Louis Archambault

Forest succession over a 20-year period following clearcutting in balsam fir-yellow birch ecosystems of eastern Québec, Canada

Abstract Vegetation development over a 20-year period following clearcutting in balsam fir (Abies balsamea (L.) Mill.)-yellow birch (Betula alleghaniensis Britt.) ecosystems was examined in a study area located in eastern Quebec, Canada. Vegetation, physiographic and soil data were collected in 10 mature ecosystems and in 30 ecosystems harvested 5 years ago (10), 10 years ago (10), or 20 years ago (10). The 40 ecosystems had similar physiographic and soil characteristics. They were typically located on mesic sites situated on ground moraines thicker than 50 cm. Following harvesting, sites were invaded by competing species. Mountain maple (Acer spicatum Lamb.) was the most important competing species. Twenty years after logging, it fully occupied the sites with 7040 stems ha−1 (diameter at breast height ≥ 1 cm). Its regeneration stocking reached 88% with a density of 22775 stems ha−1. Wild red raspberry (Rubus idaeus L. var. strigosus (Michx.)) and fireweed (Epilobium angustifolium L.) were abundant during a 10-year period after logging, but disappeared almost completely afterwards. The abundance of competing species has considerably reduced site production for a period of 20 years and will probably continue to do so for 20 to 30 more years. The proportion of commercial deciduous species increased from 36% of the total number of stems (diameter at breast height ≥ 1 cm) in mature stands to 89% in stands harvested 20 years ago. Balsam fir and white spruce (Picea glauca (Moench) Voss) advanced regeneration was considerably reduced. Stocking of these species went down from 76% in mature stands to only 27% in 20-year-old stands. As a result, it is unlikely that the harvested areas will naturally evolve toward the original climax balsam fir-yellow birch forest type in the foreseeable future.

An analytical framework to assist decision makers in the use of forest ecosystem model predictions

The predictions from most forest ecosystem models originate from deterministic simulations. However, few evaluation exercises for model outputs are performed by either model developers or users. This issue has important consequences for decision makers using these models to develop natural resource management policies, as they cannot evaluate the extent to which predictions stemming from the simulation of alternative management scenarios may result in significant environmental or economic differences. Various numerical methods, such as sensitivity/uncertainty analyses, or bootstrap methods, may be used to evaluate models and the errors associated with their outputs. However, the application of each of these methods carries unique challenges which decision makers do not necessarily understand; guidance is required when interpreting the output generated from each model. This paper proposes a decision flow chart in the form of an analytical framework to help decision makers apply, in an orderly fashion, different steps involved in examining the model outputs. The analytical framework is discussed with regard to the definition of problems and objectives and includes the following topics: model selection, identification of alternatives, modelling tasks and selecting alternatives for developing policy or implementing management scenarios. Its application is illustrated using an on-going exercise in developing silvicultural guidelines for a forest management enterprise in Ontario, Canada.

Influence of drainage and edge vegetation on levels of attack and biological performance of the white pine weevil

Abstract The influence of selected ecological factors was studied in relation to the levels of attack by the white pine weevil and the biological performance of this insect in Norway spruce plantations. Results showed that in plantations growing on medium-textured soils, those situated on imperfectly drained soils supported higher levels of infestation than those on well-drained sites. The presence of shelterbelts creating an edge effect near a plantation was associated with higher levels of infestation. The biological performance of the weevil was affected by drainage but was not affected by the presence of shelterbelts. On imperfectly-drained soils, adult mean weight was smaller than on well-drained soils. The number of insects per leader was not affected by drainage regime. Adult mean weight and the mean number of insects per leader were not affected by the presence of shelterbelt vegetation. Host and site selection are discussed in relation to the biological performance of the weevil.