Dengler et al. (2014) Agriculture, Ecosystems & Environment

Jürgen Dengler, Monika Janišová, Péter Török, Camilla Wellstein (2014): Biodiversity of Palaearctic grasslands: a synthesis. Agriculture, Ecosystems & Environment, in press, DOI: dx.doi.org/10.1016/j.agee.2013.12.015

Abstract
This article introduces a Special Issue on biodiversity of Palaearctic grasslands and provides a synthesis of the current knowledge on this topic. Four major categories of grasslands can be distinguished in the Palaearctic biogeographic realm: (a) zonal steppes (in areas too dry for forests), (b) arctic-alpine grasslands (in areas too cold for forests), (c) azonal and extrazonal grasslands (where hydrology, soil conditions, relief or natural disturbances within the forest biomes prevent tree growth locally) and (d) secondary grasslands (which replace natural forests in consequence of human land use). We summarize the present knowledge about species richness patterns (mainly of vascular plants) along abiotic and land use gradients. Further, we highlight the usefulness of diversity measures not based on species richness, namely functional diversity, phylogenetic diversity and within-species diversity. The strong differences observed for diversity patterns according to analyzed biodiversity parameter, spatial scale or taxonomic group call for comparative studies and caution when generalizing results. A particular challenge are the extreme plot-scale species richness values found in grasslands of a few European regions. We propose a conceptual model that explains the findings by an interplay of various factors acting at different levels: (i) The largest species pool is expected for habitats under conditions that prevailed over the last few million years, with a slight shift towards intermediate positions, i.e. for the Palaearctic in open, semi-dry, base-rich situations. (ii) The landscape-level species pool is increased by continuity of a grassland patch in space and time and heterogeneity of the surrounding landscape. (iii) The coexistence of regionally available species at a plot scale is due to reduced competitive exclusion according to Intermediate Disturbance Hypothesis, mowing once a year without fertilization being particularly effective. Ecosystem functions and services of Palaearctic grasslands are often positively connected to their biodiversity. At the same time, these communities and their biota are nowadays highly endangered. The semi-natural (High Nature Value) grasslands of Europe are mainly threatened by agricultural intensification or abandonment on low-productive sites in remote areas, while the natural steppes of the Palaearctic have largely been destroyed by conversion into arable land. Finally, we present some promising conservation and management approaches and call for a strong and comprehensive Convention on Grassland Conservation.

Highlights
•The paper deals with natural, semi-natural and improved Palaearctic grasslands.
•High species richness at plot-scale occurs in semi-dry basiphilous grasslands.
•Palaearctic grasslands have a big species pool including many threatened biota.
•Semi-natural grasslands are threatened by intensification and abandonment.
•Natural steppes have largely been converted to arable land.

Keywords
Conservation, Disturbance, Land use, Semi-natural, Species richness, Steppe

Kelemen et al. (2013) Journal of Vegetation Science

Kelemen, A., Török, P., Valkó, O., Miglécz, T., Tóthmérész, B. (2012), Mechanisms shaping plant biomass and species richness: plant strategies and litter effect in alkali and loess grasslands. Journal of Vegetation Science. doi: 10.1111/jvs.12027

Abstract
Question: Explaining the biomass–species richness relationship is key to understanding vegetation dynamics. Several possible mechanisms have been suggested, but complex analysis of plant strategies, major biomass and species richness components along a long productivity gradient is still lacking. We provide a detailed analysis of the relationship between major biomass components (total above-ground biomass, green biomass and litter), plant strategies and species richness along a long gradient of alkali and loess grasslands in a steppe landscape in Central Europe.
Location: Hortobágy, Great Hungarian Plain, East Hungary.
Methods: Above-ground biomass of characteristic alkali and loess grassland stands was sampled along a gradient of increasing productivity. In each grassland stand, a 25-m2 sample site was randomly selected. Within each site, ten above-ground biomass samples (20 × 20 cm) were collected randomly in June 2009, at the peak of biomass production. We classified all species into mixed C-S-R strategy types. To obtain correlations between various biomass and species richness data, Spearman rank correlation was used. The relationship between plant strategies and species composition were displayed with a DCA ordination.
Results: The frequently detected humped-back relationship was valid for the relation of total biomass and species richness. With increasing amount of total biomass, we detected an increasing proportion of competitors, and a decreasing proportion of stress tolerators in green biomass. A low proportion of ruderals was detected at both low and high biomass levels. Species richness was affected positively by litter at low litter scores, but there was a negative litter effect from much lower scores than detected previously (from 400 g·m−2). There was a positive relationship between green biomass production and species richness.
Conclusions: The study revealed that at the initial part of a productivity gradient, stress is likely responsible for low species richness. Our results show that litter can shape changes in species richness along the whole biomass gradient, thus the litter effect is one of the major mechanisms structuring grassland diversity.


Keywords

Alkali landscape, Competition, C-S-R strategies, Humped-back, Plant trait, Productivity, Stress, Steppe