However, according to conventional principles of economic analysis it is necessary that a resource is used for it to acquire a value. Consequently economists traditionally value biological resources in terms of their direct uses, the raw materials they supply for human production and consumption. For example, a living tree can only be valued in terms of the price it would fetch in the market place as timber; natural forest will be valued based on timber value; coastal and marine ecosystems are valued in terms of fisheries. This disregards all those vital services and functions of biodiversity that are not directly seen or perceived. Consequently they are taken for granted although irreplaceable and vital to sustain local economies.
Species and genetic ma terial have long been exchanged in Asian markets (e.g. rice, timber and fish, utensils, cloth, etc) but there has been failure to give a value for the services provided by natural systems which therefore remain "worthless" in market terms. For example, the disruption in natural water regulation due to forest loss in the central highlands of Vietnam accounts for around 50 percent of seasonal fluctuations in rice production. It is important to recognize the vital importance of biodiversity services for local/national economy apart from sustaining life support systems.