Carbon, water and energy exchange from an old growth mountain ash forest

Abstract

Increases in atmospheric C02 concentration are projected to have substantial impacts on climate and the growth dynamics of forest ecosystems. Therefore, knowledge about the current distribution, magnitude and the processes that control the terrestrial carbon sink are essential to predict the future responses of ecosystems to global environmental change. Old growth forests are of particular relevance with respect to the long-term permanence of forest carbon sinks since little is known about the annual carbon sink/source status of these ecosystems. Therefore, this thesis investigates the carbon, water and energy exchanges from an old growth Mountain Ash (Eucalyptus regnans) ecosystem. This is achieved through an integrated approach combining eddy covariance flux measurements above and below the canopy and in situ measurements.The research conducted for this dissertation initially explored the robustness and data quality of eddy covariance (EC) flux measurements over a tall old growth Mountain Ash forest located in south eastern Australia. One such quality assessment is the surface energy balance (SEB) closure as it indicates the amount of turbulent energy exchange captured by the EC instrumentation. This investigation measured and modeled storage components over half hourly periods, as well as evaluated the spectral signal of the turbulent flux exchange over different averaging periods. Accounting for all the storage terms in the radiation balance suggested that 93% of the turbulent fluxes were captured. Although this initial quality assessment indicated that the flux measurements were reliable, night time ecosystem respiration (Re) measurements are typically underestimated using the EC technique at many flux sites. Therefore, Re and its components (belowground, leaf, wood) were measured and scaled up using chamber based techniques and compared to Re derived from EC night timedata. Results showed that annual Re estimate from the eddy flux tower was 13% lower than scaled chamber based estimates. [...]