As droughts become longer and more intense, impacts on terrestrial primary productivity are expected to increase progressively. Yet, some ecosystems appear to acclimate to multiyear drought, with constant or diminishing reductions in productivity as drought duration increases. We quantified the combined effects of drought duration and intensity on aboveground productivity in 74 grasslands and shrublands distributed globally. Ecosystem acclimation with multiyear drought was observed overall, except when droughts were extreme (i.e., ≤1-in-100-year likelihood of occurrence). Productivity losses after four consecutive years of extreme drought increased by ~2.5-fold compared with those of the first year. These results portend a foundational shift in ecosystem behavior if drought duration and intensity increase, from maintenance of reduced functioning over time to progressive and profound losses of productivity when droughts are extreme.

Dryland organisms exhibit varied responses to changes in precipitation, including event size, frequency, and soil moisture duration, influencing carbon uptake and reserve management strategies. This principle, central to the pulse-reserve paradigm, has not been thoroughly evaluated in biological soil crusts (biocrusts), essential primary producers on dryland surfaces. We conducted two experiments to investigate carbon uptake in biocrusts under different precipitation regimes. In the first, we applied a gradient of watering amounts to biocrusts dominated by moss or cyanobacteria, hypothesising distinct pulse-response strategies. The second experiment extended watering treatments over three months, varying pulse size and frequency. Our results revealed distinct carbon uptake patterns: moss crusts exhibited increased CO2 uptake with larger, less frequent watering events, whereas cyanobacteria crusts maintained similar carbon uptake across all event sizes. These findings suggest divergent pulse-response strategies across biocrust types, with implications for modelling dryland carbon dynamics and informing land management under changing precipitation regimes.

Mineral-associated organic carbon (MAOC) constitutes a major fraction of global soil carbon and is assumed less sensitive to climate than particulate organic carbon (POC) due to protection by minerals. Despite its importance for long-term carbon storage, the response of MAOC to changing climates in drylands, which cover more than 40% of the global land area, remains unexplored. Here we assess topsoil organic carbon fractions across global drylands using a standardized field survey in 326 plots from 25 countries and 6 continents. We find that soil biogeochemistry explained the majority of variation in both MAOC and POC. Both carbon fractions decreased with increases in mean annual temperature and reductions in precipitation, with MAOC responding similarly to POC. Therefore, our results suggest that ongoing climate warming and aridification may result in unforeseen carbon losses across global drylands, and that the protective role of minerals may not dampen these effects..

Earth harbours an extraordinary plant phenotypic diversity(1) that is at risk from ongoing global changes(2,3). However, it remains unknown how increasing aridity and livestock grazing pressure-two major drivers of global change(4-6)-shape the trait covariation that underlies plant phenotypic diversity(1,7). Here we assessed how covariation among 20 chemical and morphological traits responds to aridity and grazing pressure within global drylands. Our analysis involved 133,769 trait measurements spanning 1,347 observations of 301 perennial plant species surveyed across 326 plots from 6 continents. Crossing an aridity threshold of approximately 0.7 (close to the transition between semi-arid and arid zones) led to an unexpected 88% increase in trait diversity. This threshold appeared in the presence of grazers, and moved toward lower aridity levels with increasing grazing pressure. Moreover, 57% of observed trait diversity occurred only in the most arid and grazed drylands, highlighting the phenotypic uniqueness of these extreme environments. Our work indicates that drylands act as a global reservoir of plant phenotypic diversity and challenge the pervasive view that harsh environmental conditions reduce plant trait diversity(8-10). They also highlight that many alternative strategies may enable plants to cope with increases in environmental stress induced by climate change and land-use intensification.

Perennial plants create productive and biodiverse hotspots, known as fertile islands, beneath their canopies. These hotspots largely determine the structure and functioning of drylands worldwide. Despite their ubiquity, the factors controlling fertile islands under conditions of contrasting grazing by livestock, the most prevalent land use in drylands, remain virtually unknown. Here we evaluated the relative importance of grazing pressure and herbivore type, climate and plant functional traits on 24 soil physical and chemical attributes that represent proxies of key ecosystem services related to decomposition, soil fertility, and soil and water conservation. To do this, we conducted a standardized global survey of 288 plots at 88 sites in 25 countries worldwide. We show that aridity and plant traits are the major factors associated with the magnitude of plant effects on fertile islands in grazed drylands worldwide. Grazing pressure had little influence on the capacity of plants to support fertile islands. Taller and wider shrubs and grasses supported stronger island effects. Stable and functional soils tended to be linked to species-rich sites with taller plants. Together, our findings dispel the notion that grazing pressure or herbivore type are linked to the formation or intensification of fertile islands in drylands. Rather, our study suggests that changes in aridity, and processes that alter island identity and therefore plant traits, will have marked effects on how perennial plants support and maintain the functioning of drylands in a more arid and grazed world. In global drylands, soils tend to be more fertile beneath tree, shrub and grass islands. Soil fertility was greater beneath taller and wider plants but was unaffected by either grazing pressure or the type of herbivore.

