Alpine Ash (Eucalyptus delegatensis) is the classic tree of the sub alpine forests and tends to be replaced by Snow Gum woodlands at higher elevations. In Victoria it is also known as Woolybutt. It only exists in south eastern Australia (there is also a sub species in Tasmania). In Victoria, it occurs at altitudes between 900 and 1,500 metres above sea level.
It has had 84% of it’s range in Victoria burnt since 2002. Large fires occurred in 2002/03 in the north of the Alps, in 2006/2007 in the south. And during 2019/20, around 83,000 hectares of Ash forest was burnt, with 17,800 hectares of this being reproductively immature ash forest that burned at high severity.
We know that large old trees in ecosystems in Victoria which are dominated by Alpine Ash are in ‘rapid decline’. The problem is that Alpine Ash need around 20 years to reach reproductive maturity, so if fires happen more frequently than this, local extinction is possible because there is no seed stock to create a new forest.
New research shows us, yet again, that increased fire regimes threaten this vegetation community. Future fire regimes increase risks to obligate-seeder forests by Sarah C McColl-Gausden, Lauren T Bennett, Dan A Ababei, Hamish G Clarke, and Trent D Penman, and published on 23 September 2021 describes the impacts of fire on Alpine Ash.
As with earlier research, it suggests that projections of future fire regimes indicate increased risk for young trees and that the shift in the fire regime are likely to mean a reduction in the distribution of alpine ash.
The following text comes directly from the report:
About the research
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.
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.
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.
Projections of future fire regimes indicate increased immaturity risk for the obligate seeding species alpine ash. The ecological implications of a shift in the fire regime are likely to mean a reduction in the distribution of alpine ash. The spatial distribution of risk was not uniform across the landscape with those closer to roads, at lower elevations and in drier, warmer parts of the landscape more likely to experience the short-interval fires that can cause localized extinction. These patterns will guide future research and provide spatially explicit information to examine and develop management practices that acknowledge changing risks created by climate-mediated shifts in fire regimes across landscapes.
You can find out more about climate change and fire impacts on Alpine Ash in the report An Icon at Risk, available here.
You can send a letter to the Victorian government, asking them to protect these forests here.
Leave a Reply