Answer from Shekar Dattatri, Conservation India:
The tiger is an extremely adaptable species that thrives in a wide variety of natural habitats and climatic conditions — from very hot (such as is Ranthambhore in Rajasthan) to very cold (such as the Russian Far East). It also lives in wet evergreen forests (such as in those in the higher elevations of the Western Ghats) and in mangrove forests (Sunderbans). As you rightly note, tigers also occur at high altitudes in the mountains of Bhutan. The main requisites for a resident, breeding tiger population in an area are a minimum of a few hundred square kilometres of relatively undisturbed forest/mixed habitat with perennial water sources and plenty of prey. A tiger needs about 3000 kg of wild prey per year, which roughly translates to about 50-60 deer sized animals. It has been estimated that to sustain one tiger in the wild, a ‘bank’ of 500 prey animals is required, with the tiger cropping the surplus. If the Gulma forests you mention meet these conditions, and there is connectivity to a source population of tigers, it wouldn’t be surprising if the big cats appear there one day.