Responses to Defoliation of Voacanga africana Are Dependent on Light Availability

Understorey plants are often subjected to damage by branches falling from forest canopies. Voacanga africana is an understorey tree that is native to tropical Africa. To investigate the combined effects of light availability and defoliation on growth of the species, seedlings were subjected to three defoliation levels (0 %, 25 %, 50 %) and two light regimes (50 % sunlight, full sunlight) in a greenhouse. The experiment followed a split-plot design with light availability as the whole plot and defoliation level as the sub-plot. Morphology, biomass, and leaf chlorophyll content were measured three months after the initiation of treatments. The lower light regime increased height while it decreased root mass and leaf chlorophyll content. No significant main effect of defoliation was detected for any parameter. There were, however, significant light × defoliation interactions for height, root-collar diameter, leaf mass, stem mass, and total mass. While the effect of the lower light regime on height was limited to the 25 % defoliation level, the treatment resulted in a decline of root-collar diameter and leaf mass only at 0 % defoliation. The 25 % defoliation level increased stem mass and total mass under the 50 % sunlight but not full sunlight treatment where differences between defoliation levels were not statistically significant. The mass ratios of leaf, stem, root, and leaf area ratio were unresponsive to light availability and defoliation either individually or in combination. The findings indicate that growth compensatory responses of Voacanga africana to defoliation are controlled by light availability.