For many decades, and even centuries in certain localities, the forests over vast areas of the earth have slowly degenerated under the joint impact of fuelwood and forage gatherers and of slash and burn (swidden) agriculture. Recently, this degeneration has gathered speed, primarily because of increases in population, but aided by war, civil unrest, the ebb and flow of refugees and the increasing price of kerosene. Now the provision of firewood and forage - upon which 1.5 thousand million people depend - presents problems comparable to those of providing food in many of the countries in the subtropical zone. The outcome in many areas has been disastrous. Forests have retreated before the onslaught of man and animals and erosion has become increasingly severe. Without sufficient fuelwood, animal dung is being burnt as fuel, with a consequent loss of fertilizer and a dramatic fall in agricultural yields.
NAS (1980) estimates that there are 0.6 billion hectares of arid and semi-arid woodlands in the world receiving less than 500 mm of annual precipitation and additional areas of seasonally-dry tropical regions which experience six or more completely rainless months. It is within the developing countries of this region, inhabited by some 450 million ‘dry-zone’ dwellers that the fuelwood scarcity is most acute. Deforestation of ecosystems often leads to desertification, a phenomenon which is increasing rapidly. Vigorous and urgent action is needed to protect, conserve and efficiently utilize existing natural resources in these areas, and to accelerate tree planting programmes.
The problems of deforestation in arid and semi-arid zones have been recognised by the FAO Panel of Experts on Forest Gene Resources who recommended early action to explore, collect, evaluate, conserve and utilize the genetic resources of arboreal species for fuel, food, fodder, soil stabilization, shade, shelter and farm forestry (FAO 1974b, 1977). The panel also drew up a short-list of priority species falling into these categories (see Appendix 1). On the basis of the recommendations made by the Panel and with financial assistance from the International Board for Plant Genetic Resources (IBPGR), FAO's Forestry Department initiated in 1979 a project to conserve and better utilize genetic resources of arboreal species for the improvement of rural living, in which the emphasis was laid on fuelwood species (FAO 1980). The main aims of the FAO/IBPGR Fuelwood Project, of which this handbook is a part, are to act as a catalyst for remedying the acute lack of genetic information on arid and semi-arid zone species, and to aid countries in the practical application of any results which may become available in its course (Palmberg 1981).
Acacias are prominent in discussions and species lists of potential fuelwood species, as they embody many desired attributes (FAO 1977; Burley 1980; NAS 1980; Moss and Morgan 1981). In very general terms, and depending on the species under consideration, acacias are robust, wide-ranging plants frequently adapted to harsh environments. They grow relatively quickly, coppice readily and are a source of nitrogen in forest ecosystems. Many have considerable value as emergency fodder and in dry zones play an important role as browse plants. The wood is useful for fuel, fence posts and poles, while the trees provide shade and shelter and are important in soil conservation. In view of these attributes, and in accordance with the recommendations of the FAO Panel and the wishes expressed by potential co-operators, the FAO/IBPGR Forestry Project has given priority to the exploration, collection and conservation of a few select species in the genera Acacia, Eucalyptus and Prosopis (FAO 1980).
The acacia species that have been selected for special attention are A. albida, A. aneura, A. caven, A. nilotica, A. senegal and A. tortilis. A short digest on each is given in Appendix 2.
All of the selected acacias are wide-ranging and diverse with associated taxonomic problems (Ross 1979, Hall et al. 1979). Both botanical and genecological exploration is necessary to give a sound basis for their efficient utilization and conservation. The proper selection of seed from appropriate stands may ultimately determine the success or failure of any afforestation project. Money expended on the careful selection of seed sources represents a wise long-term investment. Due attention to seed collection, extraction, storage and presowing treatment is essential. Incorrect assessment of seed maturity, inefficient seed collection methods, careless extraction of the seed, inadequate control of storage conditions or inappropriate treatment to promote germination will result in more expensive seed of low viability, with a reduced storage life.
The aim of this handbook is to summarise experience on seed collection, extraction, cleaning, protective treatment, storage and presowing treatment of dry-zone acacias, and in particular those identified in the FAO/IBPGR Forestry Project. The first two chapters on habit, taxonomy, occurrence, ecology and reproductive biology are to introduce readers to the genus. The handbook is intended for use by, and as a training aid for, personnel directly involved in the exploration and collection phase of the Project.