Heterobasidion annosum (Fr.) Bref. s. lato causes severe damage to forests. This study describes a model for simulating the infection and spread of Heterobasidion spp. in stands of Picea abies (L.) Karst. and Pinus sylvestris L. The model includes submodels for stand dynamics (plot simulation, growth and yield, and cross-cutting of trees) and disease dynamics: (i) spore infection, (ii) stump colonization, (iii) colonization of stump roots, (iv) vegetative transfer to tree roots, (v) spread of disease in tree roots, (vi) spread of decay in stems, and (vii) disease effect on tree growth and survival. To illustrate the model, a simulation was carried out on a Swedish Norway spruce stand where logging occurred during the high-risk season for spore infection. The model provides a means of incorporating the impact of root disease into forest planning. A change of parameters indicated that model predictions were sensitive to the spread rate and presence of initial disease centers. Further research is called for in areas related to the development of coarse root systems of various tree species and the probability and rate of transfer of disease from various sources of inoculum to healthy trees. Résumé :Heterobasidion annosum (Fr.) Bref. s. lato cause des dommages sévères en forêts. Cette étude décrit un modèle pour simuler l'infection et la propagation de Heterobasidion spp. dans les peuplements de Picea abies (L.) Karst. et de Pinus sylvestris L. Le modèle inclut des sous-modèles de la dynamique du peuplement (simulation de parcelles, croissance et rendement et coupe radiale des arbres) et de la dynamique de la maladie : (i) infection par les spores, (ii) colonisation des souches, (iii) colonisation des racines associées à la souche, (iv) transfert végétatif dans les racines des arbres sains, (v) propagation de la maladie dans les racines des arbres sains, (vi) progression de la carie dans la tige et (vii) effet de la maladie sur la survie et la croissance des arbres. Pour illustrer le modèle, nous avons fait une simulation pour un peuplement d'épicéa commun en Suède qui a été coupé pendant la saison où le risque d'infection par les spores est élevé. Le modèle permet d'incorporer l'impact de la maladie de racine dans la planification forestière. Une modification des paramètres indique que les prédictions du modèle sont sensibles au taux de propagation et à la présence, initialement, de centres d'infection. D'autres recherches sont nécessaires dans les domaines reliés au dé-veloppement du système racinaire grossier de différentes espèces d'arbres et à la probabilité et aux taux de propagation de la maladie à partir de différentes sources d'inoculum vers des arbres sains.[Traduit par la Rédaction] Pukkala et al. 84

The number of airborne deposits of the root pathogen Heterobasidion annosum was counted with a wood disc method at distances 5-1000 m from one S-type and one P-type infection centre in stands of Picea abies in June, July and August, 1995. The level of background deposition in the area was determined in four healthy control stands. Based on intersterility group determination of deposits, only measurements within 100 m of the infection centres could be used in estimations of dispersal gradients owing to confusion with background deposition. A power law gradient model adequately described the reduction of deposits with increasing distance from the infection centres. Gradients were fairly similar in four directions around the infection centres as the wind speeds were low (<3.2 m/s) during the collection periods. The gradients were steeper around the P-type centre, probably due to its lower spore production capacity. The background deposition level (2.8 colonies/m x h) was reached at distances 1255 m and 98 m from the S-type and P-type centre, respectively.

International audienceContext Fusarium circinatum is an invasive forest pathogen causing pitch canker in Europe. It attacks several pine species and Douglas firs. It has already invaded a few places in the Iberian Peninsula and Italy. Aims The aim of this study is to develop a model for simulating the spread of F. circinatum once it enters Europe via various entry points such as harbours, border stations and from nurseries containing tree seedlings. Methods The spread rate was modelled as a function of the spatial distribution of pine and Douglas firs, climatic suitability of different locations to F. circinatum, seedling transportation, insect-mediated transfer from tree to tree, and spread of airborne spores.ResultsThe fungus is likely to spread to the pine forests of northern Spain (Galicia, Cantabria and Basque Country) and southwest France (Aquitania). There will be some spread towards northern Portugal and southern Italy. Unless there are new arrivals to Central and North Europe, the fungus will not spread to the more northern parts of Europe. Due to the short dispersal distance of spores, F. circinatum cannot easily cross spatial discontinuities in the distribution of host species .Conclusion F. circinatum is a serious potential invasive forest pathogen in Europe. New admittances of the spores from international trading should be controlled

A simulation model was developed to predict the growth of a Norway spruce stand under risk of butt rot caused by Heterobasidion annosum stump infection and logging injuries. The simulation model was distance-dependent; tree growth was predicted with a distance-dependent model, and the spread of butt rot through root contacts depended on tree location. Infection of stumps and injured trees, and the spread of butt rot in the stand were stochastic processes whereas tree growth and mortality were treated as deterministic processes. The simulation model was used with the nonlinear optimization algorithm of HOOKE and JEEVES (J. Assoc. Comput. Mach, 8, 212-229, 1961) to find the most profitable management schedule for an even-aged, young stand. Optimization used four different stump infection rates and two spreading capacities from infected stumps. The profitability was evaluated by the expected soil expectation value (SEV) at a 3% interest rate. Two thinnings, both in winter-time, and hence without H. annosum infections, resulted in the highest SEV. If any stump infection by H. annosum occurred, only one thinning and a shortened rotation were suggested. The optimal thinning rate tended to decrease but also large trees were removed with the increasing infection rate. With one thinning during a rotation, stump treatment was profitable above a stump infection rate of 10%.

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