High diversity mixed plantations of Eucalyptus and native trees: An interface between production and restoration for the tropics

Despite the high diversity of trees in the tropics, very few native species have been used in plantations. In a scenario of high international demand for nature conservation, ecological restoration and for the provision of forest products, mixed species forestry in the tropics emerges as a promising option. In this study, we examine three large experiments in the Atlantic Forest region of Brazil that combine early Eucalyptus wood production with a high diversity (23-30 species) of native tree species. We tested the following hypotheses: (1) Eucalyptus growth and survival is higher in mixed plantations than in monocultures, while that of native species is lower when intercropped with Eucalyptus; (2) The diameter of target native trees is influenced by the size and by the identity of neighboring trees; (3) The negative effect of competition from Eucalyptus on native species is directly related to their growth rate. We compared mixtures of Eucalyptus and a high diversity of native tree species with Eucalyptus monocultures and with plots containing only native species, replacing Eucalyptus by ten native species. To test our hypotheses, we examined inventory data considering the stand- and the tree-levels. We calculated survival rate, diameter and height growth and basal area of whole stands and groups of species. We also used a neighborhood index analysis to separate the effect of total competition (i.e. stand density) and the influence of groups of species (intra- and inter-specific competition). The Eucalyptus trees in high diversity mixtures grew larger and yielded nearly 75% of the basal area produced by Eucalyptus monocultures even though this genus accounted for only 50% of seedlings in the mixtures. In the mixtures, Eucalyptus negatively affected the growth of native species proportionate to the native species' growth rate. With some exceptions, the mixed plantations had no overall negative effect on tree survival or height growth. We conclude that mixtures of Eucalyptus and a high diversity of native tree species are feasible and represent a potential alternative for establishing multipurpose plantations, especially in the context of forest and landscape restoration.