Public Thesis Defense - ELI

Radial growth response to climate and drought of four non-native tree species in their area of introduction in Wallonia (Belgium) by Camille GUISSET

Pour l'obtention du grade académique de Doctorat en Sciences agronomiques et Ingénierie biologique

Climate change and increasing disturbances such as drought are threatening forest resilience worldwide. In this context, promoting specific and functional diversity in forests at the regional scale may be a key element to maintain their productivity, and foster their ability to cope with extreme events. Given the significant decline of several of the most abundant European tree species, complementing them with non-native, more tolerant to drought species could be a promising avenue.

The overall objective of this thesis was to improve our current understanding of the radial growth response to climate, and in particular to drought, of four non-native species in their area of introduction in Western Europe (Wallonia, Belgium). To this end, we used a dendroecological approach in 24 forest stands and 11 arboreta.

To begin with, we focused on Douglas fir (Pseudotsuga menziesii (Mirb.) Franco), a well-established non-native species in Western European forests, usually promoted for its drought tolerance. Yet, Douglas fir has recently shown increased sensitivity to warm and dry conditions. First, we identified the main climatic driver of its radial growth, taking into account the influence of site conditions and stand density. Second, we characterized its response to climatic droughts of different timing, intensity, and consecutive occurrence.

Then, we focused on three novel non-native species: Nordmann fir (Abies nordmanniana (Steven) Spach.), Lawson cypress (Chamaecyparis lawsoniana (A.Murray bis) Parl.), and Western redcedar (Thuja plicata Donn ex D.Don.), which are not currently widely planted in Western European forests, although they may represent promising alternatives. Drought resilience of these species was assessed and compared to Douglas fir using the same dendroecological approach.

This thesis provides insights into the potential of promoting these species to increase forest tree diversity at regional scale, and thereby promote its resilience to global change.

Jury members :

• Prof. Quentin Ponette and Prof. Caroline Vincke (UCLouvain) (Supervisors)
• Prof. Emmanuel Hanert (UCLouvain) (Chairperson)
• Prof. Nathalie Bréda (INRAE, France)
• Prof. Xavier Draye (UCLouvain)
• Prof. Mathieu Lévesque (ETH Zurich, Suisse)

Pay attention : the public defense of Camille GUISSET will also take place in the form of a videoconference

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