His research interest is the ecology of mountain areas, looking at the interaction of organisms with their environment, focusing on classical environmental variables such as soil, rocks, and minerals as well as surrounding water sources and the local atmosphere. Mark has current or past research activities in many of the mountain ranges throughout the world, including the Rocky Mountains, Sierra Nevada of California, the Tien Shan and Qilian Shan, China, Andes of South America, European Alps, and the Himalayas.