The tropical highlands of the Northern Andes are well suited to permanent, intensive cropping. Before the Spanish introduction of, and emphasis on, cattle raising, these areas were intensively cultivated by the Indian populations who grew maize, beans, squash, manioc, and other crops. Volcanic or alluvial soils are found in most of the region, and thus soil fertility is not as serious a constraint as it is in the tropical lowlands of the coast, the Llanos of Colombia and Venezuela, and the Amazon of those two countries and Ecuador. Moreover, the Northern Andes generally has sufficient rainfall and a distribution pattern which permits two crops per year. With favourable soils and climate, human population densities have always been high. Based on calculations using the most recent censuses for the three countries, approximately 53 percent of the population of the Northern Andes, almost 25 million people, is concentrated in the mountain areas. Excluding Venezuela, the statistics become 69 percent and 23 million, respectively. Small farmers predominate numerically in the Northern Andes; however, large farmers control most of the land in the more fertile valleys, forcing many of the small farmers to locate on the steeply sloping mountain lands.