Increases in the abundance of woody species have been reported to affect the provisioning of ecosystem services in drylands worldwide. However, it is virtually unknown how multiple biotic and abiotic drivers, such as climate, grazing, and fire, interact to determine woody dominance across global drylands. We conducted a standardized field survey in 304 plots across 25 countries to assess how climatic features, soil properties, grazing, and fire affect woody dominance in dryland rangelands. Precipitation, temperature, and grazing were key determinants of tree and shrub dominance. The effects of grazing were determined not solely by grazing pressure but also by the dominant livestock species. Interactions between soil, climate, and grazing and differences in responses to these factors between trees and shrubs were key to understanding changes in woody dominance. Our findings suggest that projected changes in climate and grazing pressure may increase woody dominance in drylands, altering their structure and functioning.

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.

Variability of the terrestrial global carbon sink is largely determined by the response of dryland productivity to annual precipitation. Despite extensive disturbance in drylands, how disturbance alters productivity-precipitation relationships remains poorly understood. Using remote-sensing to pair more than 5600 km of natural gas pipeline corridors with neighboring undisturbed areas in North American drylands, we found that disturbance reduced average annual production 6 to 29% and caused up to a fivefold increase in the sensitivity of net primary productivity (NPP) to interannual variation in precipitation. Disturbance impacts were larger and longer-lasting at locations with higher precipitation (>450 mm mean annual precipitation). Disturbance effects on NPP dynamics were mostly explained by shifts from woody to herbaceous vegetation. Severe disturbance will amplify effects of increasing precipitation variability on NPP in drylands.

Rangelands comprise 40% of the conterminous United States and they supply essential ecosystem services to society. A scenario assessment was conducted to determine how accelerating biophysical and societal drivers may modify their future availability. Four scenarios emerged: two may maintain rural communities by sustaining the prevailing ecosystem service of beef cattle production, and two may transform rural communities through expansion of renewable energy technologies and infusion of external capital from amenity land sales. Collaborative organizations representing diverse societal sectors may most effectively identify and manage trade-offs among ecosystem service availability, and equitably prioritize food and energy security, environmental quality and cultural identity. Rangelands provide critical ecosystem and societal services and are central to livestock husbandry across the United States. How these considerations are balanced, and possibly expanded on, will shape the future of rangeland ecosystems and communities moving into the future.

Despite substantial progress in understanding global biodiversity loss, major taxonomic and geographic knowledge gaps remain. Decision makers often rely on expert judgement to fill knowledge gaps, but are rarely able to engage with sufficiently large and diverse groups of specialists. To improve understanding of the perspectives of thousands of biodiversity experts worldwide, we conducted a survey and asked experts to focus on the taxa and freshwater, terrestrial, or marine ecosystem with which they are most familiar. We found several points of overwhelming consensus (for instance, multiple drivers of biodiversity loss interact synergistically) and important demographic and geographic differences in specialists’ perspectives and estimates. Experts from groups that are underrepresented in biodiversity science, including women and those from the Global South, recommended different priorities for conservation solutions, with less emphasis on acquiring new protected areas, and provided higher estimates of biodiversity loss and its impacts. This may in part be because they disproportionately study the most highly threatened taxa and habitats. Front Ecol Environ 2022;

Climate change is predicted to cause alterations in precipitation patterns in grasslands around the globe. The implications of these changes for soil biota and multiple key ecosystem functions that they regulate in grasslands is little known. We used soil nematodes as biological indicators in grassland ecosystems experiencing large shifts in precipitation in an arid, semiarid, and mesic grasslands. By calculating the nematode plant parasite index, maturity index, and its extensions: the enrichment, basal, channel, and structure index, we assessed grassland ecosystem response to five levels of manipulated precipitation over the course of two years. Nematode community structure described by these indices was sensitive enough to reflect community changes from the altered precipitation treatments and responded uniquely at each of the three sites. With increasing precipitation, nematode communities at the arid site became more enriched in species and switched to a more fungal-dominated decomposition pathway. The semiarid site showed a decline in nematode maturity, structure, and fungally dominated decomposition, but greater levels of enrichment, basal resources, and herbivory. In the mesic site increasing precipitation led to a nematode community with greater maturity and structure and shifted toward a fungal decomposition channel that also reflected a lower level of enrichment and plant parasites. We performed an indicator analysis to identify nematode genera representative of each grassland site and precipitation level. Nematode indicator composition was found to be significantly affected by the levels of applied precipitation and across sites, highlighting specific genera that may be affected by future precipitation regimes such as Eucephalobus in the arid site or Trichodorus from the mesic site. Nematode community analysis allowed for the detection of strong influences on the soil food web caused from extreme and moderate precipitation manipulations. This finding stresses the need for more genera level studies to be done to reflect specific ecosystem responses to climate change as well as the need for more cross site studies as site-specific differences must be accounted for ecological interpretations.

