A scientifically based management system has not been developed that allows people to use the tropical forest without converting it (the forest) to grassland or barren "waste land". As a result, the world's tropical forest area has been reduced substantially. Among the many factors accounting for the disappearance of the tropical forest is the fact that the timber harvesting is not based on the rate of replacement of the trees that are harvested. The direct consequence is that when valuable trees, such as mahogany in Mexico and Central America, disappear or are reduced in numbers, there is an increased probability that the forest will be transformed into agricultural land or grassland used to raise cattle.