Tree and grass rooting patterns in an African humid savanna

Spatial and temporal soil partitioning between roots of the two savanna plant components, i.e. trees and grasses, were investigated in a West African humid savanna. Vertical root phytomass distribution was described for grass roots, large (> 2 mm) and fine (< 2 mm) tree roots, in open sites and beneath tree canopies. These profiles were established monthly over one year of vegetation growth. Natural C-13 abundance measurement was used to determine the woody/herbaceous phytomass ratio in root samples. Tree and grass root distributions widely overlapped and both were mostly located in the top 20 cm of the soil. Grass root phytomass decreased with depth whereas woody root phytomass peaked at about 10 cm depth. No time partitioning was detected. These structural results do not support the hypothesis of soil resource partitioning between trees and grasses and are thus consistent with functional results previously reported.