Hakea decurrens subsp. physocarpa is
an invasive fire-adapted shrub of Australian origin
that is quickly expanding in Portugal with potential
impacts on fire behavior and fire regime. In this
study we examined the effects of H. decurrens on
fire hazard by assessing fire behavior indicators at
the landscape scale, using a modeling and simulation
approach. Six fuel models for H. decurrens
were developed through fuel characterization and
experimental fires. The fuel models correspond to
combinations of developmental stages of H. decurrens
populations (Early, Intermediate and Mature)
and management (Standing and Slashed fuels).
These combinations were used with three levels of
H. decurrens invasion, corresponding to 25%, 50%
and 75% of cover of the landscape, applied to five
real landscapes in northern Portugal (replicates)
under three fuel moisture conditions (Low, Medium
and High), used as surrogates of weather severity.
Fire behavior simulations were conducted with
FlamMap software. The relationships between fire
behavior indicators (flame length, rate of spread
and burn probability) at the landscape level and the
four factors tested were analyzed using Generalized
Linear Mixed Models. Standing fuels were found
to be more hazardous than slashed fuels. Fire-hazard
increased with H. decurrens stand maturity and slash, regardless of moisture conditions. The results
of this study indicate that H. decurrens expansion
might negatively affect the fire regime in the north of
Portugal. Our findings add to other known negative
impacts of the species on native ecosystems, calling
for the need to reinforce its control.
