These landscapes represent some of “the last portions of the Earth that are not significantly affected by human influence,” said Lars Laestadius, a forest expert, consultant on natural resources policy and co-author of the new study. “As we lose these, we lose something that is bigger than ourselves.”

The study defines “intact forest landscapes” as areas greater than 500 square kilometers, or 193 square miles, containing a mosaic of forests and other associated ecosystems, such as plains or wetlands. The key is that these areas must be undisturbed by human activities — they can’t be fragmented by roads or deforestation or other industrial operations. Once that happens, the ecosystems cease to be considered “intact.” And as the new study indicates, this is happening more and more frequently around the world.

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Using satellite data, the researchers investigated changes to the world’s intact forest landscapes between 2000 and 2013. In 2000, they found that intact forest landscapes covered a total global area of 12.8 million square kilometers, or nearly 5 million square miles. But in the years since, human activities have altered and fragmented many of these areas.

In total, truly intact forest landscapes declined by 7.2 percent. More than half these losses occurred in three countries alone: Russia, Brazil and Canada. In general, though, tropical parts of the world tended to suffer the greatest declines.

The researchers note that these declines don’t necessarily mean that the trees and natural landscapes are disappearing entirely. In many cases, they’re simply being divided up by human activities, fragmented into smaller pieces that no longer qualify as “intact” forest landscapes by the study’s definition.

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The rate at which these losses are happening is speeding up, the study suggests. The researchers found that the rate of reductions to intact forest landscapes between 2011 and 2013 was triple the rate between 2001 and 2003.

The reason for the acceleration is not immediately clear, Laestadius noted, although he said he suspects a big factor is that these ecosystems are simply not as remote as they used to be. As human societies continue to expand, many wilderness areas are just closer to civilization and more accessible than they used to be.

Overall, the researchers found that about 14 percent of the losses were caused by direct alteration of the landscape by activities such as logging and land-clearing. The rest of the losses were caused by fragmentation brought on by road-building and other forms of construction. Timber harvesting, agricultural expansion and human-caused wildfires were the top three specific causes of all losses worldwide, although the greatest disturbances did tend to vary from one region of the world to the next.

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This means that the type of action needed to safeguard these landscapes largely varies by country, Laestadius noted. However, the study did indicate that protected areas generally fared better all over the world, suggesting that setting aside nature preserves can be an effective way to reduce forest losses. Worldwide, the researchers found that losses for reasons other than wildfires were 3.4 times higher outside protected areas than inside.

The speed at which these landscapes are being fragmented and destroyed has produced the alarming possibility that they may disappear altogether in many places by the end of the century. If the current reduction rates continue, the study concludes that at least 19 nations around the world will lose all of their intact forest landscapes in the next 60 years. Four of these — Paraguay, Laos, Cambodia and Equatorial Guinea — may lose them all in the next two decades.

Preventing this from happening is important for a variety of reasons, the researchers note. Intact forest landscapes, by virtue of their size and pristine condition, can provide critical habitat for all kinds of wildlife — conserving them is an important way to safeguard the world’s biodiversity. Many of them are also significant carbon sinks, making them important components of global climate mitigation strategies. Laestadius also noted that the forest landscapes most at risk of destruction are often those with the greatest carbon stores.

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“If you’re a logger … of course you’re going to look for the area with the biggest trees, and those will be the areas with the most carbon,” he said.

But he added that these natural landscapes have value beyond their obvious ecosystem services as well. By virtue of being mainly untouched, they provide an important reference point that shows us how healthy ecosystems function without the influence of human activities.