Relationships between mature trees and fire fuel hazard in Australian forest

Abstract

Increasing density of mid-storey vegetation since European settlement has been observed in forests and woodlands in several parts of the world and may result in greater fire fuel hazard. This phenomenon is often attributed to a longer interval between fires since European settlement, but may also be influenced by tree removal during the same period. We hypothesised that the number of mature trees in a stand reduces mid-storey vegetation cover and the associated fire fuel hazard through competition. To test this hypothesis, we examined associations between mid-storey cover and fire fuel hazard and the mean diameter of trees within stands of open forest and woodland in south-eastern Australia, a region prone to wildfires. We found that vegetation cover between 2 and 4 m and 4 and 6 m above the ground and two measures of fire fuel hazard were negatively associated with the quadratic mean tree diameter. Our results suggested that the removal of mature trees since European settlement may have triggered tree and shrub regeneration, resulting in higher mid-storey cover and fire fuel hazard. Thus, managing stands for the persistence and replacement of mature trees may contribute to long-term fuel reduction in Australian forests and woodlands.