Researchers at the Carnegie Institution for Science, in Washington DC, have rolled out their latest carbon-counting methodology in partnership with Colombian scientists, mapping carbon stocks across 40% of the Colombian Amazon using a method that relies almost entirely on airborne and satellite observations.
Led by Greg Asner, a remote-sensing expert in Carnegie’s Department of Global Ecology in Stanford, California, the team combined a sophisticated analysis of run-of-the-mill satellite data with an advanced aerial laser system to quickly assess vast swaths of tropical forests. In this particular study, published in the journal Biogeosciences, the team documented some 1.5 billion tonnes of carbon across an area that is roughly four times the size of Switzerland.
As discussed in a 2009 feature (‘Counting Carbon in the Amazon’), Asner continues to work with tropical countries to deploy Carnegie’s free software for monitoring deforestation as well as forest degradation. A separate aerial system known as LiDAR (Light Detection and Ranging) essentially blasts the forest with laser pulses and then analyses the return signal to build a three-dimensional map of the forest structure (for a high-resolution version of the image at top right, click here; the colours indicate spectronomic data that are geared towards separate biodiversity research). When combined, the two systems can be used to rapidly estimate carbon stocks, which is what the Carnegie team did in its partnership with the Colombian government.
Whereas the original system relied on a network of ground plots for calibration of the detailed aerial laser measurements and the regional satellite data, Asner’s crew has since analysed ground plots throughout the tropics to develop an independent calibration that can be applied anywhere. The new system is based mainly on topographical data from a detailed radar survey conducted in 2000 by NASA’s Space Shuttle Endeavor as well as minimal ground measurements of wood density and the diameter of tree trunks. Overall, the team calculated the uncertainty for the LiDAR-based carbon maps at 14%, based on a resolution of 1 hectare, and the larger regional map carries an uncertainty of 28% in any given hectare.
Despite the diversity of tropical rainforests, the relationship between biomass and the structure of the forest measured by the LiDAR is generally consistent through different forest types and soil conditions, Asner says. This frees the team from expensive and time-consuming ground plots as well as questionable (or non-existent) vegetation maps, he says. “We are reducing the role of field plots to validation rather than calibration.”
Asner’s goal has been to help tropical countries monitor their forests and participate in an international system that provides funding for countries that can demonstrate a reduction in deforestation (and, consequently, carbon emissions). That system has been slow to develop, but he says that countries such as Peru and Colombia are still aggressively deploying the technology. Just in case there was any doubt in this particular case, Carnegie’s news release quoted none other than the president of Colombia.
“We celebrate a true collaboration that not only advances science and human knowledge, but also builds our national scientific capacity,” said President Juan Manuel Santos Calderón. “In a continuing partnership with Carnegie we aim at becoming world leaders in the use of state-of-the-art science and technology for environmental monitoring that can inform our decision making and planning efforts for managing and protecting our precious natural resources.”
Photo Credit: Carnegie Airborne Observatory