Structure related to the age of Gleditsia triacanthos forests in LaSala Valley (Tucuman, Argentina).
Gleditsia triacanthos is an exotic invasive species in Argentina, widely distributed in several ecoregions. This species forms monospecific forests whose structure and dynamics remain poorly understood. These aspects are key to assess the behavior of the invader and the capacity of native species to colonize invaded forests. In this study we describe the structure and composition, and infer the temporal dynamics of G. triacanthos forests in La Sala Valley, an area highly invaded by this species in the province of Tucuman. In 2019, in four forest patches of 9, 18, 25-29 and 36-37 years old dominated by G. triacanthos, we established experimental plots and registered density, species richness and height of trees ≥5 cm in diameter, recruits, and other characteristics such as tree health and presence of cattle, gaps or open spaces. The 9-year-old forest had low height, low density and open spaces not yet colonized by G. triacanthos. The 18-year-old forest had higher density than the rest. In older forests (25-29 and 36-37-years-old patches), we detected an increase in the height and diameter of trees, and in the number of fallen and leaning trees. We suppose that Vachellia aroma, a native tree species that colonize early stages of invaded forests, was rapidly outcompeted by G. triacanthos. Lately, other native species colonized forests, but at low densities. G. triacanthos forests were almost monospecific because of its high density and the facilitation effect of the cattle in the valley, which consume and disperse the seeds.