Maps show how humans are destroying the world's forests

Farms, roads, and towns are slicing up the world's wilderness, leaving 70% of the world's remaining forested land less than half a mile from a forest edge, according to reserach published in the journal Science Advances.

The report examined forests on five different continents and included data that covers the past 35 years. The researchers concluded that a rising human population is putting more pressure on forest animals and plants, which suffer greater risk of extinction as their habitats become fragmented.

"We found the results surprising and frightening," Nick Haddad, a professor of biological sciences at North Carolina University who led the study, told Reuters. "The signs are all still downwards."

The Amazon and Congo basins were the main areas where vast tracts of forests remained far from human activity, according to maps published with the study. Still, there's a very visible decline:

In these maps of South America and Africa, only the blue color shows areas that are greater than half a mile from the forest's edge:

In Asia, New Guinea, Russia, Canada and the Nordic nations, human activity steadily encroached on other huge forests.

Again, only the areas in blue represent forests that are more than one half mile from the forest's edge:

Overall, the scientists wrote that "70 percent of remaining forest is within one km of the forest's edge" - equivalent to a few city blocks.

"The expansion of human populations will inevitably continue to reduce and fragment natural areas," they wrote, unless there were gains in agricultural yields and efficiency.

Another scientific report in 2011 projected that the world's cropland would have to expand by 18 percent by 2050 from the current 1.53 billion hectares (3.78 billion acres) to feed a rising world population. And other estimates indicate that urban areas will also have to expand sharply, to 0.18 billion hectares by 2030.

The study said animals and plants are under threat from fragmentation which puts forests in range of humans, changing micro-climates and new, rival species from outside the forests.

"Fragmented habitats reduce the diversity of plants and animals by 13 to 75 percent, with the largest negative effects found in the smallest and most isolated fragments of habitat," it said.

Deforestation is a threat to animals ranging from jaguars in Brazil to orangutans in Indonesia, as well as other creatures such as birds, butterflies and frogs in addition to many rare plants. In 2010, governments agreed a goal of setting aside 17 percent of the world's land area in wildlife parks and other protected areas by 2020, up from 12.7 percent in 2010.

(Reporting By Alister Doyle; Editing by Larry King)