An analysis of the drivers and impacts of landuse change in the tropical uplands of Mindanao, Philippines
Walpole, Peter W.
PublisherKing's College London (University of London)
MetadataShow full item record
Landuse change in upland Mindanao is driven by the history of commercial logging, the disregard for indigenous communities, the lack of tenure for migrants and the limited development of sustainable resource management strategies. The area's climate, forest hydrology and nutrient balances are a source of sustainability, yet with landuse change the potential for erosion and loss of the limited nutrient base, broader environmental degradation is probable without greater accountability and better options. Responses from traditional management indicate some of the possible options to be involved The main forest type is a tangile-oak association (premontane) with total estimated biomass being 479 tha-I. High clay levels, low bulk density and porosity are reflective of the undisturbed forest, estimated infiltration rates start at 10,000 mmhr-l levelling off in 30 minutes at 1,700 mmhr-l, high throughflow allows for fast delivery, yet baseflow is sustained during dry season. The other five land uses reflect lower clay, porosity, infiltration rates and nutrient loss especially maize with coffee being an exception given associated activities of soil fauna. The annual precipitation is over 2500mm, while during El Nifto (1997-8) less than 2000mm fell, registering 3 to 6 months drought in the broader area. Hydrographs give a discharge pattern of quick return to base flow which is sustained at half rate during droughts. Calculated potential evapotranspiration for maize area is around 28% while for forest is 55%of rainfall. More than 30% of the rainfall events are potentially erosive. Establishing the rainfall pattern and forest water budget gives a definite characterisation and importance to the uplands as valuable water producing areas. Nutrients in precipitation are in the order of sodium, calcium and potassium and, other than magnesium from weathering, are the crucial inputs in a tight forest nutrient cycle. For Bendum, high infiltration may be enough to give constant stream chemistry with established equilibria between aqueous and solid phases, due to the storage time in the soil for where there is good land cover. Ranking of landuses according to levels of sustainability on-site and off site were established ..... . With expanding agriculture and forest utilization greater soil and water conservation, utilization of buffer zones and a new level of integrated water resource management is needed locally and in both extension work and landuse planning by local government.