Frequently asked questions

Scroll down to find answers to key questions on assisted migration and MigFoRest. This FAQ will be regularly updated.

With climate change, we observe an increase in frequency and intensity of disturbances causing majors forest mortality (droughts, forest fires, pest outbreaks…). Those are expected to further increase over the next decades, in Europe and all around the world.

Climate change causes a form of South-to-North climate migration. This pushes species, both animal and plant, to adapt or move in order to “follow” the conditions that enable their development. The climatic niches of the different tree species will be modified to a greater or lesser extent in north-western Europe.

The rapid pace of change today places severe constraints on the adaptation and migration of tree species. Estimates of the migration rate required for species to keep pace with climate change are commonly higher than 1000 m a year, which is much higher than the capacity of trees to migrate. Indeed, it is thought that tree species dispersal capacities allow them to migrate less than 500 m a year (and often less than 100 m a year).

In order to prevent the potential collapse of certain species' populations, and to maintain forests and the services they provide (wood production, carbon storage, water regulation, etc.), this movement can be encouraged by man. This is known as assisted migration.

 

Assisted migration is a general term that encompasses a variety of different potential actions, which have substantial differences in terms of risk, ecological implications, and policy considerations. Here are some of the commonly used terms that distinguish between different forms of assisted migration:

  • Assisted population migration (also assisted genetic migration or assisted gene flow) – moving seed sources or populations to new locations within the historical species range. Example: planting in Belgium of sessile oaks (Quercus petraea) from Southern France.
  • Assisted range expansion – moving seed sources or populations from their current range to suitable areas beyond the historical species range, facilitating or mimicking natural dispersal. Example: planting in Belgium of maritime pines (Pinus pinaster)
  • Species introduction - (also species rescue, managed relocation, or assisted species migration) – moving seed sources or populations to a location far outside the historical species range, beyond locations accessible by natural dispersal.  In other words, species introduction happens when species are translocated beyond physical barriers that could not be crossed naturally (oceans, deserts, …) Example: planting in Belgium of liquidambar (Liquidambar styraciflua)

In the context of MigFoRest, only the 2 first forms of assisted migration are experimented.  

Within the MigFoRest framework, only movements of origin and species from the European continent will be considered. This is a stricter vision of assisted migration, in which only movements that might occur naturally in response to climate change are included. Intercontinental movements are excluded. The species proposed are indigenous to the target region (e.g. sessile oak  (Quercus petraea)of southern provenance) or to regions close to it (e.g. Hungarian oak : Quercus frainetto). As these species have evolved in the presence of a complex of European organisms (fungi, bacteria, insects, etc.), the risks (invasive and sanitary) associated with such introductions are limited. The term “introduction” is used in this document to describe these intra-continental movements. This approach should not be confused with the introduction of totally new species.

Typically, good candidates for assisted migration are species with a wide distribution in Europe, with populations present in southern regions in particular, and certain provenances of which are therefore “pre-adapted” to the climatic conditions expected here, such as sessile oak (assisted provenance migration, see above). The same applies to species found only in latitudes lower than ours and likely to migrate naturally northwards, such as downy oak (Quercus pubescens).

Thus, only European species will be planted.

The ten selected species belong to four genera:

🌲 Abies (firs) : ​silver fir (A. alba), Greek fir (A. cephalonica), Spanish fir (A. pinsapo);

🌳 Quercus (white oaks) : sessile oak (Q. petraea), pedunculate oak (Q. robur), pubescent oak (Q. pubescens);

🌳 Tilia​ (lime trees) : small-leaved lime (T. cordata), large-leaved lime (T. platyphyllos);

🌳 Sorbus (rowans) : wild service tree (S. torminalis), ​service tree (S. domestica).

These are the species from which genetic diversity will be studied and seedlings will be produced by the project partners. 

 In addition to these, other species could be planted, depending on their availability in the nurseries: Hungarian oak (Quercus frainetto), Pyrenean oak (Quercus pyrenaica), zean oak (Quercus canariensis), silver lime (Tilia tomentosa), whitebeam (Sorbus aria), Oriental beech (Fagus orientalis), etc.

 🌍 All of these species originate from Europe.

  • Increase the resistance and resilience of our forests by enhancing the genetic diversity, particularly in currently vulnerable stands
  • Assisted population migration and assisted range expansion may not add much cost to existing practices of forest regeneration for species that are routinely planted
  • Provenance trial data are available for many widespread, commercially valuable tree species, which will help managers make informed decisions about the performance of seed sources from outside their local area
  • The genetic diversity of seed orchards can be controlled or increased to provide a suitable seed source for commercially valuable trees
  • Assisted migration can help maintain crucial ecosystem functions (wildlife habitat, carbon sequestration, etc.), particularly when local species are already declining or are anticipated to decline in the future


  • The main risk of assisted migration failure is linked to uncertainties about the current and future climate. In other words, a tree species that would be adapted to a warmer climate in the future may not be able to withstand a current climate that is still too marked by late frosts, for example.
  • Although the risk is low based on the selected species (see below), the introduction of a new species into a territory is always associated with an invasive risk. Ideally, the species should spread, but not excessively. To minimize these risks, introductions are always accompanied by monitoring over time, so that the species can be eradicated if necessary.
  • Although here also, the risk is mitigated by the species selection, migrated species may unknowingly introduce pests or diseases into new areas, particularly with longer transfer distances. This will also be closely monitored over time. This risk will also be strongly reduced by growing the imported seedlings in nurseries in NWE. There will be in consequence no importation of soil and soil biota.
  • Disturbing the ecosystem in place. The biological potential of every migrated species will be closely monitored over time. Biological potential refers to the ability of an introduced species to host a range of organisms (non-pest insects, among others). For example, the aim will be to assess which oak from southern Europe is currently associated with insect communities similar to our native oak groves and would therefore be the most likely to maintain the ecosystem in place.


