Allelopathic effects of eucalyptus and the establishment of mixed stands of eucalyptus and native species

Allelopathic effects of eucalyptus are widely reported and are considered the major factor limiting the establishment of native species in eucalyptus forests. However, reports of the allelopathic effects of eucalyptus are mostly based on laboratory bioassay, not on field trials. In the present study, we conducted field trials to determine the allelopathic effects of eucalyptus and to develop strategies for establishment of mixed stands of native species and eucalyptus. In the field, seed germination and seedling survivorship of native species were determined in the presence and absence of eucalyptus leaf litter or living roots. In the seed germination experiment, seed germination rate of Delonix regia was higher than for Elaeocarpus sylvestris and Tsoongiodendronodorum. Seed germination rates of E. sylvestris and T.odorum were low in both the presence and absence of eucalyptus treatments. The germination rate of D. regia was significantly inhibited by all eucalyptus treatments, but only during the early period. In the seedling establishment experiment, seedling survivorship of E. sylvestris and Michelia macclurel was not inhibited by any treatments, but the seedling survivorship of Schima superba was significantly inhibited by eucalyptus litter addition alone. Seedling height of S. superba and M. macclurel was significantly suppressed when eucalyptus roots were present in treatments, but the seedling height of E. sylvestris was only significantly suppressed by the treatment of roots alone. We propose two strategies for establishment of mixed stands of native species and eucalyptus: (1) direct seed-sowing is effective only for those species (e.g. D. regia) with high germination rates in natural conditions; (2) seedling transplants are more efficient approach for establishing species (e.g. E. sylvestris) with low germination rates. We suggest that mixed plantations of eucalyptus and E. sylvestris can be established by transplanting seedlings of E. sylvestris into eucalyptus plantations.