Le mélange d’espèces permet-il de moduler l’impact de la cécydomie (Contarinia sp.) sur la vitalité du Douglas (Pseudotsuga menziesii (Mirb.) Franco) dans les jeunes plantations ?

Details

Supervisors

Ponette, Quentin ; San Martin Gilles

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en sciences et technologies de l'environnement

Abstract

This thesis is part of an approach aimed at understanding the impact of the diversity of woody species on the functioning of forest ecosystems. It is based on the FORBIO device from Gedinne, installed in 2010, which test the effect of richness (monocultures and mixtures of 2, 3 and 4 species) and of specific composition (5 modalities per level of richness). Thus, this thesis aims to determine whether the mixture of species modulates the impact of Contarinia sp. on the vitality of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) in young plantations. To do this, we sampled Douglas-fir in monoculture, as well as in stands with 2 (2), 3 (3) and 4 (4) species in a block of the device. The level of attack by Contarinia (needles n-1), as well as the defoliation of the twigs of the year n-1 and n-2 were determined in 2018, 2019 and 2020. Likewise, the trees and their immediate neightbour (adjacent trees) were subject to dendrometric characterization in September 2020. Our results indicate an average level of attack over all three years of 2.49 as well as an average level of defoliation of 3.94. Additionally, Contarinia's attack levels appear to have little impact on the level of defoliation of target trees. This defoliation is believed to be caused by another fungus, Phaeocryptopus gaeumannii, more commonly known as Swiss rust. Then, it seems that the impact of Contarinia's attacks on subsequent years wears off after two years, and that these attacks cannot be considered cumulative. We have also observed that the growth and height of target trees do not seem to be impacted by Contarinia attacks but rather by the presence of species, such as larch, maple and oak in its immediate environment. Finally, the height growth of the target trees is primarily affected by the size of the plants, with no significant impact of Contarinia damage.