SECONDARY FOREST SUCCESSION IN ABANDONED AGRICULTURAL FIELDS: SITE AND LANDSCAPE SCALE INTEGRATED ANALYSIS IN THE UPPER PARANA ATLANTIC FOREST (MISIONES, ARGENTINA)

HOLZ, SILVIA CRISTINA; GUERRERO, VERÓNICA; PLACCI, GUILLERMO; QUINTANA, RUBEN DARIO

Campos do Jordao, Brasil

Conferencia; 2009 IALE Latin American Conference; 2009

International Association of Landscape Ecology

  Introduction: The natural forest regeneration process is influenced by multiple variables which interact in various time-space scales, and whose importance varies according to the intensity and duration of disturbances. This study proposed to respond to the following question: what is the relative contribution of different types of variables (historic, topo-edaphic, and landscape) in explaining floristic composition of Secondary forest?. Methods: The study was carried out in northern zone of the Misiones province, in three different landscapes (Eldorado, Andresito y San Antonio). Using satellite images, field survey and key informant interviews, we selected a set of sites with known historical use: type of agriculture and time since abandonment of agriculture use (chronosequenses). All sites belong to small and mid size producers that own the land since the agricultural activity was implemented and abandoned. The historical agricultural uses were: a) Ilex paraguariensis crops, b) Pinus sp. plantations, c) cattle pastures with cultivated grasses, and d) annual crops. We used transects to surveyed the vegetation and measured topo-edaphic variables (slope and rockiness) at each site. Through satellite images analysis we described the landscape patterns (forest surface, complexity of forest patches, average distance between forest patches, distance to largest patch, average size of forest patches). We explored the relation between the floristic composition and the topo-edaphic and landscape variables using multivariate techniques (principal components analysis, canonic correspondence analysis and correlation). Results: Despite current deforestation, the three landscapes maintain a large quantity of forest patches of various sizes, forming a relatively continuous network; average distance between patches showed very little correlation with forest cover and landscape heterogeneity. Floristic composition across sites can be mainly explained by the age of the forest and the historical use. All sites share many species, but showed differences in terms of their abundance and/or constancy. Differences related to historic use were clearly reflected in the analysis of forest structure, which considered basal area, density sizes categories, and coverage of understory herbaceous and shrub species; pastures with few years since abandonment showed high differences in all parameters considered, with lowest regeneration and highest grass coverage. Discusion: This study suggests that during the first two decades of succession, historic variables (forest age and historic use) most greatly influence floristic composition and forest structure. After this time other variables such as those related to landscape would be most important in determining forest characteristics. In the northern zone of Misiones, anthropogenic disturbances are relatively recent, and remnant forest patches are not found as isolated fragments, but rather maintain a certain level of connectivity, forming a mosaic of forests of distinct ages and states of conservation. Therefore, effects of current fragmentation could be buffered since this network of forests which functions as a source of propagules would contribute to a relatively rapid regeneration of secondary forests and to maintenance of species diversity on a landscape scale.