Effects of liana load, tree diameter and distances between conspecifics on seed production in tropical timber trees

Seed production in tropical timber trees is limited by abiotic resources, pollination and pre-dispersal seed predation. Resource availability is influenced by the number of competing trees and by lianas that often reach high densities in disturbed parts of tropical forests. The distance between conspecific trees affects pollination efficiency and seed predation intensity, and may therefore indirectly affect the long-term sustainability of selective logging. Here we investigate how reproductive status and the number of seeds dispersed per tree are affected by liana load, distance to the nearest conspecifics, number of competing neighbours and tree diameter in the timber trees Cariniana ianeirensis and Terminalia oblonga. The study is based on a large-scale silvicultural experiment in lowland Bolivia. We found that the reproductive status of the two species was negatively correlated with liana cover and positively with tree diameter. In C. ianeirensis the most liana-infested trees dispersed fewer seeds. In T. oblonga the intensity of pre-dispersal seed predation decreased with distance to the nearest conspecifics. There was no evidence that seed viability or seed production decreased with distance to nearest conspecifics in either species as would be expected if isolation resulted in increased self-pollination. Our results indicate that reproduction can be severely reduced in timber trees if the largest, most healthy and least liana-covered trees are logged, but that liana cutting on the remaining seed trees can considerably improve seed production. In some species seed production may be further improved by ensuring that seed trees are located far apart.