A variety of causes lead to deforestation. Logging for valuable tropical hardwoods, such as teak and mahogany, is, of course, a major factor. Loggers may take only one or two of the largest trees per hectare, but because the canopy of tropical forests is often strongly linked by vines and interlocking branches, felling one tree can bring down a dozen others. In many places, land also is cleared for cattle ranching, banana or pineapple plantations, or for other export crop production. In Southeast Asia, forest clearing for large-scale oil palm plantations is a major cause of forest destruction. Roads cut in the forest for logging make it possible for land-less farmers to move into the forest in search of land. Unfortunately, soils in tropical forests are often thin and nutrient-poor. Crops may grow well in the first few years of farming in the ashes of a burned forest, but the nutrients are quickly exhausted, and farmers must move on to new land. Thus, the cycle of destruction continues over and over again.