Climate change is shifting forest conditions faster than local tree species can adapt. Higher temperatures, more frequent droughts and less predictable winters can weaken species that have been established in a region for centuries. In light of this, one idea is gaining ground: assisted migration.Assisted migration involves deliberately moving tree species or populations to regions where the future climate is expected to be more favourable. The aim is to anticipate changes rather than wait for forests to decline. While this approach may sound logical, it raises several important questions. Helping forests adapt is a legitimate ambition, but ecosystems are complex, and any intervention has its limits. Five key issues help us better understand the potential of assisted migration and the precautions it requires.As an assistant professor at the Eau Terre Environnement (ETE) Research Centre at the Institut national de la recherche scientifique (INRS), I have been working on the DREAM project, specifically on aspects related to carbon dynamics. My co-author, Mariétou Diouf, is a specialist in tree ecophysiology, and Alison Munson is currently working on several assisted migration projects for trees in Québec.The risk of invasionThe primary concern relates to the risk of ecological invasion. Moving a species outside its natural range can, in some cases, disrupt the balance of local ecosystems. Some newly introduced species can spread rapidly and take over at the expense of existing vegetation.However, this does not happen systematically, since the establishment of a tree depends on numerous factors that change over time, including soil quality, the local climate, interactions with other living organisms and the specific characteristics of the species itself. Studies have shown that some displaced species struggle to establish themselves or have lower survival rates in their new environment, while others benefit from favourable conditions that facilitate their establishment.So far, most assisted migration projects have been experimental, which limits the observation of potential impacts in different contexts. International studies have demonstrated that certain species introduced can permanently alter the biological properties of the soil and influence how other species establish themselves, sometimes several years after introduction. This possibility highlights the importance of proceeding with caution and closely monitoring transplant sites.Surviving today, but withering tomorrowEven when a tree successfully establishes itself, there is no guarantee that it will adapt to future conditions. The climate continues to change, sometimes more rapidly than anticipated.Scientists use climate models to anticipate these changes and guide planting decisions. These tools are valuable, but they cannot predict the future with certainty. Some trees may find themselves ill-suited to new climate extremes, such as intense heatwaves or late frosts.Researchers favour using a step-by-step approach to limit this risk. They test different populations of the same species, sourced from various climatic regions, and observe how they behave in new environments. Experimental programs in North America illustrate this cautious method, based on learning over time. This is the case with the DREAM project, as well as initiatives such as the Assisted Migration Adaptation Trial and TransX, which study the survival and growth of trees relocated to different sites and climates. Despite these efforts, some uncertainty remains, particularly in fragmented landscapes where forests have fewer opportunities to adapt naturally.Invisible effects on the soilWhen we talk about assisted migration, we often think of the trees themselves, but the soil plays an equally important role. Roots interact with an underground world of bacteria, fungi and other microorganisms that are essential to forest health.These organisms help trees absorb water and nutrients, and strengthen their resistance to environmental stresses. If a tree is moved to a site where these partners are absent or different, its growth may be hindered.Conversely, the presence of certain species can permanently alter the soil and, as a result, shape future vegetation through what’s known as the ecological legacy effect.These changes are often invisible in the short term, but can have long-term consequences for the entire ecosystem. To better understand these subtle yet crucial interactions, assisted migration projects incorporate soil analyses and preliminary trials.Interactions with herbivoresInsects, pathogens, deer or rodents can significantly influence the survival and growth of young plants. Although assisted migration can help certain vulnerable wildlife species adapt to habitats disrupted by climate change, relocated trees still have to contend with local wildlife.Some newly introduced species may be tasty to local herbivores, leading to significant damage. Other species, meanwhile, may be consumed less frequently, thereby altering existing food balances. In any case, these interactions play a key role in the success or failure of tree migration.To address this, researchers are working with forest managers to test various solutions, such as temporary fencing, selecting more resilient seedlings and management practices that promote better coexistence with wildlife. These approaches show that assisted migration is not limited to climate, but involves the entire ecological network.Logistical constraints, economic risksEven when ecological aspects are taken into account, assisted migration poses practical challenges. Producing seedlings, transporting them, planting them and monitoring them represent a significant investment of time and resources. On a large scale, these costs can become considerable, especially since forests are often fragmented by roads and agricultural or urban areas, complicating the planning and implementation of plantations.Assisted migration also raises economic issues related to risk-taking. Introducing unfamiliar species creates new uncertainties that forest owners — especially private ones — must learn to manage. This raises questions about the allocation of investments and the role of public land in implementing these strategies. Social and ethical questions then arise: Which species should be prioritized? Who decides? And how can climate adaptation, biodiversity and local forest uses be reconciled?Guiding the forests of tomorrowAssisted migration offers promising prospects for protecting forests from climate change. It is based on a simple idea: anticipating and acting rather than suffering the consequences.However, challenges relating to invasions, long-term adaptation, interactions with soil and wildlife and practical constraints serve as a reminder that forest ecosystems are complex.Ongoing research is helping to improve our understanding of these mechanisms and to provide a framework for best practices. By recognizing the limitations of assisted migration and integrating it into a broader forest management strategy, it becomes possible to use it as a complementary and flexible tool.Helping forests adapt to climate change does not mean controlling everything but, rather, learning to intervene with discernment while respecting the diversity and dynamics of living systems.Alison Munson has received funding from the Fonds de Recherche du Québec for the ENGAGE Program -- Citizens.Mariétou Diouf has been awarded a grant as part of a project on assisted tree migration, funded by the Fonds de Recherche du Québec through the ENGAGE Program.Anne Ola ne travaille pas, ne conseille pas, ne possède pas de parts, ne reçoit pas de fonds d'une organisation qui pourrait tirer profit de cet article, et n'a déclaré aucune autre affiliation que son organisme de recherche.