A question from a Permaculture Design Course student came in the other day:
Does anyone have some quick reference to equivalent measures of green house gas reductions per tree? Especially for the urban context?
Basically biomass equations are often used to estimate the amount of carbon a tree can sequester at any given size which often increases with age to a certain peak. The equations are derived from humans actually harvesting and weighing real trees by species, in numerous studies. Scientists literally cut up a tree, weigh it, combust the carbon and weigh it again. br It’s obviously a lot of work. So, for north America, there is fairly good data by species already in existence. All one needs to do is look up the species in a table (U.S. Forest Service’s national Forest Inventory and Analysis data set is commonly used for the US) and make some conversions to CO2 equivalents from biomass tons/ac to get a general idea of how much carbon a certain tree may be sequestering. Here’s a slideshow from Winrock International on the subject of soil carbon sequestration.
Remember most of science is a compilation of statistics, and there is no real way to know exactly what is going on in a complex ecological system, only our best attempts to use good scientific methods to get as close an approximation as possible with given technology and resources.
In the tropics, there are many more species so it can be more difficult to find a biomass equation so you may have to do the initial ground work as well, but starting with a good search of existing research is a good place to start (try searching for biomass equations in http://www.googlescholar.com).
One of the equations I’ve used is called the Jenkins equation, but there are many, and they give you different results. That’s science for you. For developing carbon projects where you are looking to sell carbon credits, the general good practice is to use a conservative estimate, then actually do your own baseline and long term monitoring – this gives you a better idea how much carbon you actually have on your site, and that is the number you ultimately use to sell the carbon you’ve sequestered, depending on the agreement you’ve reached with your buyer (this ends up being a cost/bennefit analysis – the estimates with the biomass equations help you determine how much carbon you may have to sell, if it’s a lot, then you assess if the monitoring study costs will be adequately covered to make them worth your while rather than using a more conservative estimate using a biomass equation, etc.)
Here are some good links: http://www.nasa.gov/centers/ames/news/features/2009/Trees.html – a general description of new remote sensing methods to determine carbon
http://files.harc.edu/Sites/HoustonRegionalForest/Events/CarbonWorkshop/ScienceWinrockInternational.pdf – a powerpoint that describes the science behind carbon sequestration
http://www.fs.fed.us/ccrc/topics/urban-forests/docs/construct%20WBE%20gen%20equations%20gtr_nc230_096.pdf – comparison of some biomass equations for US species
Here are a couple of references which will have even more references cited (first one includes a couple of authors who won a nobel prize for their carbon science work):
Brown Sandra, David Shoch, Tim Pearson and Matt Delaney 2004. “Methods for Measuring and Monitoring Forest Carbon Projects in CA.” Winrock International: Arlington VA, for the Regents of California/ California Institute of Energy Efficiency.
Halpern, Charles B, Miller, Eric A., Geyer, Melora A. 1996. Equations for predicting aboveground biomass of plant species in early successional forest of the western Cascade Ranges, Oregon. Northwest Science. 70(4): 306-320
Carbon Farming 