The world's forest areas have declined from 4.1 billion hectares in 2000 to 4 billion hectares in 2015, according to the U.N. Forests and trees make vital contributions to both humanity and nature, such as supporting livelihoods, ensuring clean water and air, preserving biodiversity and responding to climate change.

The world's forest areas have decreased from 31.6% of the global land area to 30.6% between 1990 and 2015, the United Nations' Food and Agriculture Organization (FAO) said in its analysis of The State of the World's Forests 2018. In Australia and New Zealand, forest areas as a proportion of total land fell from 17.4% to 17%, while in Europe and North America, it rose from 40.3% to 41%, the FAO said. This trend increased from 28.5% to 29.6% in East and Southeast Asia and decreased from 30.6% to 27.1% in sub-Saharan Africa.

In Latin America and the Caribbean, the ratio decreased from 51.3% to 46.4%, while in Central and South Asia, it rose from 9.5% to 10%. About one-fifth of the Earth's land surface covered by vegetation showed persistent and declining trends in productivity from 1999 to 2013. This trend threatens the livelihood of more than 1 billion people, the U.N. said in The Sustainable Development Goals Report 2018.