Comparison of the severity of invasion associated to pathways with different disturbance levels in a temperate rainforest in southern Chile

Abstract

Alien species introduction in protected areas is a phenomenon promoted primarily by human activity. This fact has increased
the concern for implementing risk assessment methods to assess the species that may potentially become invasive (‘Weed
Risk Assessment’, WRA), and estimate how invaded is a site (severity of invasion, SI). Moreover, the diversity of a
community could regulate the introduction of species, which is scale dependent. At regional scale the relationship between
both native and alien plant species is often positive, because greater environmental heterogeneity allows the development
of this type of species. At a local scale, the relationship between native and alien diversity might be negative, because the
competition would be inevitable. The Puyehue National Park corresponds to a temperate rainforest ecosystem that present
55 alien plant species. In this protected area we determined alien species that show both a high invasive potential (high
WRA) and invasion success (high coverage). We also assessed whether there is positive relationship between these two
parameters. We also compare the SI of sites that differ in disturbance intensity and evaluate the relationship between the
diversity of native and introduced species at local level. Applying risk assessment methods, we found that all alien species
occurring in roadsides showed high invasive potential and that these were the most abundant too. The SI was greater in
more disturbed sites and no relationship was found between native and alien species diversity between sites with different

disturbance intensity associated with roadsides. We propose to take into consideration the most dangerous species in the
park for mitigation plans. In addition to the WRA is a method that could be applied to conduct risk assessments in protected
areas. Finally we highlight the role of roads in protected areas can be a major source of the spread of introduced species,
increasing the severity of invasion.