Future fire regimes increase risks to obligate-seeder forests

Aim Many species are adapted to a particular fire regime and major deviations from that regime may lead to localized extinction. Here, we quantify immaturity risks to an obligate-seeder forest tree using an objectively designed climate model ensemble and a probabilistic fire regime simulator to predict future fire regimes. Location Alpine ash (Eucalyptus delegatensis) distribution, Victoria, south-eastern Australia. Methods We used a fire regime model (FROST) with six climate projections from a climate model ensemble across 3.7 million hectares of native forest and non-native vegetation to examine immaturity risks to obligate-seeder forests dominated by alpine ash (Eucalyptus delegatensis), which has a primary juvenile period of approximately 20 years. Our models incorporated current and future projected climate including fuel feedbacks to simulate fire regimes over 100 years. We then used Random Forest modelling to evaluate which spatial characteristics of the landscape were associated with high immaturity risks to alpine ash forest patches. Results Significant shifts to the fire regime were predicted under all six future climate projections. Increases in both wildfire extent (total area burnt, area burnt at high intensity) and frequency were predicted with an average increase of up to 110 hectares burnt annually by short-interval fires (i.e., within the expected minimum time to reproductive maturity). The immaturity risk posed by short-interval fires to alpine ash forest patches was well explained by Random Forest models and varied with both location and environmental variables. Main conclusions Alpine ash forests are predicted to be burned at greater intensities and shorter intervals under future fire regimes. About 67% of the current alpine ash distribution was predicted to be at some level of immaturity risk over the 100-year modelling period, with the greatest risks to those patches located on the periphery of the current distribution, closer to roads or surrounded by a drier landscape at lower elevations.

Automated summary

Predictions show significant shifts in fire regimes for alpine ash forests in the future, with increased intensity and frequency of wildfires. About 67% of current alpine ash distribution is expected to face immature risks over a 100-year period, particularly for patches on the outskirts of the current distribution, closer to roads, or surrounded by drier landscapes at lower elevations.