Assessing the role of light availability in the regeneration of Araucaria angustifolia (Araucariaceae)

The role of Brazilian pine (Araucaria angustifolia) in the process of forest succession is a topic of increasing controversy. While some authors consider the species to be pioneer, others consider it to be a climax species in relict temperate forests. We designed a field experiment to assess the role of light availability on the regeneration of A. angustifolia. The following three forests, with contrasting patterns of the species regeneration, were selected at a National Forest in southern Brazil: a Pinus plantation, an Araucaria plantation and a native araucarian forest. We analysed the population structure of Brazilian pine, the vegetation architecture, the light regime experienced by seedlings and the height growth of seedlings and sprouts. Brazilian pine colonisation and regeneration were observed in the Pinus and Araucaria plantations, respectively. No seedlings were found in the native forest. The greatest foliage area index and canopy cover were found in the native forest and the smallest in the Pinus plantation. In spite of the architectural differences, the native forest and the Araucaria plantation had similar light conditions and they both had lower levels of irradiances than the Pinus plantation. Seedlings and sprouts of Brazilian pine were found to occupy spots in the Araucaria plantation with canopy cover greater than the average forest conditions. Considering the similarity of understorey light conditions between the Araucaria plantation and the native forest (where no regeneration was taking place), we concluded that light availability was not limiting the regeneration of the species. Tolerance to shading and other aspects of the species indicate that Brazilian pine is not strictly heliophyllous and pioneer and is able to be established in the forest understorey.