“Daba” Forestry: How hoe farming enhances tree establishment and growth in a West African savanna

Abstract

Trees and grasses compete for space and resources in savanna landscapes resulting in a mix of both life forms. In mesic savannas, it is well-established that key disturbance regimes restrict tree cover and favor grasses. Demographic bottle-neck models indicate that tree early-life stages are the critical moments for determining the ratio of trees to grasses savanna landscapes. As such, researchers increasingly focus on the transitions from seedling to sapling to mature tree. Research shows, for example, that juvenile trees are often caught in a firetrap and prevented from maturing, while tree seedlings are outcompeted for resources by dense grasses. This study examined the establishment, growth, and survival rates of trees at different life stages on plots subjected to five different grass removal treatments (grazing, clipping, herbicide, fire, and hoeing) on experimental plots in mesic savannas. Our main objective was to determine whether grass competition significantly slowed tree growth and establishment rates. Secondarily, we wanted to determine which treatment(s) increased tree seedling establishment and juvenile tree growth the most. To compare how treatments affected tree growth, we conducted annual grass treatments over a 3-5 year period for three study sites. Data were analyzed using statistical analysis of variance with treatment type as a fixed factor. We found that grass competition limited both tree establishment and growth rates and that this varied by study site, but hoe farming resulted in the highest overall growth rates. Hoe treatments also resulted in the lowest death rates of juvenile trees and the highest seedling establishment.