New research from the University College London (UCL) demonstrates the first application of laser technology for the measurement of volume and biomass of giant trees - used in the great Californian redwoods in this case.
"Large trees are disproportionately important in terms of their above-ground biomass (AGB) and carbon storage, as well as their wider impact on ecosystem structure," said Mat Disney, lead author of the study from the geography department at UCL. He also noted that these are difficult to measure, leading them to remain underrepresented in measurements and AGB model generations.
The groundbreaking technology is detailed in their report, published in the journal Scientific Reports, illustrating the 3D structure of trees and helping researchers better understand the AGB and carbon storage volumes of these giant trees.
3D Terrestrial Laser Scanning
Researchers show the first detailed 3D terrestrial laser scanning (TLS) estimates of the AGB of large coastal redwoods from three different locations in Northern California. Observing Sequoia sempervirens trees yielded TLS estimates that are accurate to within 2 percent AGB, using species-specific model researchers based on manual crown mapping of these redwoods' 3D structure.
"Big questions within climate science in response to rising CO2 levels are whether and where more trees should be planted and how best to conserve existing forests," said Professor Disney in a press release. He added that to answer those questions, scientists first have to understand the volume of carbon stored across different species of trees.
The UCL team worked with their colleagues at NASA through the space administration's Carbon Monitoring System program. Researchers at the site used ground-based laser measurements to generate a 3D mapping of the redwood trees. NASA, on the other hand, uses its latest Global Ecosystem Dynamics Investigation (GEDI) mission to help map forest carbon footprints from Earth's orbit. Furthermore, NASA's GEDI team takes the UCL study as input toward improving their own models.
Revolutionizing Ecological Studies
Even before the use of laser technology by the UCL researchers, estimating the size and mass of giant trees like the Californian redwoods has been especially challenging. These trees could only be weighed by cutting the giant trees, or by indirect techniques like remote sensing or making scaled extrapolation of manual data measurements like trunk diameter. Unfortunately, conventional measurement techniques are prone to large margins of error.
Among the scanned specimens in the study led by Professor Disney include the Colonel Armstrong Tree: an 88-meter tall tree with a diameter-at-breast height of about 3.39 meters, or more than 11 feet. The oldest tree in the Armstrong Redwoods State Natural Reserve was estimated to weigh around 110 tons or about 10 double-decker buses.
Researchers behind the TLS study compared their estimates with other techniques, discovering that their measured values agree with 3D crown mapping - a method first pioneered by American botanist and old-growth specialist Stephen C. Sillett, requiring expert climbers to scale big trees and manually take measurements.
"Estimating the biomass of large trees is critical to quantifying their importance to the carbon cycle, particularly in Earth's most carbon-rich forests," said Laura Duncanson, a co-author in the study from NASA Earth Sciences and the University of Maryland.
"This exciting proof of concept study demonstrates the potential for using this new technology on giant trees," Duncanson added.
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