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Assessing the potential of Araucaria angustifolia (Araucariaceae) as a nurse plant in highland grasslands of south Brazil

The expansion of forests over natural grasslands is observed in many parts of the world. This study aimed to contribute to the investigation into the nursing effects promoted by Araucaria angustifolia during the process of forest expansion over grasslands in southern Brazil. Air temperature and humidity, and soil chemistry were evaluated beneath the canopy of isolated trees of A. angustifolia, and compared with values in adjacent grassland areas and under the canopy of the shrub Baccharis uncinella. Milder summer temperatures and vapour pressure deficits were measured under Araucaria and Baccharis compared with open grassland. There were also ameliorating effects on soil chemistry under individuals of these two species, but these were more pronounced for Araucaria than for Baccharis. The results suggest that the large number of seedlings commonly found beneath the canopy of Araucaria is due not only to perching, but also to nursing, through the amelioration of environmental conditions.