Optimizing the management of a Picea abies stand under risk of butt rot

A simulation model was developed to predict the growth of a Norway spruce s tand under risk of butt rot caused by Heterobasidion annosum stump infectio n and logging injuries. The simulation model was distance-dependent; tree g rowth was predicted with a distance-dependent model, and the spread of butt rot through root contacts depended on tree location. Infection of stumps a nd injured trees, and the spread of butt rot in the stand were stochastic p rocesses whereas tree growth and mortality were treated as deterministic pr ocesses. The simulation model was used with the nonlinear optimization algo rithm of HOOKE and JEEVES (J. Assoc. Comput. Mach, 8, 212-229, 1961) to fin d the most profitable management schedule for an even-aged, young stand. Op timization used four different stump infection rates and two spreading capa cities from infected stumps. The profitability was evaluated by the expecte d soil expectation value (SEV) at a 3% interest rate. Two thinnings, both i n winter-time, and hence without H. annosum infections, resulted in the hig hest SEV. If any stump infection by H, annosum occurred, only one thinning and a shortened rotation were suggested. The optimal thinning rate tended t o decrease but also large trees were removed with the increasing infection rate. With one thinning during a rotation, stump treatment was profitable a bove a stump infection rate of 10%.