Fuelwood uses and properties of nitrogen-fixing trees

Abstract

World deforestation and reforestation values are cited, and the increasing need for fuelwood tree plantings is noted. Tropical reforestation involves about 1 million hectares annually, of which less than 20% is believed to survive. Estimated tropical fuelwood needs alone, however, require 3 million hectares annually. Fuelwood remains the most cost-effective source of energy for rural poor, and charcoal demands are increasing worldwide. World deforestation is occurring primarily in the tropics (10-20 million ha/year), largely in relation to fuelwood demands (1,200 million m³/yr). The loss of newly planted forests to fire is stressed as a serious problem, notably for pine and eucalypt forests. It is suggested that over half the 650 known species of nitrogen-fixing trees (NFT) are suitable for fuelwood and charcoal, and many have wide present use. The fuelwood properties of 32 major NFT species are given, together with information on their uses and environmental constraints. Leucaena data are used to illustrate that tree age and density have little effect on calorific values, but have major influence on moisture content and specific gravity of the wood. It is stressed that calorific values should be quoted for the bone-dry wood, and then readjusted downward to reflect moisture in the wood as burned. The need is stressed for yield data from NFT biomass plantings at high densities, with appropriate controls of locally-important trees (including non-fixing trees, notably eucalyptus). Disadvantages are cited for monocultural plantings of single fuelwood species, and advantages suggested for mixed plantings of NFT species together with high-yielding trees that lack the ability to fix nitrogen.