Plant Pioneers - Assisting The Migration Of Climate-Endangered Species

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As our climate changes, many different species are already beginning to shift their distributions towards higher latitudes and elevations - travelling across continents and moving up mountains in response to changing environmental conditions⁸. Some species, however, are only able to disperse slowly, and others are unable to migrate at all due to natural barriers such as oceans and mountain ranges, or human-created barriers such as large cities and highways. So what happens when there's nowhere left to run? Or you can't run fast enough?

Worst-case scenarios have projected extinction rates of up to 35-40%^5,7, which in one study represented a potential loss of some 56,000 endemic plant species and 3,700 endemic vertebrate species⁵. It seems a bit of a no-brainer, in the conservation world, that we should do something to help prevent this, but when you start to consider what we should do the decision is never simple. Conservation in the face of climate change raises some tricky scientific and ethical dilemmas as to what we are working to preserve, and at what cost. Should we really be striving so desperately to preserve "status quo" ecological communities? Or should we "let nature take it's course"?

Lending a helping hand

Historically, our main method of protecting different habitats and species has been through in-situ conservation, often by creating parks and reserves. But as climate change causes geographical shifts in the ideal ranges of different species, the environmental conditions in these parks are likely to become less suited to the species they were created for (although they may become more suited to other species migrating into the area from elsewhere). In the face of climate change, we therefore need to "rethink what it means to save a species in the 21^st century", potentially by adopting a more hands-on approach than we are used to.

Unsurprisingly, however, assisted migration is a pretty controversial idea, not only due to the risk of translocated species becoming invasive, but also because it treats the symptoms of the problem rather than the cause³. The debate also centres around both whether we should help to facilitate the migration of "climate refugees", and if so whether we can do so without destroying other species and ecosystems in the process.

There's plenty of discussion (some rather heated) regarding assisted migration, and these papers by Hewitt et al. and Klenk & Larson give good overviews of the pros and cons raised. Including, but not limited to, the practical infeasibility of it (i.e political boundaries, failures to colonize), high levels of uncertainty and information gaps, and the ineffectiveness of assisted migration for many species in tropical biodiversity hotspots which have "disappearing climates" and no suitable sites for relocation¹.

The mostly commonly raised concern is that introduced species will have similar impacts to invasive alien species, such as uncontrolled population growth and negative impacts on resident species³. These uncertainties then present conflicting conservation priorities between the preservation of the individual species you are translocating, and the protection of the ecological community to which you are introducing that species.

So if moving species around in the wild seems to be a bit of an ecological, ethical and political minefield, perhaps doing the equivalent in ex-situ conditions could help to sidestep some of these landmines?

Plant pioneers

As mentioned in this Nature news item last month, plans are afoot to develop a network of botanic gardens between which the "chaperoned" migration of plants could be made possible.

The project is being led by Adam Smith and Matthew Albrecht from Missouri Botanical Garden and uses data from Botanic Gardens Conservation International's GardenSearch - a database of botanic gardens across the globe.

"The world's botanic gardens already cultivate around one third of the world's known plant species, many of which are increasingly threatened in the wild by climate change" says Suzanne Sharrock, Director of Global Programmes, BGCI. "BGCI is very interested in the potential to develop a network of gardens to support the ‘controlled' movement of such species into more favourable climate zones".

The aims of the project are to characterize the distribution of botanical gardens in both geographic and climatic space, and to assess the capability of a network of gardens to engage in ex-situ assisted migration. In other words they want to see if botanic gardens could potentially act as "chaperones" for the translocation of species, passing them from garden to garden, within biogeographic provinces, but outside of the species's current range. Once a climatic network of gardens has been mapped out, they will also be able to identify any significant gaps between sites.

This approach has several advantages over wild translocations: not only would the gardens provide these threatened plant species with extensive horticultural expertise, regular care, and recordkeeping, but relocations from within one garden to another will be both safer and easier than transfers between two wild locations.

Prevention is better than cure

Assisted migration is certainly no quick-fix for climate change-induced extinctions, but it is likely to become part of the solution as climate change calls for a more proactive approach to conservation. If ecological communities are already receiving "climate refugee" species, ensuring that some of these immigrant species are "climate-endangered" species could help to reduce the net rate of extinction⁸. As usual, more research will help to assess the potential impact of different translocations, as will decision-making tools and frameworks, especially when projects require inter-governmental co-ordination³. As far as scientific technicalities are concerned the result is likely to be a trade-off between the ecological risks (e.g of translocated species becoming invasive) and benefits (avoiding species extinctions)⁴. The final decision, however, is unlikely to be made by scientists as the issue is so thoroughly enmeshed in numerous practical, political and ethical dilemmas.

One of the biggest stumbling blocks is that moving a species will not always be an option. Those living on melting ice caps, or at the tops of mountains, for example, will have nowhere left to move to once these environments alter beyond a species' adaptative capabilities, or disappear altogether. Ongoing fragmentation will only make it more difficult for species to disperse across an increasingly disjointed landscape in response to changing climatic conditions, making us even more dependent on assisted colonisation. For this reason it is important that we continue to address the root causes of extinction (in this case human-induced climate change and habitat fragmentation) as well as finding the best and safest ways to slow the resulting biodiversity loss¹.

What do you think should be our priority - mitigating against climate change itself? Finding ways to lessen the impacts? Or a combination of both? Does your opinion change when you think about human climate-refugees?

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