An expansion of farmland has damaged nature beyond a "safe" limit on 58 percent of the world's land surface, threatening natural services such as crop pollination by insects, scientists said on Thursday.
Grasslands, such as in United States, Argentina, South Africa or Central Asia, are among natural systems most affected by declines in animals and plants caused by human activities, they wrote in the journal Science.
Northern pine forests and tundra are least affected, they said.
Overall, the study said the diversity of animals and plants on 58 percent of the world's land area, home to 71 percent of all people, had fallen below a safe threshold, driven mainly by an expansion of farmland as well as by roads and bigger cities.
They defined "safe" as places where the local abundance of species was at least 90 percent of levels in comparable regions untouched by human activity. They based the conclusions on 2.38 million records for 39,123 species at 18,659 sites.
The declines raise risks for natural services such as pollination of food crops by insects, production of nutrients by soils, or the ability of forests to absorb carbon dioxide as a natural brake on climate change.
Still, the study said there was uncertainty about the 90 percent threshold for damage - some other scientists believe nature can withstand bigger declines.
Intact natural systems are most resilient to shocks such as droughts, floods, disease or global warming.
The report complements work by a separate group of scientists seeking to outline planetary boundaries, or safe limits for human prosperity in areas such as biodiversity, climate change, ocean acidification and freshwater use. (Reuters)
PHOTO: Cows graze on deforested Amazon rainforest, next to another tract recently cleared and burned, near the city of Novo Progresso, Brazil, September 23, 2013.
CREDIT: REUTERS/Nacho Doce/File Photo.