The outcome of alien tree invasions in Puerto Rico

Invasive alien tree species in Puerto Rico often form monospecific stands on deforested lands that were previously used for agriculture and then abandoned. Most native pioneer species are incapable of colonizing these sites, and thus introduced species have little competition from native trees. Alien trees may dominate sites for 30 to 40 years, but by that time native species begin to appear in the understory. By 60 to 80 years, unique communities comprising both alien and native species are found on these sites. This phenomenon is a response to a change in the disturbance regime of Puerto Rico's landscape, brought about by intensive agricultural land use and abandonment. The invasion of a site and the formation of an alien-dominated forest serve important ecological functions, such as repairing soil structure and fertility, and restoring forest cover and biodiversity at degraded sites.