Sustainable development refers to development that can continue on an ongoing basis because it does not do irreversible harm to the environment. Development like this should balance social, economic and environmental concerns. This is not easy because these three concerns often compete with each other. For example, a sustainable forestry industry should allow a certain number of trees to be cut down and used by people, but at the same time make sure that enough trees are left to be cut down and used in the future. This could be achieved by cutting down some of the trees and also planting new trees to replace those harvested, so that there will be trees in the years ahead. It is clear that sustainable development is an international issue. South Africa has signed and ratified certain important international agreements that aim to protect the environment.