...because human beings have controlled most of the places we have lived. Following discoveries that places like the Amazon and Serengeti were shaped by their inhabitants to be more productive and safer for human beings it is becoming impossible to ignore our effects on the environment. Conservation efforts have sometimes excluded the inhabitants and relocated them to other areas in order to preserve the pristine natural reserve or sanctuary.
In Australia conservation laws forbid the felling of eucalyptus without a permit. Unfortunately this has led to a uniform ecosystem in many places. The Aborigines had cleared woodland for pasture, encouraging some prey species and diversifying the species of plants, etc. found there. Most importantly to the inhabitants the grasslands acted as firebreaks, preventing the disastrous massive firestorms that are becoming more common in Australia today.
This BBC article sums it up. It should be remarked that pure eucalyptus oil straight from the distillery can be used to run a vehicle tuned for high-octane petrol.