Scientists Use Google Earth and Crowdsourcing to Map Uncharted Forests
By Katie Fletcher, Tesfay Woldemariam and Fred Stolle
No single person could ever hope to count the world's trees. But a crowd of them just counted the world's drylands forests—and, in the process, charted forests never before mapped, cumulatively adding up to an area equivalent in size to the Amazon rainforest.
Current technology enables computers to automatically detect forest area through satellite data in order to adequately map most of the world's forests. But drylands, where trees are fewer and farther apart, stymied these modern methods. To measure the extent of forests in drylands, which make up more than 40 percent of land surface on Earth, researchers from UN Food and Agriculture Organization, World Resources Institute and several universities and organizations had to come up with unconventional techniques. Foremost among these was turning to residents, who contributed their expertise through local map-a-thons.
Technical Challenges, Human Solutions
Traditional remote sensing algorithms detect tree cover in a pixel rather than capturing individual trees in a landscape. That means the method can miss trees in less-dense forests or individual trees in farm fields or grasslands, which is most often the nature of dryland areas.
Google Earth collects satellite data from several satellites with a variety of resolutions and technical capacities. The dryland satellite imagery collection compiled by Google from various providers, including Digital Globe, is of particularly high quality, as desert areas have little cloud cover to obstruct the views. So while difficult for algorithms to detect non-dominant land cover, the human eye has no problem distinguishing trees in the landscapes. Using this advantage, the scientists decided to visually count trees in hundreds of thousands of high-resolution images to determine overall dryland tree cover.
Local Map-a-thons Using Collect Earth
Armed with the quality images from Google that allowed researchers to see objects as small as half a meter (about 20 inches) across, the team divided the global dryland images into 12 regions, each with a regional partner to lead the counting assessment. The regional partners in turn recruited local residents with practical knowledge of the landscape to identify content in the sample imagery. These volunteers would come together in participatory mapping workshops, known colloquially as "map-a-thons."
To lay the groundwork for the local map-a-thon events the team identified both an entry point, usually a university, that could help recruit participants, as well as a facility with the capacity and internet to host the map-a-thon. Once trained, any given analyst could identify 80 to 100 plots per day.
Example of Collect Earth grid set for data collection.
Quality control was carried out afterwards by comparing the identified land cover with the number of trees counted. For example, if a local participant identified an image as having just three trees but later identified the same image as forest, the researchers knew there was human error and further review was required.
The Collect Earth tool allows users to navigate between multiple windows and select the best imagery for each particular data point.
These map-a-thons were designed so that people with first-hand knowledge of local landscapes could participate. No knowledge of remote sensing or any technology beyond internet literacy was required. The expertise needed was the understanding of regional landscape and land use. This practical knowledge of the region was critical as the participants were not only able to count individual trees but also identify the type of land use and trees they saw on the Google Earth images.
This research only "discovered" new forest in the sense that Columbus "discovered" the New World. The drylands forest was always there, and the people who live in the area always knew it was there. In fact, they were the only ones who had the background knowledge to identify subtleties like whether an image of a plant in their region was a shrub or actually a young tree, or if what appeared to be a tree was just a perennial plant. A few common perennial crops, including coffee and banana, looked like shrubs in the satellite images, but local participants had no problem identifying them correctly as perennial crops instead of shrubs, a distinction that would have been impossible with satellite imagery analysis alone.
Collect Earth Map-a-thon Event in Gatsibo, Rwanda.
This human identification component, along with the ability to zoom into sub-meter resolution with cheap and available technology, has helped achieve the breakthrough result of forest cover identification 9 percent higher than previously reported.
Local Ownership of the Map and the Land
Utilizing local landscape knowledge not only improved the map quality but also created a sense of ownership within each region. The map-a-thon participants have access to the open source tools and can now use these data and results to better engage around land use changes in their communities. Local experts, including forestry offices, can also use this easily accessible application to continue monitoring in the future.
Global Forest Watch uses medium resolution satellites (30 meters or about 89 feet) and sophisticated algorithms to detect near-real time deforestation in densely forested area. The dryland tree cover maps complement Global Forest Watch by providing the capability to monitor non-dominant tree cover and small-scale, slower-moving events like degradation and restoration. Mapping forest change at this level of detail is critical both for guiding land decisions and enabling government and business actors to demonstrate their pledges are being fulfilled, even over short periods of time.
The data documented by local participants will enable scientists to do many more analyses on both natural and man-made land changes including settlements, erosion features and roads. Mapping the tree cover in drylands is just the beginning.
