Shifts from grassland to woody alternative states have been occurring more frequently across the globe over the last century. Although it is clear that these shifts lead to dramatic changes in ecosystem properties and services, it is unclear how the culmination of such transitions on a landscape can alter large-scale system processes. We investigate how the abundance and distribution of woody patches in grass-tree co-dominated landscape can influence large wildfire pattern. Our objective was to determine how changes in large wildfire size and number manifest as woody patches transitions from being the rare to dominant patch type in the landscape matrix. We overlaid 21 years of large (>400 ha) wildfire data for the entire Great Plains biome on woody and grassland vegetation land cover classifications. Patterns in the abundance and organisation of woody:grass alternative states were documented in relation to each wildfire.
Results/Conclusions
We found that large wildfires occurred more frequently than expected in areas where woody cover was greater than 10 %, suggesting that a potential threshold in large wildfire occurrence exists at low levels of woody plant cover. Moreover, wildfire size changed in relation to the configuration of woody patches on the landscape, where wildfire size increased with decreasing woody patch shape complexity. Between 1993 and 2014, the percent woody vegetation that burned within individual wildfires increased from 20 to 40% in the Great Plains. We conclude that even small changes in the relative abundance of woody and grassland patches, as well as their organisation on the landscape, can alter large wildfire regime characteristics.