A third of world's nature reserves severely degraded by human activity

New study's author says failure to protect biodiversity in places identified for that purpose is 'staggering'

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A third of global protected areas such as national parks have been severely degraded by human activities in what researchers say is a stunning reality check of efforts by nations to stall biodiversity loss.

A University of Queensland-led study, published on Friday in the prestigious academic journal Science, analysed human activity across 50,000 protected areas worldwide.