Simulating the extent of decay caused by Heterobasidion annosum s. l. in stems of Norway spruce Thomas Seifert * Technische Universita ¨t Mu ¨nchen, Am Hochanger 13, 85354 Freising, Germany Accepted 8 February 2007 Abstract 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. # 2007 Elsevier B.V. All rights reserved. Keywords: Heterobasidion annosum; Picea abies; Stem decay; Rot model; Growth simulation; Wood quality 1. Introduction Annosum root rot caused by the wood decaying basidio- mycetous fungus Heterobasidion annosum [FR.] BREF. accounts for severe financial losses in forestry, e.g. within stands of Norway spruce (Picea abies [L.] Karst). In this publication H. annosum is referred to in sensu lato because most of the cited older publications which include the ones used for the model development do not distinguish between the different species of Heterobasidion. H. annosum is able to infect a tree either by spores through wounds in the bark and the root collar or by intrusion via the roots from infected neighbouring trees and stumps. These two ways of infection may involve a distinct difference in pathogenesis (von Pechmann and von Aufsess, 1971; von Pechmann et al., 1973; Binder, 1995). Typically the fungus spreads via spores, which colonize freshly cut stumps creating an effective platform for the fungus to spread to living trees over the root system (Stenlid and Redfern, 1998). In contrast, H. annosum is often outcompeted by other species in the colonization of stem wounds (Isoma ¨ki and Kallio, 1974). The damage caused by this pathogen is manifold. Most obvious of all is the deterioration of the timber by stem decay, a white rot where lignin is degraded. The damage is especially high because the most valuable butt log is decayed, which in turn limits the timber use for aesthetical and mechanical purposes. As a result, the attainable timber prices are reduced (Seifert, 2003). Schumacher et al. (1997) identified stem rot in grading trials of Norway spruce logs according the European grading rule EN1927-1 to be the most important grading variable together with branchiness. There is also a risk of severe collateral damage as decayed trees obviously have higher probabilities of being thrown or broken by storms or snow (Bazzigher and Schmid, 1969; www.elsevier.com/locate/foreco Forest Ecology and Management 248 (2007) 95–106 * Tel.: +49 8161 714 713; fax: +49 8161 714 721. E-mail address: seifert@lrz.tum.de. 0378-1127/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2007.02.036