Modelling carbon dioxide and water vapour over European forests

• Main Author: Zhang, Rui
• Published: University of Edinburgh 2007
• Subjects: 581.7
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.664229

We tested several hypotheses which all link the carbon cycling in European forests using the Soil-Plant-Atmosphere model (SPA) and eddy covariance measurements from the CARBOEUROPE project. Firstly we run the model against flux data and obtained the optimised set of parameters for ten flux sites at a variety of climatic conditions. The inter-site model parameters are investigated to test whether the variations in parameters display a pattern which can be used in up-scaling of model application. It was found that maximum carbonylation rate (V_cmax) displays a simple linear relationship with latitude (R² = 0.72) and the ratio of autotrophic respiration to GPP remains at a constant (0.47). Furthermore we applied a Bayesian calibration method, which quantifies both flux measurement error and parameter priori distribution, to the same ten flux sites to tackle the uncertainty of model outputs. It was found that given amount of data and associated errors, model parameters and the confidence intervals that are related to plant functional type (PFT) can be identified. The third hypothesis we tested in the thesis is that carbon uptake by plant is enhanced under diffuse radiation. We compared the light use efficiency (LUE) under both direct and diffuse regime for eight contrasting ecosystems using both flux data and modelled outputs. Our results show that diffuse radiation results in a higher LUE for both forests and grasslands and response of forests to diffuse radiation is even higher. The model produced strikingly similar results. Finally we applied the model to a specific flux site experiencing drought to test the hypothesis that soil moisture and precipitation may influence the carbon uptake of forests and further have an impact on the carbon cycling.