The invasion of two native Eucalypt forests by Pinus radiata in the Blue Mountains, New South Wales, Australia

Invasions of Pinus species are a major environmental concern in South Africa and New Zealand where pines are beginning to dominate native grasslands and shrublands. Pines are widely cultivated in Australia with almost a million hectares growing in large plantations. Plantations are commonly bordered by native Eucalypt vegetation resulting in a high potential for invasion and providing an opportunity to study pine invasion processes within forest environments.In order to determine if Pinus radiata equally invades different dry Eucalypt woodland vegetation types, two areas in the upper Blue Mountains in New South Wales, Australia were surveyed. Similar levels of invasion were observed in both Eucalypt forest types. An average pine abundance of 55 individuals for the Eucalyptus oreades and Eucalyptus sieberi vegetation type and 49 individuals for the Eucalyptus mannifera and Eucalyptus dives vegetation type was recorded in 20 m by 20 m plots located 50 m from the plantation boundary. To characterise the spatial distribution of the pines, transects were placed perpendicular to the plantation edge. As expected pine numbers diminished with distance from the plantation, however, large reproductive pine trees were found up to 4 km from the seed source signifying long distance dispersal.Investigation of wildling pine response to fire suggests that it may not always be an appropriate management tool. Fire stimulated seed release from cones and resulted in high recruitment of seedlings around reproductive pines which were large enough to survive the burn. Infrequent fires at intervals greater than time to maturity will lead to increased pine densities and further spread into the native vegetation.