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VI. Techniques for forest conversion and new land development

A. Land-use capability
B. Land clearing and development

The conversion of TRF should be done with careful planning and thorough analyses of all the factors and processes involved. An important step in this endeavor is land-use capability assessment. Subsequently, only land suitable for arable, pastoral, or silvicultural use should be cleared by appropriate methods.

A. Land-use capability

Successful land development from TRF depends on careful planning by assessing climate, vegetation, terrain, and soil characteristics. Suitability assessment of TRF lands at a detailed level is critical to sustainable land use. General guidelines for conversion of TRF to different land uses are outlined in Table 11 and briefly described below:

Protected Forests: These are marginal lands and should be left untouched as "protected forest reserves". These lands are characterized by steep slopes, shallow soils, and rocky and uneven terrain. Such forest reserves can be used for harvesting minor products and/or as wildlife reserves.

Plantation Forests: Soil and terrain characteristics are favorable for complete removal of existing vegetation and planting quick-growing timber or plantations (e.g., rubber, oil palm, Gmelina, teak).

Pasture: Terrain and soils are suitable for conversion to pastoral land use with improved pastures and a low stocking rate.

Arable Crops: Suitable land characteristics for arable land use include deep and fertile soils responsive to science-based inputs, gently rolling or flat terrain with predominant slopes of less than 5%, and the availability of institutional support, marketing facilities, and post-harvest drying and storage technology.

A capability assessment for these land uses can be done through an assessment of natural resources (e.g., biophysical and socio-economic factors). A flow chart indicating a sequence of steps required for the detailed assessment of resources for scientific land use is indicated in Fig. 10. Institutional support for the development of appropriate farming systems is critical for the sustainable use of these land resources.

Table 11 Guidelines for forest conversion to different land uses

Land use




Social factors

Protected forest Pre- montane Steep lands. slope > 20% Shallow, rocky. low fertility Low demographic pressure, inaccessible
Production forest Pre- montane Undulating. slope 10-20% Medium depth. low water and nutrient holding capacity Modest access and infrastructure
Planted forest Lowland Rolling terrain, gentle slopes 5-10% Deep soils with good water and nutrient- holding capacity Good infrastructure. and accessibility, timber-processing facilities
Pasture land Pre- montane/ lowland Rolling terrain. gentle slope 5-10% Good and productive soils institutional support, marketing facilities
Crop land Lowland Gentle to flat terrain, slightly sloping < 5% Deep soils. good fertility input-responsive Good infrastructure. institutional support, marketing, storage and drying facilities

B. Land clearing and development

Land clearing or removal of TRF vegetation is the first step toward bringing new land under cultivation. Improper and incompatible methods of deforestation and subsequent land development can lead to soil degradation and a rapid decline in crop yields (Weert, 1974; Seubert et al., 1977; Lal, 1981a, b; Hulugalle et al., 1984; Lal et al., 1992). The severity of soil degradation depends on the intensity and speed of mechanized methods of land clearing. The heavier and quicker the equip mental the more the degradation of soil structure. Different types of equipment and attachments used for manual and mechanized clearing techniques are shown in Plates 11-15.

Fig. 10 Natural resource assessment for an appropriate land use

Technological options for different methods of deforestation, land development, and trees, pastures, and crop management are outlined in Fig. 11. These technological options for land clearing are based on the following assumptions:

- The food production capacity of most potentially available soils of the humid tropics (especially Oxisols and Ultisols) is low and inferior to areas already producing food crops. Therefore, it is important to adopt improved soil and crop management practices to improve production on existing lands rather than clear new land.

- If deforestation for developing new land is deemed absolutely necessary, it must be done with careful planning after land evaluation and assessment of all natural resources.

- Whenever possible, manual clearing is preferable to mechanized clearing. If burning fell biomass is necessary, it must be done in situ. Indiscriminate use of heavy machines is to be discouraged.

- If mechanized clearing is inevitable, the use of front-mounted shear blades is preferred over tree pushers/tree crushers and other equipment that causes severe soil disturbance. Root rakes are to be avoided.

- Soil and water conservation measures are installed and the cleared land is immediately sown with an aggressively growing cover crop.

Guidelines for land clearing and development were outlined in the symposium held at IITA (Lal et al., 1986), and some important dos and donuts of land clearing are listed in Table 12. These guidelines are based on the assumption that locale-specific packages of cultural practices for improved cropping and farming systems are available. It is difficult to sustain productivity on newly cleared lands if these cultural practices are not known. If not available, these cultural practices are to be developed on the basis of the following research information available for site-specific ecological conditions:

- the comparative economics of land clearing by different methods (e.g., manual vs. mechanized);

- permissible slope limits for different land uses (e.g., arable, pastoral. silvicultural, and mixed farming systems);

- restorative technologies for compacted soils and those with low soil pH;

- nutrient management techniques based on soil test values;

- appropriate cover crops, woody perennials, and herbaceous shrubs for use in innovative farming/cropping systems; and - mulch farming techniques, including ways to procure mulch and grow crops through it.

Fig. 11 Options for methods of forest conversion for different land uses

Table 12 Some dos and don'ts of land-clearing methods in the humid tropics



Increase production from existing land to reduce the need for clearing new land Clear steep lands > 5% slope
Use shear-blade clearing where possible Construct windrows too far apart
Burn biomass in situ rather than in windrows Drag trees over long distances
Sow cover crops soon after clearing land clearing with untrained operators Use construction equipment for
Adopt conservation tillage with residue mulch Remove litter roots and stumps
Use multiple cropping systems to provide ground cover implement soil and water conservation measures Scrape off or disturb the top soil
Adopt controlled grazing with low stocking rate on pasture land Follow plow tillage and equipment that cause soil disturbance
Use science-based inputs for soil, crop. trees, and pasture management Follow productivity mining techniques and resource-based methods

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