Quantification of carbon sequestration by riparian restoration projects in California: Scientific and policy considerations

<b>Background/Question/Methods <p> </b>Under California's cap-and-trade system for greenhouse gases (GHG), revenues from auctioning off GHG emissions allowances must be spent on reducing emissions in the state, and these emissions reductions must be quantified rigorously. The state's Department of Conservation desires to fund restoration projects on agricultural land as part of its commitment to preserving open space and wildlife habitat, using monies from the Greenhouse Gas Reduction Fund. Accordingly, there was a need for a quantification methodology that could account for GHG emissions reductions associated with the restoration of rivers and streams in agricultural regions of the North Coast, Sierra foothills, and Central Valley of California. I used data from published and unpublished studies of biomass accumulation in riparian restoration projects to parameterize the Forest Vegetation Simulator, a model widely used to predict changes to forest yields. Then, using actual project plans from conservation organizations and consulting firms, I created hypothetical planting schemes typical of restoration projects in the state to generate yield tables for a range of potential projects. <p><b>Results/Conclusions <p> </b>The carbon density of restored forests 30 years after project initiation varied according to the proportion of non-canopy shrubs in the planting mix, planting density, and climate. Other considerations in developing the quantification methodology included dealing with potential changes to grazing pressure, increase in the size of riparian wetlands, and intentional removal of carbon stocks in invasive species biomass. Ultimately, in order to encourage habitat quality and discourage perverse outcomes, counsel was given to the Department of Conservation to avoid tying approval of habitat projects directly to the quantity of carbon sequestered.