Throughout the period of the protectorate, most of its people were subsistence farmers growing maize, millet and other food crops for their own consumption. As the protectorate had no economic mineral resources, its colonial economy had to be based on agriculture, but before 1907 this had hardly started to develop. In pre-colonial times trade was limited to the export of ivory and forest products such as natural rubber in exchange for cloth and metals and, for the first few years of the protectorate, ivory and rubber collected from indigenous vines were the principal elements of a tiny export trade. The first estate crop was coffee, grown commercially in quantity from around 1895, but competition from Brazil, which had flooded the world markets with coffee by 1905, and droughts led to its decline in favour of tobacco and cotton. Both these crops had previously been grown in small quantities, but the decline of coffee prompted planters to turn to tobacco in the Shire Highlands and cotton in the Shire Valley. Tea was also first planted commercially in 1905 in the Shire Highlands, but significant development of tobacco and tea growing only took place after the opening of the Shire Highlands Railway in 1908.