Direct and productivity‐mediated indirect effects of fertilization, mowing and grazing on grassland species richness

Abstract

Summary1. Recent declines in biodiversity have given new urgency to questions about the relationship between land-use change, biodiversity and ecosystem processes. Despite the existence of a large body of research on the effects of land use on species richness, it is unclear whether the effects of land use on species richness are principally direct or indirect, mediated by concomitant changes in ecosystem processes. Therefore, we compared the direct effects of land use (fertilization, mowing and grazing) on species richness with indirect ones (mediated via grassland productivity) for grasslands in central Europe. 2. We measured the richness and above-ground biomass in 150 grassland plots in 3 regions of Germany (the so-called Biodiversity Exploratories). We used univariate and structural equation models to examine direct and indirect land-use effects. 3. The direct effects of mowing (À0.37, effect size) and grazing (0.04) intensity on species richness were stronger compared with the indirect effects of mowing (À0.04) and grazing (À0.01). However, the strong negative effect of fertilization (À0.23) on species richness was mainly indirect, mediated by increased productivity compared with the weak direct negative effect (À0.07). 4. Differences between regions in land-use effects showed five times weaker negative effects of mowing (À0.13) in the region with organic soils (Schorfheide-Chorin), strong overall negative effects of grazing (À0.29) for the region with organic soils opposed to a similar strong positive effect (0.30) in the Hainich-Dün region, whereas the Schwäbische Alb region displayed a five times weaker positive effect (0.06) only. Further, fertilization effects on species richness were positive (0.03) for the region with organic soils compared to up to 25 times stronger negative effects in the other two regions. 5. Synthesis. Our results clearly show the importance of studying both direct and indirect effects of land-use intensity. They demonstrate the indirect nature, via productivity, of the negative effect of fertilization intensity on plant species richness in the real-world context of management-induced gradients of intensity of fertilization, mowing and grazing. Finally, they highlight that careful consideration of regional environments is necessary before attempting to generalize land-use effects on species diversity.

Effect of Grazing and Mowing on the Micro Coenological Composition of a Semi - Arid Grassland in Hungary

“…Mowing found to decrease the abundance of disturbance sensitive species, while increased the disturbance-tolerant ruderal species by frequent destruction of above-ground plant organs (Socher et al, 2012). Enrichment of species or recovery after mowing might be due to enhanced seedling germination by the removal of litter and above-ground biomass, which creates gaps that act as suitable micro-sites for the establishment of small-seeded species (Socher et al, 2012). The species richness could change even during a short period of three years of mowing (once per year), however with unfavourable effects on the original dry grassland community (Jantunen, 2003).…”

“…In contrast, grazing was found to increase (due to light grazing of cattle, Fritch et al, 2011) or decrease (due to overgrazing by horses, Penksza, 2005) the species richness compared to the mowing treatment (Fritch et al, 2011, Penksza, 2005. Mowing found to decrease the abundance of disturbance sensitive species, while increased the disturbance-tolerant ruderal species by frequent destruction of above-ground plant organs (Socher et al, 2012). Enrichment of species or recovery after mowing might be due to enhanced seedling germination by the removal of litter and above-ground biomass, which creates gaps that act as suitable micro-sites for the establishment of small-seeded species (Socher et al, 2012).…”

“…Therefore, it is hard to separate the direct effects of species composition change from other related effects (changes of leaf area index, soil bulk density, and soil water holding capacity) on carbon sequestration (Klumpp et al, 2011). Management regime shifts from grazing to mowing could have a significant, but varying (negative vs. positive) effect on species composition (Fritch et al, 2011, Jacquemyn et al, 2011, Socher et al, 2012. In general grasslands mostly benefit from light grazing and mowing and degrade in terms of species composition from frequent mowing and intense grazing but the direction of change also depends on the initial status of the grassland (Jantunen, 2003, Socher et al, 2012.…”

“…In general grasslands mostly benefit from light grazing and mowing and degrade in terms of species composition from frequent mowing and intense grazing but the direction of change also depends on the initial status of the grassland (Jantunen, 2003, Socher et al, 2012. However, comparative studies on the effects of mowing and grazing in the same areas are rare (Jantunen, 2003) and studies are mostly focusing on the changes in species richness (Jantunen, 2003, Pykälä, 2005, Socher et al, 2012, rather on fine scale structural changes in the grassland, which could early indicate the direction of changes (Virágh et al, 2000.…”

Mean age of carbon in fine roots from temperate forests and grasslands with different management

“…Previous studies have already demonstrated the negative effects of fertilization on species richness Stewart and Pullin, 2008;Zechmeister et al, 2003). Recently, a study by Socher et al (2012) conducted in the same study regions has shown a loss of 19 % of the total number of vascular plant species on a grassland site with an annual fertilization input of 35 kg of N per hectare. Given the limited amount of grazed and mowed sites in our dataset, we did not find any significant effect of these management practices on root C age.…”