Growth and survival of hybrid dipterocarp seedlings in a tropical rain forest fragment in Singapore.

Background:Although natural hybridisation between dipterocarp trees is considered rare, putative dipterocarp hybrids (Shoreaspp.) are found in a forest fragment in Singapore. Understanding the performance of hybrids is critical to inform conservation efforts and has implications for the demographic and genetic viability of these small populations. Aims:First, is there a difference in the frequency of hybrids between the mature and seedling stages, and second, do parent and hybrid seedlings have different ecological traits? Methods:We analysed seedling survival and growth rates in relation to environmental variables forShorea curtisii, S. leprosulaand hybrids of the two species. We monitored the height and diameter of seedlings for 4 years, as well as light conditions and soil moisture. Results:The proportion of hybrids at the seedling stage was 41% forS. leprosulaand 17% forS. curtisii, respectively. Hybrids were more frequent at the seedling stage than at the mature stage. Hybrid individuals had growth and survival rates comparable to their parent species, with the exception of slower growth rates thanS. leprosula. Conclusions:Hybrid seedlings lacked obvious heterosis, and might therefore have similar fitness to that of parent species in the present forest environment. [ABSTRACT FROM PUBLISHER]