Tanzania is facing an unprecedented loss of its forests and other woodlands. Over the last three decades, blocks of forests in Tanzania have been heavily impacted by official forest excisions as well as illegal, irregular and unplanned settlements. Evaluation of vegetation cover change based on time-series satellite images and repeated aerial surveys showed that between 1990 and 2010, the country lost an average of 403,350 ha or 0.97 percent per year and also, between 1990 and 2010 the total loss was estimated to be 19.4 percent (about 8,067,000 ha) of the forest cover . Within this period, Tanzania was, among the ten countries that had the largest annual net loss of forest area. A recent report indicates that the country had already lost about 38 percent of its forest cover . According to the report, the rate of loss is 400,000 ha per annum and, the risk is deemed high as the country’s entire forests can be depleted within the next 50 to 80 years if the current trend remains unabated.
Although there are information gaps for some disciplines on a sustained basis, already links have been suggested between population growth, land cover change, land degradation and an acute shortage of water . Among the reasons for desertification caused by population growth are deforestation, overgrazing and overcultivation. Expansion of agriculture, especially the massive clearance of land for cultivation of cash crops such as cotton and tobacco to increase export earnings has been mentioned as one of the leading causes of deforestation in Tanzania .
While data for various land vegetation in Tanzania from 1990 to 2010 indicate the declining trend for forests and other wooded lands, subsistence agriculture alone is responsible for 48 percent of deforestation while commercial agriculture contributes 32 percent . In Tanzania, the impact of agriculture on deforestation (see figure 1) is affected by a number of factors including human population growth, poverty and government policies. Human population increase translates into the expansion of land under agriculture in forest areas in order to meet the growing requirement for food and income. As pointed out earlier, poverty is linked to incapability to afford the agricultural inputs for bumper crop production. Consequently, people are forced to abandon the existing farms and clear virgin forests for new farms, the practice commonly known as shifting cultivation. To farmers, virgin forest lands have a number of advantages, making it less laborious. Virgin forest soils are easy to work with; new farms are more fertile and productive; after clearing, the area is burned and is ready for planting; new farms have fewer weeds for about two seasons. Therefore, weeding is very much reduced; new farms are less infested by pests; newly cleared forest soil is well drained and requires zero or minimum tillage before planting .
With reference to the 2002-2012 intercensal period, Tabora region’s 2.9 percent average annual population growth rate was the 9th highest in the country . It was also the 24th most densely populated region with 30 people per square kilometre. Census data for the last two decades indicate a dramatic population increase in Tabora region. The projections show that population growth rate will increase from 3.8 percent in 2003 (with a population of 1,777,437) to 3.9 percent in 2025 (with a population of 4,181,327) . The rapid population increase since 1980 has occurred mainly due to the influx of farmers, attracted by fertile forest soils and improving infrastructure. The demand for water and other natural resources to serve basic needs is growing steadily as the population continues to increase. This is putting tremendous pressure on what are already scarce and highly vulnerable natural resources. Tabora region’s land converted from natural vegetation to cultivated land between 1984 and 1995 was 4.7 percent compared to 11.2 percent that was converted between 1995 and 2000 . There is a total of 33 Forest Reserves which have a total area of 3,422,500 hectares out of which about 119,691 hectares are catchment forests, and as of now about 201,017 hectares have disappeared through encroachment . As a result of the high deforestation rate and subsequent fire-based agricultural land preparation with little or no fertilizer input, soil fertility has declined tremendously in the area. Natural secondary succession in the left bush lands and grasslands is also prevented by constant annual recurrence of fire.
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