Today, more than half of the world's population live in urban areas. By 2050, this is expected to increase to almost seventy percent. Yet even people living in cities have begun to realize how vital access to forests, urban parks and green spaces is for our mental health and well-being.

There is clear evidence to show that spending time in forests reduces stress and lowers blood pressure and the risk of heart attacks. Last month, a new study by Italian universities suggested that simply breathing forest air can reduce anxiety due to the volatile compounds released by trees. 'Green prescribing' programmes, a holistic approach to health and care, are also gaining momentum in many countries.

As we mark the International Day of Forests on March 21, it is worth remembering that there are many reasons to appreciate forests – and that even if we never set foot in them, forests keep us all healthy.

Forests help combat the biggest threat facing us today - climate change. Forests are huge carbon sinks, containing 662 billion tonnes of carbon. That is more than half the stock of carbon in soils and vegetation around the world. They also shield us from rising heat and extreme weather events. They regulate rainfall and protect against landslides and floods.

Forests also act as a natural barrier to the spread of disease from animals to humans. As deforestation continues, this barrier is fraying. More than 30 percent of new diseases reported since 1960 have been linked to changes in land-use, including deforestation.

Our forests are also natural pharmacies. Around 50 000 plant species – many of which grow in forests – have medicinal value and are used by local communities to treat conditions from snake bite and diarrhoea to rheumatism and diabetes. But also many common pharmaceutical medicines are derived from forest plants – for example, cancer-treating drugs from the Madagascar periwinkle.

Our green spaces are the world's gift to humankind.

But our forests are under threat. Ten million hectares of forests are lost to deforestation each year.

They are also under threat from wildfires, pests and weather extremes. Fire affected approximately 98 million hectares of forest in 2015 alone. About a third of the world's tree species are reported to be at risk of dying out forever.

So what can we do to keep our forests – and ourselves – healthy?

We must take a more innovative and hands-on approach to managing forests sustainably. We need to halt deforestation, but we also need to grow new forests using species and techniques that maximise their resilience. We need forest-friendly policies in place to ensure we can feed the world population without destroying forests in the process, boosting agricultural productivity rather than expanding the land needed. And we need to increase the financial benefits of managing forests sustainably.

We must monitor natural forests and develop early warning and rapid response systems to stamp out pests and diseases faster. We must prevent the risk of wildfire before the first spark flies.

And we must support the communities, living in and near forests, to have their tenure rights over land and forest resources recognised. Often among the poorest in the world, these communities are best placed to manage our forests well.

The more urbanised our society becomes, the more we must work together, bearing in mind that we are part of nature, and that our health and well-being depends on it. We must act now to safeguard forests and ensure they remain for our own health, and that of our children and future generations.

Wu Zhimin, Director, Forestry Division, Food and Agriculture Organization of the United Nations.