The functional complex network approach aims at increasing the resilience of forests by maximising their resistance and their recovery potential from major disturbances.

The forest ecosystem can be seen as a network of stands that are interconnected through seed and pollen exchanges. Species are considered according to their functional traits, i.e. the measurable characteristics that influence their performance in terms of growth, survival or reproduction (seed mass or rooting depth, for example). This allows to evaluate characteristics of the ecosystem that potentially ensure its resilience, particularly:

  • Functional diversity: the diversity of “functions” of the trees present. High diversity enables the forest to cope with a wide range of disturbances.·
  • Functional redundancy: the presence of several species fulfilling the same “functions”, which will subsist in the ecosystem even if a species disappears.
  • Connectivity: connectivity between stands through seed and pollen dispersal. Following a disturbance, connectivity enables the regeneration of a damaged stand from seeds of nearby species.
  • Centrality: central stands are the ones that contribute the most to the network connectivity and allow the efficient dispersion of species.

In the context of assisted migration, the planting distribution is optimized through the strategic establishment at landscape level of species or provenances resistant to climate change. The planting efforts are distributed to maximise diversity and its spread across the network. It can therefore be seen as a form of “vaccination” of the landscape against disturbances caused by climate change.


How will planting sites be selected?

In practice, MigFoRest planting sites will be selected following the functional complex network approach (see above), giving priority to:

  • The least diverse sites
  • Stands composed of species that are most at risk from climate change
  • Central sites, which will allow the dissemination of planted species and provenances in the landscape


Where will MigFoRest experiment assisted migration?

The MigFoRest project partners have preselected the forest areas where assisted migration will be proposed for deployment. You see the 7 areas on the map below. The next step will be to define the exact boundaries of the planting sites that will make up the pilot territories within those proposed areas. Talks are ongoing with public and private forest owners eager to take part in the project.





Assisted migration is not a miracle solution, but one strategy among others (based, for example, on natural regeneration) for adapting forests to the effects of climate change. Combining different strategies will maximize chances to preserve strong and multifunctional forests. It is MigFoRest's mission to weigh up the pros and cons of assisted migration, within a well-defined framework based on real experiments in pilot areas. The lessons learned will be shared with public authorities, foresters and all forest lovers.


Bibliography:

Williams, M.I., Dumroese, R.K., 2013. Preparing for Climate Change: Forestry and Assisted Migration. Journal of Forestry 111, 287–297. https://doi.org/10.5849/jof.13-016 

Handler, S.; Pike, C.; St. Clair, B.; 2018. Assisted Migration. USDA Forest Service Climate Change Resource Center. https://www.fs.usda.gov/ccrc/topics/assisted-migration 

Musch Brigitte ; Paillassa Eric, 2024 « Migration assistée des essences forestières : un levier d’adaptation parmi d’autres », in Annales des Mines n°115 RE 2024 07 Numéro complet version internet v03 (annales.org) 

Société Royale Forestière de Belgique, Silva Belgica 3/2024, “MigFoRest, un nouveau projet d’envergure porté par la SRFB” 

Loarie, S.R., Duffy, P.B., Hamilton, H., Asner, G.P., Field, C.B., Ackerly, D.D., 2009. The velocity of climate change. Nature 462, 1052–1055. https://doi.org/10.1038/nature08649

Pearson, R., 2006. Climate change and the migration capacity of species. Trends in Ecology & Evolution 21, 111–113. https://doi.org/10.1016/j.tree.2005.11.022

Svenning, J., Skov, F., 2007. Could the tree diversity pattern in Europe be generated by postglacial dispersal limitation? Ecology Letters 10, 453–460. https://doi.org/10.1111/j.1461-0248.2007.01038.x

Patacca, M., Lindner, M., Lucas‐Borja, M.E., Cordonnier, T., Fidej, G., Gardiner, B., Hauf, Y., Jasinevičius, G., Labonne, S., Linkevičius, E., Mahnken, M., Milanovic, S., Nabuurs, G., Nagel, T.A., Nikinmaa, L., Panyatov, M., Bercak, R., Seidl, R., Ostrogović Sever, M.Z., Socha, J., Thom, D., Vuletic, D., Zudin, S., Schelhaas, M., 2023. Significant increase in natural disturbance impacts on European forests since 1950. Global Change Biology 29, 1359–1376. https://doi.org/10.1111/gcb.16531

Seidl, R., Thom, D., Kautz, M., Martin-Benito, D., Peltoniemi, M., Vacchiano, G., Wild, J., Ascoli, D., Petr, M., Honkaniemi, J., Lexer, M.J., Trotsiuk, V., Mairota, P., Svoboda, M., Fabrika, M., Nagel, T.A., Reyer, C.P.O., 2017. Forest disturbances under climate change. Nature Clim Change 7, 395–402. https://doi.org/10.1038/nclimate3303

Messier, C., Bauhus, J., Doyon, F., Maure, F., Sousa-Silva, R., Nolet, P., Mina, M., Aquilué, N., Fortin, M.-J., Puettmann, K., 2019. The functional complex network approach to foster forest resilience to global changes. For. Ecosyst. 6, 21. https://doi.org/10.1186/s40663-019-0166-2

Violle, C., Navas, M., Vile, D., Kazakou, E., Fortunel, C., Hummel, I., Garnier, E., 2007. Let the concept of trait be functional! Oikos 116, 882–892. https://doi.org/10.1111/j.0030-1299.2007.15559.x