The jhum method was ecologically sustainable as long as population increase was minimal and cultivable land was plentiful. But even a favourable population-land ratio did not guarantee against periodic famines called "mautam". Such famines are associated with the flowering of bamboo whose seeds lead to the multiplication of rats and other pests. In this sense, bamboo was both a curse and a blessing. In the traditional Zou economy, bamboo was a source of food (bamboo shoots), building material, household utensils, fencing and handicrafts. In fact, bamboo was the backbone of their subsistence economy.