Effects of tree species composition and spatial arrangement on juvenile growth of four tree species in a tree diversity experiment (Notre-Dame-de-la-Paix, Québec)

Details

Supervisors

Ponette, Quentin ; Gendreau-Berthiaume, Benoit

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en sciences et technologies de l'environnement, à finalité spécialisée

Abstract

Mixed-species plantations are drawing increased interest from scientists as a sustainable alternative to monospecific stands, which have been predominantly used over the past centuries. This silvicultural model has gradually reached its limits due to its growing vulnerability to climate change. Yet, knowledge regarding the design of mixed plantations, particularly the species composition and the horizontal distribution of these species within forest plots—two non-exhaustive but important characteristics of a forest plantation—remains incomplete. This study, based on data from an experimental plantation in Outaouais, Quebec, established in 2020, aims to investigate the impacts of these two characteristics by analyzing the diameter and height growth after three growing seasons for four tree species with contrasting traits: the sugar maple (Acer saccharum), the tamarack (Larix laricina), the white spruce (Picea glauca), and the red oak (Quercus rubra). The experiment comprised a total of 10 different species compositions in three different spatial distributions – Complex, Random, and Regular. Following data collection in this plantation, the impact of species composition and spatial distribution on tree height and diameter growth at plot-level was tested using linear models. Another analysis aimed at examining the effect of tree size and neighborhood characteristics on individual tree growth was also conducted, using linear regression and a Neighborhood Competition Index (NCI). Through its analyses, this thesis has demonstrated the importance of spatial arrangement. The first analysis showed that most studied species are sensitive to the interaction of horizontal distribution and species composition, highlighting the four-species composition in a Complex horizontal distribution as the most beneficial for overall growth and species protection. The second analysis revealed that the growth of young plants is primarily influenced by their initial size and that they experience less intense positive or negative neighborhood effects. The low explanatory power of the variability in the models suggests that other factors also significantly impact growth, such as accompanying vegetation, climate (drought, late frost), and rodent influence. These factors notwithstanding, this document supports recent research on the beneficial effect of species diversity compared to monocultures. It also suggests that implementing silvicultural interventions regarding species arrangement from the inception of a new forest plot would be beneficial for the growth and health of young trees.