The influence of prescribed fire treatments on the abundance of Hakea sericea in fire-prone areas in Northern Portugal

Abstract

Reinforced by fire occurrence, the invader Hakea sericea is increasingly emerging in burned areas in Portugal. Being able to alter ecosystem properties and threatening local biodiversity, management of invasive species should have high priority. Prescribed burning is a widely applicated tool in the Mediterranean regions to reduce fuels loads, and more recently, it seems also a promising way to control particular invasive species. However, research on the effectiveness of prescribed burning regarding this issue is barely documented, especially for the European Mediterranean regions. In this study, the short-term influence of two types of prescribed burning treatments (slash and burn vs. burn) on the vegetation community, soil surface cover, plant community structure and the abundance of the invader Hakea sericea is examined. The experiment was carried out with a total of 6 5x2 m plots, with 3 replicates for each treatment. During the burn, fire temperature and duration were recorded in the surface, duff, and soil layer using thermocouples. Soil burn severity was estimated directly after the fire. The study area was visited every 1-2 months, in which development of the soil surface cover was documented together with species abundance. A point-intercept method at 25-cm intervals along a 5 m transect was applied to measure vegetation structure. Furthermore, vegetation species diversity was determined in 3 subplots located in the bottom, middle and top of each plot. The main findings of this study show that the relative abundance of Hakea sericea is slightly higher in burned plots, but not significant. In contrast to our expectation, soil burn severity was significantly higher in the burned plots. This possibly explains why the species amount was in general lower for the burned plot, as some vegetative buds or seeds might be destroyed. Both treatments seemed to be effective in reducing Hakea sericea density in the short term. However, more research to fire characteristics, combined with local soil-, and vegetation development in the long-term, is needed to get a complete overview of the effect of prescribed burns on invasive species such as Hakea.