Szilárd Szentes

Worldwide evidence of a unimodal relationship between productivity and plant species richness

Grassland diversity and ecosystem productivity The relationship between plant species diversity and ecosystem productivity is controversial. The debate concerns whether diversity peaks at intermediate levels of productivity—the so-called humped-back model—or whether there is no clear predictable relationship. Fraser et al. used a large, standardized, and geographically diverse sample of grasslands from six continents to confirm the validity and generality of the humped-back model. Their findings pave the way for a more mechanistic understanding of the factors controlling species diversity. Science, this issue p. 302 The humped-back model of plant species diversity is confirmed by a global grassland survey. The search for predictions of species diversity across environmental gradients has challenged ecologists for decades. The humped-back model (HBM) suggests that plant diversity peaks at intermediate productivity; at low productivity few species can tolerate the environmental stresses, and at high productivity a few highly competitive species dominate. Over time the HBM has become increasingly controversial, and recent studies claim to have refuted it. Here, by using data from coordinated surveys conducted throughout grasslands worldwide and comprising a wide range of site productivities, we provide evidence in support of the HBM pattern at both global and regional extents. The relationships described here provide a foundation for further research into the local, landscape, and historical factors that maintain biodiversity.

Seminatural grassland management by mowing of Calamagrostis epigejos in Hungary.

Abstract Regeneration of seminatural grasslands are often threatened by the invasion of Calamagrostis epigejos, which can slow down or arrest secondary succession. Here we report the results of a 9-year mowing experiment designed to suppress the spread of C. epigejos in mid-successional grasslands in Hungary. The experimental design consisted of 16 permanent plots of 3 × 3 m. Half of the plots were mowed twice a year (in June and September), the other half was left as control. Vegetation was sampled in 2 × 2 m quadrates before mowing in each year between 2001 and 2009. The effects of mowing were tested using repeated–measure analyses of variance (ANOVA) and Tukey HSD for post hoc tests. Significant decrease of C. epigejos appeared after 2 years of mowing. Species richness increased after 4 years, while diversity after 8 years. By this time the target native species Brachypodium pinnatum become dominant. Similar trends appeared in the control plots during spontaneous succession but at much slower rates. Our results suggest that C. epigejos disappears spontaneously in secondary grassland succession after ca. 40–50 years. However, mowing twice a year can speed up this process by opening a “colonization window” to the valuable target species. For successful control, mowing should be maintained for approximately 8 years.

Grazed Pannonian grassland beta-diversity changes due to C 4 yellow bluestem

This study investigates how yellow bluestem affects biodiversity in a typical Pannonian grassland. Beta diversity (i.e. the finescale spatial variability of species compositions), was estimated by the realized number of species combinations sampled at various scales. Sampling was performed by a standard protocol. Presences of plant species were recorded along 52.2 m long belt transect of 1044 units of 0.05x0.05 m contiguous microquadrats. According to the results the massive presence of tested C4 grass significantly reduced species richness of the grassland. Beta diversity assessment revealed that 90% of species combinations were lost due to yellow bluestem invasion. Fine-scale spatial pattern analyses showed complete local extinctions of other species from microsites dominated by yellow bluestem. This local extinction is enhanced by the specific clonal architecture of this species and by the accumulation of litter. Other dominant grasses had no effect on fine scale diversity, i.e. they could coexist well with other elements of the local flora. This study presents currently developed microhabitat types, forecasts and also draws attention to the danger that climate warming will probably enhance the spread of this detrimental C4 species.

Comparative researches and evaluations on grassland management and nature conservation in natural grasslands of the Transdanubian mountain range

Management takes place on the Hungarian natural grasslands as well. This usually means extensive activities such as mowing or grazing. The total cover of grasslands exceeds 1148000 hectares, that is 11% of the total area of Hungary, 213468 hectares of this being under nature protection. This is why harmonizing aims and tasks of agriculture and nature conservation is highly important on these areas (Angyan 2000). Observations on vegetation of pastures and its changes have got a high importance, especially in case of grass species (Poaceae), since it is mainly these species that ensure the most valuable forage for grazing animals (Vinczeffy 1998, Barcsak and Kertesz 1986, Szeman 1994/95, 2003). Organic matter content plays an important role as nutrient (Ercoli et al. 2006, Hoyk 2005), and Shallow soils have extreme water regime (Birkas et al. 2005). Any activity that reduces the soil cover by removing the vegetation is unfavorable, increases the effect of erosion processes, especially considering the effect of future climate change (Mudri et al. 2005). Natural grasslands were observed during the researches on botany and grassland management, and laying emphasize on the maintenance of nature conservation values as well. The current contribution presents a common view on extensively cultivated Transdanubian grasslands and detailed results on the Inner Lake (Belsi-to) area of the Tihany peninsula, because even magamenet type has changed in this area. This is why change in vegetation, management type and nature conservation values are all important.

Comparative study on grasslands dominated by Festuca vaginata and F. pseudovaginata in the Carpathian Basin

The aim of our study was to reveal the differences in the species composition and soil properties of open sandy grasslands dominated by different Festuca species, Festuca vaginata and F. pseudovaginata. Due to the arid conditions, sandy grasslands are generally covered by xerothermic vegetation in which F. vaginata is a typical dominant species. Festuca pseudovaginata, a species newly described by the authors, can also gain dominance in sandy grasslands. However, species composition and soil properties of grasslands dominated by this recently discovered species are still undiscovered. Based on previous coenological studies, we hypothesised that the grasslands characterised by the endemic F. vaginata are more species-rich than those with F. pseudovaginata. Coenological sampling was carried out in May 2009 at two study sites using the Braun-Blanquet method in quadrats of 2 m × 2 m. Five relevés were sampled in stands dominated by F. vaginata and F. pseudovaginata respectively at two study sites in Central Hungary, resulting in a total of twenty relevés. Analyses were based on the cover scores of vascular plant species and cryptogam crust and values of seven soil properties (pH [KCl], pH [H2O], humus, total N, Ca, P2O5 and K2O) measured in the 0–15 and 15–30 cm soil layers. Soil properties of the grasslands dominated by F. pseudovaginata and F. vaginata (dependent variables) were compared by linear mixed models, where ‘grassland type’ was the fixed factor and ‘site nested in grassland type’ was considered as random factor. Data were analysed by cluster analysis, fusion algorithm was a combinatorial method (minimising increase of variance), and the correlation was used as comparative function. We compared the cover of subordinate species by Mann-Whitney U test. We found that F. pseudovaginata and F. vaginata samples were well separated, and grasslands dominated by F. pseudovaginata had nearly two times more species than those dominated by F. vaginata. Based on the cluster analyses using plant cover and upper 0–15 cm soil layer data, F. pseudovaginata Manuscript received 12 December 2016, accepted 04 July 2017 Co-ordinating Editor: Balázs Deák ©Floristisch-soziologische Arbeitsgemeinschaft; www.tuexenia.de; download unter www.zobodat.at