Understory plant interactions along a successional gradient in Central Amazon

Abstract

Plant-plant interactions, other than competition for light, may be responsible for arrested succession in secondary forests dominated by species of the genus Vismia. We aimed to investigate seedlings’ responses to the cumulative effect of root competition and the presence of understory vegetation in Vismia stands. We conducted a trenching and understory vegetation removal experiment in Vismia-dominated secondary forests of different ages. We planted three species with contrasting functional traits. For each seedling, we measured biotic damage, functional traits, and final mass. In each experimental block, we measured canopy openness, vegetation cover, and clay content of the soil. The effect of root and understory competition was not related to secondary forest age. However, the net effect had a quadratic relationship with site suitability for all species. Specifically, facilitation occurred only at low levels of suitability, when biotic damage was intense; competition, however, was stronger at intermediate levels of suitability. The net effect of plant-plant interactions in Vismia-dominated forests depends on the site suitability for each species. We conclude that seedlings are negatively affected mainly by other types of plant-plant interactions, but facilitation can occur when biotic damage is high.