Effects of logging rotation in a lowland dipterocarp forest on mating system and gene flow in Shorea parvifolia

Selective logging is one of several silvicultural practices used in sustainable forest management in the lowland dipterocarp forest in Indonesia. Selecting only trees with diameters >50 cm for logging can reduce the density of reproductive trees, thereby affecting pollen dispersal and influencing the mating system among remaining trees. We evaluated the effect of logging rotations on the mating system, gene flow and genetic diversity in populations of Shorea parvifolia in primary forest, and in first and second rotation forest. Our results revealed that multiple (or at least two) selective logging events with a 30-year logging rotation had a significant impact on the genetic diversity of pollen clouds. However, the average pollen dispersal distance did not differ significantly among the multiple selective logging rotations. The multiple rotations reduced the outcrossing rate and the number effective of pollen donors in the logged forest. Moreover, the number of pollen donors in a plot was affected by the basal area of reproductive trees present. These results suggest that reducing the number of reproductive trees by logging with multiple rotations might increase the bi-parental inbreeding rate due to the reduction in density of reproductive trees in a selectively logged forest. We conclude that multiple rotations with a 30-year cycle of selective logging as currently practiced would reduce the density of reproductive trees, and would not be sustainable in terms of maintaining genetic diversity in tropical forests of Southeast Asia.