Sampling and Mapping Forest Volume and Biomass Using Airborne LIDARs

—Since around 1995, extensive research efforts have been made in Scandinavia to develop airborne Light Detection and Ranging (LIDAR) as an operational tool for wall-to-wall mapping of forest stands for planning purposes. Scanning LIDAR has the ability to capture the entire three-dimensional structure of forest canopies and has therefore proved to be a very efficient technique to determine biophysical properties such as stand volume and biomass. In Norway and Sweden, airborne scanning LIDAR is now used operationally to estimate merchantable volume on forest stands remotely across areas from 50 km to 2,000 km. Complete scanning LIDAR coverage over larger regions (e.g., counties, States, provinces, and countries) is not economically feasible at this time due to data acquisition and processing costs. Despite these challenges, it has been demonstrated that airborne profiling LIDARs can provide reliable estimates of forest volume and biomass when used in a sampling mode (i.e., a number of flight lines are flown as linear, parallel transects separated by many kilometers). Scanning systems can be similarly employed for regional forest inventory by considering the flight lines as part of a strip sampling design. In this article, we report on a joint research effort by the Norwegian University of Life Sciences, National Aeronautics and Space Administration, Norwegian national forest inventory (NFI), Yale University, Swedish University of Agricultural Sciences, and Swedish NFI to develop and test airborne LIDARs as regional forest sampling tools. Background Ever since the first public Norwegian national forest inventory (NFI)—the first NFI in the world—took place 1919 through 1932, the Norwegian NFI has provided vital information of the timber resources. During its 87-year history, the NFI has produced statistics at the national and regional levels and has thus been an important prerequisite for the formation of a national policy for the management of the resources and the control of the policy’s implementation in various regions of the country. Even though the main focus of the NFI over all these years has been on the quantification of the timber resources, additional characteristics of the ecosystems have been incorporated as the society has focused on “new” aspects, such as, (e.g.,) the preservation of biodiversity, the effects of air pollution, and the forests’ role as sinks and sources for greenhouse gases. Over the years, the NFI has applied various designs of fieldbased strip and plot surveys as basic sampling models, and the sampling density has been adjusted from county to county to provide reliable estimates at national and regional (county) levels over time. Currently, the NFI is facing at least three major challenges: (1) to reduce costs by adopting remote-sensing techniques to some of the tasks in which remote sensing can provide reliable and cost-efficient estimates, (2) to provide statistical estimates of the timber resources at local scales (subcounty) to support the local public forest administration, and (3) to provide cost-efficient and reliable estimates of biomass or carbon stocks of forest and nonforest land to meet the Kyoto Protocol requirements. This third challenge includes biomass or carbon estimates of thousands of square kilometers of mountain forest above the official tree line, which is currently not part of the NFI or any other national monitoring systems. This ecotone 1 Professor, Norwegian University of Life Sciences, Department of Ecology and Natural Resource Management, P.O. Box 5003, NO-1432, Ås, Norway. E-mail: [email protected]. 2 Associate Professor, Norwegian University of Life Sciences, Department of Ecology and Natural Resource Management, P.O. Box 5003, NO-1432, Ås, Norway. E-mail: [email protected]. 3 Physical Scientist, National Aeronautics and Space Administration/Goddard Space Flight Center, Biospheric Sciences Branch, Greenbelt, MD 20771. E-mail: [email protected].