Calorific value of Prosopis africana and Balanites aegyptiaca wood: relationships with tree growth, wood density and rainfall gradients in the West African Sahel

Abstract

Prosopis africana and Balanites aegyptiaca are native tree species in the West African Sahel and provide wood for fuel, construction and other essential products. A provenance/progeny test of each species was established at one relatively dry site in Niger, and evaluated at 13 years. Gross calorific value of the wood was determined for a random sample of trees in each test: gross CV and CVm3 = gross calorific value in MJ kg-1 and MJ m-3, respectively. The major objectives were to determine if gross CV was positively correlated with wood density and tree growth, and if gross CV and/or CVm3 varied with rainfall gradients in the sample region. Provenances were grouped into a drier and more humid zone, and correlations were computed among all trees and separately in each zone. Results indicated that gross CV was not significantly correlated with density in either species. Gross CV was positively correlated with growth of pafricana (but not B. aegyptiaca) only in the drier zone. Gross CVm3 was positively correlated with growth of both species, and the correlations were stronger in the drier zone. Multiple regressions with provenance latitude, longitude and elevation indicated that provenance means for gross CV increased, in general, from the drier to the more humid zones. Regressions with gross CVm3 were not significant. Results are compared with earlier research reports from the provenance/progeny tests and with other tropical hardwood species; and practical implications are presented for tree improvement and conservation programs in the region