Distinct tree regeneration patterns in Araucaria forest and old monoculture tree plantations

Abstract

Throughout the world, plantations of tree species (native and exotic) for production purposes make up an important part of tree cover, often at the expense of natural forests. Monocultures of exotic and native species generally show a very distinct vegetation physiognomy when compared to natural forests. In the case of abandoned plantations, existing tree regeneration may provide a high potential for restoration of these areas. In this study, we evaluated composition and structure of the adult (upper layer) and regenerative (lower layer) tree component of natural Araucaria forest and of monoculture plantations of Araucaria angustifolia (Bertol.) Kuntze and Pinus sp., and their relationship with edaphic variables and sunshade discontinuity. We aimed to answer the following questions: To which extent do regeneration patterns of native species in the plantations resemble those in natural forests? Does natural regeneration provide a potential for transformation of plantations into natural forests? Does the exotic species regenerate in high abundances, and do other exotic/invasive species establish? Which environmental factors influence regeneration of native species? We expected to find differences in the species composition of the planted areas in relation to the native forest, and more pronounced in the regenerative component. Therefore, the soil parameters and the canopy discontinuity should also be distinct in the distinct vegetation formations. Density of species and tree individuals of the regenerative layer was significantly lower in the plantations, especially in the pine plantation, at the plot level. However, overall species richness was quite similar between vegetation types, with a total of 98 species distributed into 38 families. While light availability did not differ significantly, the soil parameters organic matter, pH, phosphorus and potassium showed significant differences among the vegetation types (in general, lower fertility in plantations). These variables were related to the specific composition of areas, indicating influence of the vegetation on soil conditions and regeneration patterns. Overall, we conclude that restoration of plantations into natural forest based on the existing forest regeneration seems possible, but should be done with caution and under monitoring.