• Energy Research

Global change is associated with variable shifts in the annual production of aboveground plant biomass, suggesting localized sensitivities with unclear causal origins. Combining remotely sensed normalized difference vegetation index data since the 1980s with contemporary field data from 84 grasslands on 6 continents, we show a widening divergence in site-level biomass ranging from +51% to -34% globally. Biomass generally increased in warmer, wetter and species-rich sites with longer growing seasons and declined in species-poor arid areas. Phenological changes were widespread, revealing substantive transitions in grassland seasonal cycling. Grazing, nitrogen deposition and plant invasion were prevalent in some regions but did not predict overall trends. Grasslands are undergoing sizable changes in production, with implications for food security, biodiversity and carbon storage especially in arid regions where declines are accelerating.

Climate change is increasing the frequency and severity of short-term (~1 y) drought events—the most common duration of drought—globally. Yet the impact of this intensification of drought on ecosystem functioning remains poorly resolved. This is due in part to the widely disparate approaches ecologists have employed to study drought, variation in the severity and duration of drought studied, and differences among ecosystems in vegetation, edaphic and climatic attributes that can mediate drought impacts. To overcome these problems and better identify the factors that modulate drought responses, we used a coordinated distributed experiment to quantify the impact of short-term drought on grassland and shrubland ecosystems. With a standardized approach, we imposed ~a single year of drought at 100 sites on six continents. Here we show that loss of a foundational ecosystem function—aboveground net primary production (ANPP)—was 60% greater at sites that experienced statistically extreme drought (1-in-100-y event) vs. those sites where drought was nominal (historically more common) in magnitude (35% vs. 21%, respectively). This reduction in a key carbon cycle process with a single year of extreme drought greatly exceeds previously reported losses for grasslands and shrublands. Our global experiment also revealed high variability in drought response but that relative reductions in ANPP were greater in drier ecosystems and those with fewer plant species. Overall, our results demonstrate with unprecedented rigor that the global impacts of projected increases in drought severity have been significantly underestimated and that drier and less diverse sites are likely to be most vulnerable to extreme drought.

Understanding the interactive effects of global change drivers on vegetation is critical for ecosystem management and restoration, particularly in the Mediterranean‐climate biodiversity hotspots of the world. Climate change, habitat loss and nitrogen deposition have been identified as the key threats to biodiversity loss in these regions, yet their combined effects are poorly understood. We measured the interactive effects of rainfall manipulation (reduction, control, addition) and nitrogen deposition (N addition, N 1 P addition, and unfertilised) on the establishment of 19 Banksia‐woodland species planted at three sites in southwestern Australia. Seedling survival and aboveground biomass was increased with water addition but was not affected by rainfall reduction. N addition alone did not impact seedling survival and growth, but interacted with rainfall manipulation and site in unpredictable ways. Treatment effects were context dependent, which we attributed to historic nutrient enrichment and competitive exotic species that prevented seedling establishment. Plant species (n 5 6) varied greatly in their water‐use efficiency and nitrogen‐use efficiency responses to the imposed treatments, which underscores the difficulty of generalising results to larger numbers of species. Despite our finding that rainfall manipulation and nutrient addition have complex, and in some cases antagonistic effects on seedling survival and growth in Banksia woodlands, our results suggest that local context (i.e. invasive species, land‐use history) will have as much influence on seedling establishment as global changes in climate and nitrogen deposition. We call for more field experiments and predictive models to explore further the importance of ecological context in determining the interactive effects of multiple global change drivers on ecosystems. Finally, to realize effective biodiversity conservation, local management interventions that address invasive species and associated habitat degradation will be as critical in the future as they are now.

Abstract Ecological restoration increasingly aims at improving ecosystem multifunctionality and making landscapes resilient to future threats, especially in biodiversity hotspots such as Mediterranean‐type ecosystems. Plants and their traits play a major role in the functioning of an ecosystem. Therefore, successful restoration towards long‐term multifunctionality requires a fundamental mechanistic understanding of this link under changing climate. An integrated approach of empirical research and simulation modelling with a focus on plant traits can allow this understanding. Based on empirical data from a large‐scale restoration project in a Mediterranean‐type ecosystem in Western Australia, we developed and validated the spatially explicit simulation model Modelling Ecosystem Functions and Services based on Traits (ModEST), which calculates coupled dynamics of nutrients, water and individual plants characterised by functional traits. We then simulated all possible combinations of eight plant species with different levels of diversity to assess the role of plant diversity and traits on multifunctionality, the provision of six ecosystem functions that can be linked to ecosystem services, as well as trade‐offs and synergies among the functions under current and future climatic conditions. Our results show that multifunctionality cannot fully be achieved because of trade‐offs among functions that are attributable to sets of traits that affect functions differently. Our measure of multifunctionality was increased by higher levels of planted species richness under current, but not future climatic conditions. In contrast, single functions were differently impacted by increased plant diversity and thus the choice and weighting of these functions affected multifunctionality. In addition, we found that trade‐offs and synergies among functions shifted with climate change due to different direct and indirect (mediated via community trait changes) effects of climate change on functions. Synthesis and application. With our simulation model Modelling Ecosystem Functions and Services based on Traits (ModEST), we show that restoration towards multifunctionality might be challenging not only under current conditions but also in the long‐term. However, once ModEST is parameterised and validated for a specific restoration site, managers can assess which target goals can be achieved given the set of available plant species and site‐specific conditions. It can also highlight which species combinations can best achieve long‐term improved multifunctionality due to their trait diversity.

Increased attention to species movement in response to environmental change highlights the need to consider changes in species distributions and altered biological assemblages. Such changes are well known from paleoecological studies, but have accelerated with ongoing pervasive human influence. In addition to species that move, some species will stay put, leading to an array of novel interactions. Species show a variety of responses that can allow movement or persistence. Conservation and restoration actions have traditionally focused on maintaining or returning species in particular places, but increasingly also include interventions that facilitate movement. Approaches are required that incorporate the fluidity of biotic assemblages into the goals set and interventions deployed.

SignificancePredicting the effects of anthropogenic nutrient enrichment on plant communities is critical for managing implications for biodiversity and ecosystem services. Plant functional types that fix atmospheric nitrogen (e.g., legumes) may be at particular risk of nutrient-driven global decline, yet global-scale evidence is lacking. Using an experiment in 45 grasslands across six continents, we showed that legume cover, richness, and biomass declined substantially with nitrogen additions. Although legumes benefited from phosphorus, potassium, and other nutrients, these nutrients did not ameliorate nitrogen-induced legume decline. Given global trends in anthropogenic nutrient enrichment, our results indicate the potential for global decline in grassland legumes, with likely consequences for biodiversity, food webs, soil health, and genetic improvement of protein-rich plant species for food production.