First, because service buyers are paying for a service that is dependent on specific land use practices, they will want to be certain that they are entering in a contract with those who are able to determine land use over the long term. Second, because ecosystem services often involve a considerable investment, for example planting trees, service sellers are unlikely to participate unless their rights to the land are strong enough to guarantee that their investment will not be lost. This reluctance has been seen by the forest communities in Northern Thailand who have opposed payments for carbon sequestration citing concerns about unresolved land tenure arrangements. Early PES-related schemes in Viet Nam faced similar difficulties.