Trenching Effects on Seedling Growth and Survival in Tropical Forests

To evaluate seedling responses to belowground competition with adult trees, we carried out three root-trenching experiments in the forest understory of the Barro Colorado Nature Monument (BCNM), using four tree species: Aspidosperma des?manthum, Tachigali versicolor, Gustavia superba, and Simarouba amara. Each experi?ment was crossed with a second treatment to increase the availability of light (treefall gap experiment), water (irrigation experiment), or nutrients (fertilization experiment). Trenching increased seedling growth in both the understory and gap treatments of the treefall gap experiment and in both the unirrigated and irrigated treatments of the irriga?tion experiment, but not in any treatment for the fertilization experiment. Trenching did not affect seedling survival in any of the experiments. A review of the effects of trenching on seedling growth and survival showed positive effects of trenching on growth in rain forests with a range of soil fertilities and on seedling growth and survival in the only experiment in a tropical dry forest.