THE ECOPHYSIOLOGY OF ALLOSYNCARPIA-TERNATA (MYRTACEAE) IN NORTHERN AUSTRALIA - TREE PHYSIOGNOMY, LEAF CHARACTERISTICS AND ASSIMILATION AT CONTRASTING SITES

Allosyncarpia ternata S.T.Blake, a large, evergreen tree endemic to th e northern part of the Northern Territory, Australia, dominates the ca nopy in a wide variety of habitats, including monsoon rainforest on ra vine floors, open forest and woodland on cliffs, screes and sandsheets , and open woodland on ridges and hilltops. This study examines tree p hysiognomy, leaf characteristics and leaf assimilation rates of A. ter nata growing at sites with strongly contrasting micro-climates near Ba roalba Springs, Kakadu National Park. By comparison with trees growing on the ravine floor, cliff and hilltop trees are generally shorter, t hey branch lower, are more frequently multi stemmed and have higher ra tios of canopy width to height, while their leaves are generally small er and thicker and contain less chlorophyll a and chlorophyll b per un it dry weight. They have lower mean specific leaf areas and higher mea n stomatal densities. Assimilation measurements on leaves at a cliff s ite showed significantly higher rates of light-saturated assimilation during the morning than in the afternoon. On the ravine floor, by cont rast, assimilation responses to changes in light flux density did not vary significantly through the day. Leaves of trees growing on the rav ine floor had lower values oi light-saturated assimilation and light c ompensation point, and higher values of apparent quantum yield than cl iffside leaves.