Ecologists have long sought to understand the factors controlling the structure of savanna vegetation. Using data from 2154 sites in savannas across Africa, Australia, and South America, we found that increasing moisture availability drives increases in fire and tree basal area, whereas fire reduces tree basal area. However, among continents, the magnitude of these effects varied substantially, so that a single model cannot adequately represent savanna woody biomass across these regions. Historical and environmental differences drive the regional variation in the functional relationships between woody vegetation, fire, and climate. These same differences will determine the regional responses of vegetation to future climates, with implications for global carbon stocks.

Tropical savannas are a globally extensive biome prone to rapid vegetation change in response to changing environmental conditions. Via a meta-analysis, we quantified savanna woody vegetation change spanning the last century. We found a global trend of woody encroachment that was established prior the 1980s. However, there is critical regional variation in the magnitude of encroachment. Woody cover is increasing most rapidly in the remaining uncleared savannas of South America, most likely due to fire suppression and land fragmentation. In contrast, Australia has experienced low rates of encroachment. When accounting for land use, African savannas have a mean rate annual woody cover increase two and a half times that of Australian savannas. In Africa, encroachment occurs across multiple land uses and is accelerating over time. In Africa and Australia, rising atmospheric CO , changing land management and rainfall are likely causes. We argue that the functional traits of each woody flora, specifically the N-fixing ability and architecture of woody plants, are critical to predicting encroachment over the next century and that African savannas are at high risk of widespread vegetation change.

International audienceWe expand the concept of “old growth” to encompass the distinct ecologies and conservation values of the world's ancient grass-dominated biomes. Biologically rich grasslands, savannas, and open-canopy woodlands suffer from an image problem among scientists, policy makers, land managers, and the general public, that fosters alarming rates of ecosystem destruction and degradation. These biomes have for too long been misrepresented as the result of deforestation followed by arrested succession. We now know that grassy biomes originated millions of years ago, long before humans began deforesting. We present a consensus view from diverse geographic regions on the ecological characteristics needed to identify old-growth grasslands and to distinguish them from recently formed anthropogenic vegetation. If widely adopted, the old-growth grassland concept has the potential to improve scientific understanding, conservation policies, and ecosystem management

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Forest expansion into Brazilian savanna due to fire suppression causes precipitous species loss.

The World's grasslands are under severe threat from on-going degradation, yet they are largely ignored in sustainable development agendas. This degradation is undermining the capacity of grasslands to support biodiversity, ecosystem services, and human wellbeing. In this Perspective, we examine the current state of grasslands worldwide and explore the extent and dominant drivers of global grassland degradation. We identify actions that are critical to the development of socio-ecological solutions to combat degradation and promote restoration of global grasslands. Specifically, we argue that progress can be made by: increasing recognition of grasslands in global policy, developing standardised indicators of grassland degradation, using scientific innovation for effective restoration at regional and landscape scales, and enhancing knowledge transfer and data sharing on restoration experiences. The integration of these strategies into sustainability policy should help to halt grassland degradation and enhance restoration success, and protect the socio-economic, cultural and ecological benefits that grasslands provide.Grasslands, comprising open grassland, grassy shrublands and savannah, cover about 40% of the Earth's surface and some 69% of the world's agricultural land area 1-3 . Not only do they serve as an important global reservoir of biodiversity, including many iconic and endemic species, but also, they provide a wide range of material and non-material benefits to humans and our quality of life. These benefits include a wide range of ecosystem services, such as food production, water supply and regulation, carbon storage and climate mitigation, pollination, and a host of cultural services 1-3 . Despite its importance, grassland degradation is widespread and accelerating in many parts of the world 4-6 with as much as 49% of grassland area worldwide having been degraded to some extent 5,7,8 .Grassland degradation poses an enormous threat to the hundreds of millions of people who rely on grasslands worldwide for food, fuel, fibre and medicinal products, as well as their multiple cultural values 9,10 . In terms of livestock production, the global cost of grassland degradation has been estimated at $6.8 billion 11 , with the impact on human welfare being particularly severe in regions where most the population is below the poverty line Grassland degradation also creates major environmental problems, given that grasslands play a critical role in biodiversity conservation, climate and water regulation, and global biogeochemical cycles 2,4 . For example, the conversion of tropical grassy biomes to arable cropland poses a significant threat to biodiversity given that they have a vertebrate species richness comparable to forests 12 , while the recent expansion of croplands in United States has caused widespread conversion of prairie grasslands, with considerable cost to wildlife 6 . Moreover, the conversion of grasslands to arable cropland and disturbance through overgrazing, fire and invasive species can lead to signif...

MotivationThe BioTIME database contains raw data on species identities and abundances in ecological assemblages through time. These data enable users to calculate temporal trends in biodiversity within and amongst assemblages using a broad range of metrics. BioTIME is being developed as a community‐led open‐source database of biodiversity time series. Our goal is to accelerate and facilitate quantitative analysis of temporal patterns of biodiversity in the Anthropocene.Main types of variables includedThe database contains 8,777,413 species abundance records, from assemblages consistently sampled for a minimum of 2 years, which need not necessarily be consecutive. In addition, the database contains metadata relating to sampling methodology and contextual information about each record.Spatial location and grainBioTIME is a global database of 547,161 unique sampling locations spanning the marine, freshwater and terrestrial realms. Grain size varies across datasets from 0.0000000158 km2 (158 cm2) to 100 km2 (1,000,000,000,000 cm2).Time period and grainBioTIME records span from 1874 to 2016. The minimal temporal grain across all datasets in BioTIME is a year.Major taxa and level of measurementBioTIME includes data from 44,440 species across the plant and animal kingdoms, ranging from plants, plankton and terrestrial invertebrates to small and large vertebrates.Software format.csv and .SQL.

Summary1. The Cerrado is a fire-dependent savanna requiring a clear and urgent fire management policy. The extensive misuse of fire for deforestation or pasture management in Brazil has created an overall perception that its use is always deleterious. This view, reinforced by threats of global warming and climatic change, has lead to current policies of fire suppression. 2. Cerrado ecosystems depend on the historical fire regime to maintain their structure, biodiversity and functioning. The suppression of fire has transformed savanna vegetation into forests, causing biodiversity losses and drastic changes in ecological processes. 3. Policy implications. The National Fire Policy required by law must be urgently implemented in Brazil, including use of fire for Cerrado conservation in public and private lands on the basis of existing knowledge of indigenous people and scientists. Objective regulations on prescribed burning, land manager training, incentives for fire research and experimentation and a broad campaign to disseminate the benefits of fire for Cerrado conservation should be the cornerstones of the policy. If implemented, the policy can give the biodiversity of the Cerrado a future that has previously been severely threatened by fire suppression.