A framework for debate of assisted migration in an era of climate change

The Torreya Guardians are trying to save the Florida torreya (Torreya taxifolia Arn.) from extinction (Barlow & Martin 2004). Fewer than 1000 individuals of this coniferous tree remain within its native distribution, a 35-km stretch of the Apalachicola River, and these trees are not reproducing (Schwartz et al. 2000). Even if the Florida torreya was not declining toward extinction, the species would be at risk from climate change. Warming is projected to either significantly reduce or eliminate suitable habitat for most narrowly endemic taxa (Thomas et al. 2004; Hannah et al. 2005; Peterson et al. 2006), forcing species to colonize new terrain to survive.

The focus of the Torreya Guardians is an “assisted migration” program that would introduce seedlings to forests across the Southern Appalachians and Cumberland Plateau (http://www.TorreyaGuardians.org). Their intent is to avert extinction by deliberately expanding the range of this endangered plant over 500 km northward. Because planting endangered plants in new environments is relatively simple as long as seeds are legally acquired and planted with landowner permission, the Torreya Guardians believe their efforts are justified. Introducing this species to regions where it has not existed for 65 million years is “[e]asy, legal, and cheap” (Barlow & Martin 2004).

If circumventing climate-driven extinction is a conservation priority, then assisted migration must be considered a management option. Compelling evidence suggests that climate change will be a significant driver of extinction (McCarthy et al. 2001; McLaughlin et al. 2002; Root et al. 2003; Thomas et al. 2004). Researchers typically conclude that mitigating climate change and providing reserve networks that foster connectivity and movement should be a priority (e.g., Hannah et al. 2002). Ecologists must recognize, however, that even optimistic estimates of naturalmovement may be insufficient for species to keep pace with climate change.

Assisted migration is a contentious issue that places different conservation objectives at odds with one another. This element of debate, together with the growing risk of biodiversity loss under climate change, means that nowis the time for the conservation community to consider assisted migration. Our intent here is to highlight the problem caused by a lack of a scientifically based policy on assisted migration, suggest a spectrum of policy options, and outline a framework for moving toward a consensus on this emerging conservation dilemma.