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[Background]: ‘Megafire’ is an emerging concept commonly used to describe fires that are extreme in terms of size, behaviour, and/or impacts, but the term’s meaning remains ambiguous. [Approach]: We sought to resolve ambiguity surrounding the meaning of ‘megafire’ by conducting a structured review of the use and definition of the term in several languages in the peer-reviewed scientific literature. We collated definitions and descriptions of megafire and identified criteria frequently invoked to define megafire. We recorded the size and location of megafires and mapped them to reveal global variation in the size of fires described as megafires. [Results]: We identified 109 studies that define the term ‘megafire’ or identify a megafire, with the term first appearing in the peer-reviewed literature in 2005. Seventy-one (~65%) of these studies attempted to describe or define the term. There was considerable variability in the criteria used to define megafire, although definitions of megafire based on fire size were most common. Megafire size thresholds varied geographically from > 100–100,000 ha, with fires > 10,000 ha the most common size threshold (41%, 18/44 studies). Definitions of megafire were most common from studies led by authors from North America (52%, 37/71). We recorded 137 instances from 84 studies where fires were reported as megafires, the vast majority (94%, 129/137) of which exceed 10,000 ha in size. Megafires occurred in a range of biomes, but were most frequently described in forested biomes (112/137, 82%), and usually described single ignition fires (59% 81/137). [Conclusion]: As Earth’s climate and ecosystems change, it is important that scientists can communicate trends in the occurrence of larger and more extreme fires with clarity. To overcome ambiguity, we suggest a definition of megafire as fires > 10,000 ha arising from single or multiple related ignition events. We introduce two additional terms – gigafire (> 100,000 ha) and terafire (> 1,0

Millions of trees are expected to be planted in forested and non-forested ecosystems during the United Nations Decade of Restoration. Trees and soil organisms are known to interact, and are both crucial for maintaining multiple ecosystem functions. However, little is known about how the bidirectional relationships among above- and below-ground diversity and ecosystem functions differ across forested and non-forested ecosystems.We collected data from 126 sites from humid to arid areas in eastern Australia to explore bidirectional relationships among above-ground (richness of trees and other plants) and below-ground (richness of bacteria, fungi, invertebrate, protist) diversity and multiple ecosystem functions (multifunctionality, litter and labile carbon storage, nutrient pools, decomposition, groundstorey plant biomass production, soil stability) in forested (tree cover >10%) and non-forested (tree cover ≤10%, open woodlands, shrublands) systems.We found that the relative importance of above- and below-ground diversity differed among forested and non-forested systems. Ecosystem functions, such as litter and labile carbon storage and soil stability, were associated mainly with tree richness in forested systems. By comparison, ecosystem functions of non-forests were related to the richness of soil organisms. Such bidirectional biodiversity–ecosystem function relationships varied with the target function, and the relationships among ecosystem functions and the relative abundance of species varied with tree and soil taxa. The richness of other plants (i.e. all plants excluding trees) and soil organisms was positively coupled in forests only, but there were no linkages among above- and below-ground diversity and ecosystem functions in non-forests for groundstorey plant biomass production. Furthermore, increases in aridity and soil pH further weakened the biodiversity–ecosystem function relationships in forested and non-forested systems, by suppressing above-ground divers

The effects of mammalian ecosystem engineers on soil microbial communities and ecosystem functions in terrestrial ecosystems are poorly known. Disturbance from livestock has been widely reported to reduce soil function, but disturbance by animals that forage in the soil may partially offset these negative effects of livestock, directly and/or indirectly by shifting the composition and diversity of soil microbial communities. Understanding the role of disturbance from livestock and ecosystem engineers in driving soil microbes and functions is essential for formulating sustainable ecosystem management and conservation policies. We compared soil bacterial community composition and enzyme concentrations within four microsites: foraging pits of two vertebrates, the indigenous short-beaked echidna (Tachyglossus aculeatus) and the exotic European rabbit (Oryctolagus cuniculus), and surface and subsurface soils along a gradient in grazing-induced disturbance in an arid woodland. Microbial community composition varied little across the disturbance gradient, but there were substantial differences among the four microsites. Echidna pits supported a lower relative abundance of Acidobacteria and Cyanobacteria, but a higher relative abundance of Proteobacteria than rabbit pits and surface microsites. Moreover, these microsite differences varied with disturbance. Rabbit pits had a similar profile to the subsoil or the surface soils under moderate and high, but not low disturbance. Overall, echidna foraging pits had the greatest positive effect on function, assessed as mean enzyme concentrations, but rabbits had the least. The positive effects of echidna foraging on function were indirectly driven via microbial community composition. In particular, increasing activity was positively associated with increasing relative abundance of Proteobacteria, but decreasing Acidobacteria. Our study suggests that soil disturbance by animals may offset, to some degree, the oft-reported negative e