Primary productivity determinants of different land uses in humid subtropical ecosystems: from native forests to tree plantations

Abstract

Land-use changes in forest ecosystems may alter the amount of carbon sequestration. The main objective of this study was to characterize the impact of different land-use practices on structure and functioning of humid subtropical forests that are under severe threat. We emphasize the characterization of canopy photosynthetic activity, assessed by the Enhanced Vegetation Index (EVI), the Leaf Area Index (LAI) and the fraction of Absorbed Photosynthetically Active Radiation (fPAR), using a combination of ground base measurements and remote sensing data on native well-preserved forests, impacted forests by selective logging and pine plantations in NE Argentina. Even though selective timber extraction resulted in a substantial decrease in stand’s tree density, EVI values were as high as those from preserved forests. In these forests, an increase in the understory cover appears to compensate the response of stand’s EVI to timber extraction. Removal of canopy trees enhances incoming solar radiation, allowing active growth of understory vegetation. The pine plantations exhibited the lowest values of LAI, fPAR and EVI. However, when EVI was normalized by LAI, the pine plantations exhibited the highest EVI/LAI values. Our results suggest that after 15 years of forest recovery from selective timber extraction, photosynthetic capacity was similar to that of preserved forests. Increases in the understory cover may compensate the potential decrease in the canopy photosynthetic activity. Pine plantations resulted in substantially lower productivity as depicted by lower EVI and LAI but exhibited higher growth efficiency than native forests.