A Linked Model for Simulating Stand Development and Growth Processes of Loblolly Pine

Linking models of different scales (e.g., process, tree-stand-ecosystem) is essential for furthering our understanding of stand, climatic, and edaphic effects on tree growth and forest productivity. Moreover, linking existing models that differ in scale and levels of resolution quickly identifies knowledge gaps in information required to scale from one level to another, indentifies firture research needs to fill these information gaps, and provides a test of the present state of modeling sciences for creating model systems for predicting responses to natural and human-based disturbances. Today there is a need to assess how such interacting stressors as air pollutants, (e.g., carbon dioxide (CO,), ozone, acid rain), and climate change will affect forest health (forest function), tree growth, and stand productivity. Standard growth and yield models usually operate at an annual or longer resolution level and assume environmental conditions remain constant over time. As such, they are of limited use for assessing the effects of changes in weather and atmospheric chemistry on forest functioning or growth. However, growth and yield models are our best tools for predicting tree morphology and stand structural characteristics as a function of stand density, age, and site quality. Conversely, process models operate at hourly or daily levels and are suitable for estimating the effects of annual regimes of air pollution or weather on individual tree functioning (net photosynthesis, respiration, allocation, growth), but require that tree and stand characteristics be provided as model inputs (Landsberg, 1986). Because of the large input data requirements, hourly time steps, and inability to account for