Hybrid forest models

Hybrid models were developed from complementary merging of well understood processes and reliable tree/stand empiricism aiming to have a process model for the manager in which the shortcomings of both approaches can be overcome to some extent. The improvement of both process-based and empirical models will lead to better hybrid models.
There is a combination of causal (at level of the process such as: carbon balance, water balance, soil carbon cycling, soil carbon cycling) and empirical (at the higher stand level the model is empirical) elements.

Overall, the range of models presently available does not fully meet the requirements for evaluating the sustainability of multi-functional forest management. Some examples of current models shortcomings include:

• The need to improve representation of forest ecosystem behaviour (scientific limitation). Here, the challenge lies in progressing understanding and model description of the complex interactions between relevant plant and soil processes and atmosphere that underpin the improved prediction of stand growth and forest development under changing environmental and management conditions.
• For forestry practice, there is a need to improve output detail as well as the accuracy of predictions (operational limitations). For instance, high-resolution information on stand structure is essential to assess wood quality or harvesting procedures and costs.
• Current models do not usually account for risk assessment such as storm damage, fire, pests and diseases (process limitation). These are natural elements that contribute extensively to changing growth performance and whose effects should be taken into account.
• Forest growth models do not presently account for the quality of plant material used in the forest sector. Quality ranges from the use of genetically improved material in intensive cultivated forestry through the use of natural regeneration in more nature-identical silvicultural systems.
• Most models predict only wood quantity, while wood quality and non-wood products or assessment of recreational and amenity value of the forests are rarely included.