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An experimental study was undertaken on a complex ecological system in the semi-arid Sahelian region of Senegal. The effects of tree cover on the above- and below-ground phytomass of the herbaceous layer were studied. The results show that: (1) herbaceous above-ground production was 1.5 to 4 times greater under the canopy than in the open sun light; (2) understory root phytomass was about two-fold greater than the root phytomass of the open grassland; and (3) the root/shoot ratio was 2.5 higher: in the open than in the shade. Increased herbaceous layer productivity was interpreted as a result of better climatic conditions and greater soil fertility within the canopy zones.

By promoting the development of herbaceous vegetation, trees increase the long-term production potential of the zone and, in. consequence, improve conditions for livestock husbandry. (C) 1997 Academic Press Limited.