Climate change is expected to exert pressure on species to either adapt or move. Climatic ranges for many tree species in Canada are expected to shift northward by roughly 300 kilometres (km) over the next 50 years. Given that tree species have an average migration rate of about 5 km per 50 years, it is unlikely that they will be able to keep up with these projected shifts. Tree species therefore may no longer be suited to their environment, which could reduce forest health and productivity and have related impacts on forest biodiversity.
Conservation concern versus risks
Assisted migration is the human-assisted movement of plants and seeds to new locations where they will be suited to projected future climate conditions. Some species are thought to be particularly vulnerable to climate change, and proponents of assisted migration suggest that this approach may be the only means to save them. But there are well-documented risks associated with the movements of species, including invasive spread of the species and introduction of new pests and diseases throughout the new location, as well as wasted resources associated with failed attempts to move species. These risks have led to debate about whether there is an appropriate role for assisted migration in biodiversity conservation efforts.
Lower risk with commercial tree species
However, a different style of assisted migration has emerged in the context of forest management. Because major tree species generally have large geographic ranges, assisted migration of seeds or seedlings can occur within, or slightly beyond, existing current range limits, significantly reducing the risks. In Canada, while provincial resource management agencies have previously restricted the movement of seeds to ensure that sites are regenerated using locally adapted sources, interest in assisted migration is growing, and several provinces have recently modified policies to allow expanded northward and “upslope” seed movements (i.e., using seeds at higher elevations).
Scientific advances in this area are being made through the use of data from forest genetics trials, which provide insights into how seed sources may respond to rapid climate change. Given that hundreds of thousands of hectares of forest are regenerated annually in Canada, assisted migration of commercial tree species could represent a relatively low-risk and potentially effective approach to introducing a degree of climate change resilience into Canadian forests in the future.
- McKenney, D.W., Pedlar, J.H., et al. 2011. Revisiting projected shifts in the climate envelopes of North American trees using updated general circulation models. Global Change Biology 17, 2720–2730.
- McLachlan, J.S., Clark, J.S., et al. 2005. Molecular indicators of tree migration capacity under rapid climate change. Ecology 86, 2088–2098.
- McLachlan, J.S., Hellmann, J.J., et al. 2007. A framework for debate of assisted migration in an era of climate change. Conservation Biology 21, 297–302.
- Pedlar, J., McKenney, D.W., et al. 2011. The implementation of assisted migration in Canadian forests. Forestry Chronicle 87, 766–777.
- Pedlar, J.H., McKenney, D.W., et al. 2012. Placing forestry in the assisted migration debate. BioScience 62, 835–842.
- Ricciardi, A., and Simberloff, D. 2009. Assisted colonization is not a viable conservation strategy. Trends in ecology and evolution 24, 248–253.
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