DOES IRRIGATION AFFECT LEAF PHENOLOGY IN DECIDUOUS AND EVERGREEN TREES OF THE SAVANNAS OF NORTHERN AUSTRALIA

Soil moisture was augmented experimentally during two successive dry s easons and the intervening wet season in a humid tropical savanna in D anwin, northern Australia. Leaf phenology was monitored in four common tree species Terminalia ferdinandiana and Planchonia careya (both dec iduous species), and Eucalyptus miniata and Eucalyptus tetrodonta (bot h evergreen species). Irrigation produced consistently significant eff ects in only T. ferdinandiana. In this species leaf-flush was signific antly earlier, canopy decline and leaf-fall were significantly later a nd the attainment of full canopy was earlier in irrigated compared wit h non-irrigated trees. Litterfall, and the seasonal patterns of contra ction and expansion of stems (a measure of stem water status or storag e) were not significantly affected by irrigation in any species. Leaf longevity in the deciduous species was 6-8 months; some eucalypt leave s lived for approximately 1 year, but none lived longer than 18 months . Irrigation had relatively little effect on leaf longevity. While var iation in soil moisture is a potentially important cue to both leaf-fa ll and leaf-flush, stem water status and climatic factors such as vapo ur pressure deficit may also be important climatic cues to phenologica l behaviour.