Forests are the most widespread terrestrial ecosystem on Earth. In 2015, natural forests accounted for 93% (3.7 billion ha) of this global forest area (FAO 2016), albeit only 26% of these are primary forest (i.e. old-growth or ancient woodland). Since 1990, 31 million ha of primary forest have been modified or cleared, and a net loss of 129 million ha of natural forest has occurred (–0.13%/year) (FAO 2016). This deforestation has largely been in tropical South America and Africa, where forests have been cleared and converted for agricultural uses, resulting in habitat loss and carbon emissions.