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Doctor Jinyan (Jim) Yang

Candidature

Graduated PhD 2019

Thesis Title

Modelling carbon uptake of Australian evergreen ecosystems under rising [CO2] and water limitation

Research Project

Jim YangA modelling approach of the economy, equilibrium and dynamics of LAI.

Leaf area index (LAI) is one of the most important ecosystem properties, but also remains difficult to predict. Some current land surface models take LAI as an input, whereas others attempt to predict it based on NPP. For example, one common assumption is that a fixed proportion of net primary production (NPP) is used to grow new leaves. Very few models consider top-down constraints on LAI, which can result in unrealistic predictions under altered climate patterns.

In general, my research interest is in developing innovative methods of LAI prediction under varying environments. There are three directions I'm currently exploring:

  1. MAESPA simulation of EucFACE. Because the unique features and the well-documented data, EucFACE is an ideal first step with the potential of revealing LAI economy under elevated [CO2] and water stress;
  2. LAI equilibrium. Incorporating optimization theory, Darcy's law, and optimal stomatal behavior model, I hope to determine equilibrium LAI based on water availability at large spatial and temporal scales;
  3. LAI dynamics. Predict LAI through optimal leaf dropping strategy based on costs and benefits at small spatial and temporal scales.


I use R as my major modelling tool, although MAESPA is in FORTRAN. My field work includes LAI measurements in IF site and, in the near future, the leaf dropping measurements in the collaborated drought experiment. There are also possibilities of incorporating airborne and satellite-based remote-sensing data.

My research will, hopefully, benefit current climate change studies by providing both an assessment of current LAI prediction methods and evidence-based LAI models that account for environmental variations in the future.

Publications

Yang J, Medlyn BE, De Kauwe MG, Duursma RA, Jiang M,  Kumarathunge D, Crous KY, Gimeno TE, Wujeska-Klause A, Ellsworth DS, (2020) 'Low sensitivity of gross primary production to elevated CO2 in a mature eucalypt woodland', Biogeosciences, vol.17, no.2, pp 265-279

Yang J, Duursma RA, De Kauwe MG, Kumarathunge D, Jiang M, Mahmud K, Gimeno TE, Crous KY, Ellsworth DS, Peters J, Choat B, Eamus D, Medlyn BE, (2019) 'Incorporating non-stomatal limitation improves the performance of leaf and canopy models at high vapour pressure deficit', Tree physiology, vol.39, no.12, pp 1961-1974

Yang J, Medlyn BE, De Kauwe MG, Duursma RA, (2018) 'Applying the Concept of Ecohydrological Equilibrium to Predict Steady State Leaf Area Index', Journal of Advances in Modeling Earth Systems, vol.10, no.8, pp 1740-1758

Research Project Supervisors

Professor Belinda Medlyn, A/Professor Remko Duurmsa, Dr Martin De Kauwe