Professors J. Ge, Q. Guo, and X. Kou of Beijing Normal University (BNU) Biology Department had introduced the concern of few Amur tigers in a Chinese tiger reserve area to Xuemei Han (now Dr. Xuemei Han), my PhD student who had under the professors at BNU as an undergraduate.
Xuemei and I attended many meetings and field excursions facilitated by BNU and sometimes attended by others, including Russian wildlife scientists (across the border from the Chinese tiger reserve). Xuemei documented that most of the tiger reserve had been clearcut between about 40 and 90 years previously and that the regrown, dense forest shaded the understory. Without understory, there were few deer and so few tigers, who depended on the deer as food.(Reference 1, below). See also film.
A different theory is that tiger poaching by local people is the primary cause of the few tigers. (Reference 2, below)
Proponents of both theories united in a paper promoting an expanded tiger reserve in northern China (Reference 3, below), which was instituted with the scientific leadership of Dr. J. Ge (BNU).
Reference 1. Han, Xuemei, C.D. Oliver, J. Ge, Q. Guo, and X. Kou. 2012. Managing forest stand structures to enhance conservation of the Amur tiger in northeast China’s natural forest protection program. Book Chapter in (J.A.Stanturf, D. Lamb, and P. Madsen, editors) Forest Landscape Restoration: Integrating Natural and Social Sciences (World Forests). Springer Publishing, New York. 93-128.
Reference 2. Conniff, Richard. 2010. Can China Save the Amur Tiger? Environment Yale. Spring, 2010. (see link)
Reference 3. Wang,T., L. Feng, P. Mou, J. Wu, J. Smith, W. Xiao, H. Yang, H. Dou, X. Zhao, Y. Cheng, B. Zhou, H. Wu, L. Zhang, Y. Tian, Q. Guo, X. Kou, X. Han, D. Miquelle, C. Oliver, R. Xu, Ji. Ge. 2016. Amur tigers and leopards returning to China: direct evidence and a landscape conservation plan. Landscape Ecology 31: 491-503.