Effects of Eucalyptus litter and roots on the establishment of native tree species in Eucalyptus plantations in South China

Transforming plantation monocultures into sustainable, mixed-species forests that contain native species is an important goal in South China. The establishment of native species in Eucalyptus plantations is generally considered difficult, however, because of the potential allelopathic effects of Eucalyptus. In this study, a field trial with completely randomized block was conducted to determine the degree to which Eucalyptus litter and Eucalyptus roots limit the establishment of native trees in Eucalyptus plantations. Growth of seedlings of four native tree species (Schima superba, Michelia macclurei, Cinnamomum burmannii, Cinnamomum camphora) that were tested was inhibited by Eucalyptus roots. Seedling emergence was less sensitive than subsequent seedling growth to inhibition by Eucalyptus roots. In contrast, litter enhanced the emergence and growth of seedlings of most of the tested species (Castanopsis chinensis, Elaeocarpus sylvestris, S. superba, Liquidambar formosana, C. burmannii, and C. camphora), suggesting that retaining litter on the forest floor may promote the establishment and growth of native tree species in Eucalyptus plantations. We propose the following strategies for establishing native tree species in Eucalyptus plantations: (1) direct sowing of the native tree species C. chinensis, Castanea henryi, Erythrophleum fordii, and C. camphora; (2) transplanting of E. sylvestris, S. superba, and Tsoongiodendron odorum, which had low germination rates but high seedling establishment rates; and (3) the exclusion of Eucalyptus roots via inter-row trenching to enhance the establishment of S. superba, L. formosana, C. burmannii, and C. camphora.