While it is true that individual trees are immobile, at the species level they can move and migrate as well as birds! But on a different time window.
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This is what we will delve into in this article, the first of our new summer series. As researchers in forest ecophysiology, we study the functioning of trees in relation to ecological dynamics on a larger scale. The rapidly changing climate presents many challenges that must be addressed to ensure the sustainability of forest ecosystems. Faced with these new problems, we are looking for new tools. Among these is assisted tree migration.
And to inspire us, this excerpt from a song by our national poet, Gilles Vigneault.
I planted an oak tree at the end of my field,
will I lose my pain?
am I wasting my time?
Let's get rid of definitions first: assisted migration refers to the “human-assisted movement of species in response to climate change” . We are used to associating the term “migration” with the movement of people or the seasonal flights of birds.
It may therefore seem strange to associate migration with trees, which are typically rooted in the ground and do not move. But is this really the case?
The moving forest
Tree migration occurs through seed dispersal, germination, and then the establishment of new seedlings. These, after a time, produce new seeds and contribute to a slow geographical expansion.
Migration strategies may differ between tree species: samaras of maple , carried by the wind, can travel faster and farther than the acorns of an oak tree, limited by their imposing weight. However, new seedlings need years, often decades, to grow and produce seeds that can migrate further than their parents.
This movement, which takes place on a scale of centuries, generally too slow for our conception of time, can become limiting in the face of rapid human-induced changes in climatic systems.
Fast changes, slow shafts
Current climate changes induce rapid changes in environmental conditions; no natural warming event in the past has occurred at a comparable rate. These climate changes thus exert strong pressures on forest ecosystems, in particular by modifying habitat conditions.
The vast majority of trees have migration speeds lower than the speed of movement of favorable habitats . This means that their migration to new favorable habitats (eg cold regions becoming warmer in the north) will not be able to compensate for the loss of habitats in other areas (eg warm regions becoming drier in the south).
This lag between the modification of habitat conditions and the natural migration of trees results in a loss of forest vigour. Many species are predicted to decline which may compromise local forest ecosystems.
Help trees migrate
We are called upon to find strategies to harmonize forests with new climatic conditions. This motivates researchers and managers to consider new approaches to solving this problem, for example by resorting to assisted migration .
Artificial displacement and seed planting can speed up the natural migration process and help overcome geographical barriers, such as mountain ranges or large bodies of water.
Assisted migration can therefore be applied to maintain functional forest ecosystems in the future. This is not only important for the conservation of species, but also for the maintenance of all the services provided by forests, for example the production of wood or the sequestration of carbon from the atmosphere.
In general, transfers over short distances are easier to accomplish, while migration over longer distances requires more careful planning. As the latter poses higher ecological risks, it is generally only considered for conservation action .
But enough about theory, let's move on to concrete examples.
A Canadian example
The sugar maple ( Acer saccharum ) is an iconic tree species in Canada. As climate change intensifies, southern sugar bushes (in the south) suffer from increased competition from trees that are more tolerant of hotter, drier conditions, such as American beech ( Fagus grandifolia ).
At the same time, researchers have found that regions north of the maple's range are becoming increasingly suitable for this species . In this case, assisted migration could promote faster adaptation of northern forests to new conditions, and provide services appreciated by local forest owners, such as the production of maple syrup. So why not just go ahead with this technique?
In 2019, the University of Quebec at Chicoutimi (UQAC) established an experimental sugar maple plantation at the northern edge of its range, in the Saguenay region of Quebec. The experiment is carried out in partnership with a family farming business in the region, which has chosen to devote part of its land to scientific research and to its vision of a productive sugar bush for future generations.
The plantation, which has approximately 500 young trees from several populations in Quebec and the United States, will celebrate its fourth year of life in the spring of 2024. In a few decades, excellent maple syrup could be produced, in addition to the valuable scientific data collected so far.
Similar studies have been carried out by the DREAM research network, a project of the Government of Quebec (MRNF), the USDA Forest Service and Université Laval. The trials, including a dozen species of trees planted in a mixture, are located in the Portneuf region in Quebec and in Wisconsin (United States). It tests the effects of different factors, such as microclimate, browsing and plant competition, on the acclimatization of plants. In addition, we compare the performance of plants from southern populations, adapted to conditions similar to the predictions of the future climate, with that of local populations.
Carrying out this type of experimental study provides valuable information on the characteristics that can help or hinder the success of assisted migration projects. For example, one can understand which species or populations are more susceptible to late frost events or herbivore browsing .
Implementing scientific trials today can help to fully understand the dynamics and risks associated with assisted migration, so that we can make the best forest management choices for years and generations to come.
Climate change is happening fast and forests are not growing at the same rate, so it's important to start planting tomorrow's forests today.
The authors thank Emilie Champagne of the Direction de Recherche Forestière du Québec (Ministry of Natural Resources and Forests) for contributions and comments to the written text and Les Jardins Gobeil for collaboration and material assistance with the maintenance of the experimental plantation.
Claudio Mura , PhD student in Forest Ecophysiology, University of Quebec at Chicoutimi (UQAC) ; Patricia Raymond , Research Scientist and Associate Professor, University of Quebec at Chicoutimi (UQAC) and Sergio Rossi , Professor, Department of Fundamental Sciences, University of Quebec at Chicoutimi (UQAC)