Abstract
In the Palaearctic steppe zone, overgrazing was identified as one of the key drivers of declining grassland biodiversity, which underlines the necessity of the functional evaluation of increased grazing pressure on grassland vegetation. We tested the following hypotheses: (a) The effect of grazing intensity on species and functional diversity is strongly dependent on grassland type. (b) The magnitude of diet selectivity of grazers decreases with increasing grazing intensity. (c) Increasing grazing intensity increases evenness and functional evenness of the subjected grasslands. We analyzed vegetation patterns in four types of grasslands (Dry alkali short‐grass steppes, Dry loess steppes, Non‐alkali wet and Alkali wet grasslands) along an intensity gradient of beef cattle grazing at 73 sites in Hungary. Species richness, Shannon diversity, evenness, and four leaf traits were analyzed. We calculated community‐weighted means for each single trait, and multi‐trait functional richness, functional evenness, and divergence for all leaf traits. All species and functional diversity metrics were significantly affected by the grassland type, except leaf dry matter content. The effect of interaction between grazing intensity and grassland type was also significant for functional richness, functional evenness, community‐weighted means of leaf area, and for species richness and evenness. An upward trend of specific leaf area was detected in all grasslands with the highest scores for the overgrazed sites, but the change was also grassland type dependent. The detected trend suggests that with increased intensity the overall selectivity of grazing decreased. We found that evenness was affected but functional evenness was not affected by grazing intensity. Functional evenness scores were more related to the grassland type than to changes in grazing intensity, and displayed a high variability. We stress that one‐size‐fits‐all strategies cannot be recommended and actions should be fine‐tuned at least at the level of grassland type.
Highlights
Grasslands and other open habitats are usually maintained by livestock grazing (Evans et al, 2015)
We found that functional richness was significantly affected both by grassland type and grazing intensity (Table 1)
leaf dry matter content (LDMC) was not affected by the grassland type; a decreasing tendency with increasing grazing intensity was typical in all grasslands, with significantly lower scores in the overgrazed than in the less intensively grazed dry loess steppes and alkali wet grasslands (Figure 3e)
Summary
Grasslands and other open habitats are usually maintained by livestock grazing (Evans et al, 2015). Former research suggested that the grazing behavior of livestock is strongly influenced by the biomass production (Mládek, Hejcman, Hejduk, Duchoslav, & Pavlů, 2011) and the species composition and richness (Liu et al, 2015) of the subjected habitat. Former research suggests that grazers’ selectivity and feeding strategy may change with increasing stocking rates and/or between communities (Liu et al, 2015), and diet selectivity targets vegetation or species with higher nutritive value (Carmona et al, 2012). With the increase in stocking rates, the livestock is forced to select lower quality fodder because of the limited availability of high quality fodder (Mládek et al, 2013) This decreasing selectivity might be expressed indirectly in the increase of specific leaf area values and in the decrease of leaf dry matter contents (Tóth et al, 2018). Former research supports that cattle grazing is less selective for forbs, sustaining a higher species richness compared
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