(CNN)It's bigger than Switzerland and has one of Africa's largest elephant populations.
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Inside Selous: The incredible African game reserve few have heard of
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It has more lions than any other game reserve.
It's one of the most diverse undisturbed ecosystems on the planet.
So why have few people outside of Tanzania ever heard of its Selous Game Reserve?
A new book by American photographer Robert J. Ross could help change all that.
With photos culled from more than 100,000 shot over four years, "The Selous in Africa: A Long Way from Anywhere" captures the fauna, flora and dramatic landscapes of this UNESCO World Heritage site.
As Ross tells CNN, it's like the reserve has been "hiding in plain sight."
"I went there initially just to do a couple of magazine stories, but after a couple of weeks in one small part of the reserve, I realized how incredibly beautiful it is, how varied. It's still an incredibly wild and pristine place."
However, in recent years Selous has seen a dramatic increase in poaching and other threats to the reserve's environment.
Between 2009 and 2013, the years Ross was working on the project, as many as 25,000 elephants were killed in the Selous -- about two thirds of the reserve's population.
"It's a dramatic and tragic decrease," he says.
"The rhinos are almost completely gone from the game reserve and it's unlikely that without a major reintroduction program that you'd ever see a significant rhino population back in the game reserve.
"Elephants at this point could come back, with proper management and care."
Efforts are being made today today to preserve the region's unique resources and withstand future threats.
"The Selous World Heritage site is our common heritage," Kishore Rao, former head of UNESCO's World Heritage Center, writes in the foreword to Ross's book.
"We cannot let the Selous die, it is our common responsibility to save it. Together we can make it happen."
"The Selous in Africa: A Long Way from Anywhere" by Robert J. Ross is published by Officina Libraria and distributed in the U.S. by ACC. It's available to buy now on Amazon.