Site index has traditionally been estimated using height over age curves in the province of Quebec (e.g., Vézina and Linteau 1968, Boudoux 1978, Pothier and Savard 1998. While such curves tend to be effective tools for estimating site index in mature stands, they are unreliable for estimating site index in juvenile stands, i.e., stands that are younger than 20 years old at breast height (Nigh 1995). Conversely, variable growth intercept models are being increasingly used outside Quebec to give reliable site index estimates for young stands by relating the average annual height growth of trees to site index. These models have the advantages of being: 1) developed specifically for estimating site index, not height; 2) intended for young stands; 3) not constrained to pass through the site index at index age; and 4) less sensitive to small deviations from the mean height when compared to height-age models (Nigh 1996).Because of the commercial importance of black spruce, jack pine and balsam fir as major wood supply species in Quebec, a need existed for growth intercept models for these species. ABSTRACTThe objective of this study was to develop variable growth intercept models for coniferous species of major importance in Quebec using Nigh's (1997a) modelling technique. Eighty-three, 68, and 70 stem analysis plots of black spruce (Picea mariana [Mill.] BSP), jack pine (Pinus banksiana Lamb.) and balsam fir (Abies balsamea (L.) Mill) were used, respectively. The growth intercept models for black spruce were the most precise, followed by those for jack pine and finally by those for balsam fir, based on the root mean square errors. Results indicated that the accuracy of the models was good, relative to those previously published for other species in Canada. Interim testing of the models revealed a low mean error for all three species that may not be of practical significance for site index determination, although more data should be obtained to further test the models.
Keywords:top height / site trees / mortality rate / site index / permanent sample plots Abstract • Although comparisons between methods of selecting trees for site index estimates are well documented in the literature, little is known on mortality rates of different canopy tree cohorts used for that purpose.• This study was initiated to test the hypothesis that the mortality rates of top height trees are lower than those of codominants only or a combination of codominant and dominant trees. To test this hypothesis, we used records from a network of permanent sample plots in Québec and studied the fate of different cohorts of site trees for five different species.• Our results did not show clear evidence of lower mortality rates for top height trees. Instead we found that depending on the species, top height trees have lower (Populus tremuloides, Pinus banksiana), higher (Picea mariana, Abies balsamea) or equal mortality rates (Betula papyrifera) than codominant trees or codominant and dominant trees combined.• These results suggest a tendency for shade intolerant species to maintain lower top height tree mortality rates over time when compared to shade tolerant species. In the latter case, it is also shown that spruce budworm epidemics (Choristoneura fumiferana) did not change the pattern of mortality rates of site trees of A. balsamea. Mots-clés :hauteur dominante / arbres indicateurs de la station / taux de mortalité / indice de qualité de station / placette-échantillon permanente Résumé -Étude comparative des taux de mortalité entre les arbres dominants et les arbres indicateurs moyens de la station.• Bien que des études comparatives sur les méthodes servant à déterminer l'indice de qualité de station sont disponibles dans la littérature, on connaît peu de choses sur les taux de mortalité des différentes cohortes d'arbres utilisées à cette fin.• Cette étude a été initiée dans le but de tester l'hypothèse selon laquelle les taux de mortalité des arbres dominants sont plus faibles que ceux des arbres codominants ou de ceux d'une combinaison d'arbres codominants et dominants. Afin de tester cette hypothèse, nous avons utilisé la base de données des placettes-échantillons permanentes du Québec et nous avons suivi la destinée de différentes cohortes d'arbres indicateurs de la station pour cinq espèces différentes.• Nos résultats n'ont pas montré de façon tranchée que les arbres dominants ont un taux de mortalité inférieur à celui des autres cohortes à l'étude. Nos résultats démontrent plutôt que selon les espèces, les arbres dominants ont un taux de mortalité inférieur (Populus tremuloides, Pinus banksiana), supérieur (Picea mariana, Abies balsamea) ou égal (Betula papyrifera) au taux de mortalité des arbres codominants ou à une combinaison d'arbres codominants ou dominants.• Ces résultats suggèrent que les taux de mortalité des espèces classées intolérantes à l'ombre ont tendance à demeurer plus faibles dans le temps lorsqu'on les compare aux taux de mortalité des espèces tolérantes à l'ombre. Pour ces dernières,...
The objective of this study was to develop variable growth intercept models for coniferous species of major importance in Quebec using Nigh's (1997a) modelling technique. Eighty-three, 68 and 70 stem analysis plots of black spruce (Picea mariana [Mill.] BSP), jack pine (Pinus banksiana Lamb.) and balsam fir (Abies balsamea (L.) Mill) were used, respectively. The growth intercept models for black spruce were the most precise, followed by those for jack pine and finally by those for balsam fir, based on the root mean square errors. Results indicated that the accuracy of the models was good, relative to those previously published for other species in Canada. Interim testing of the models revealed a low mean error for all three species that may not be of practical significance for site index determination, although more data should be obtained to further test the models.
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