Grazing‐induced patchiness, not grazing intensity, drives plant diversity in European low‐input pastures

Abstract

1. Livestock grazing at low stocking rates is widely recommended to maintain grassland biodiversity. However, empirical evidence of grazing-intensity effects on plant diversity is contradictory. Explicitly considering the small-scale heterogeneity of short, frequently grazed and tall, rarely grazed patches typical of low-input grazing systems may be crucial to the understanding of paddock-scale grazing effects.2. We studied three patch types (short, intermediate, tall) within an unfertilised long-term cattle grazing experiment in Lower Saxony, Germany, comparing three paddock-scale grazing intensities. We analysed soil nutrient concentrations and recorded vegetation composition at a total of 135 plots. We determined species richness, Simpson diversity, Simpson evenness and beta diversity of individual plots (plot scale) and patch types within paddocks (patch scale). To quantify paddock-scale diversity, we resampled plot-scale species composition across a gradient of relative proportions of short and tall patches within a paddock.3. Patch type, not paddock-scale grazing intensity, was the main driver of plant diversity at both plot and patch scale. Short patches were more diverse than tall patches, but the effect was not strongly mediated by the lower soil nutrient concentrations in the short patches. By contrast, both patch type and grazing intensity affected vegetation composition at plot and patch scale. 4. Beta-diversity within and between patch types was independent of grazing intensity; consequently, paddock-scale diversity was determined by the relative proportion of short versus tall patches. Higher alpha diversity of short patches compared to tall patches was more important than beta diversity between the two patch types in shaping paddock-scale diversity. Consequently, with increasing short-patch proportion, paddock-scale diversity increased. Synthesis and applications.Our study identifies the grazing-induced patch structure as the most important driver of plant diversity across different grazing intensities in low-input, that is, unfertilised and continuously stocked, pastures. To optimise grazing management for biodiversity, understanding plant-diversity responses to grazing at the patch scale is indispensable. Our results suggest that, in unfertilised, continuously stocked European pastures, trade-offs between biodiversity and | 1625Journal of Applied Ecology TONN eT al.

Space use, herbage selection, and animal performance of grazing heifers on a peaty river valley section

“…This became particularly apparent in autumn and shows that the shorter day length is a serious limitation when the need for selection is great. The creation of patches as a compensatory measure, which was frequently observed in more suitable plant associations (Distel et al 1995;Tonn et al 2019), did not work as hoped here. This can probably be attributed to the inadequate suitability of sedges: they are only bitten in the upper leaf areas, which does not lead to young shoots.…”

“…Nevertheless, the compatibility of extensive beef production with the promotion of biodiversity while at the same time conserving soil and water resources remains a major economic challenge. Forage selection of grazing cattle and associated space use are at the core of this challenge for two reasons: on the one hand, because the forage selection success is decisive for the individual animal performance (Breitsameter et al 2017) and thus for the economic efficiency of land use, and on the other hand, because the heterogeneity pattern in vegetation created by selective grazing is a prerequisite for a high level of biodiversity (Tonn et al 2019). Therefore, the following sections deal with the spatial and temporal processes necessary to understand the interaction between herbage selection and the generation of animal performance.…”

The Effect of Grazing Intensity and Sward Heterogeneity on the Movement Behavior of Suckler Cows on Semi-natural Grassland

“…Further studies showed that within grazing intensities, the botanical composition differed between short and tall patches as a consequence of modified resource availability for light and soil nutrients ( 4 ). Tonn et al ( 11 ) observed larger phytodiversity in short patches compared to tall ones, and Perotti et al ( 29 ) found that species in tall patches had higher competitiveness and the ones in short patches higher stress tolerance according to the competitor, stress tolerator, ruderal (CSR) theory after Grime ( 30 ).…”

“…Patch grazing is characterized by a pronounced spatial heterogeneity in forage intake ( 9 ) with intensive and extensive grassland utilization occurring in close proximity within the same pasture. Several studies in semi-natural grassland found that the productivity ( 10 ), soil nutrient contents ( 10 , 11 ), and the vegetation composition ( 4 , 12 ) are driven by these temporally stable patches ( 7 ) rather than by the pasture-scale grazing intensity. The extent of patch grazing is controlled by the pasture stocking rate, i.e., the herbage allowance per grazing animal.…”

Niche differentiation, competition or habitat filtering? Mechanisms explaining co‐occurrence of plant species on wet meadows of high conservation value

“…Bartha et al, 2014;Merriam et al, 2018;Mangano et al, 2019), as well as on the impact of shifts in the management type and its intensity (e.g. Köhler et al, 2005;Doležal et al, 2018;Tonn et al, 2019). Recently, a great emphasis is placed on the examination of ecological mechanisms shaping the community composition (see review in Mudrák et al, 2019), and thus on the exploration of the community assembly rules (Maire et al, 2012;Hedberg et al, 2014).…”