Climate change is projected to cause shifts in precipitation regimes globally, leading to intensified periods of precipitation and droughts. Most studies that have explored the influence of changing precipitation regimes on ecosystems have focused on changes in mean annual precipitation, rather than the variance around the mean. Soil fungi are ubiquitous organisms that drive ecosystem processes, but it is unknown how they respond to long‐term increased interannual precipitation variability. Here, we investigated the influence of long‐term increased precipitation variability and host type on soil fungal diversity and community composition in a dryland ecosystem. We collected 300 soil samples from two time points and different host type substrate types at a long‐term precipitation variability experiment at the Jornada Long Term Ecological Research site. Next, we used amplicon sequencing to characterize soil fungal communities. Soil fungal alpha diversity and community composition were strongly affected by host type and sampling year, and increased precipitation variability caused a modest, statistically insignificant, decrease in soil fungal evenness. Furthermore, results from our structural equational model showed that the decrease in grass‐associated soil fungal richness was likely an indirect result of host decline in response to increased precipitation variability. Synthesis . Our work demonstrates effects of increase in interannual precipitation variability on soil fungi, and that plant hosts play a key role in mediating soil fungal responses.

Woody-plant encroachment is a global phenomenon that has been affecting the southwestern United States since the late 1800s. Drought, overgrazing, herbivory, and competition between grasses and shrub seedlings have been hypothesized as the main drivers of shrub establishment. However, there is limited knowledge about the interactions among these drivers. Using a rainfall manipulation system and various herbivore exclosures, we tested hypotheses about how precipitation (PPT), competition between grasses and shrub seedlings, and predation affect the germination and first-year survival of mesquite (Prosopis glandulosa), a shrub that has encroached in Southern Great Plains and Chihuahuan Desert grasslands. We found that mesquite germination and survival (1) increased with increasing PPT, then saturated at about the mean growing season PPT level, (2) that competition between grasses and shrub seedlings had no effect on either germination or survival, and (3) that herbivory by small mammals decreased seedling establishment and survival, while ant granivory showed no effect. In addition to its direct positive effect on survival, PPT had an indirect negative effect via increasing small mammal activity. Current models predict a decrease in PPT in the southwestern United States with increased frequency of extreme events. The non-linear nature of PPT effects on Mesquite recruitment suggests asymmetric responses, wherein drought has a relatively greater negative effect than the positive effect of wet years. Indirect effects of PPT, through its effects on small mammal abundance, highlight the importance of accounting for interactions between biotic and abiotic drivers of shrub encroachment. This study provides quantitative basis for developing tools that can inform effective shrub management strategies in grasslands and savannas.

Free‐living nematodes are one of the most diverse metazoan taxa in terrestrial ecosystems and are critical to the global soil carbon (C) cycling through their role in organic matter decomposition. They are highly dependent on water availability for movement, feeding, and reproduction. Projected changes in precipitation across temporal and spatial scales will affect free‐living nematodes and their contribution to C cycling with unforeseen consequences. We experimentally reduced and increased growing season precipitation for 2 years in 120 field plots at arid, semiarid, and mesic grasslands and assessed precipitation controls on nematode genus diversity, community structure, and C footprint. Increasing annual precipitation reduced nematode diversity and evenness over time at all sites, but the mechanism behind these temporal responses differed for dry and moist grasslands. In arid and semiarid sites, there was a loss of drought‐adapted rare taxa with increasing precipitation, whereas in mesic conditions increases in the population of predaceous taxa with increasing precipitation may have caused the observed reductions in dominant colonizer taxa and yielded the negative precipitation–diversity relationship. The effects of temporal changes in precipitation on all aspects of the nematode C footprint (respiration, production, and biomass C) were all dependent on the site (significant spatial × temporal precipitation interaction) and consistent with diversity responses at mesic, but not at arid and semiarid, grasslands. These results suggest that free‐living nematode biodiversity and their C footprint will respond to climate change‐driven shifts in water availability and that more frequent extreme wet years may accelerate decomposition and C turnover in semiarid and arid grasslands.

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 speciespoor 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.

