GLOBAL TREES:IMAGING THE WORLD'S FORESTS

How many trees are there on Planet Earth?

A widely accepted previous estimate, based on analysis of satellite data, put the world's tree population at about 400 billion. 

The latest study by an international team of scientists, published in September 2016, makes that figure 3 trillion trees. This figure is more reliable because it combines satellite data with 'ground truth.'
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The scientists first collected together existing ground tree-counting surveys for every continent except Antarctica, covering a total area of about 430,000 hectares. This enabled them to improve the tree-density estimates from satellite imagery of those same areas. It also allowed them to apply tree-density estimates to remote areas that have not been inventoried on the ground.


The study shows that the highest tree densities were found in the boreal forests of North America, Scandinavia and Russia. These are tightly packed with skinny conifers and hold roughly 750 billion trees, 24% of the global total. Tropical and subtropical forests, with the greatest area of forested land, are home to 1.3 trillion trees, or 43% of the total.

Humans have had an astonishing impact on the tree cover of the Earth. Researchers estimate that, since the onset of agriculture 12,000 years ago, we have reduced the number of trees worldwide by 46%.

Currently we are cutting down about 15 billion trees a year.


Source: 'Global count reaches 3 trillion trees' - Rachel Ehrenberg [Nature/02 September 2015

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FOREST SENTRIES

In a more recent Nature story, they profile the work of Matthew Hansen described as one of 'the world's foremost forest sentries', spotting deforestation as it's happening.

 'In 2013, he and his colleagues used satellite data to produce the first global, high-resolution maps of where trees are growing and disappearing. Those images revealed some large-scale patterns for the first time, such as that Indonesia had nearly equalled Brazil as the country with the world's highest rate of tropical deforestation. Since then, his team has refined its methods and can now reveal the loss of trees within days.

'Just as important is what Hansen does with the underlying data. Unlike some scientists, he makes them freely available online, giving activists, companies and others the ability to monitor activities such as illegal logging and mining, which have destroyed millions of hectares of forest per year over the past few decades. The data have enabled non-governmental organizations (NGOs) and officials in Peru, Congo and other nations to see deforestation as it happens. And they let countries monitor each other's trees — potentially a crucial step in enforcing the international climate agreement signed in Paris last December.'

Source: 'Warning to forest destroyers: this scientist will catch you' - Gabriel Popkin [Nature/ 04 October 2016]. 

See also: 'Satellite alerts track deforestation in real time' - Gabriel Popkin [Nature/ 23 February 2016]. 

The Global Land Analysis and Discovery (GLAD) laboratory in the Department of Geographical Sciences at the University of Maryland is led by Drs. Matthew Hansen and Peter Potapov.

One of their current high-profile projects is a collaboration with the World Resources Institute, creating operational global data on forest extent and change, part of the Global Forest Watch initiative http://www.globalforestwatch.org/ .

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SPACE LASER FOREST SURVEY

GEDI, a NASA Earth-observing system set to go on the International Space Station in 2018, will enable the government to understand the architecture of forests, as this 3-D rendering depicts. By fully analyzing the structure of forests, researchers will be able to more accurately measure the amount of carbon they store. Photo courtesy of NASA.

'In 2018, America's space agency, in collaboration with the University of Maryland, is going to send a laser into the galaxies to assess the world's trees. 

It won't be the first time NASA dabbles in lidar technology -- shooting lasers onto things and recording what comes back -- but it will be the first time the agency sends a laser specifically designed to measure the intricate structure of forests.

The goal of the mission, fittingly named GEDI, an acronym for Global Ecosystem Dynamics Investigation lidar, is to map forests trunk to canopy -- or, to put it another way, to measure the volume of the world's forests and visualize them in 3-D.

By combining data on how much carbon is stored in wood with GEDI measurements, researchers are hoping to compile a solid estimate of the carbon stored in forests for the first time.

"It will absolutely be a game changer," said Laura Duncanson, a postdoctoral fellow at NASA's Goddard Space Flight Center who works on the GEDI team. "Lidar is the only technology that can penetrate the forest floor and estimate carbon."

Globally, forests are estimated to suck up between 10 and 14 percent of current gross emissions. The activities of the land-use sector, which includes forests but also agriculture and land-use changes, account for about 24 percent of global greenhouse gas emissions. Many researchers who tally emissions have conceded that the world has little chance of keeping warming below the agreed 2-degree-Celsius threshold without the carbon sequestration of forests.

But not all forests are created equal in their carbon-storing abilities. Furthermore, as forest-rich nations consider how to meet their climate goals set forth at the Paris climate talks late last year, understanding where and how carbon is being stored in their trees will become increasingly important.

GEDI, many hope, will unlock the next frontier of forest and carbon mapping.'

Source: 'Seeing the trees in 3-D, a 'game changer' for forest policy' - Brittany Patterson, E&E News reporter/ ClimateWire: Tuesday, March 8, 2016.

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BRAZIL DEFORESTATION RISES

The Global Forest Watch interface showing Amazonian forest losses in 2014
Source: 'Earth Engine Creates A Living Map of Forest Loss'
https://www.google.com/green/projects/forest-watch/

'Illegal deforestation in the Brazilian Amazon has spiked since 2015, bringing the rate to its highest level in 8 years. The finding has raised fears that the country could lose a decade’s worth of progress in forest protection. 

In an analysis of satellite data released on 29 November, Brazil’s National Institute for Space Research (INPE) in São José dos Campos estimates that 7,989 square kilometres of land — nearly the size of Puerto Rico — was cleared between August 2015 and July 2016. The total was 29% above the previous year and 75% above the 2012 level, when deforestation hit a historic low of 4,571 square kilometres (see ‘Going up’).

Brazil basked in the international limelight for nearly a decade after deforestation began to drop in 2005, thanks in part to stronger government enforcement as well as high-profile commitments to halt deforestation by the beef and soya-bean industries. But the government’s success sparked a political backlash. The Brazilian Congress relaxed the country’s forest protections in 2012, and many Brazilian lawmakers are pushing to further relax environmental laws to promote development across the Amazon.'

Source: 'Deforestation spikes in Brazilian Amazon' - Jeff Tollefson [Nature /30 November 2016]