This means that there should be a high degree of certainty that the improvements in ecosystem management are attributable to the PES programme. It also means that the services should not be lost to deteriorating ecosystems elsewhere, as environmental pressures (for example from logging activity) move from an area protected via PES, to an area which is not protected. This situation, known as "leakage" only has real significance to a PES programme if the area where ecosystem services deterioriate, is important for the provision of the ecosystem services. If a critical watershed is protected via payments for hydrological services, and logging activity moves out of the critical watershed, then the desired ecosystem services in that watershed are still secure.