Subantarctic Forest Dynamic (Santa Cruz, Argentina) and its Importance for Paleoecological Reconstruction

SOTTILE, G.; MANCINI, M. V.

Boulder, Colorado.

Workshop; AIMES Young Scientist´s Network “Cultural Uses and Impacts of Landscape Fire: Past, Present and Future”.; 2008

Universidad de Cornell, Department of Earth and Atmospheric Sciences

  The study objective is to study the relationship between the forest vertical structure and topography with the understory composition. This information will be usefull to reconstruct the past vegetation dynamic related with fire trough the charcoal particles and the pollen records from a peat bog sequence. We surveyed 6 sites of Nothofagus pumilio and Nothofagus antarctica forests in the Glaciares National Park, Santa Cruz Province, Argentina.   Tree DBH average allow as to divide all sites in three similar aged structure forests (P< 0.001one- way ANOVA). The old non disturbed forest (Glacial Perito Moreno and Ñire forest); the  young forests, with high homogeneous young tree density patches (Chorrillo del Salto and Camino mte de Loros) and the bimodal aged forests, with patches of old, tall trees that have survived to the wildfires, and high young tree density patches (Monte de los loros and laguna Toro). Tree density average of Glaciar Perito Moreno, Chorrillo del Salto and Monte de los loros differ significantly from the rest of the sites and between them (P< 0.001one- way ANOVA). There is a significantly negative correlation between DBH and Tree Density (Spearman coefficient= -0.735, p<0.001). Most Nothofagus trees, like N. pumilio and N. antarctica are shade- intolerant species, so they sprout or germinate vigorously after disturbance creating canopy gaps. When the competition for light turns high, only the individuals which may reach the upper levels of the canopy will be able to survive. Similar vegetation communities are grouped by altitude, the  slope exposure (Canyon) and Gap stands. The oldest forest understory composition with non fire evidence are grouped together at the same group (red circle), the understory from Laguna Torre is grouped alone (blue circle) and this may be related to the absolute lack of a tree canopy, due to all the Nothofagus antarctica individuals are growing like shrubs. So the abundance of light reaching to the ground floor, may allow shade intolerant herbs and shrubs species to grow there. The pattern between the rest of the sites it is not clear. The preliminary comparison of the peat bog records suggest that the charcoal peak period (1807-1688) is followed by a small decrease of Nothofagus pollen percentage which increase rapidly to 1866. Otherwise Poaceae pollen suffers a continuous decrease after the charcoal peak period. There is also an increase of shrub and herbs richness.