Climate can influence nutrient dynamics and subsequently productivity through its impact on organic matter decomposition rates. Recent litter decomposition studies have shown that temperature and soil moisture influence mass loss and mineralization rates (Figure 1). Modelling tools are required to help forest planners navigate the potential implications of climate change on timber supply through the use of scenario analysis and case studies. Although detailed physiological models have been useful in exploring climate impacts on tree growth and ecosystem processes, they are often data intensive and difficult to apply for management related applications. To be effective for guiding management, such tools must be able to capture the current understanding of the effect of specific climate variables on ecosystem processes governing forest growth, but still be practical for estimating impacts on tangible projections of forest growth and yield and other ecosystem values.

The FORECAST Climate model (presently in the testing stage of model development) has been developed and designed in such a way to give it the capability to explicitly represent the potential impacts of climate change on forest growth and development. In the general version of FORECAST, tree growth is limited by light and nutrient availability. The FORECAST Climate model includes an explicit representation of soil moisture and forest hydrological processes based on a linkage to the Forest Water Dynamics (ForWaDy) model. ForWaDy is a vegetation-oriented model originally developed as a companion forest hydrology model to FORECAST. The model was designed to provide a representation of the impacts of forests management activities on water competition among different tree species and between trees and minor vegetation. Potential evapotranspiration (PET) in ForWaDy is calculated using an energy balance approach. Incoming radiation is partitioned among vertical canopy layers (vegetation type) and the forest floor to drive actual evapotranspiration (AET) calculations. The model is structured for portability, with minimum soil data requirements and parameter values that are relatively easy to estimate. It has a simplified representation of the soil physical properties dictating moisture availability, storage, and infiltration. The linkage with ForWaDy provides an additional feedback on tree growth rates based on a climate-driven quantification of tree water stress (Figure 2). Moreover, the simulation of soil and litter moisture content in FORECAST Climate facilitate a climate-based representation of organic matter decomposition and associated nutrient mineralization rates. These developments in combination with a simulation of temperature effects on length of growing season and forest growth rates will provide the foundation for the representation of climate impacts on forest growth in FORECAST. The completed FORECAST Climate model will allow users to explore the potential impacts on varying climate scenarios on indicators of multiple forest values.

Figure 1. Interactions between climate and ecosystem-level processes

Figure 2. Links between ForWaDy and FORECAST to create FORECAST Climate