Competitive Effects of Three Tropical Tree Species on Two Species of Piper

Abstract

Owing to differences in morphology and growth rates among tree species, monospecific tree stands may differ in their ability to suppress the growth of understory plants through shading and root competition. I assessed relative understory suppression and intensity of root competition in year-old stands of Cordia alliodora, Hyeronima alchorneoides, and Cedrela odorata by measuring the growth of seedlings of the pioneer tree Piper auritum and cuttings of the shadetolerant shrub P. phytolaccaefolium that were planted into trenched and untrenched sites under the trees. After 5 mo, growth of P. auritum was significantly less under Cordia and Hyeronima than under Cedrela or in the open. The most severe growth reductions occurred under Hyeronima, the species with the highest leaf area index (LAI). Lack of a significant trenching response under Hyeronima suggests the competitive effects of this species were largely the result of shading. In contrast, the competitive effects of Cordia, a species with relatively high fine root density and open canopy, were almost entirely below ground. Nonetheless, the effects of Cordia and Hyeronima on the growth of P. auritum seedlings were equivalent when compared on a per-unit of tree canopy LAI basis. Lack of P. auritum growth suppression under Cedrela is likely the result of the open canopies and relatively low fine root densities of the Cedrela stands. In contrast to the growth of P. auritum, P. phytolaccaefolium growth did not differ among tree overstories. These results suggest that, among tree species, differences in morphology can lead to differences in understory suppression, but these differences depend upon the understory species.