Integrating mechanistic disturbance models and stand dynamics of Norway spruce

Disturbances, caused by abiotic and biotic agents, are discrete events in time disrupting the ecosystem and resulting in the reduction of plant biomass. They play a key role in forest ecosystems, but in the managed forests pose a risk to forest productivity. The projected climate change is expected to increase the risk of various disturbances in the boreal forests. In Europe, the major risks threatening the Norway spruce (Picea abies) dominated stands are caused by Heterobasidion root rot, wind storms, and European spruce bark beetle (Ips typographus). Heterobasidion root rot causes growth losses, mortality and decreases the timber quality. It also decreases the mechanical stability of the tree against wind load and increases the stand vulnerability for wind damages. Bark beetles benefit from the low resistance breeding material, i.e., wind damaged trees, when the population is low and can emerge as outbreaks in the right conditions. This thesis presents a simulation framework WINDROT to simulate the interactive dynamics of these disturbance agents. WINDROT consists of four simulation models, each responsible for either the dynamics of the host or one of the disturbance agents. A stand level decision support system, MOTTI, simulates the growth and dynamics of tree stands as affected by forest management, and provides inputs for mechanistic models Hmodel, HWIND and BBDYN simulating the dynamics and effects of disturbance agents. The model performance analyses in tree and stand scale showed that; i) the Heterobasidion dynamics are driven by primary and secondary infections on large stumps; ii) increasing intensity of Heterobasidion root rot damages increases the risk for wind damages; and iii) the increasing wind damages increased the subsequent bark beetle damages. The simulation framework can be used to analyze the sensitivity of different forest management regimes to the risks posed by these damages alone and in various combinations.