Abstract
Assisted migration of forest tree populations through reforestation and restoration is a climate change adaptation strategy under consideration in many jurisdictions. Matching climates in which seed sources evolved with near future climates projected for plantation sites should help reduce maladaptation and increase plantation health and productivity. For threatened tree species, assisted migration outside of the species range could help avert extinction. Here, we examine lessons, limitations, and challenges of assisted migration through the lens of three assisted migration field trials of conifers in Canada and Mexico: Pinus albicaulis Engelm., an endangered subalpine tree species in the mountains of western North America; the Picea glauca (Moench) Voss × P. engelmannii Parry ex Engelm hybrid complex, of great economic and ecological importance in western Canada, and Abies religiosa (Kunth) Schltdl. & Cham., a tree species that provides overwintering sites for the monarch butterfly. We conclude that: (a) negative impacts of climate change on productivity of Picea glauca × P. engelmannii may be mitigated by planting seed sources from locations that are 3 °C mean coldest month temperature warmer than the plantation; (b) it is possible to establish Pinus albicaulis outside of its current natural distribution at sites that have climates that are within the species’ modelled historic climatic niche, although developing disease-resistant trees through selective breeding is a higher priority in the short term; (c) Abies religiosa performs well when moved 400 m upward in elevation and local shrubs (such as Baccharis conferta Kunth) are used as nurse plants; (d) new assisted migration field trials that contain populations from a wide range of climates tested in multiple disparate climates are needed, despite the costs; and (e) where naturalization of a migrated tree species in recipient ecosystem is viewed as undesirable, the invasive potential of the tree species should be assessed prior to large scale establishment, and stands should be monitored regularly following establishment.
Highlights
Climate change is expected to decouple forest tree populations from the climates to which they have become locally adapted over many generations [1,2,3,4]
Natural migration of some tree populations via seed dispersal to more polar latitudes and higher elevations has already been observed [15,16,17], this is not happening at the speed needed to keep populations coupled with the climatic habitat to which they have evolved
We present three case studies of field experiments established to evaluate assisted migration in forest trees. Two of these studies pertain to tree species of conservation concern (Pinus albicaulis in Canada and Abies religiosa (Sacred fir) in Mexico) and the other deal with economically important tree species (Picea glauca × engelmannii hybrid complex known as interior spruce, in Canada)
Summary
Climate change is expected to decouple forest tree populations from the climates to which they have become locally adapted over many generations [1,2,3,4]. Natural migration of some tree populations via seed dispersal to more polar latitudes and higher elevations has already been observed [15,16,17], this is not happening at the speed needed to keep populations coupled with the climatic habitat to which they have evolved Such ongoing decoupling is creating increasing stress for tree populations. We present three case studies of field experiments established to evaluate assisted migration in forest trees Two of these studies pertain to tree species of conservation concern (Pinus albicaulis (whitebark pine) in Canada and Abies religiosa (Sacred fir) in Mexico) and the other deal with economically important tree species (Picea glauca × engelmannii hybrid complex known as interior spruce, in Canada). The aim of this paper is to summarize and discuss what we have learned, including limitations and challenges to the establishment and maintenance of the field tests, based on cases that we consider illustrative from Canada and México, in order to document our current understanding and identify past pitfalls and future research priorities for new assisted migration experiments
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