Climate change is intimately linked with carbon sinks – natural and artificial reservoirs that sequester carbon dioxide from the atmosphere. Measuring the extent of global carbon stocks is key to better management of current resources and to mitigating further climate change. Gregory Asner from the Carnegie Institution for Science, USA and colleagues combine several techniques, including airborne LiDAR (Light Detection and Ranging) to measure the carbon stocks stored in Panama’s tropical vegetation. Asner discusses the advances they’ve made in accurately mapping carbon reserves, as published in a recent study in Carbon Balance and Management, and suggests the potential impact these developments may have.
What led to your interest in ecological research and in particular airborne and satellite mapping?
I’ve been an ecologist for 20 years, coming into my field originally from the ground-based perspective interested in biodiversity, invasive species, and ecosystem function. However, throughout this period, I have also recognized and quantitatively documented the often extreme bias associated with ground-based measurements and observations. To address these issues, I have combined field, airborne and satellite approaches in ways that hopefully allow us to not only ’scale up‘ to larger geographic areas, but also to obtain measurements that simply could never be acquired in the field alone. The airborne technology that my team and I have developed actually can deliver quantitative information on vegetation structure and chemistry that cannot be obtained on the ground, at any scale, even in a field plot.
How have carbon stocks been traditionally measured?
Traditionally, carbon stocks have been estimated in the field using tape measures and wood samples. We measure the diameters and heights of the trees, take wood samples for density analysis, and then apply allometric equations to estimate the carbon stock of a forest. It is a crude process even with the very best field techniques and allometric equations. This approach, while in extremely widespread use worldwide, has inherent errors of sometimes 20 percent or more, even under the best conditions.
What is LiDAR and how does it work?
LiDAR stands for Light Detection and Ranging. It is a technology that uses emitted laser pulses to measure the time, and thus the distance, between objects. We can adjust the wavelength of the lasers so that they penetrate the forest canopy from above, allowing us to measure the height of the vegetation as well as the vertical partitioning of the foliage within the canopy.
Why is it useful to integrate LiDAR estimates with field inventory plots?
Certain types of airborne LiDAR, such as the Carnegie Airborne Observatory system, allow us to very precisely measure the height of the forest canopy and also the vertical partitioning of the foliage and other elements like branch architecture. We have developed scientific methods using these canopy structural measurements as stand-ins for the types of measurements we traditionally make in field inventory plots. From these, we can easily scale up from plots to larger landscapes and regional levels.
Why did you choose to test your method on carbon stocks in Panama?
We’ve been developing and testing our approach in many regions of the world, including Hawaii, California, Madagascar, South Africa, Costa Rica and throughout the Amazon basin. However, Panama offered two new and unique opportunities to apply our latest, improved carbon mapping methodology. First, Panama presented us with a chance to do an entire nation. That alone is a powerful statement in the context of carbon and resource policy development as well as climate change mitigation activities. Second, Panama hosts the Smithsonian Tropical Research Institute’s field plot network, which offered us a chance to test the accuracy of our airborne and satellite mapping methods.
How do you think your findings could impact policy for climate change mitigation programs?
The Panama project is the first in the world to provide proper estimates of uncertainty for measurements taken in high-resolution, nationwide carbon mapping. No other project has done so. The errors are quite low – 10-20 percent in any given hectare (2.5 acres) of land, which is the critical scale and threshold of uncertainty needed for policy-makers to ‘make deals’ based on carbon stock measurements for the use of forests to sequester carbon from our atmosphere – thereby reducing our climate change footprint worldwide. This is the critical scientific contribution to their process. Panama proved that it can be done.
What other applications do you predict high-fidelity carbon mapping will have in the future?
As ecologists, we know that vegetation carbon stock is an expression of a huge range of processes ranging from evolution to land use change. By mapping and monitoring the carbon locked up in and/or released from vegetation, we can understand the biogeography of plant communities, the role of natural disturbances in mediating the flow of carbon, nutrients and water in ecosystems, the role of humans in managing ecosystems, the impact of policy decisions on natural resources, and much more. Carbon is a keys component of all ecosystems and their functions.
What’s next for your research?
I am currently mapping the biomass and the biodiversity of the Western Amazon. I plan to reveal it over the next few years in ultra-high fidelity. I hope it will inspire everyone, from presidents to preschoolers, to think about 3.5 billion years of evolution leading to the most amazing ecoregion on our planet.