More forest than previously thought

A research term led by the UN food organisation has discovered significantly more forest in drylands. Hiding in plain sight, detailed satellite data suggests that the global forest cover is at least nine per cent higher than previously thought. Elke Bunge reports.

An international team of researchers have discovered there is around 9 per cent more forest on Earth than previously thought. As forests are an important carbon sink, the study’s results are important for climate modelling. (Image credit: Jean-Paul Gaillard, flickr/Creative Commons)

Good news for a change from the field of ecology: there is more forest on Earth after all. An international research team working under the UN Food and Agriculture Organization (FAO) analysed satellite data for more than 200,000 plots of land and discovered that there is around nine per cent more forest cover on Earth that previously thought. Their findings were published in the latest issue of Science.

“The methods used so far to estimate forest cover by means of aerial photographs and satellite surveys were insufficient,” said study co-author Jean-François Bastin.

A researcher at the Free University of Brussels and FAO consultant, he pointed out that especially in drylands around the world, vegetation forms exist that are difficult to capture with previous imaging techniques.

Satellites can’t see the woods for the trees

For example, acacia woodlands in Australia or baobabs in the savannah of sub-Saharan Africa were not represented by previous satellite imagery as the trees do not cast a strong enough shadow for them to be captured in the photographs.

“First, the vegetation is quite sparse, so the signal is often a mix between vegetation and non-vegetation, like soil or even tree shadow,” explained Bastin. “Second, the vegetation in drylands is quite particular. To adapt to arid conditions, and therefore limit evapotranspiration, trees are leafless most of the year which makes it difficult to detect with classic mapping approaches.”

Remarkable observations

The team of researchers – consisting of experts from all continents – analysed satellite data from Google Earth that captured more than 200,000 plots of land, each no larger than half a hectare, from around the globe. This size selection was on purpose as it corresponds to the FOA definition of forest: at least 10 per cent of a land area of half a hectare has to be covered by trees if it is to be considered a forest.

Using these criteria, the scientists studied the drylands of Australia, Africa, Eastern Europe, the Siberian steppes, as well as the prairies of North American and the grasslands of South America. They made remarkable observations.

40-47% more forest

Drylands make up around two-fifths of the Earth’s surface area. But until now there was little information about their forest cover. By analysing the extensive data sets, the scientists have now been able to establish that there is around 40 to 47 per cent more forest cover in the Earth’s drylands than previous models had indicated.

This corresponds to an additional forest cover of 467 million hectares.

In Africa, the researchers even found around eight times more forest than what had been previously thought.

“Our projections show that there is up to 10 per cent more forested areas (5,055 million hectares instead of 4,628 million hectares) and up to 11 per cent more contiguous forest (4,357 million hectares instead of 3,890 million hectares),” said Bastin.

Discovery helps against climate change

“Our discovery can help us better understand how the global carbon cycle works” said Bastin on one of the practical implications of the study.

Trees absorb carbon dioxide from the atmosphere. If there is more forest on Earth, then it means more carbon dioxide is being stored in these massive carbon sinks than had previously been thought.

“But it also shows the importance of maintaining forest cover, especially in poorer regions, if we are to succeed in the fight against climate change,” concluded the FAO research team.

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