Forest Structure and Functioning in the Semideciduous Atlantic Forest of Northen Argentina: Effects of native invasive bamboos and lianas on the tree regeneration and diversity.

PAULA I. CAMPANELLO; LÍA MONTTI; M GENOVEVA GATTI; SUSANA BRAVO; GUILLERMO GOLDSTEIN

San Carlos de Bariloche- Argentina

Workshop; Understanding biodiversity loss: A Workshop on forest fragmentation in South America.; 2006

The Semideciduous Atlantic Forest in Misiones province constitutes the most diverse and complex ecosystem of Argentina. This type of forest, although highly fragmented, occurs also in southern Brazil and southeastern Paraguay. Argentina has the largest continuous remnant of this region (10.000 km2). However, most of the forests in Misiones province have been subjected to selective logging. This kind of management alters gap size and dynamics, creating environmental conditions that favor the growth of native invasive plants such as lianas and bamboos. In Misiones, most forests are invaded by the monocarpic bamboo species Chusquea ramosissima, and Merostachys clausenii, while lianas of the genus Arrabidaea, Adenocalymna and Acacia are very abundant. We have studied the effects that bamboos and lianas have on forest structure, dynamics and environmental conditions, and how these changes affect tree diversity (i.e. seed dispersal, tree seedling mortality and acclimation ability to environmental changes, and tree growth). We found that bamboos intercept radiation reducing light availability to other plants, affecting tree sapling growth and mortality. Although the abscence of these plants, either by cutting or after a massive flowering event, increase light penetration, it does not change pioneer tree species recruitment in gaps. This is probably due to the accumulation of bamboo biomass with low decomposition rates and/or the establishment of other understory species (i.e., ferns and other herbaceous plants). Besides, bamboo invasion alters seed dispersal processes. Its presence deterrents the use of sites by big mammals, seed dispersers and seedling predators, and also increases seed predation by rodents. Lianas, on the other hand, have a detrimental effect on some canopy tree species growth, and thus forest colonization by lianas can alter tree species composition in the long term. Liana invasion has also ecosystem level consequences, particularly on nutrient and water cycling. When lianas are removed by cutting, soil nutrient content and water availability largely increase. Light levels reaching the understory also increase after liana removal which enhances canopy trees seedlings growth rate. Our results suggest that forest management in Misiones changed forest structure and functioning by favoring growth of native invasive species that arrest succession in gaps. At present, some of our research activities are oriented to elucidate if forest degradation and fragmentation affected gene flow and genetic diversity of tree species. At the same time, we are using restoration techniques which are needed in many cases to recover a multi-stature and diverse forest in Misiones Province.