Scenarios for ecosystems in the year 2100

What might ecosystems look like following substantial global change? We considered change by 2100 as potentially including the following: 4°C of global warming and >800 ppm CO2, with associated changes in extreme weather events; cessation of livestock grazing owing to meat and milk being replaced by cell-culture products; and capacity to selectively suppress particular species by using gene technologies. Future scenarios for four different Australian ecosystems were considered in relation to these drivers. Scenarios were formulated as state-and-transition (ST) diagrams. Some common themes emerged. (1) Increased extreme fire weather will shorten intervals between hot fires, unless fire control can somehow become much more effective. This will strongly affect vegetation structure and species persistence. (2) Warming by 4°C will displace many plant species from their present-day temperature envelopes. There is a major difficulty in forecasting the consequences, because solid evidence is rarely available about what controls species range boundaries. Is it physiological tolerance, or competition, or susceptibility to pathogens, or something else? (3) We need urgently to decide how much to try to support species in their present locations, versus how much to assist them to move polewards or uphill. (4) Certain species can strongly shape ecosystem structure by influencing fire or successional regimes. Gene technology for suppressing selected invasive species would have potential for improved ecosystem management. (5) If livestock grazing declines, this will interact strongly with future fire regimes and will also make lands available where future ecosystems can be deliberately constructed. These themes apply globally as well as in Australia. ST methodology is set to underpin nature-positivity assessments in Australia. In a changing world, measuring nature-positivity by similarity to past ecosystem states may no longer be helpful. Hence, there is value in building ST diagrams that include potential future states.