Plant Biomass, Nutrient Concentration and Nutrient Storage in a Tropical Dry Forest in the South–west of Madagascar

Plant biomass, mineral composition and the amounts of nutrients in the different fractions of the vegetation were determined for a dense dry deciduous forest growing on light red sands in south-western Madagascar. Complete harvesting and soil coring were used to determine the above- and below-ground biomass respectively. The above-ground biomass, weighing 118 t ha−1 (dry matter), was mostly (96%) made up of phanerophytes (woody trees and shrubs >25 cm tall). Dead material (litter and dead wood on the soil surface) represented 13.8 t ha−1. These results fit well into the range of values reported for other tropical ecosystems. The below-ground biomass was 17.8 t ha−1 giving a root/shoot ratio of 0.15. Rooting is superficial. The nutrient concentration in this dry forest on light reddish-brown sands is, as in other dry forests, considerably higher than that usually found for humid forests. Calcium is the most abundant element. The plant biomass Ca/K ratio is much higher than that of humid tropical forests. In spite of its high originality, this Madagascan dry forest has the same behaviour as other dry forests of the world.