Open access (OA) is a term best used for published research that is free for everyone to read. In my opinion, in its current use this term is a misnomer because it does not refer to research that is truly free to use. The name, “open access”, suggests an a priori value. Who would be for closed access? I suggest that a better description of the status quo would be to distinguish between readers-paid versus authors-paid. For most academic journals, historically libraries have paid subscriptions to publishers so readers can have access to articles in those journals. In this case, readers or their institutions pay through their library support. In the authors-paid model, commonly called “open access”, authors pay a publication cost that varies among journals but can be as high as $6000 per article. If the author cannot pay, no one has access. While the readers-paid model excludes some readers, OA clearly excludes many authors, and hence a substantial portion of potential readership. OA particularly excludes those without big grants or other institutional support that can pay for OA publication fees. This exclusion is especially felt among researchers and scholars in developing nations and at institutions where research may be secondary to teaching or outreach (eg conservation organizations, private liberal arts or community or Tribal colleges in the US). Because journals are expensive to publish, most publishers are for-profit businesses, and most countries have limited public (ie government) support for academic publishing, there is not a clear best option for who pays. The readers-paid model excludes less affluent readers, as well as individuals working in non-academic institutions. The authors-paid model excludes all authors who cannot afford OA fees, hence stifling the diversity of content and views. Therefore, communities of scholars and researchers, and society at large, miss the knowledge, ideas, and experience of those who do not have the resources to pay for publication. In the OA model, scientific societies will face dwindling resources that originate in subscriptions. These funds have historically been used to support society activities that members enjoy and depend on. The landscape of readers and authors and the resources to support OA and libraries varies among regions and institution types. In the US, library fees are paid by institutions, such as universities and agencies at the federal or state levels. They recover part of the cost from the overhead on research grants and student fees. And, some grantmaking agencies partially support OA. The situation is quite different for smaller liberal arts, community, and tribal colleges with libraries that do not subscribe to many journals. In Western Europe, the situation is similar to the US although with a larger appetite for paying for OA. China has a relatively affluent science enterprise that also pays for most subscription fees. In Latin America and Africa, the system operates quite differently. Grants are smaller and overhead represents a small fraction of research budgets. Therefore, library fees are paid from university or research organization budgets competing for resources with fellowships, faculty, and infrastructure. Whereas support for libraries exist in different forms throughout the world, support for publication fees is extremely rare and concentrated among the most affluent organizations. We must maximize access to novel ideas for the broadest and most diverse group of individuals. This benefits society at large by providing intellectual tools to tackle the wicked problems of our generation. Nobody wants to explicitly exclude groups of readers or authors. How can we optimize scholarly publishing? What system yields the greatest number and diversity of readers and authors? Both readers-paid and authors-paid have costs in the form of library fees or publication costs. What system provides the highest return on investment, where the return is evaluated by the number of readers and authors, their diversity, and impact? Should significant public funding be allocated to support readers or authors? Should we give preference to readers and authors from the developing world? Should we give priority to place-based or potential high-impact articles? Scientific knowledge is universal, created by individuals collaborating across the world, and is central to solving wicked problems from global change to inequality. Therefore, designing a fair system that maximizes development and application of novel ideas is a global problem that cannot be solved in a piecemeal fashion by a small number of individuals. The questions described above should be addressed by stakeholders with diverse perspectives keeping in mind the overall goal of maximizing global scientific outcomes and their applications. Osvaldo Sala

Cycles of plant growth, termed phenology, are tightly linked to environmental controls. The length of time spent growing, bounded by the start and end of season, is an important determinant of the global carbon, water, and energy balance. Much focus has been given to global warming and consequences for shifts in growing-season length in temperate regions. In conjunction with warming temperatures, altered precipitation regimes are another facet of climate change that have potentially larger consequences than temperature in dryland phenology globally. We experimentally manipulated incoming precipitation in a semiarid grassland for over a decade and recorded plant phenology at the daily scale for 7 years. We found precipitation to have a strong relationship with the timing of grass greenup and senescence but temperature had only a modest effect size on grass greenup. Pre-season drought strongly resulted in delayed grass greenup dates and shorter growing-season lengths. Spring and summer drought corresponded with earlier grass senescence, whereas higher precipitation accumulation over these seasons corresponded with delayed grass senescence. However, extremely wet conditions diluted this effect and caused a plateaued response. Deep-rooted woody shrubs showed few effects of variable precipitation or temperature on phenology and displayed consistent annual phenological timing compared with grasses. Whereas rising temperatures have already elicited phenological consequences and extended growing-season length for mid and high-latitude ecosystems, precipitation change will be the major driver of phenological change in drylands that cover 40% of the land surface with consequences for the global carbon, water, and energy balance.