Résumé
The dry forests of New Caledonia are an excep- tional ecosystem because of
their numerous endemic botan- ical species and their highly diversified
fauna of insects, mollusks, reptiles and birds. Unfortunately, the area of
the dry forests has been significantly reduced, mainly by human
activities. Ecological, phenological and genetic analysis of Ixora
margaretae, a symbolic species of the sclerophyll forest, has revealed
contrasting traits among natural stands. The division of the natural range
and then the separation of forest islands has greatly reduced the existing
genetic vari- ability of this species. The genetic diversity is strongly
structured in genetic clusters which correspond well to spe- cific
ecotypes according to the environmental conditions and the forest types.
Furthermore, genetic analysis of the reproductive and non-reproductive
trees as well the half- sib families obtained by complete protection of
mother trees has revealed substantial genetic drift which has resulted in
increased loss of allelic variability. The total consumption of seeds by
mainly rats confirms the ob- served absence of natural regeneration. All
these results show that measures taken to protect the stands of dry
forests will not be enough to maintain sufficient genetic variability of
I. margaretae populations in the long term. Assisted regeneration with
control of the increase in var- iability will be necessary to maintain the
biodiversity of the species. The results obtained for I. margaretae must
be confirmed with other symbolic species in order to take the necessary
measures for the effective preservation of the dry forests in New
Caledonia.