Mating system parameters of Dryobalanops aromatica gaertn. f. (Dipterocarpaceae) in three different forest types and a seed orchard

Abstract

The mating system of Dryobalanops aromatica in three different forest types and a seed orchard was quantified by allozyme analysis of progeny arrays using a mixed-mating model. The primary forest (Bukit Sai) had the highest multilocus outcrossing rate (tm = 0.923 ± 0.035), followed by logged forest (Lesong; tm = 0.766 ± 0.056) and artificial forest (FRIM; tm = 0.661 ± 0.066) with seed orchard showing the lowest (Tampin; tm = 0.551 ± 0.095). Deviations from the mixed mating model were evident from differences in pollen and ovule allele frequencies, and heterogeneity of pollen pools in all three different forest types and the seed orchard. A high rate of outcrossing in primary forest (tm = 0.92) may indicate that the species is self-incompatible, but a lower value in the seed orchard (tm = 0.55) might suggest further that the self-incompatibility system is weak. The outcrossing rate was greater in the primary forest (tm = 0.92) than in logged forest (tm = 0.77). It is argued that this might be a consequence of the lower density of flowering trees and alteration of pollinator foraging behaviour in logged forest. Higher values of correlated mating (rp) and biparental mating (tm - ts) in primary forest (0.08 and 0.39, respectively) in comparison with logged forest (0.03 and 0.11, respectively) demonstrate that logging activities might reduce the seeds produced through consanguineous mating. Compared with primary forest, it is argued that lower rates of outcrossing in artificial forest (tm = 0.67) and seed orchard (tm = 0.55) might be attributed to lack of flowering synchrony and insufficient number of pollinators. The high level of correlated mating (rp = 0.43) and biparental mating (tm - ts = 0.12) in the seed orchard may further suggest that the seed orchard was established using related seed sources.