Stand boundary effects on obligate seeding Eucalyptus delegatensis regeneration and fuel dynamics following high and low severity fire: Implications for species resilience to recurrent fire

Abstract

Increased fire frequency can result in a decline of obligate seeding plants, which rely on re-seeding for population persistence following canopy scorching fire. The resilience of obligate seeding plants to fire at any point in time depends on plant maturity and the size of plants in relation to potential fire scorch height. We investigated variation in the resilience of post-fire regenerating Eucalyptus delegatensis subsp. delegatensis (alpine ash) to a short inter-fire interval at its boundaries with E. fastigata (brown barrel) stands. The resilience of postfire E. delegatensis regeneration was modelled across these stand boundaries as a function of the height of the plants, their reproductive maturity and predicted fire behaviour derived from local fuel characteristics. We measured these attributes 14 years following the Canberra 2003 wildfires and stratified study sites by fire severity. The height and reproductive maturity of post-fire E. delegatensis saplings decreased at stand boundaries with E. fastigata, while fuel was uniformly abundant and capable of supporting canopy scorching fire under mild fire weather conditions. This suggests that E. delegatensis is less resilient to frequent fire in the presence of interspecific competition and other environmental conditions that occur at stand boundaries, which represent the edge of the species’ realised niche. With forecasts for increased fire frequency in south eastern Australia, persistence of E. delegatensis may be greatest in pure stands corresponding to the core of the species’ realised niche, and in moist and sheltered topographic areas that are less prone to frequent canopy scorching fire. Our findings suggest the importance of considering fine-scale spatial variation in important obligate seeding plant traits when predicting and managing the response of obligate seeding species to frequent fire.