Invasion by Ligustrum lucidum (Oleaceae) in NW Argentina: early stage characteristics in different habitat types

Currently biological invasions are considered one of the world’s most serious conservation problems. Ligustrum lucidum is the most abundant exotic tree in secondary forest patches of montane forests of NW Argentina. We studied the determinants of success of the early stages of its life cycle in distinct habitat types, with the hope of identifying vulnerabilities that could be exploited to control the invasion. Seed arrival, germination, seedling recruitment and survival, and sapling growth were studied in edges, gaps and forest interior. Seed arrival was also assessed under perches and in open fields. Germination was studied in forest and grass-land patches. L. lucidum seedling survival and sapling growth were compared with the most abundant native species survival and growth. Seed arrival was strongly seasonal with a peak in mid-August. Seed rain did not differ significantly among habitat types, however there was a tendency for edges to receive more seeds when only dispersed seeds were considered. Perches strongly enhanced seed arrival; more than 40 times the number of seeds were dispersed beneath citrus plants (i.e. perches) than found in paired open areas. In the forest, seeds in gaps and edges had higher germination rates, but there was no difference in seedling survival. Fruits under closed canopy exhibited the lowest germination. Germination and survival were low in open areas. Neither seedling recruitment nor sapling growth differed between gaps and forest interior. L. lucidum saplings grew significantly more than saplings of the most common native species, and also showed higher seedling survival. L. lucidum is a prolific fruit producer, is capable of germinating and surviving in a broad range of forest environments, it is relatively shade tolerant and has higher survival and faster growth rate in comprison to the most common native species. All these characteristics highlight its potency as a successful invader, and point to few vulnerabilities that could be targets of control measures.Las invasiones biológicas son consideradas actualmente uno de los problemas de conservación más serios. Ligustrum lucidum es el árbol exótico mas abundante en los bosques secundarios del NO de Argentina. Estudiamos llegada de semillas, germinación, reclutamiento y crecimiento de renovales en claros, bordes e interior del bosque La llegada de semillas también se estudió bajo perchas y en sitios abiertos. La supervivencia y el crecimiento de renovales de L. lucidum fueron comparados con los de las especies nativas mas abundantes. El arribo de semillas fue estacional y los bordes mostraron una tendencia a recibir mas semillas dispersadas. La presencia de perchas aumentó la llegada de semillas. Dentro del bosque, las semillas germinaron mas en claros y bordes, pero no hubo diferencia en sobrevivencia. La germinación y la supervivencia fue baja en sitios abiertos. El reclutamiento y crecimiento de renovales no difirió entre claros e interior del bosque. Los renovales de L. lucidum crecieron mas que los renovales de las especies nativas mas comunes. L. lucidum se establece y sobrevive en un amplio rango de condiciones, es relativamente tolerante a la sombra y tiene una rápida tasa de crecimiento. Estas características indican su capacidad invasora, y señalan escasas vulnerabilidades que puedan ser usadas para su control.