For centuries, the industrial approach to forestry was reductionist. A forest was measured in board-feet, cubic meters, and dollar values. The non-timber functions of a forest—water filtration, carbon sequestration, biodiversity conservation, soil stability, and recreational value—were considered "externalities." They were vital to human survival, yet economically invisible. You could not invoice a watershed for cleaning the water; you could not trade a songbird for preserving biodiversity.