- Redwoods are the world's tallest trees.
- Now scientists have discovered they are even bigger than we thought.
- Using laser technology they map the 80-meter giants.
- Trees are a key plank in the fight against climate change.
They are among the largest trees in the world, descendants of forests where dinosaurs roamed.
Pixabay / Simi Luft<p><span>Until recently, measuring these trees meant scaling their 80 meter high trunks with a tape measure. Now, a team of scientists from University College London and the University of Maryland uses advanced laser scanning, to create 3D maps and calculate the total mass.</span></p><p>The results are striking: suggesting the trees <a href="https://www.nature.com/articles/s41598-020-73733-6" target="_blank" rel="noopener noreferrer">may be as much as 30% larger than earlier measurements suggested.</a> Part of that could be due to the additional trunks the Redwoods can grow as they age, <a href="https://www.nature.com/articles/s41598-020-73733-6" target="_blank" rel="noopener noreferrer">a process known as reiteration</a>.</p>
New 3D measurements of large redwood trees for biomass and structure. Nature / UCL<p>Measuring the trees more accurately is important because carbon capture will probably play a key role in the battle against climate change. Forest <a href="https://www.wri.org/blog/2020/09/carbon-sequestration-natural-forest-regrowth" target="_blank">growth could absorb billions of tons</a> of carbon dioxide from the atmosphere each year.</p><p>"The importance of big trees is widely-recognised in terms of carbon storage, demographics and impact on their surrounding ecosystems," the authors wrote<a href="https://www.nature.com/articles/s41598-020-73733-6" target="_blank"> in the journal Nature</a>. "Unfortunately the importance of big trees is in direct proportion to the difficulty of measuring them."</p><p>Redwoods are so long lived because of their ability to <a href="https://www.nature.com/articles/s41598-020-73733-6" target="_blank" rel="noopener noreferrer">cope with climate change, resist disease and even survive fire damage</a>, the scientists say. Almost a fifth of their volume may be bark, which helps protect them.</p>
Carbon Capture Champions<p><span>Earlier research by scientists at Humboldt University and the University of Washington found that </span><a href="https://www.sciencedirect.com/science/article/pii/S0378112716302584" target="_blank" rel="noopener noreferrer">Redwood forests store almost 2,600 tonnes of carbon per hectare</a><span>, their bark alone containing more carbon than any other neighboring species.</span></p><p>While the importance of trees in fighting climate change is widely accepted, not all species enjoy the same protection as California's coastal Redwoods. In 2019 the world lost the equivalent of <a href="https://www.worldwildlife.org/threats/deforestation-and-forest-degradation" target="_blank" rel="noopener noreferrer">30 soccer fields of forest cover every minute</a>, due to agricultural expansion, logging and fires, according to The Worldwide Fund for Nature (WWF).</p>
Pixabay<p>Although <a href="https://c402277.ssl.cf1.rackcdn.com/publications/1420/files/original/Deforestation_fronts_-_drivers_and_responses_in_a_changing_world_-_full_report_%281%29.pdf?1610810475" target="_blank" rel="noopener noreferrer">the rate of loss is reported to have slowed in recent years</a>, reforesting the world to help stem climate change is a massive task.</p><p><span>That's why the World Economic Forum launched the Trillion Trees Challenge (</span><a href="https://www.1t.org/" target="_blank" rel="noopener noreferrer">1t.org</a><span>) and is engaging organizations and individuals across the globe through its </span><a href="https://uplink.weforum.org/uplink/s/uplink-issue/a002o00000vOf09AAC/trillion-trees" target="_blank" rel="noopener noreferrer">Uplink innovation crowdsourcing platform</a><span> to support the project.</span></p><p>That's backed up by research led by ETH Zurich/Crowther Lab showing there's potential to restore tree coverage across 2.2 billion acres of degraded land.</p><p>"Forests are critical to the health of the planet," according to <a href="https://www.1t.org/" target="_blank" rel="noopener noreferrer">1t.org</a>. "They sequester carbon, regulate global temperatures and freshwater flows, recharge groundwater, anchor fertile soil and act as flood barriers."</p><p><em data-redactor-tag="em" data-verified="redactor">Reposted with permission from the </em><span><em data-redactor-tag="em" data-verified="redactor"><a href="https://www.weforum.org/agenda/2021/03/redwoods-store-more-co2-and-are-more-enormous-than-we-thought/" target="_blank">World Economic Forum</a>.</em></span></p>
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