Mt. Malindang range is one of the ecologically valuable areas in Mindanao and is an important biodiversity refuge.  However, conversion of forest to agricultural lands is posing a serious problem.  Forests are continually denuded and converted to grasslands because of logging and smallscale or subsistence upland farmers aggravating soil erosion and degradation.

Boniao et.al. (MSU) assessed the soil physicochemical and biological properties in Mt. Malindang and related the change of such properties with the increasing degree of disturbance in the area from June 2003 to May 2005.

Investigating soil properties and their relationship to soil biodiversity may provide the necessary data for sustainable land use plan and may give information on the level of disturbance of the ecosystem.

Findings

• Soil properties are at their optimum or best levels in ecosystems where human activities are almost absent.  Soils have low bulk density, well-aggregated loamy soil texture, high soil respiration rate, and diverse earthworm population.  In contrast, forestlands converted into agricultural lands and later abandoned into grasslands have critically reduced soil properties.  These had lower cation exchange capacity (CEC) and organic matter (OM) and the dominant earthworm species was Pontoscolex corethrurus. The nematodes present were mostly, semiendoparasitic, the species closely associated with crops.
• In forest areas where human intrusion was less, highest amount of organic matter (20.2%), highest CEC (43 to 57 cmol_c kg^-1 soil), and lowest bulk density (0.4 Mg m^-3)  were obtained.

Based on the results of the study, the good soil quality was partly maintained by the integrity of the forest cover.  Disturbance due to logging and conversion of land to agroecosystems without proper soil management can ultimately compromise soil quality.

Earthworms and nematode species composition and a number of biophysicochemical soil properties can be used as indicators of disturbance.

The researchers also recommend that farmers be kept from converting forest lands into agriculture by keeping their existing farms productive via continuous planting of cash crops.

Source:Philippine Council for Agriculture, Forestry and Natural Resources Research and Development.  Highlights 2005. Los Baños, Laguna:  PCARRD, 2006. 167p.