• Energy Research

Adler et al . (Reports, 23 September 2011, p. 1750) reported “weak and variable” relationships between productivity and species richness and dispute the “humped-back” model (HBM) of plant diversity. We show that their analysis lacks sufficient high-productivity sites, ignores litter, and excludes anthropogenic sites. If corrected, the data set of Adler et al . would apparently yield strong HBM support.

Les prairies permanentes ont la faculté de fournir des services écosystémiques aux bénéfices de la production agricole et plus largement de la société. Ces services résultent d’interactions fortes entre la biodiversité animale et végétale et le fonctionnement des écosystèmes (e.g. les cycles biogéochimiques). Avec les changements climatiques et de pratiques agricoles en cours, ces liens entre biodiversité et fonctions sont susceptibles d’être modifiés, si bien que la capacité des prairies à fournir simultanément divers services (i.e. leur multifonctionnalité) pourrait êtrealtérée. Nous illustrons les liens complexes entre pratiques, climat et biodiversité et leurs effets sur la multifonctionnalité des prairies par la synthèse de plusieurs études conduites dans le Massif central. Nous montrons que la biodiversité est un déterminant majeur de la capacité desprairies à assurer de manière simultanée la production, la qualité fourragère, la stabilité, le stock de carbone, la valeur patrimoniale des prairies et la résistance aux sècheresses. Les pratiques agricoles influencent alors directement cette multifonctionnalité, mais aussi indirectement enmodifiant la biodiversité des prairies. Nos résultats illustrent également comment les changements climatiques pourraient bouleverser ces relations. Plus précisément nous montrons que la hausse des températures pourrait rendre les pratiques de fertilisation actuelles fortement délétèrespour la biodiversité et ainsi la fourniture simultanée de nombreux services écosystémiques. Ces travaux invitent à repenser nos dispositifs de recherche pour mieux anticiper la réponse des écosystèmes prairiaux aux changements globaux et adapter les pratiques agricoles en faveur de la conservation de leur biodiversité et ainsi de leur multifonctionnalité Permanent grasslands have the ability to simultaneously provide numerous ecosystem services for the benefit of agricultural production and, more broadly, society. This multifunctionality results from strong interactions between animal and plant biodiversity and biogeochemical cycles. These links are, however, modulated by local pedoclimatic conditions, the biogeographic/landscape context and management practices, thus determining a great variability in the structures and dynamics of permanent grasslands. Today these balances are threatened due to rapid changes in climatic conditions and modifications in agricultural activities. We illustrate the complex links between practices, climate and biodiversity and their effects on the multifunctionality of grasslands through the synthesis of several studies conducted in the Massif central. We show that biodiversity is a major determinant of the capacity of grasslands to simultaneously ensure production, forage quality, stability, carbon stock, heritage value of grasslands and resistance to drought. By modifying the biodiversity of grasslands, practices impact their functioning (biological functions) and indirectly the ecosystem services they provide. Our results further illustrate how climate change could disrupt these relationships. More specifically, we show that rising temperatures could lead to deleterious effects of actual fertilization practices on biodiversity and thus on the provision of ecosystem services. Our findings invite to rethink our research devices to better anticipate the response of grassland ecosystems to global changes and adapt agricultural practices in favour of the conservation of their biodiversity.

Thresholds of aridity Increasing aridity due to climate change is expected to affect multiple ecosystem structural and functional attributes in global drylands, which cover ∼45% of the terrestrial globe. Berdugo et al. show that increasing aridity promotes thresholds on the structure and functioning of drylands (see the Perspective by Hirota and Oliveira). Their database includes 20 variables summarizing multiple aspects and levels of ecological organization. They found evidence for a series of abrupt ecological events occurring sequentially in three phases, culminating with a shift to low-cover ecosystems that are nutrient- and species-poor at high aridity values. They estimate that more than 20% of land surface will cross at least one of the thresholds by 2100, which can potentially lead to widespread land degradation and desertification worldwide. Science , this issue p. 787 ; see also p. 739

Grazing represents the most extensive use of land worldwide. Yet its impacts on ecosystem services remain uncertain because pervasive interactions between grazing pressure, climate, soil properties, and biodiversity may occur but have never been addressed simultaneously. Using a standardized survey at 98 sites across six continents, we show that interactions between grazing pressure, climate, soil, and biodiversity are critical to explain the delivery of fundamental ecosystem services across drylands worldwide. Increasing grazing pressure reduced ecosystem service delivery in warmer and species-poor drylands, whereas positive effects of grazing were observed in colder and species-rich areas. Considering interactions between grazing and local abiotic and biotic factors is key for understanding the fate of dryland ecosystems under climate change and increasing human pressure.

Abstract Temperate seminatural grasslands harbour unique biodiversity, support livestock farming through forage production, and deliver many essential ecosystem services (ESs) to human society; they are highly multifunctional. However, temperate grassland ecosystems are also among the most threatened ecosystems on earth due to land use and climate changes. Understanding how biodiversity, climate and land use intensification impact grassland multifunctionality through complex direct and indirect pathways is critical to better anticipate the future of these fragile ecosystems. Here, we evaluate how local plant species richness (SR) modulates the effect of land use intensification and climate on grassland multifunctionality (using six key ESs: biomass productivity and stability, forage quality, carbon storage, pollination and local plant rarity) in the French Massif Central, the largest grassland in Western Europe. We sampled 100 grasslands with contrasted fertilization rates and SR, over large elevational and latitudinal gradients related to variation in mean annual temperature (MAT), and drought severity (DS), two key climate change drivers predicted to increase in the future. Using a confirmatory path analysis, we found that SR was the main driver of multifunctionality. We also found significant SR × MAT and SR × fertilization interactions suggesting that warm climate and high fertilization rates alter the biodiversity–ecosystem multifunctionality relationships. Furthermore, increasing temperature and fertilization indirectly influenced multifunctionality by decreasing SR and consequent multifunctionality in warm lowland and highly fertilized grasslands compared to colder montane grasslands or less fertilized ones. DS only impacted some ES individually (e.g. forage quality). Synthesis and applications: We identified species richness (SR) as a pivotal factor mediating the effects of land use intensification and climate on multifunctionality through both direct and indirect pathways. Failing to account for changes in SR could thus bias any prediction of, or aggravate, the effects of land use intensification and climate change on ecosystem services delivery in temperate grassland ecosystems. Considering that SR, mean annual temperature and fertilization are major proxies of three main global change drivers (biodiversity loss, climate change and land use intensification) our study may help to better anticipate the effect of multiple interacting global change drivers on grassland ecosystems.