In the framework of BIODESERT, we have conducted a standardized field survey carried out at 98 sites from 25 countries and six continents to evaluate how the impacts of grazing pressure on nine essential ecosystem services depend on biodiversity, climate, and soil conditions across global drylands. Interactions among grazing, climate, and biodiversity were critical to explain the delivery of ecosystem services across drylands worldwide. For instance, increasing grazing pressure reduced ecosystem service delivery in warmer and species-poor drylands, while positive effects of grazing were observed in colder and species-rich areas. We also found positive relationships among plant species richness and carbon storage, organic matter decomposition, erosion control, and both forage quality and quantity, and between belowground diversity and organic matter decomposition, irrespective of grazing pressure. Greater herbivore richness was also correlated with higher carbon storage regardless of grazing pressure.
During the project we have also synthesized >50,000 observations from global drylands, has been the discovery of three ecosystem thresholds linked to aridity values of 0.54 0.69 and 0.83 respectively, which led to systemic and abrupt ecological transitions (Science 367: 787–790). These changes occurred sequentially in three phases characterized by abrupt decays in plant productivity, soil fertility and plant cover/richness. These results set the stage for future studies exploring temporal changes in dryland ecosystems, particularly in areas that will likely cross these aridity thresholds in the future. For example, it is forecasted that 18% of the terrestrial surface will cross one/several of these thresholds by 2100. Areas expected to cross the 0.8 aridity threshold are particularly sensitive as they may undergo massive vegetation collapse and species loss.
We have also developed novel conceptual, analytical, modelling and synthesis approaches to achieve the objectives of the project. For example, we evaluated the relationship between biodiversity and ecosystem stability for the first time in natural ecosystems at the global scale (Proc Natl Acad Sci USA 115: 8400-8405). To do so, we coupled 14 years of temporal remote sensing measurements with field surveys in 123 drylands from six continents to show a strong climate dependency of the biodiversity–ecosystem stability relationship. Our findings suggest that land management should be adapted to the aridity conditions if we aim to secure stable plant production. Another example is the use of a novel combination of remote sensing, artificial intelligence, paleoclimatic data, and advanced statistical analyses to evaluate the drivers, extent, and future distribution of dryland forests (Nat Plants 8: 879–886). Our analyses show that mid-Holocene climates and aquifer trends are key predictors of the distribution of dryland forests worldwide. We also updated the global extent of dryland forests to 1,283 million hectares and showed that failing to consider past climates and aquifers has resulted in ignoring or misplacing up to 130 million hectares of forests in drylands. Our findings also indicate that about 11% of the current extent of dryland forests (~180 Mha) can be lost in the period 2081–2100. These results can guide restoration actions by avoiding unsuitable areas for tree establishment in a warmer and drier world.
Using 10 yrs of data from a field climate change experiment, we showed that increased soil respiration rates with short-term warming returned to control levels in the longer-term (Global Change Biol 26: 5254-5266). These results highlight the importance of evaluating short- and longer-term soil respiration responses to warming to reduce uncertainties in predicting the soil carbon–climate feedback in drylands. We have also coupled results from that experiment to those from global surveys to address key scientific questions related to the objectives of the project. By doing so we observed that warmer temperatures increase the relative abundance of soil-borne potential fungal plant pathogens worldwide, with hotspots of these pathogens being present in drylands (Nature Clim Change 10: 550–554). This work advances our understanding of the global distribution of potential fungal plant pathogens and their sensitivity to global change drivers.
