TROPICAL TREE STAND STRUCTURES ON A SEASONALLY FLOODED ELEVATION GRADIENT IN NORTHERN AUSTRALIA

The variation in the stem size-class distributions of five dominant tr opical tree species was studied in a grid established on a 7 m elevati on gradient in a monsoon forest adjacent to a treeless floodplain on t he north coast of the Northern Territory. Acacia auriculiformis was wi despread over the gradient. The size-class distribution of sterns was irregular and poorly related to elevation. These patterns are consiste nt with this species' ability to colonise rainforest gaps. Nauclea ori entalis had the narrowest range on the elevation gradient and was also spatially restricted to a corner of the grid. It is unknown why the s ize-class distribution of this species was biased toward larger stems, with few stems < 2 cm dbh. The size-class distribution of Lophostemon lactifluus was irregular and thought to reflect phasic regeneration e vents; stems greater than or equal to 31 cm dbh were restricted to the 3-6 m elevation classes. Syzygium nervosum appears to continuously re generate as evidenced by the reverse-F-shaped size class distributions . A cohort of sterns < 10 cm dbh may reflect recent zip-slope expansio n into forest dominated by A. auriculiformis and L. lactifluus. Melale uca cajuputi appears to periodically regenerate, and a cohort of stems < 31 cm dbh may have colonised the adjoining treeless floodplain. The re is some evidence that M. cajuputi is excluded from sites dominated by S. nervosum and N. orientalis. The effect of a single fire on the s ize-class distributions of the five species was minor, affecting a sma ll proportion of the smaller stems.