Tree migrations: a matter of scale

By Benjamin Seliger

In everyday life, trees may appear as stationary, permanent fixtures of the landscape, but in reality they are far from it. I will argue that all trees are constantly migrating, and summarize the means by which they do so in this post.

When I tell people I study tree migration, I often get funny looks. After all, how can an organism that cannot even move migrate? The answer to this, like many other phenomena in ecology, is time. Every year, mature trees release thousands of seeds in all directions, and when one of those seeds grows into an adult in a place where others of its own kind were not growing before, the species is migrating. Note that this perspective of migration is not limited to the cyclical movement of animals with the seasons, but rather an adjustment of a species’ range to preferred conditions as climate changes. I will refer to the latter as a range migration and the former as a seasonal migration. The two definitions are really explaining the same process at different scales; seasonal migration being the movement of individuals within their lifespan, and range migration as the movement of populations over the course of multiple generations. The end result for either definition is all the members of a species living in a different place than they did previously due to a change in environmental conditions. Continue reading