Influence of trees on above‐ground production dynamics of grasses in a humid savanna

Abstract. Above‐ground grass biomass, necromass and tree litter were measured monthly over a vegetation cycle under tree clumps and in the open, in a humid savanna in Côte d'Ivoire. Grass production was calculated using several methods to better discriminate the contribution of the different grass compartments. Above‐ground grass biomass is higher in the open than under canopies during the second part of the growing season, but there is no difference in grass necromass dynamics. Physical protection of grass necromass by tree litter against decaying under tree canopies was assumed to explain this discrepancy. Grass production, calculated as the sum of positive increments of biomass and necromass, equals 1073 g m ‐2 yr ‐1 in the open, against 74 % underneath trees. However, basal ground cover is only 50 % of that in the open. Comparison with other savanna studies as a whole does not show any significant effect of rainfall on the relationship between under‐canopy and outside‐canopy grass production. However, in arid conditions, grass production tends to increase under light‐canopied trees (mostly Acacia legumes) which hardly affect grass photosynthesis, but add high quality litter to the soil surface.