MAIDENiso: A multiproxy biophysical model of tree-ring width and oxygen and carbon isotopes

Abstract

MAIDENiso is a new version of the process-based biogeochemical model MAIDEN of tree growth. Isotopic modules have been implemented to simulate stable oxygen and carbon isotopes in tree-ring cellulose (TRC). In addition to annual increment biomass, this new model version estimates δ 18O and d 13C associated with the daily amount of carbon allocated to the stem. MAIDENiso only requires daily input data: minimal and maximal air temperatures, amount of precipitation, CO2 atmospheric concentration, and δ 13C in CO 2. MAIDENiso simulates tree-ring width, d 18O in precipitation (δ 18OP), δ 18O in soil water (δ 18OSW), δ 18O in xylem water (δ 18OXW), δ 18O in cellulose (δ 18OTRC), and δ 13C in cellulose (δ 13CTRC). The model has been calibrated and validated with tree-ring series sampled in the Fontainebleau Forest (France) from 1953 to 2000. We first calibrated several parameters for the 1977-2000 period and then validated it for the independent 1953-1976 period. Over the complete interval (1953-2000), we obtained correlations between observations and simulations above 0.5 for both isotopic series and above 0.65 for tree growth series. An important feature of the model is its ability to simulate not only extreme values of tree growth, such as the effect of 1976 drought, but also its persistence over several years.