we could help educate and support locals on how to best conserve and preserve their local area. They have started this in Gambia and it is quite expensive. But it is very effective because the people who will care the most about an area are the locals.
This would work if it is the locals who are causing the environmental damage. However in many parts of the world it is not the locals who are causing the damage but governments and large companies. Often the local people are fully aware of the decline in biodiversity and how this will impact their lives but are powerless to do anything about it.