Abstract. Practicing ecologists who excel at their work (''experts'') hold a wealth of knowledge. This knowledge offers a wide range of opportunities for application in ecological research and natural resource decision-making. While experts are often consulted ad-hoc, their contributions are not widely acknowledged. These informal applications of expert knowledge lead to concerns about a lack of transparency and repeatability, causing distrust of this knowledge source in the scientific community. Here, we address these concerns with an exploration of the diversity of expert knowledge and of rigorous methods in its use. The effective use of expert knowledge hinges on an awareness of the spectrum of experts and their expertise, which varies by breadth of perspective and critical assessment. Also, experts express their knowledge in different forms depending on the degree of contextualization with other information. Careful matching of experts to application is therefore essential and has to go beyond a simple fitting of the expert to the knowledge domain. The standards for the collection and use of expert knowledge should be as rigorous as for empirical data. This involves knowing when it is appropriate to use expert knowledge and how to identify and select suitable experts. Further, it requires a careful plan for the collection, analysis and validation of the knowledge. The knowledge held by expert practitioners is too valuable to be ignored. But only when thorough methods are applied, can the application of expert knowledge be as valid as the use of empirical data. The responsibility for the effective and rigorous use of expert knowledge lies with the researchers.

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A spacing trial was established near Thunder Bay, Ontario in Une plantation a kt6 kalisk B titre exphimental prbs de Thunder 1950. This trial consisted of black spruce (Picea rnariana (Mill.) Bay en Ontario en 1950. Cet essai portait sur l'kpinette noire B.S.P.), white spruce (Picea glauca (Moench) Voss.), and red pine (Picea mariana (Mill.) B.S.P.), l'kpinette blanche (Picea glauca (Pinus resinosa Ait.) each established at three different spacings:(Moench) Voss.), et le pin rouge (Pinus resinosa Ait.) chacune des 1.8 m, 2.7 m, and 3.6 m. This study examines the differences in e s e e s plant& selon trois espacements: 1.8 m, 2.7 et 3.6 m Cette growth and crown development as attributed to initial spacing, after ktude se penche sur les diffkrences en croissance et en dkveloppe-37 years. In addition, a benefivcost analysis was performed to evalment de la cime en fonction de l'espacement initial, 37 ans plus tard. uate the economic efficiency of the various species/spacing comDe plus, une analyse des Mnkfices en fonction des coats a kt6 effecbinations. Diameter at breast height, live crown length, and tuCe afin d'kvaluer l'efficacite kconomique de diffkrentes combicrown width, all exhibited significant (P < 0.001) increases as ini-tial spacing increased, irrespective of species, but, height demonpoitrine, la longueur de la cime vivante et le diambtre de la cime ont strated a decreasing trend (P < 0.020). Gross total and mertous dkmontd des augmentations significatives (P < 0.001) en foncchantable stem volume per tree increased for all species as initial tion de l'augmentation de l'espacement initial, pour toutes les spacing increased; however, volume production per unit area espbces, mais la hauteur suivait une tendance inverse (P < 0.020). decreased significantly for all species as spacing increased. The shift Le volume total et le volume marchand par arbre a augment6 pour to higher-valued products from the wider-spaced plantations toutes les esp2ces B mesure que s'accroissait l'espacement initial, appeared to provide the best economic return. As a result of both alors que le volume par unit6 de surface diminuait significativement greater merchantable volumes and greater percentages of these volpour toutes les esp&ces en fonction de l'augmentation de l'espaceumes available as a higher-valued product, benefitlcost ratios for ment. Le changement vers des produits de plus grande valeur tirks red pine (0.995 to 1.337) were greater than those for the spruces des plantations B espacement plus grand semble procurer le meilleur (0.595 to 0.866). Although red pine currently represents less than retour sur l'investissement. Les ksultats B la fois au niveau des vol-4% of Ontario's total regeneration effort, the results from this study umes marchands supkrieurs et du plus fort pourcentage de ces suggest it deserves further consideration on some boreal sites.volumes disponibles en tant que produit de valeur supkrieure ont permis d'obtenir des ratios des b6n6fices en fonction des coats pour Key words: spacing trial, plantat...

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