Department of Earth Sciences, University of Hamburg, 20148 Hamburg, GERMANY.
Dynamic Global Vegetation Models (DGVMs) typically abstract the immense diversity of vegetation forms and functioning into a relatively small set of predefined semiempirical Plant Functional Types (PFTs). There is growing evidence, however, from the field ecology community as well as from modelling studies that current PFT schemes may not adequately represent the observed variations in plant functional traits and their effect on ecosystem functioning. Also, these PFTs are defined a priori and their simulated distribution is often based on observed relationships between present-day climate and vegetation patterns. Climate model projections, however, point towards the possibility of regional climates without present-day analogs. This PhD study concerns the development, evaluation, and application of a novel global vegetation model, the Jena Diversity-DGVM, which seeks to overcome these deficits with a richer representation of functional diversity more closely based on first-principles.
JeDi-DGVM simulates the performance of a large number of randomly-generated plant growth strategies (PGSs), each defined by a set of 15 trait parameters which characterize various aspects of plant functioning including carbon allocation, ecophysiology and phenology. Each trait parameter is involved in one or more functional tradeoffs. These tradeoffs ultimately determine whether a PGS is able to survive under the climatic conditions in a given model grid cell and its performance relative to the other PGSs. The biogeochemical
uxes and land-surface properties of the individual PGSs are aggregated to the grid cell scale using a mass-based weighting scheme based on the `biomass-ratio hypothesis.
Simulated global biogeochemical and biogeographical patterns are evaluated against a variety of field and satellite-based observations following a protocol established by the Carbon-Land Model Intercomparison Project. The land surface uxes and vegetation structural properties are reasonably well simulated by JeDi-DGVM, and compare favorably with other state-of-the-art terrestrial biosphere models. This is despite the parameters describing the ecophysiological functioning and allometry of JeDi-DGVM plants evolving as a function of vegetation survival in a given climate, as opposed to typical approaches that assign land surface parameters for each PFT a priori.