The Food and Agriculture Organisation (FAO) said on Monday that the world had lost forests the size of South Africa, over the past 25 years.
It said in a report in Johannesburg that it was a decline of more than 3 per cent, although the rate of forest loss had significantly slowed.
It said a growing global population and increased demand for food and land were driving deforestation.
The report noted that the rate of global forest area change had slowed by more than 50 per cent since 1990.
FAO said the biggest forest area loss occurred in the tropics, particularly in South America and Africa, although the rate of loss in those areas had decreased substantially in the past five years.
It said the rate of loss had declined due to reduced forest conversion rates in some countries and increased forest area expansion in others.
“Countries have more knowledge of their forest resources than ever before and as a result we have a better picture of global forest change.
“The world has just less than four billion hectares of forests in 2015 from 4.1 billion in 1990,’’ FAO said.
It said forests give protection against climate change as trees absorb carbon dioxide.
It said that the International Union of Forest Research Organisations noted in May that deforestation had been blamed for worsening soil erosion, landslides and floods.
It said an estimated 1.2 billion people rely on forests for their livelihood, including about 60 million indigenous people who were almost entirely dependent on them.
FAO said the most important challenges remain as the existence of sound policies, legislation and regulation was not always coupled with effective incentives or enforcement.