Pointing to rapid economic and population growth in the region, the researchers say their projections likely underestimate the true extent of future deforestation.
Population densities have increased over 20 percent in the past decade, the scientists add.
Pandit says global warming may spur even higher extinction rates than those predicted in his study.
The scientist says that as global temperatures rise, species adapted to cool mountain living will have to move to higher elevations.
"Competition for space between species is likely to result in shrinking ecosystems," he said.
The team's findings contradict figures from the Indian government, which suggest deforestation is no longer a major problem in the region.
Official statistics suggest Himalayan forest cover will increase more than 40 percent between 1970 and 2100driven mainly by reforestation programs and a halt to commercial logging.
But the new study says such official projections don't take into account the increased deforestation caused by human activities, such as grazing livestock and cutting firewood.
The researchers say Indian government officials have also misinterpreted the satellite evidence.
"As many [study] authors before us have pointed out, the government agencies lack necessary expertise, methodology, and competence to interpret the satellite data," Pandit said.
The World Wildlife Fund (WWF), the international environmental group, supports the study's findings.
"Deforestation is indeed the key conservation challenge in the Himalaya," said Jennifer Headley, a WWF program officer for the eastern Himalaya.
She says several factors are driving the loss of Himalayan forests. They include population growth, increased farming, livestock overgrazing, unplanned development, and unsustainable use of natural resources.
Her group is particularly worried for the future of large mammals native to the Himalaya, including the tiger, Asian elephant, and greater one-horned rhinoceros.
WWF says the animals are now confined to relatively small and isolated patches of forest.
"This affects their ability to breed and thus the viability of the species," Headley said.
Headley expects the project to increase community participation in forest management and promote alternative sources of energy and income for locals.
She poaching for the illegal wildlife trade and retaliatory killings sparked by more conflicts between humans and wildlife pose additional major threats to rhinos, big cats, and other large mammals in the region.
Pandit, the University of Delhi scientist, agrees. He said that despite the existence of national parks and wildlife sanctuaries in the Himalaya, "poaching goes on unabated."
His team says large-scale conservation efforts, including reforestation and government-enforced protection of remaining forest habitat, are needed to prevent a wave of extinctions in the region.
Pandit called for "a strict enforcement of law by agencies responsible, strong political will, and honest bureaucracy."
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