. Sampling was conducted in 80×60 m grids of 10 m resolution with 78 sampling points in both study plots. Soil respiration was monitored nine times, and N 2 O flux was monitored twice during the study period. Altitude, soil organic carbon, and total soil nitrogen were used as background factors at each sampling position, while aboveground biomass, soil water content, and soil temperature were considered as covariates in the spatial analysis. Data were analyzed using variography and kriging. Altitude was autocorrelated over distances of 40-50 m in both plots and influenced spatial patterns of soil organic carbon, total soil nitrogen, and the covariates. Altitude was inversely related to soil water content and aboveground biomass and positively related to soil temperature. Autocorrelation lengths for soil respiration were similar on both plots (about 30 m), whereas autocorrelation lengths of N 2 O flux differed between plots (39 m in the grazed plot vs. 18 m in the mowed plot). Grazing appeared to increase heterogeneity and linkage of the spatial patterns, whereas mowing had a homogenizing effect. Spatial patterns of soil water content, soil respiration, and aboveground biomass were temporally variable especially in the first 2 years of the experiment, whereas spatial patterns were more persistent (mostly significant correlation at p<0.05 between location ranks) in the second 2 years, following a wet year. Increased persistence of spatial patterns after a wet year indicated the recovery potential of grasslands following drought and suggested that adequate water supply could have a homogenizing effect on CO 2 and N 2 O fluxes.