Abstract& Key message A climate-sensitive aboveground biomass (AGB) equation, in combination with nonlinear mixedeffects modeling and dummy variable approach, was developed to examine how climate change may affect the allometric relationships between tree diameter and biomass. We showed that such changes in allometry need to be taken into account for estimating tree AGB in Masson pine. & Context As a native species and being widely distributed in subtropical China, Masson pine (Pinus massoniana Lamb.) forests play a pivotal role in maintaining forest ecosystem functions and mitigation of carbon concentration increase at the atmosphere. Traditional biomass allometric equations do not account for a potential effect of climate on the diameterbiomass relationships. The amplitude of such an effect remains poorly documented. & Aims We presented a novel method for detecting the longterm (2041-2080) effects of climate change on the diameterbiomass relationships and the potential consequences for long-term changes of biomass accumulation for Masson pine. & Methods Our approach was based on a climate-sensitive AGB model developed using a combined nonlinear mixedeffects model and dummy variable approach. Various climaterelated variables were evaluated for their contributions to model improvement. Heteroscedasticity was accounted for by three residual variance functions: exponential function, power function, and constant plus function. & Results The results showed that diameter at breast height, together with the long-term average of growing season temperature, total growing season precipitation, mean temperature of wettest quarter, and precipitation of wettest quarter, had significant effects on values of AGB. Excessive rain during the growing season and high mean temperature in the wettest quarter reduced the AGB, while a warm growing season and abundant precipitation in the wettest quarter increased the AGB.