Soutenance de M. Degi Harja Asmara

23 septembre 2020 14 h à 17 h

Lieu : À distance

Agroforestry on post-mining restoration: a challenge beyond plant mixture system

Agroforestry is a dynamic system of ecological management of renewable natural resources, which by integrating woody species into agricultural fields, farms and other landscapes, diversifies and sustains production for increased socio-economic and environmental benefits. As a solution for the provision of ecosystem services, its application to the restoration of degraded, damaged, or destroyed (3-D) ecosystems becomes very important. 3-D lands by mining are characterized by low fertility soil and sometimes high levels of contaminants. These conditions make them difficult to obtain a short-term advantage from agroforestry compared to arable lands, but agroforestry main restorative function of restoring ecosystem services and increasing resilience can be beneficial in the long term. The challenge is to develop the best strategy to accelerate plant productivity while improving the soil and the ecosystem through a combination of ecological engineering techniques for bioremediation of mining areas. Here we explore the mixture of plants, microbial inoculation, and biochar amendment, in a woody-herbaceous agroforestry system. The goal is to find the best bioremediation scenario from the combined effects of mixing plants and other related ecological factors. Previous research on agroforestry and restoration has been reviewed worldwide, including the application of the agroforestry concept in bioremediation of post-mining land area. The known restoration strategy in a given environment is not a universal solution. Thus, the identification of any important aspect of previous work on restoration and agroforestry is crucial. The strategy of mixing plants is an important factor in the successional process. In this research, we applied the concept of modified nelder plots for the combination of plant species in a greenhouse experiment on waste rock and fine tailing to explore the interaction at the start of planting. We also applied microbial inoculum and biochar to the plant mixture in greenhouse and field tests on waste rock and fine tailing as soil materials. The performance of the co-planting of four woody species green alder (Alnus viridis (Chaix) DC. ssp. crispa (Aiton) Turrill),  white spruce (Picea glauca (Moench) Voss), aspen (Populus tremuloides Michx.) and littletree willow (Salix arbusculoides Andersson) with the herbaceous plant species oat (Avena sativa L.), red fescue (Festuca rubra L .),  and white clover (Trifolium repens L.) was tested. Mixing plants is a very important principle in restoration practices, given its known role to increase biodiversity and functional diversity in the sustainable ecological system. Although the plant mixing strategy has been rarely explored, we have found that the combination of species has a neutral effect (neither advantages nor disadvantages) compared to a single species in the nelder plots experiment. At the same time, the positive effect of the density suggested that the microclimate improvement had played a role in the early growth of the plantations. The field trial confirms the positive effect of the microclimate modification on plant productivity in higher planting density. The trade-off on plant competition has shown, however, that the highest density does not necessarily show an optimal condition for plant productivity. The interaction effect of biochar and inoculation treatment shows the benefit of this treatment, although the impact varies according to the density of planting. We suggest that improving the microclimate is important for early plant growth. This improvement can be achieved by adjusting the planting density and the combination of the mixture of plant growth forms. The effect of biochar on albedo and soil surface temperature can be as important as it alters the physical characteristics of the soil. In conclusion, we recommend plant mixture in bioremediation practices in order to improve the microclimate, biodiversity and bio-productivity.

Informations supplémentaires :

Membres du jury

Président

M. André Desrochers
Université Laval, Faculté de foresterie, de géographie et de géomatique

Examinateurs

M. Damase Khasa
Université Laval, Faculté de foresterie, de géographie et de géomatique

Mme Suzanne Allaire
Geca Environnement

M. Lin Chung-Ho
University of Missouri

M. Nathan Basiliko
Laurentian University

M. Silvio José Gumiere
Université Laval, Faculté des sciences de l'agriculture et de l'alimentation

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