Fire is a worldwide phenomenon that appears in the geological record soon after the appearance of terrestrial plants. Fire influences global ecosystem patterns and processes, including vegetation distribution and structure, the carbon cycle, and climate. Although humans and fire have always coexisted, our capacity to manage fire remains imperfect and may become more difficult in the future as climate change alters fire regimes. This risk is difficult to assess, however, because fires are still poorly represented in global models. Here, we discuss some of the most important issues involved in developing a better understanding of the role of fire in the Earth system.

Humans and their ancestors are unique in being a fire-making species, but ‘natural’ (i.e. independent of humans) fires have an ancient, geological history on Earth. Natural fires have influenced biological evolution and global biogeochemical cycles, making fire integral to the functioning of some biomes. Globally, debate rages about the impact on ecosystems of prehistoric human-set fires, with views ranging from catastrophic to negligible. Understanding of the diversity of human fire regimes on Earth in the past, present and future remains rudimentary. It remains uncertain how humans have caused a departure from ‘natural’ background levels that vary with climate change. Available evidence shows that modern humans can increase or decrease background levels of natural fire activity by clearing forests, promoting grazing, dispersing plants, altering ignition patterns and actively suppressing fires, thereby causing substantial ecosystem changes and loss of biodiversity. Some of these contemporary fire regimes cause substantial economic disruptions owing to the destruction of infrastructure, degradation of ecosystem services, loss of life, and smoke-related health effects. These episodic disasters help frame negative public attitudes towards landscape fires, despite the need for burning to sustain some ecosystems. Greenhouse gas-induced warming and changes in the hydrological cycle may increase the occurrence of large, severe fires, with potentially significant feedbacks to the Earth system. Improved understanding of human fire regimes demands: (1) better data on past and current human influences on fire regimes to enable global comparative analyses, (2) a greater understanding of different cultural traditions of landscape burning and their positive and negative social, economic and ecological effects, and (3) more realistic representations of anthropogenic fire in global vegetation and climate change models. We provide an historical framework to promote understanding of the development and diversification of fire regimes, covering the pre-human period, human domestication of fire, and the subsequent transition from subsistence agriculture to industrial economies. All of these phases still occur on Earth, providing opportunities for comparative research.

Biodiversity bill update I n its second year before Congress, the biological diversity bill has gained additional cosponsors in both the House and Senate and continues to wind its way through the legislative process. At press time, HR 1268, introduced by James H.

Wildland fire research has historically orbited around a physical paradigm of fire. This strategy has yielded remarkable results, yet increasingly it cannot speak to the core issues that concern fire management. Two additional paradigms are needed. One would build on fire’s origins in the living world. The other would evolve out of fire’s significance to humanity, and humanity’s unblinking importance to fire’s presence on Earth. Note that each paradigm is coherent in itself, that each is capable of absorbing the others, and that each is insufficient on its own. It is unlikely that a master synthesis of these conceptions will emerge, and is not necessary. The need is to sustain research that addresses how fire really exists, not how select sciences can handle it. This essay sketches what the resulting fire-research triangle might look like.

One contribution of 24 to a discussion meeting issue 'The interaction of fire and mankind'.