AOBPreview originally published online on October 2, 2002
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Annals of Botany 90: 599-605, 2002
© 2002 Annals of Botany Company
Size Distribution, Growth and Inter-year Variation in Sex Expression of Bischofia javanica, an Invasive Tree
1 Hokkaido Research Centre, Forestry and Forest Products Research Institute (FFPRI), Hitsujigaoka 7, Toyohira, Sapporo 062-8516, Japan and 2 Forestry and Forest Products Research Institute (FFPRI), PO Box 16, Tsukuba Norin Danchi, Ibaraki 305-8687, Japan
* For correspondence. Fax +81 11 851 4167, e-mail naokoy{at}ffpri.affrc.go.jp
Received: 14 March 2002; Returned for revision: 3 July 2002; Accepted: 24 July 2002 Published electronically: 2 October 2002
Flowering activity and sex expression of Bischofia javanica Blume were investigated for 3 years. B. javanica is an invasive dioecious tree of subtropical forests on the Bonin Islands in the western Pacific of Japan. The sex ratio showed a significant male bias (1·25–2·33). Smaller trees were significantly male biased, whereas larger trees showed no significant difference in sex expression, suggesting that males tend to be more precocious in sexual reproduction. We found evidence for sex changes in B. javanica; these have not been reported previously. Most of the 1653 census trees remained non-flowering (58·1 %); 3·7 % of them showed sex changes, and the percentage of trees repeatedly flowering as males and females was 10·5 and 3·4 %, respectively. Sex changes were observed in both directions but a larger percentage of male trees became female. Flowering frequency and sex expression were significantly related to tree size (i.e. diameter at breast height). Over the 3 years, trees that were consistent females were the largest; inconsistent trees (switching sex between years) were intermediate in size, whereas consistent males were the smallest. There were no significant differences in relative growth rate (RGR) among trees of different sex or flowering frequencies. These results suggest that the maintenance of female reproduction is not related to changes in RGR of diameter but to flowering frequency or the reversal to the male form, dependent upon the internal resource status of individual trees.
Key words: Bischofia javanica (Blume), sex ratio, dioecy, sex change, invasive tree, size distribution, growth rate, subtropical oceanic island.
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