The effect of tree spacing on the production of flowers in Eucalyptus nitens

The effect of spacing on the production of flowers and capsules in Eucalyptus nitens was studied in two spacing trials located in northern Tasmania. Tree density in these trials ranged from 468 to 4216 stems ha -1. Reproductive structures were collected in litter traps and these data were used to calculate reproductive output on a per tree and per hectare basis. Between 8735 (5-y-old site, 1333 stems ha-1) to 234098 (13-y-old site, 1082 stems ha-1) flowers were produced per hectare over a single flowering season at these two study sites at the planting densities expected of a pulpwood plantation. This represented 8 and 211 flowers per tree respectively. As tree density decreased, the production of flowers and capsules increased on both a per-tree and per-hectare basis. It is estimated that the number of flowers per hectare is likely to be anywhere between between 1.4 and 10-fold greater under the spacing expected in sawlog regimes (250 trees ha-1). This difference in reproductive output between plantations of E. nitens that use different spacing regimes is one of the many factors that need to be considered in assessing the risk of wilding establishment or hybridisation with adjacent native eucalypts.