Species richness in European steppes : role of productivity, soil depth and pH
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| Year of publication | 2008 |
| Type | Conference abstract |
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| Description | Productivity and soil pH are commonly recognised as influential determinants of grassland vegetation diversity. So far, little is known about factors influencing local richness in steppe grasslands of subcontinental and continental areas of Europe. We sampled steppe vegetation in two regions: the Southern Urals, situated within the Euro-Siberian steppe zone, and the Czech Republic, situated at the margin of the forest-steppe zone. By simultaneously studying these contrasting regions we aimed to recognise major patterns in species richness and see how they relate to productivity, soil depth and pH. Steppe vegetation types varying in soil depth, pH and productivity were represented in both data sets. Vascular plant species richness was determined for 100 m2 plots. Aboveground non-woody biomass was collected from a 0.25 m2 subplot located in each plot and used as an estimate of site productivity. Soil depth was measured in three places of each plot and averaged. Similarly, soil pH was measured from a mixed soil sample taken from three places in each plot. Species richness increases with productivity in both the Czech and the Uralian steppes. Due to their general dryness, productivity of most steppe vegetation types is relatively low. In addition, strong moisture fluctuations in steppe soils make it difficult for competitive species to become dominant in the stands. Competitive exclusion is probably not a major force, therefore we do not observe the typical unimodal or even decreasing response of species richness to productivity, commonly reported from grasslands with higher and more balanced water supply. Productivity is strongly related to soil depth. Interestingly, in the Uralian steppes soil depth is a markedly better predictor of species richness than their productivity, while in the Czech steppes the effect of both predictors is comparable. This implies that soil depth not only affects species richness through its effect on productivity, but also in its own way. Species richness increases along the pH gradient in both regions. However, in the Uralian steppes, there is a peak at pH 6.8 followed by a decrease towards the highest-pH soils. In the Czech steppes, such indication of unimodality also appears once soil depth is included in the model. Low species richness at low-pH soils corresponds to a relatively small species pool of acidic substrates. The decrease in number of species at high pH may by due to severe site dryness, often connected with these high-pH soils. To conclude, in European steppes most species occur at deep, productive soils with pH of 6-7.5. Soil depth and pH can together explain about half of the variation in species richness both in the Uralian and the Czech steppes. |
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