Evaluating the long-term influence of alternative commercial thinning regimes and harvesting systems on projected net present value of precommercially thinned spruce-fir stands in northern Maine

Commercial thinning (CT) is an important silvicultural practice in the northeastern United States. Relatively little is known, however, about the interaction of harvest system and treatment (removal intensity or timing of entry) on the overall profitability of CT. To address this question, 10-year measurements from a controlled CT experiment across six sites in Maine were used to project the long-term effect of removal intensity (33% and 50% relative density reduction) and timing of entry (no delay, 5-year delay, 10-year delay) on (i) maximum net present value (NPV), (ii) timing of maximum NPV, and (iii) the effect of three harvesting systems (cut-to-length, whole-tree, hybrid systems) on maximum NPV. A regional growth and yield model was used to project individual-tree growth and mortality into the future. Harvest costs for the harvesting systems were estimated using regional cycle-time equations. No difference was found in maximum NPV between the CT and non-CT areas or the timing of CT entry. Stand age at time of maximum NPV differed between delays but not between the two removal intensities. Our results indicate that there is no economic benefit in delaying a CT or removing more volume at the time of thinning for the range of stand conditions evaluated. Key words: commercial thinning, New England, net present value, harvesting system, spruce and fir. L'eclaircie commerciale (EC) est une pratique sylvicole importante dans le nord-est des Etats-Unis. Toutefois, on connait relativement peu l'effet de l'interaction entre le systeme de recolte et le traitement (l'intensite de recolte ou le calendrier d'application) sur la rentabilite globale de l'EC. Dans le but d'etudier cette question, des mesures prises dans un dispositif controle d'EC vieux de 10 ans et etabli dans six stations du Maine ont ete utilisees pour projeter l'effet a long terme de l'intensite de recolte (33 et 50 % de reduction de la densite relative) et de la periode d'application (pas de delai, delai de 5 ans, delai de 10 ans) sur (i) la valeur actualisee nette (VAN) maximale, (ii) le moment ou la VAN maximale est atteinte et (iii) l'effet de trois systemes de recolte (bois tronconne, arbre entier et systeme hybride) sur la VAN maximale. Un modele regional de croissance et de production a ete utilise pour projeter la croissance et la mortalite des arbres individuels dans le futur. Les couts relies aux systemes de recolte ont ete estimes a l'aide d'equations regionales pour la duree totale du cycle. Il n'y avait pas de difference de VAN maximale entre les superficies eclaircies ou non ni entre les periodes d'application de l'EC. L'age des peuplements au moment ou la VAN maximale est atteinte etait different selon le delai d'application, mais pas selon l'intensite de recolte. Nos resultats indiquent que pour la gamme de conditions de peuplements qui ont ete evaluees, il n'y a pas d'avantage economique a retarder une EC, ni a prelever plus de volume lors de l'eclaircie. [Traduit par la Redaction] Mots-cles: eclaircie commerciale, Nouvelle-Angleterre, valeur actualisee nette, systeme de recolte, epinette et sapin.
Introduction The management of forests for timber production generally includes a series of treatments aimed at improving stand growth and yield. Herbicide application, precommercial thinning (PCT), and commercial thinning (CT) [...]