Mediterranean shrub communities dominate fire-prone landscapes in many parts of Portugal. It is feared that streamside anti-erosion buffers of natural shrub vegetation represent a fire hazard to plantations of eucalyptus and other trees. The FIREMAP system, which can simulate fire behavior in spatially nonuniform environments, was used to assess the extent to which fire buffers can become main vectors of fire spread in Portuguese landscapes. FIREMAP predicted that fire will spread across landscapes consisting of Eucalyptus sp. plantations and streamside borders of natural Mediterranean vegetation much more rapidly than across landscapes consisting of Eucalyptus plantations and streamborders of planted Ouercus sp.