Riparian zones provide a host of important ecosystem services related to water quality, stream bank integrity, wildlife habitat, and instream inputs of energy and woody debris (Gregory et al., 1991). Because of the combination of abundant resources and frequent disturbance, riparian forests support fast-growing trees that accumulate biomass quickly, both in live and dead pools that include standing trees, roots and soil (Van Pelt et al., 2006; Stella et al., 2012; Matzek et al., 2014). Riparian forests therefore constitute a potentially substantial carbon sink, especially in water-limited regions where grasslands or other non-forest vegetation types predominate. However, because it occupies comparatively little land area compared to forests traditionally exploited for timber, this forest carbon sink has been virtually ignored by foresters and by policymakers, and the impact of river management strategies on its size and dynamics is largely unknown.
In this proposed work, we seek to fill in the knowledge gap between our current understanding of forest dynamics in the Rhône fluvial corridor, and the development of a new paradigm for management of the Rhône that incorporates payment for ecosystem services, by characterizing the carbon stocks of naturally regenerated riparian forests (Gruel, 2014). We profit from our previous riparian forest inventory, undertaken in 2014 with the support of OHM-VR, which was intended to determine how natural forest regeneration was responding to current and historical regime changes. In that inventory of 88 plots (distributed along the four sectors of Pierre-Bénite, Péage de Roussillon, Donzère-Mondragon, and Montélimar), we measured the density and basal area of live and standing dead trees, along with the density and volume of coarse woody debris (Figure 2). Now, we request a small additional investment in fieldwork and data analysis that will allow us to calculate the carbon stocks in our inventory plots, scale the analysis to the whole river from Lyon to the Mediterranean, and provide the impetus for developing an accurate methodology to estimate carbon credits resulting from current and future management actions.