Scientists use satellite images to understand land use among farmers over time

A group of researchers have been burning the midnight oil are using data collected over more than fifty years to determine the factors that result in positive and negative land use change through understanding how soil, water and biodiversity are maintained in some areas thus managing ecosystems.

East African landscape has been changing with agricultural production impacting on the biodiversity on one of the world's most diverse ecosystems and affecting areas traditionally used by pastoralists and wildlife. Understanding the factors behind land use changes in East Africa has been the objective of a network of international researchers, known as LUCID (Land Use Change, Impacts and Dynamics), who are using data collected over more than fifty years to determine the factors that result in positive and negative land use change. Understanding how soil, water and biodiversity are maintained in some areas and not others is of interest not only to the LUCID scientists but to environmental projects elsewhere in Africa and Asia.

The impact of socioeconomic changes on the environment is often ignored in land use and biodiversity research, says Jennifer Olson, network co-coordinator, even though it is critical to understanding how land use can be improved. Working in Kenya, Uganda and Tanzania, LUCID researchers compare old and new data, using aerial photographs and satellite images to see changes over time in land use. Distinct from other projects, five decades of data identifying changes in land use is then integrated with ecological data (from soil sampling and wildlife/plant surveys) and socioeconomic data (from personal interviews and population counts).

Whether an area is maintained or degraded in terms of soil, water and biodiversity is dependent on a number of factors including inherent soil quality, local climate, population and political stability. Migration is also "a really important reason for the conversion of land from more natural vegetation to crops," stresses Olson. It is happening especially in densely populated areas and where young people have insufficient land for their families, she adds. Consequently, a greater number of people are moving out into the more marginal areas, leading after a few years to severe soil degradation which is difficult to reverse.

This is a particular problem in Kenya, says Olson, where the good land is already cultivated. People move into the drier areas and manage to get some food from the land while supplementing their income with off-farm work, but usually at the expense of the natural environment.

In Uganda, where it is generally not as dry, Olson reports that some areas, such as the former cattle corridor in the central and southern regions, which have yet to be put under cultivation, are at risk; LUCID projections suggest it is only a matter of time. In Tanzania, two predominant land use changes are the rapid conversion of pastoral areas to crop land, and large areas of the miombo woodland being cleared for tobacco and other crops.

In some areas of East Africa, however, environmental resources have been improved by people engaging in extensive agriculture. In all three countries, Olson and her team found that in areas that are more 'hooked up' to markets and where the soil quality and rainfall is adequate, farmers can derive enough income from their farms to invest the time and resources needed to institute soil erosion prevention practices, apply chemical fertilisers and/or use manure.

As a result, says Olson, soil fertility in some areas has started improving. Soil fertility has also been boosted when, in the past, governments stepped in to subsidise chemical fertiliser. However, Olson points out that "to start to use manure in a systematic way that makes a difference is quite an effort."

After some years of neglect, governments and NGO's in East Africa are beginning to pay more attention to agriculture. And in areas where the land is marginal, Olson sees agricultural extension programmes and off-farm jobs as critical to providing farmers with the means to replenish soil fertility. Olson also lists community land use planning - which involves preservation of some forest and pasture land for community use - poverty reduction, and family planning programmes as keys to halting land degradation.