Talares from northeastern Buenos Aires in the presence of Ligustrum lucidum W. T. (Aiton): Changes in forest structure and dynamics

The presence of new tree species in forest ecosystems promotes changes in stand dynamics that are reflected by forest structure. These processes are particularly relevant in native forests conservation. Tala (Celtis ehrenbergiana var. ehrenbergiana) and coronillo (Scutia buxifolia) forests are considered among the main forest communities of Buenos Aires province, in Argentina, and are included in several protected areas. In the El Destino Reserve, a very well conserved native forest is currently in the presence of Ligustrum lucidum, which has demonstrated a high invasive potential in other forest of Argentina and the world. The aim of this work was to characterize present structure of these stands and to infer changes in the dynamics promoted by the presence of L. lucidum. We found that these talares are currently dominated by L. lucidum in tree density (93%) and basal area (80%), and that native forest structure has departed from the characteristic values. Around 80% of native trees are dead, widely surpassing the 20% reported natural mortality, and dead tree density is positively associated with L. lucidum density. The exotic species initially established in a non-selective and spatially random pattern and reached current canopy dominance by rapidly exceeding native species total height. Present conditions were reached approximately in 20-25 years, which indicate a high rate of structural change. These results demonstrate these talares have profoundly changed and, considering the degree of modifcation, could be treated as new ecological systems, either novel or hybrid ecosystems. Whichever the approach, the control of L. lucidum and the active restoration of the native component, as well as the eradication of the exotic species in areas where establishment is still recent, are all of high priority in order to ensure the long-term conservation of these forests.