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Forest resources in arid and semi-arid tropical zones
Assessing world forest resources is part of FAO's mandate. The last two assessments refer, in particular, to 1980 and 1990, thus making it possible to determine changes in forest cover between these two years. The 1990 evaluation was conducted in two phases: (1) a compilation of existing national forest inventory data adjusted to 1990 by mathematical function; (2) a study of the changes in forest cover based on a global sampling survey (comparative remote-sensing analysis using a series of satellite imagery). The data gathered were fed into the forest resource information system which will be regularly updated in the future. The man-forest interaction was analyzed using Geographic Information System (GIS) and modelling techniques. The system includes a number of important data such as types of vegetation, ecofloristic zones and population distribution at sub-national level. This project was made possible by extensive cooperation with several national and international institutions.
At the global level, the results show that out of a total of 1 715 million hectares of forest 1 in 1990, forest formations in arid and semi-arid zones (comprising the deciduous dry forest zone, the very dry forest zone and desert zones) cover 254.9 million hectares with the following distribution among the three continents:
1 Forest is defined as any area greater than 10 hectares covered with trees (ligneous plants with a height >= 7m covering at least 10% of the ground area.
| AFRICA: | 155. 3 million ha |
| ASIA: | 40.8 million ha |
| AMERICA: | 58.8 million ha |
This only refers to lowlands below 800 metros. Dryland hill and mountain areas should also be included (particularly certain mountain zones in northern Mexico, parts of the Andes, Ethiopia and Pakistan).
The Mediterranean countries and those in the Near and Middle East are not included in these statistics.
The following tables indicate the distribution of forest area by continent and by lowland ecofloristic zone. The ecofloristic zones have the following climatic characteristics:
| Ecofloristic zone | Average rainfall in 1950s | Ecologically dry months | Average air humidity | Average annual temperature | Average temperature in the coldest month | climatic denomination |
| Deciduous dry | 500 - 1,000 | 40 - 120 | 65 > t > 50 | 20 - 30 | > 20 | sub-moist dry |
| Very dry | 200 - 500 | 20 - 50 | < 50 | 20 - 30 | > 15 | semi-arid |
| Desert | < 200 | < 20 | < 50 | 14 - 25 | > 10 | arid |
The last column indicates the average climatic denomination corresponding to each ecofloristic zone.
The following table shows that some 950 million human beings live in the dry zones and that forest area per inhabitant varies considerably according to ecofloristic zone and continent: over one hectare per inhabitant in the deciduous dry zones of Africa and America, but an average of only 0.06 ha per inhabitant in the same ecofloristic zone of Asia.
Land area |
Total population |
Population density |
Population growth (1981-90) |
Forest area |
Annual deforested area |
Area Forest/inhab. |
|||||
'000 ha |
% total land area |
'000 inhab. |
inhab/km2 |
% per year |
‘000 ha |
% land |
%total forest area of the continent |
‘000 ha |
% |
ha/inhab |
|
AFRICA |
|||||||||||
| Deciduous dry | 335.9 | 15 | 79.1 | 24 | 3.5 | 118.0 | 35 | 20 | 1.2 | 0.9 | 1.49 |
| Very dry | 489.7 | 22 | 72.2 | 15 | 2.8 | 37.3 | 8 | 6 | 0.2 | 0.6 | 0.51 |
| Desert | 472.5 | 17.5 | 4 | 2.5 | E | E | E | E | E | E | |
| Total | 1,293.1 | 85 | 168.8 | 155.3 | 26 | 1.4 | 0.92 | ||||
ASIA |
|||||||||||
| Deciduous dry | 225.0 | 28 | 630.7 | 247 | 2.4 | 40.6 | 16 | 15 | 0.5 | 1.0 | 0.06 |
| Very dry | 43.5 | 5 | 52.6 | 121 | 3.9 | 0.1 | E | E | E | E | 0.002 |
| Desert | 30.3 | 3 | 40.9 | 135 | 4.4 | 0.1 | E | E | E | E | 0.002 |
| Total | 298.3 | 36 | 724.2 | 40.8 | 15 | 0.5 | 0.056 | ||||
AMERICA |
|||||||||||
| Deciduous dry | 129.6 | 8 | 39.6 | 31 | 1.9 | 54.3 | 42 | 6 | 0.4 | 0.81 | 37 |
| Very dry | 14.5 | 1 | 6.4 | 44 | 2.7 | 2.1 | 14 | E | E | E | 0.33 |
| Desert | 21.0 | 1 | 5.2 | 25 | 3 5 | 2.4 | 11 | E | 0.1 | 2.0 | 0.46 |
| Total | 165.1 | 10 | 51.2 | 58.8 | 6 | 0.5 | 1.15 | ||||
TROPICAL WORLD |
|||||||||||
| Deciduous dry | 720.5 | 15 | 749.4 | 104 | 2.4 | 212.90 | 30 | 12 | 2.1 | 0.9 | 0.28 |
| Very dry | 547.7 | 11 | 131.2 | 24 | 3.2 | 39.5 | 7 | 2 | 0.2 | 0.7 | 0.30 |
| Desert | 523.8 | 11 | 63.6 | 12 | 3.8 | 2.5 | E | E | 0.1 | E | 0.03 |
| Total | 1,792.0 | 37 | 944.2 | 254.9 | 14 | 2.4 | 0.27 | ||||
The level of deforestation is similar (0.8 to 1 % for the semi-deciduous dry ecofloristic zone that accounts for 80% of the total population). It should be noted, however, that the level is only a little higher in Asia (1%), with an average population density of 247 per km2, than in Africa with an average density ten times lower (24 inhabitants per km2). The relative forest abundance in the deciduous dry zones of Africa (which can also be qualified as dry sub-humid) produces a level of land clearing 21 times higher than in Asia (150 m2 cleared per inhabitant/year against 7 m2/inhabitant/year in Asia and 100 m2/inhabitant/year in America). The very high population growth (3.5 % per year) arouses considerable concern regarding the future of forest areas in these deciduous dry zones of Africa, which seem to be seriously threatened.
| Additional information on the global assessment of tropical forests can be obtained from the Forest Resource Division, Forestry Department, Food and Agriculture Organization of the United Nations via delle Terme di Caracalla, 00100 Rome (Italy) - Fax (39.6) 5797 5137 |
April 1993