However, in any country there are a number of environmental resources which are not flow resources. They include habitats for a variety of plant and animal species whose survival depends on the maintenance of key functional relationships within intact ecological systems. Indeed the regime of natural disturbance is an integral part of any ecological system. Add human induced disturbances to this natural regime and you change the entire disturbance pattern, and in turn change the functional interdependencies which make up a habitat. A good example is roading which riddles an area with access routes for predators, pests, and weeds, increases edge effects, disrupts water tables, and opens areas up to wind damage.
Roads are to forests as borer is to wood.
Accordingly, the principle of sustainability includes the necessity to leave certain areas entirely alone and manage them in an intact state which will allow natural processes to continue. Predators, pests and weeds need to be controlled as much as possible in such areas. They will evolve in their own way if we let this happen. Examples of this are common in the fishing industry, and like those fishing industry heavy-weights who make sure that Ministry of Fisheries data is ignored by the Government when setting catch quotas, the logging heavies like Timberlands will do anything to ensure that they get business as usual. They will even claim that they are protecting these forests better than we can.