When Turnbull took a pygmy guide out on an open plain where a herd of buffalo could be seen several km. It is not an environmental science whose goal is to study various aspects of the physical environment per se. It is the study of human behavior and it's relationship to the environment. It is a behavioral science. It is not a design field such as interior decorating or architecture.
Environmental psychology is one of the younger areas of psychology.
There is relatively little theoretical refinement compared to other areas, such as social psychology. Many of the theoretical frameworks are in fact borrowed from other areas, e.g., perception, stress. There has been a lot more study of the effects of the environment on people than the effects of people on the environment. APA APA contains a separate division of Population and Environmental Psychology.