A third of the world's protected areas for wildlife are suffering road-building, more farms and other man-made threats that are undermining goals to safeguard the diversity of life on Earth, scientists said Thursday.

Almost 200 nations agreed in 2010 to set aside at least 17 percent of the world's land areas in parks and other sanctuaries by 2020 as a cornerstone of a plan to shield animals and plants from pollution, land clearances and climate change.

But many protected areas fall short, according to a report in the journal Science led by researchers at the University of Queensland in Australia.