Slash and Burn Treatments Effectively Reduce Post-Fire Recruitment of the Invasive Shrub Hakea Decurrens

Invasion of native Mediterranean vegetation by fire-adapted plant species may create a feedback loop where fire facilitates the invasion process which, in turn, increases fire hazard due to fuel accumulation. This relationship may pose challenges for ecosystem management since fuel reduction and invasion control are often constrained by restrictions in the use of prescribed fire and other disturbance-based control approaches. This is the case for Hakea decurrens, an Australian woody species, which regenerates after fire through seedling recruitment. Here, we investigated the regeneration processes of H. decurrens using different treatment alternatives aimed at finding better management solutions. The objectives of this study were to examine: 1) the effects of different combinations of Slash and Burn treatments on seedling establishment of H. decurrens; 2) the plant attributes that favour resprouting after Slash; and 3) the effects of fire-related heat exposure on follicle dehiscence and seed viability. Four treatment plots were established on five stands of H. decurrens: Burn, Slash, Slash & Burn, and Control. Treatments were applied once per plot, with Slash and Slash & Burn treatments introduced at different times across sites, and plots were monitored for 1080 days to assess seedling density and resprouting capacity. Additionally, fruits (follicles) were exposed to different heat residence times and seed viability tested to evaluate responses to fire. Slash and Slash & Burn treatments were more effective in reducing H. decurrens seedling densities than the Burn treatment alone. Resprouting following slashing decreased with increasing trunk basal diameter and was virtually absent above ~3 cm. When follicles were exposed to experimental fire for 120 s or more, seed viability decreased, approaching zero at 180 s. The results of this study indicate that Slash and Slash & Burn techniques are effective for initial control of H. decurrens. However, control of this species requires several interventions to deal with new seedlings, and invaded areas must be monitored and integrated into recovery programmes, especially where fires are frequent.