Recovery of Native Grasslands after Removing Invasive Pines

The advance of exotic tree and shrub species is one of the main threats to conservation of the last relicts of natural grassland in South America; however, control actions in the region are still scarce and there are almost no evaluations of the recovery of natural ecosystems after removing invasive plants. Monitoring of the vegetation during the years after removal of invasive trees is critical in order to decide whether an active restoration strategy is necessary. The recovery of montane grassland four years after the control of a dense invasion of Aleppo pine (Pinus halepensis) is described in this study. Experimental clearing areas were followed during four years and compared to grassland controls. Variation was seen in the levels of recovery in function of the proximity of sectors of grassland that are free of invasive species and/or the density of invasive trees before control. Native species slowly replaced many exotic herbs that had appeared as pioneers, there was low recruitment of pine seedlings in spite of the quantity of seeds from trees that surrounded the clearings, and species richness and diversity were restored, including cover of the typical grasses in the controls. Recovery of grassland after felling was shown to be successful and does not seem to be seed limited if tree removal occurs early in the invasion process.