21 August 2013
The unique attribute of forest carbon, a forester would say, is that the value stays on the stump. The value, and tons of each tree, will never be known exactly, as it would if the tree were cut and hauled off to a scale in a mill. Consequently, the accurate estimation of carbon stocks “left in the forest” is a critical element to forest carbon monitoring, reporting and verification (MRV) at any scale, whether for stand-alone projects or jurisdictional REDD+ programs.
Fortunately, the estimation of forest carbon today draws on the long tradition of forest measurement that stretches back literally hundreds of years. Perhaps one of the first “spreadsheets” from a timber cruise dates to 1804 when James Mitchell compiled measurements from a 25 acre beech grove in Stanstead, England (published in his 1827 Dendrologia). The practice of forest measurement underwent a revolution in the mid-20th century with the application of sampling and statistics, and development of ingenious sampling methods pioneered by Walther Bitterlich and Lew Grosenbaugh. These latter developments made way for the use of prisms and relascopes that essentially sample trees with a controlled bias to target measurements to the most influential elements of a tree population.
These developments, particularly the vast improvements in accuracy and efficiency they offered, did not go unnoticed. Today’s forest measurement practices have been validated and refined by over 50 years of continual application by timber industry, government agencies and forest researchers, and throughout their evolution, the guiding principles have been efficiency and accuracy.
The practice of forest inventory has further evolved with the development and application of mapping technologies, with the adoption of orthophotos in the 1960s and GIS and GPS in the 1990s. More recently, high resolution satellite imagery, LiDAR and radar are offering potential to not only better map forests but also to improve the efficiency of field data collection. Forest inventory is most accurately conceived of as a collection of procedures and technologies that encompass a system, and in that context these new remote sensing technologies in development hold promise to complement, but not replace, “traditional” field measurement practices.
A well-designed forest inventory tailors sampling and measurement procedures and technologies to the particular circumstances and objectives for the area of interest. There is no “one-size-fits-all” design, and professional experience and knowledge of the wealth of available options are critical. Fixed or variable radius plots? Systematic or random sampling? Cluster samples or two stage samples? Stratification? Permanent or temporary plots? Sub-sampling or double sampling routines for some attributes? How big should the plots be? How many plots? What forest carbon pools to measure? An effective forest inventory design considers and responds to reporting needs, resource constraints, the abilities and experience of available field crews, logistics and access, stem structures and forest heterogeneity, as well as intangibles like culture and preconceptions.
Monitoring, reporting and verification of forest carbon draws on decades, even centuries, of experience in forest measurement. While perhaps forest inventory can’t be called “rocket science”, it’s grounded in a rich history of innovation, refinement and validation that serves today to deliver reliable values that can be left on the stump.
David is TerraCarbon’s Director of Forestry and Technical Services, and is approaching twenty years working in forest inventory.