Because the island's soil consists largely of porous red loam, the part played by forests in water retention is vital.
海南島土質屬熱帶濕潤紅壤，有機物豐富，最易流失，擔任水土保持任務的森林，角色尤其重要。大陸「中國林學會」就曾有學者指出，開發熱帶地區的原則是「七山一水二田」，治好七分山，才能保住二分田。