Simulating the extent of decay caused by Heterobasidion annosum s. l. in stems of Norway spruce

Heterobasidion annosum (FR.) BREF. sensu lato causes severe economic damage in stands of Norway spruce (Picea abies [L.] Karst). The primary damage is the deterioration of timber by decay. Secondary damage can be attributed to higher risks of windthrow and stem breakage, growth reduction of infected trees as well as higher machining and handling costs for decayed stems during grading and processing. Regardless of the importance of this pathogen there are very few software tools which support management decisions in red rot affected forests and none of them are parameterised with data from Central Europe.The present study aimed to develop a model which is able to spatially predict the extent and degree of decay in the stem as well as its effects on the growth of Norway spruce. This involves the integration of several sub-models into a tree growth simulator: (i) diameter of decay, (ii) height of decay, (iii) form of decay, (iv) degree of decay, and (v) feedback of the pathogen on tree growth. The model is parameterised mainly from published data of other authors. The input for the time of infection of a tree is delivered from a separate model. A grading algorithm is used to evaluate the impact of different scenarios on the revenue of infected stands in typical stands of Norway spruce in Germany. This integrated system of growth and red rot simulation is able to support management decisions on various levels and documents that if red rot is not taken into consideration in the affected stands, clear misinterpretations and thus inaccuracies will arise in the economic results from tree growth simulators. The need for further research was identified especially in model validation and the tree–pathogen interaction.