A Comparison of Soils Under Agriculture and Forests in San Carlos, Costa Rica

Increasing population in many tropical countries has encouraged settlement of forest lands. While there is little published data on the ecological impact of settlement, some ecologists have suggested that conversion of forest to agricultural lands may have lasting deleterious effects. For example, Holdridge (1959) and Tosi (1964) have postulated that the change from forest to permanent agriculture in Costa Rica might cause rapid deterioration of the soil. The logical basis for this conclusion is well established. High temperatures cause rapid decomposition of soil and litter organic matter, and high rainfall may cause rapid leaching of nutrients from the soil (Aubert and Tavernier, 1972). Thus removal of forest cover could conceivably result in a decline in soil nutrients, since in the intact forest the nutrients are taken up by vegetation immediately upon their release from decaying organic matter (Richards, 1952). The objective of this work was to compare soil characteristics of permanent agricultural fields and forest. The area chosen for the study was a farming community centered around the Centro Rural Metodista along a ridge in the Canton of San Carlos, 8 km north of Cuidad Quesada (Figure 25-1). Soils under three different crops—sugar cane, coffee, and pasture—were studied. Since forests in this region of Costa Rica were first cleared about 22 years ago by settlers moving from the south, fields ranging in age from 22 years to the present were available for study.