Environmental constraints to native woody species recruitment in invaded mountain woodlands of central Argentina

Abstract

Nowadays forests, which were formerly considered resistant to invasion due to its shady understories, are been transformed to invaded landscapes. Thus, the aim of this study was to evaluate the regeneration of native woody species in Ligustrum lucidum invaded woodlands. In addition, we aim to identify the main environmental differences between the native and invaded woodlands and evaluate the effect of those conditions in the regeneration phase of dominant native woody species. Finally, we analyze how is the emergence and survival of the exotic species in relation to that exhibited by native species in both environmental situations. For this, we performed a seed addition experiment placing three native woody species (Celtis ehrenbergiana, Lithraea molleoides, Vachellia caven) and the dominant exotic (L. lucidum) in native and invaded woodlands of the Chaco mountains, central Argentina. Also, we performed a laboratory experiment simulating the differences in light recorded at the field (main abiotic difference between both woodland types). Our field experiment indicated that, if seeds are actively added, the percentage of seedlings emergence of native species could be similar in invaded and native woodlands. However, we observed a trend of lower seedling survival after winter within the exotic monospecific stands, which was significant only for the native species C. ehrenbergiana. We suggest that this constraint could be partly related to the shadier conditions imposed by L. lucidum, since this is the major environmental change within the invaded woodlands in comparison with native ones. Consistently, the experimental simulation showed that the increased in shade reduced the overall growth of seedlings. As was mostly observed in temperate biome, our study in a subtropical seasonally dry region indicates that invaded areas may not affect the emergence stage but limit the survival of seedlings. Among the native species, C. ehrenbergiana seems to be the most suitable species to start restoration, showing the highest performance throughout the year. Combined actions of seed addition and canopy opening might counteract the abiotic constraint and contribute to restoration success of this invaded landscape.