Aridity exacerbates grazing‐induced rangeland degradation: A population approach for dominant grasses

Interplay between Livestock Grazing and Aridity on the Ecological and Nutritional Value of Forage in Semi-arid Mediterranean Rangelands (NE Spain)

Rangeland-based livestock production constitutes a primary source of livelihood for many inhabitants of dryland regions. Their subsistence relies heavily on maintaining the productivity, biodiversity and services of these ecosystems. Harsh environmental conditions (e.g., drought) combined with land use intensification (e.g., overgrazing) make dryland ecosystems vulnerable and prone to degradation. However, the interplay between livestock grazing intensity and aridity conditions in driving the conservation and nutritional value of forage in arid and semi-arid rangelands is still not fully understood. In this study, we performed structural equation models (SEM) to assess the simultaneous direct and indirect effects of livestock grazing intensity and aridity level on community structure, diversity, biomass, forage production, forage C:N ratio and forage fiber composition in two semi-arid Mediterranean rangelands, NE Spain. Not surprisingly, we found that higher livestock grazing intensity led to lower community plant cover, especially when combined with higher aridity. However, both increasing grazing intensity and aridity were associated with higher forage production after one year of grazing exclusion. We did not find any adverse effect of livestock grazing on plant diversity, although plant species composition differed among grazing intensity levels. On the other hand, we found an aridity-driven trade-off in regard of the nutritional value of forage. Specifically, higher aridity was associated with a decrease in the least digestible fiber fraction (i.e., lignin) and an increase in forage C:N ratio. More interestingly, we found that livestock grazing modulated this trade-off by improving the overall forage nutritional value. Altogether, our results provide further insights into the management of semi-arid Mediterranean rangelands, pointing out that maintaining traditional rangeland-based livestock production may be a sustainable option as long as rangeland conservation (e.g., community plant cover) is not severely compromised.

An early warning signal for grassland degradation on the Qinghai-Tibetan Plateau

Intense grazing may lead to grassland degradation on the Qinghai-Tibetan Plateau, but it is difficult to predict where this will occur and to quantify it. Based on a process-based ecosystem model, we define a productivity-based stocking rate threshold that induces extreme grassland degradation to assess whether and where the current grazing activity in the region is sustainable. We find that the current stocking rate is below the threshold in ~80% of grassland areas, but in 55% of these grasslands the stocking rate exceeds half the threshold. According to our model projections, positive effects of climate change including elevated CO2 can partly offset negative effects of grazing across nearly 70% of grasslands on the Plateau, but only in areas below the stocking rate threshold. Our analysis suggests that stocking rate that does not exceed 60% (within 50% to 70%) of the threshold may balance human demands with grassland protection in the face of climate change.

Impact of Grazing on Diversity of Semi-Arid Rangelands in Crete Island in the Context of Climatic Change

The rangelands of Crete island (Greece) are typical Mediterranean habitats under high risk of degradation due to long-term grazing and harsh climatic conditions. We explored the effect of abiotic (climatic conditions, altitude) and biotic factors (long-term grazing by small ruminants) on the floristic composition and diversity of selected lowland (Pyrathi, Faistos) and highland (Vroulidia, Nida) rangelands. In each rangeland, the ground cover was measured, and the floristic composition was calculated in terms of five functional groups: grasses, legumes, forbs, phrygana, and shrubs. The aridity index, species turnover, species richness, Shannon entropy, and Gini-Simpson index (with the latter two converted to the effective number of species) were calculated. Our results reveal that highlands are characterized by the highest aridity index (wetter conditions). Lowland rangelands, compared to highland, exhibited a higher percentage contribution of grasses, legumes, and forbs, while species turnover decreased along the altitudinal gradient. The Shannon entropy index was correlated (a) positively with Gini-Simpson and mean annual temperature and (b) negatively with mean annual precipitation, aridity index, and altitude. Moreover, the Gini-Simpson index correlated positively with mean annual temperature and negatively with altitude. Our results could help to understand the effects of grazing on rangeland dynamics and sustainability in semi-arid regions in the context of climatic change.

Livestock indirectly decrease nest abundance of two shrub-nesting species in Patagonian Monte Desert

Domestic livestock may indirectly affect bird species through changes in vegetation structure (e.g. cover), reducing the availability of food, nesting sites, refugia and, therefore, reproduction in many ecosystems worldwide. However, it remains unclear how the effect of livestock on vegetation structure can influence insectivorous birds that use shrubs for nest construction and placement rather than for feeding. Several species from the Furnariidae family inhabit Monte Desert, Argentina, exhibiting an extraordinary diversity in nest placement and structure that allows them to survive habitat aridity. Nest abundance and size of two common furnariid species, Pseudoseisura gutturalis and Leptasthenura aegithaloides, were studied across a cumulative livestock impact gradient (livestock impact by years grazed). These bird species use large, closed-nests (~40cm and ~100cm length, respectively) built with thorny branches placed on thorny shrubs. The study encompassed nine independent rangelands within the same habitat, but with increasing livestock density, establishing a gradient in grazing intensity. In each rangeland, nest abundance, nest and supporting plant characteristics, vegetation structure and the percentage of browsing were assessed. Plant cover was lower in rangelands with higher livestock impact, and this was associated with lower nest abundance and nest size. Nest abundance of L. aegithaloides was halved, whereas P. gutturalis was decreased 10-fold comparing the extremes of the livestock impact gradient (0.06 vs 1.63 cattle ha−1×years). Nests tended to be smaller and more spherical with increasing livestock impact. The significant and positive association between nest abundance and vegetation structure together with the importance of mating and reproduction for bird lifecycles suggests that the nest abundance of these species could be used as an indicator of habitat degradation. Therefore, furnariid nest abundance could be used as a first step for diagnosing ecosystem health and designing ecologically sustainable management practices in Monte Desert. Changes in vegetation structure (e.g. cover) such as those imposed by livestock may unpredictably affect plant-associated species affecting their reproduction, demography and ecosystem biodiversity.