Growing Assisted Migration: Synthesis of a Climate Change Adaptation Strategy

Introduction

This resource was submitted by the Climate Risk Institute for use by the CanAdapt Climate Change Adaptation Community of Practice.

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Climate change adaptation strategies may not be at the forefront of everyone’s mind, but within the context of seed technology for forest and conservation nurseries they have significant merit. If temperature and precipitation predictions are correct, plant populations in their native settings will have to adapt or move to avoid maladaptation and/or extinction (Peters and Darling 1985). Current climate predictions would require plants to migrate 3000 to 5000 m (9842 to 16404 ft) per year far exceeds their observed maximum rates of less than 500 m (1640 ft) per year (Davis and Shaw 2001; Aitken and others 2008; Lempriere and others 2008). Assisted migration of plants, that is, human-assisted movement, may be necessary for species that are less mobile or adaptive (Peters and Darling 1985; Hoegh-Guldberg and others 2008; Vitt and others 2010). Short-lived and annual species will likely adapt faster to changes in climate than long-lived species (Jump and Penuelas 2005; Vitt and others 2010). Despite disparity in rates between climate change and observed plant migration, survival may be more determined by available geophysical connections among landscapes needed for plants to move (Hannah 2008) and whether or not suitable recipient ecosystems exist (Aubin and others 2011). Furthermore, impacts from climate change can be so abrupt, for example, the mountain pine beetle outbreak on populations of lodgepole pine (Pinus contorta) (Regniere and Bentz 2008) that management options will be limited.

Moving plants has been practiced for a long time in human history, but the movement of species in response to climate change is a relatively new concept (Aubin and others 2011). First proposed in 1985 (Peters and Darling), assisted migration has gained attention since 2007 as a climatechange adaptation strategy (Hewitt and others 2011). Preventing species extinction, minimizing economic loss (for example timber production), and sustaining ecosystem services (for example wildlife habitat, recreation, and water and air quality) are three reasons for assisted migration (Aubin and others 2011). The only known assisted migration program in the U.S. is a grassroots effort to save Torreya taxifolia (Florida torreya), a southeast ern evergreen conifer, from extinction (McLachlan and others 2007; Barlow 2011). Since 2008, Florida torreya has been planted on private lands in five southern states (Torreya Guardians 2012). To prevent economic loss in the timber industry, some Canadian provinces have adjusted their planting guidelines. (Pedlar and others 2011). Using assisted migration to sustain ecosystem services has been addressed, but is not well-studied (Jones and Monaco 2009; Aubin and others 2011). If ecosystem function and structure become a main focus in assisted migration plans, it will prompt ecologists to consider moving assemblages of species rather than moving a single species (Harris and others 2006; Park and Talbot 2012).

Risks such as establishment failure and negative effects on the recipient and donor ecosystem are associated with assisted migration (Aubin and others 2011). Establishment failure can result from moving the species before the donor site is suitable and from any number of factors familiar to traditional planting efforts (Vitt and others 2010). The species could have negative effects on the recipient ecosystem, such as genetic pollution, hybridization, function/structure impairment, pathogens, and invasion. The risk of invasion, however, is subject to debate in regards to assisted migration and climate change because the definition itself depends upon human perception (Mueller and Hellman 2008). Some degree of “invasiveness” in an assisted-migratory might be necessary for establishment. Effects on the donor ecosystem are less definitive. Over-harvesting a population at risk of decline or extinction is a concern (Pedlar and others 2011). Removing seeds or plant materials from a donor ecosystem could hinder natural adaptation and migration (Vitt and others 2010; Aubin and others 2011).

Whether or not assisted migration is implemented or even possible, management and conservation plans need to incorporate climate change research as soon as it becomes available (Peters and Darling 1985). Unfortunately, since 1985, only a handful of assisted migration guidelines have been proposed (Hoegh-Guldberg and others 2008; Vitt and others 2010; Lawler and Olden 2011; Pedlar and others 2011; Schwartz and others 2012), largely born out of conservation biology, restoration ecology, and forestry. We present a synthesis of these guidelines and include examples of current efforts and available resources for nursery managers, land managers, and restorationists.