Modeling Approach

An Integrated Modeling System (IMS) with three modules is proposed for simulation of southern forest responses to environmental stress, disturbances, and land use changes. The first module (Linked Dynamic Model) involves linkage of seven developed simulators with differing scales of process representation. This module will provide a means for propagating physiological-scale responses of vegetation to environmental stresses and disturbances through forest succession and forest management models applicable to the scale of a forest stand. Uncertainty analysis will be an integral part of each simulator through the use of Latin hypercube sampling. Frequency distributions (rather than single values) will be used for sensitive variables in each simulator resulting in frequency distributions of output variables, some of which will become inputs to the next simulator in the linked modeling hierarchy. The two primary purposes of module I are
(1) incorporation of advances in research on forest
responses to multiple stresses and disturbance factors, and
(2) the scaling up of knowledge of physiological processes
to provide inputs to regional assessment modeling in
module II of IMS.

The second module of IMS provides spatial integration of forest responses to environmental stresses and disturbances of spatial-based modeling with a regular grid of land units. Module II will be incorporated into LUCAS, a Land-Use Change and Analysis System. LUCAS is a multidisciplinary simulation framework for investigation of regional and landscape phenomena using a cell-based approach. Spatially organized simulation results incorporating the stochastic outputs provided by the Linked Dynamic Model will be generated. The primary purpose of module II is regional assessment in a framework that can accommodate land use change, economic modeling, and demographic information. IMS will provide regional assessments that may include statistically based comparisons between alternative modeling scenarios.

The database resources needed for model development, testing, and applications will be based on the GRASS geographical information system (GIS), the third module of IMS. GRASS is already an integral part of LUCAS, thus providing a direct linkage of GIS database layers to the cellular grid structure needed for regional assessment. We will use a comprehensive range of data sources for characterization of the topography, land cover, soils, and current and future climate at a resolution appropriate to regional assessment.

IMS applications will address the current and future conditions of forests in relation to current and projected changes in environmental conditions. Adaptation and mitigation approaches to forest management as policy adjustments to changing conditions may be explored. IMS will be well suited to the Southern Global Change Program's needs for regional assessment of forest responses to a range of altered climatic conditions, air quality, and land use change influences.