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Dalwallinu Acacia Symposium: 13–14 July 2001

Reproductive potential of Acacia species in the central wheatbelt: variation between years

Mangadas Lumban Gaol1,2 and J.E.D. Fox1

(1) Department of Environmental Biology, Curtin University of Technology, GPO Box U1987, Perth, Western Australia 6845; email: J.E.Fox@curtin.edu.au
(2) Department of Biology, Nusa Cendana University, Kampus baru, Penfui Kupang, West Timor, Indonesia; email: mangadas@hotmail.com

In a study at Sandford Rocks Nature Reserve aimed at discovering how rainfall variation between years affects reproductive potential in Acacia species, the effect of phyllode number and branch position in the crown and seed quality were investigated. High rainfall in 1999 allowed heavier fruiting. More inflorescences set pods and more pods were produced. In 2000, pod yields were reduced by drought. The extent of flowering depends on good winter rainfall and fruit production depends on moisture availability in spring. Although all species suffered from drought in 2000, there were differences in their degree of susceptibility: A. fauntleroyi, A. neurophylla, A. acuminata and A. steedmanii were the least affected whereas A. stereophylla failed to develop pods; A. hemiteles did not flower, and less than 1% of inflorescences developed a pod in both A. saligna and A. lasiocalyx.

Late spring frost in 1998 limited seed development. All species produced few seed; many pods were empty; many immature and infected seed were found; and there was poor germination. Of 13 species, only three had more than 40% germination. In six species there was no germination, while all others had less than 30% germination.

Plants bearing more phyllodes had more flowers and fruits, and fewer inflorescences dried off. Generally, branches in the upper part of the crown initiated more inflorescences. In some species there were more pods in central parts of the crown. The difference in the form or architecture of branches among species presumably affected resource partitioning and consequently reproductive potential.

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