Optimizing the management of a Norway spruce stand on a site infected by Heterobasidion coll

Abstract

The management of a Norway spruce [Picea abies (L.) Karst.] stand established on a Heterobasidion coll.-infected site is problematic because the disease spreads vegetatively from the previous to the next generation. This study determined optimal management schedules for such Norway spruce stands growing in southern Finland that had Heterobasidion coll.-colonized stumps from the previous generation. A stochastic simulation model describing the infection and spread of Heterobasidion coll. was used in combination with a non-linear optimization algorithm to find the most profitable management schedules. The thinnings were always conducted in winter. The optimal number of thinnings was either one or two. Increasing discounting rate increased the optimal number and intensity of thinnings, and shortened rotations. The soil expectation value (SEV) of a healthy stand was 7–54% higher than the SEV of stands with Heterobasidion coll.-colonized stumps from the previous generation. Increasing number of colonized clear-felling stumps tended to decrease the number of thinnings, delay thinnings, increase thinning intensity and shorten rotations. The first thinning was in most cases a low thinning, whereas the second thinning, as well as the only thinning of one-thinning schedules, was always a high thinning. The optimal management schedule of a heavily Heterobasidion coll.-infected stand includes one very late and intensive high thinning. If the discounting rate is 2% or more and there are many colonized stumps, optimal rotations are up to 7 years shorter than in a healthy stand.

Keywords:

• Butt rot
• mechanistic model
• optimal management
• Picea abies
• simulation model

Acknowledgements

This study was funded by Metsämiesten Säätiö Foundation.