Carbon Dynamics of Montane Native Hawaiian Rainforests Under Climate Change: Empirical and Modeling Studies

Recent studies (e.g., Giambelluca et al., 2008) have shown that Hawaiian montane air temperature has increased over 0.8 degree C in the past three decades, with the most pronounced increases observed in minimum nighttime temperatures and a decrease in the amplitude of the diurnal temperature cycle. Yet the effects of such changes on Hawaiian Ecosystems remain unknown. In this study, we investigate the impact of climate change on native Metrosideros polymorpha rainforests using both empirical and modeling approaches. We have collected eddy covariance measurements over a period of 3.5 years in a native M. polymorpha forest at a 1219-m elevation, windward site on the Island of Hawai'i. We found that each degree C increase in air temperature causes a 15% increase in respiration, which suggests that these montane rainforests may be negatively affected by future warming (Asner et al., manuscript). To confirm our findings, we plan to extend our study to a longer period, using the combined Simple Biosphere/Carnegie-Ames-Stanford Approach (SiBCASA) terrestrial carbon cycle model (Schaefer et al., 2008). We expect to achieve a better understanding of the carbon dynamics and its interaction with hydrology of Montane Native Hawaiian rainforest under climate change through the modeling study. The model will be calibrated and validated with the eddy covariance measurements.