Faculty of Forest Sciences and Forest Ecology
PLANT MODELLING GROUP
PROJECT:
LINKING STRUCTURAL AND PROCESS-ORIENTED MODELS OF TREE GROWTH
Short description of project
Existing process-oriented and structural models of trees shall be
linked together in such a way that process-related information and
structural information can actualize each other. To achieve this
aim, certain approaches from computer science shall be applied:
rule-based systems, object-oriented simulation, communicating
processes. A mediation between different modelling concepts and
between different scales shall be realized. The prototypical
application will be the modelling of radiation interception,
transpiration and architectural development of trees. Three
basic models will be coupled together: A structure-oriented growth
model of tree crowns, a model of microclimate inside the crown,
and a model of water flow in the tree. The technical realization
will be carried out in a generic way, i.e. each of the used
basic models can be substituted by another one which simulates
the same phenomenon (although possibly in another way, or at
a differing level of detail). This linkage of models shall
contribute to a better understanding of the influence of spatial
heterogeneity in forest stands on the hydraulic regime of the
trees and on their resistance to drought stress.
Aims
(a) Models of microclimate (solar radiation, temperature, water
vapor in the air, wind speed) shall be connected with models of
tree architecture (branching structure of the crown) and water
flow in the tree, with information flows from the structural
model to the microclimatic model, and also from the environment
(microclimate) and from the structural model (architecture) to
the water flow simulation.
This will enable the calculation of a
spatially heterogeneous transpiration flux density and its use
as an input for the water flow model. In model experiments it
will be assessed which consequences this heterogeneity in the
crown will have for the dynamics of water flow and for the
risk of drought-stress induced damage (cf.
project on water flow simulation). Furthermore, such a
triple interaction of models (microclimate / architecture /
flow dynamics) is a prerequisite if stomatal control shall be
included in structure-oriented tree models.
(b) It is also planned to realize a "backward" information
flow: From microclimate and water relations to the growth model
which generates the tree architectures. This will allow some
tests of hypotheses by model experiments, concerning the question
how the processes of PAR interception and transpiration (resp.,
their disturbance by shadow or by drought) influence the control
of shoot growth in the tree crown.
It is not planned to implement a full physiology-based carbon
fixation and allocation model for this purpose. Rather, heuristic
sensitive growth rules will reflect the observed responses of
trees on changements of radiation regime or water supply. A refinement
of these rules to obtain a higher physiological realism can be
approached later (cf.
project on physiology-based models of woody plants). In any
case, the model experiments can ascertain the inner consistency of
the used model components and of their interaction, and they will
give information about sensitivity against changes of parameters
and / or model structure.
(c) Genericness and transparency of modelling tools
(process-oriented and structure-based) shall be improved.
We have therefore begun to reimplement some model components
in an object-oriented language (C++) and to use standard class and template
libraries which can be shared by several groups of researchers.
It is also planned to develop a generic software tool for
discretization of branching structures and environment according to
different criteria. To foster a broad dissemination of this tool
and of the model-connecting software, graphical user interfaces
shall be implemented for these software systems, using standardized
libraries and tools which are easily accessible for interested
modellers in other institutions.
Existing models which are used
Microclimate in tree stands: The two models MIR and MUSC were
partially reimplemented in this project and will be utilized for
the calculation of
spatially heterogeneous transpiration rate. These models were
developed by Dr. Jean Dauzat at CIRAD-amis, Montpellier; see the
Project "AMAPlux". MIR calculates the incoming radiation
and MUSC takes multiple scattering into account. Furthermore,
the energy balance of the leaf as well as stomatal conductivity are
simulated in separate modules also developed by J. Dauzat. There will
also be the option to substitute MIR/MUSC by a different radiation
model developed by Y. Knyazikhin and O. Panfyorov at the
Institute of Bioclimatology, University of Göttingen.
Tree architecture and growth: Alternatively, the models
AMAPsimpar (cf.
AMAP projects at the CIRAD, Montpellier) and
GROGRA are used for modelling the spatial architecture of the
branching system of the tree crown and its temporal development,
including the growth of the tree.
Water flow in the tree: Alternatively, the models
HYDRO, developed by J. Dauzat at CIRAD-amis in connection with the
microclimate models (see above), cf.
Project "AMAPlux",
and HYDRA (with higher temporal resolution of flow dynamics), developed
by Th. Früh in our institute and currently being subject of the
project on numerical simulation of the hydraulic system of trees, will
be used.
Since all these simulation tools are advanced systems with a rather
complex functionality and operating on heterogeneous 3D-structures,
the design and implementation of data exchange interfaces between them
is nontrivial. It requires certain steps of standardization, but we
avoid the complete reimplementation of the models. Some of the models
will get a clearer modular structure, others will only be extended
by normed data interfaces for communication.
Working programme
Tasks already done:
Final report (in German)
This project was carried out by
Gustavo Alejandro Anzola Jürgenson.
Other projects of the research group
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Last modifications: August 13, 2003