Tree Species Vulnerability

Tree Ability To Migrate

A tree species’ geographic range is determined largely by climatic conditions suitable for its reproduction, growth and survival. According to climate projections, the location of these suitable habitats could change considerably by the end of the century. For some species, areas that were previously not suitable at the northern edge of their range may become suitable. For others, the changes could push species outside of their suitable habitat entirely (see climate envelope maps from the Plant Hardiness website http://planthardiness.gc.ca/). Consequently, tree species will need to migrate great distances to keep up with changes in suitable habitats.

Strategies that underlie tree species ability to migrate

Three main strategies drive species migratory ability:

1) Reproductive capacity: Successful migration depends on the reproductive capacity of the source population. It is determined by the age at which a tree starts producing seed, how much seed they produce and the proportion of seeds that germinate.

2) Dispersal ability: Dispersal is the primary mechanism through which species expand their distribution. Species that are able to disperse seeds over long distances have a higher likelihood of keeping up with shifting suitable habitats.

3) Colonization potential at the advancing front: Once seeds reach a new site, seed germination rates, seedling survival rate, as well as the ability to rapidly produce seeds will largely determine species colonization success. Resource specialization, such as the need for specialized habitats or specific seed bed preferences, could influence colonization potential. Once colonized, species that can increase their population size rapidly will play a critical role in its migration success.

How to Interpret the Index

Index scores

Indices were developed for three strategies: Reproductive capacity, Dispersal ability and Colonization potential. An index value was attributed to each species based on its relative ability to use a given strategy when faced with rapid shifts in suitable climatic conditions. Five classes of sensitivity-tolerance were defined: highly sensitive, medium sensitive, intermediate, medium tolerant, highly tolerant.

A data confidence value is also attributed to each sensitivity index value. Data confidence is based on the number of independent sources, whether the data were quantitative or qualitative, whether there is known variation in values and the source of the data. This information was ranked into five confidence classes: low, medium-low, intermediate, medium-high, high.

Explore the Migration Indices

For direct access to data visualization tool on Tableau Public, please visit Tree Sensitivity to Climate Change - Migration Index Tool

For more information on index development and how sensitivity classes were defined, see the supplementary material from the publication “Using a Trait-Based Approach to Compare Tree Species Sensitivity to Climate Change Stressors in Eastern Canada and Inform Adaptation Practices” (PDF download available here: https://www.mdpi.com/1999-4907/11/9/989/s1).

Glossary - Glossary of terms used in vulnerability assessments

Another set of strategies that characterise species’ ability to adapt in the face of climate change are presented on this page.

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