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Contributed Talk

Session: : Biogeochemistry: New Paradigms In Biogeochem Cycling 3

COS 52-2 - Decoupling of biomass accumulation and gross primary productivity in a Madrean sky island forest

Tuesday, August 8, 2023
8:15 AM – 8:30 AM PDT
Location: B115
Abstract: Measurements of tree-ring width are often invoked as a proxy of forest productivity. However, trees have multiple pools where photosynthates may be allocated including structural biomass, root development, maintenance, and new leaves/needles. Here we assess how well the assumption that ring width is a viable proxy of productivity holds true in a montane ecosystem in southeastern Arizona. We reconstructed Gross Primary Productivity (GPP) using high-resolution C13/C12 measurements from tree-ring cellulose and a physiological modelling approach as well as sapflow and xylogenesis data. Our study site also hosts an eddy-covariance flux tower which we compare our estimates of GPP to and find that our method tracks the intra annual dynamics of carbon sequestration as estimated by the tower. We find that estimates of ring-width index do not match estimates of growing season GPP. In years where ring-width index would suggest high productivity, i.e., larger rings, we find smaller magnitudes of GPP compared to some years with smaller rings. This decoupling of biomass accumulation and productivity has large implications within carbon cycle modelling where tree rings have increasingly been used to estimate forest productivity. Our approach using tree-ring cellulose to reconstruct GPP represents a step forward for evaluating long-term forest carbon dynamics.