Nonnative conifer plantations are important economic resources in many parts of the world, but they can also generate severe environmental problems. Among the main problems is their ability to spread on their own, leading to invasions in neighboring communities. While there are many studies on distribution patterns of invasive forest species, less is known about their impact. Here we analyze the impacts of Pinus contorta (Lodgepole pine) invasion, probably the most invasive forest species in the southern hemisphere, on diverse aspects of biodiversity, ecosystem services, and fuel load. We compared non-invaded zones with invaded zones of contrasting densities, and areas where invasive trees had been removed. In areas where invasive pines were removed, which varied greatly in densities and age of the invasions, we also evaluated the costs of mechanical control in terms of labor and supplies.
Our main conclusion is that high impacts of Pinus contorta invasions are only seen when pines are both large and occur in high densities, while at low densities or when pines are small the impact is low. This is good news because it indicates that there is a relatively long period (about 10 years from the beginning of the invasion) during which appropriate management can be conducted. The results of removing pine invasions were encouraging in terms of reducing fuel material by eliminating vertical fuel connectivity between understory plants and forestry plantations, which is vital to mitigate the spread of fires. However, the removal of invasive trees did not result in improvements in biodiversity indices or ecosystem services metrics. Nonnantive plants colonized post-removal sites, especially those that occupied areas with high initial pine densities. Control costs grew exponentially with the increase in density of pines and their age. These results indicate that if forestry practices focus on early management, numerous environmental impacts will be avoided and costs associated with invasion management will be reduced. However, if forestry practices continue to ignore invasions, environmental impacts may reach an unprecedented level given the high probability of future pine invasion in South America.