The role of complementarity and facilitation in influencing tree community resilience

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Global change factors such as non-native invasion of insects and pathogens as well as climate change are negatively affecting the growth and survival of many tree species and functioning of many forest ecosystems in a great number of regions in the world. Current studies indicate that mixtures of tree species can better cope with stressful environmental events. However, what types of mixtures to use under what types of stand and environmental conditions to maximise forest resilience to natural and human-induced stressors are mostly unknown. In this discovery research program, I intend to test several hypotheses regarding how forest composition and structure are interacting with basic coexistence mechanisms to promote (or not) both tree and forest resistance and recovery (both measures of resilience) to many different permanent and/or intermittent stressors acting alone or in conjunction. I will use a combination of controlled field experiments and permanent plots set in managed and unmanaged forests to investigate these questions. I will work closely with graduate students and Post-Docs and collaborate with scientists from around the world to answer these questions.***An ambitious new field experiment where various mixtures of tree species grown in different densities and spatial arrangements is currently being established near Ripon in Quebec, Canada, to test some of these hypotheses in a controlled setting. Data from more than 25 international tree-diversity experiments will also be used to test how tree diversity affects forest resilience to various stressors in a wide set of climatic conditions and tree species mixtures. Small and large scale permanent plots established in managed and natural forests in a wide range of environmental conditions from more than 60 countries will be used to increase the practical relevance of our findings and to test the generality of our findings. The growth and mortality at the tree and plot scales will be studied in relation to known recent climatic and biotic stressors that have occurred.***The results of this study will be used to design novel management approaches for increasing the resilience and survival of trees facing global change from urban parks and gardens, agricultural crops, and managed forests to vast protected areas of forested land. A better understanding of the benefits of maintaining or increasing tree diversity and stand complexity opens up many possible applications as we face the increasing challenge of managing and restoring increasingly novel and stressed ecosystems.