Arthur Tansley turned the old plant geography into the new science of ecology, teaching botanists to look at vegetation, rather than individual plant species. He recognised that vegetation is continually changing and how, especially in the British islands, it is influenced by man's activities. Safeguarding wild places from the continuing pressures of agriculture and industry would demand, he argued, not sterile preservation but active conservation within nature reserves, places where the principles of ecology could be applied to the scientific management of plants and animals.

Author of a best-selling book on psychology, and a respected philosopher, Tansley was no mere academic. He used his authority and political skills to achieve practical results, such as the foundation of the Nature Conservancy, of which he was the first Chairman. In the ecological principles he laid out, most notably the ecosystem, he left an invaluable legacy for ecologists and conservationists worldwide.