Standards for Assisted Migration of Plants
Proposed Draft of August 2004

Note: The more of these 9 standards that apply to the plant species, subspecies, or population in question, the stronger is the case for assisted migration. Terms marked by * are defined below.


1. NEEDINESS. The plant is highly threatened or endangered in the wild in its current range*.

2. IRREVERSIBLE PROBLEMS IN CURRENT RANGE. Ecological change (habitat disruption, introduction of exotics, loss of vital partners, shift in fire regime, etc.) and/or climate change is a major cause of the plant's threatened status in its current range and that remedial efforts in that range are or would be unsatisfactory for recovery.

3. SUITABILITY OF TARGET RANGE. There is evidence (e.g., specimens thriving in botanical gardens or on other grounds within the target range) that the problems of ecological or climate change could be lessened or overcome by assisted migration.

4. LOW RISK FOR RECIPIENT ECOSYSTEMS. Dispersal mode, pathogens it may carry, and other characteristics pose little or no concern that the plant will become noxious to other organisms (especially rare or threatened organisms) in the target range*, given the oversight and precautions established in implementation plans.

5. BARRIERS TO UNASSISTED MIGRATION. Corridors adequate for unassisted and timely movement do not currently exist and are not actively being promoted. In the case of plants, unassisted migration through an "adequate" corridor may nevertheless fail to be "timely," if advance at a natural and unassisted pace is deemed too slow for population survival or thrival.

UPDATE JUNE 2021 by Connie Barlow: Owing to an April 2021 paper by Brodie et al. in the prestigious journal Science and the continuing fear that an assisted migration project might result in "invasiveness" with detrimental consequences to the recipient ecosystem, it is timely for me to amend the BARRIERS standard to include what I have learned and experienced these past 17 years. Quite simply, there are natural geographic barriers that no human-mandated "corridor" can correct for rooted life forms (especially the non-wind-dispersed species). In the case of Florida Torreya, the explanation I originally formulated for probable barrier (loss of a megafaunal seed disperser) vanished as I stood alongside a free-flowing section of the Chattachoochee River in Columbus GA, about a hundred yards from the sole remaining (late 1800s) horticultural planting of Torreya taxifolia. As the early Pleistocene epoch deepened into its first peak cooling, the seeds of Torreya floated southward toward the Gulf of Mexico along this river. During floods, the river deposited some seeds high enough along the cliff-side of the river (in Florida) to start a refugial population. As I wrote in the 2-page cover letter for my 2019 submission of a "Petition to Downlist Florida Torreya", "The Chattahoochee River offered the acorn-size torreya seeds quick passage southward during glacial cooling, but there was no way to float back north."

6. RECONSTRUCTING PAST RANGE. The historical*, near-time*, or deep-time range* of the plant encompassed the target range and/or the kinds of life communities now found in the target range.

UPDATE JUNE 2021 by Connie Barlow: Owing to an April 2021 paper by Brodie et al. in the prestigious journal Science and its use of the contentious term "neo-native", I recommend that commentators on this topic familiarize themselves with the set of terms for range distinctions (historical, near-time, and deep-time) that Paul S. Martin and I included in our 2004 draft annotated list of "Standards". It was originally intended as a sidebar in our advocacy essay published in Wild Earth, "Bring Torreya taxifolia North Now". Owing to space limitations, the journal could not print the List of Standards, but I posted the list here on the Torreya Guardians website. Rereading the draft in 2021, I call attention to our summary of past range reconstruction, and now suggest that the adjectives "historical, near-time, and deep-time" also be used to modify the noun "native." For example, Florida Torreya qualifies as both a "near-time" and a "deep-time" native of the southern Appalachian mountains. It is not a neo-native. Here is the original explanation Paul and I offered in 2004:
"... For T. tax, these two standards [#4 and 5 above] can best be evaluated in tandem. Here is where our own expertise comes into play (e.g., Martin 1957; Barlow 2001), as we search for an understanding of the near-time (15,000 years ago until the time of historical records) and deep-time story of genus Torreya. It is this attention to the past that leads us to regard assisted migration for T. tax to the southern Appalachians as not so much relocation for a plant struggling with global warming as repatriation of a once-native. It is thus a form of rewilding that uses a near-time or deep-time baseline for determining native range."


7. WILLING VOLUNTEERS / PRIVATE PROPERTIES. A group of people, "plant guardians," has manifested to pursue assisted migration for the plant in question and to do so on private lands in the target range, and from private seed stocks or cuttings, such that no governmental permits would be required. This group may or may not include professional botanists and horticulturalists, and not all members of the group will necessarily agree on actions that a subset determines to take.

8. ACCESSIBILITY AND ACCOUNTABILITY. The group of Plant Guardians has established a means (e.g., a website) by which plans, actions, and results undertaken by an individual or group can be publicly posted and through which interested parties can communicate advice, concerns, and offers to assist.


* Assisted migration - Human actions intended to help a species, subspecies, or population establish and maintain populations in natural life communities outside of its current range.

* Current range - where the plant is found "in the wild" right now.

* Historic range - the range of confirmed specimen locations as evidenced by written or other human records.

* Near-time range - the range of the plant during prehistoric human occupation.

* Deep-time range - the range of the plant (species or genus) in any time period from its origin to the arrival of the first humans.

* Target range - the chosen destination(s) for assisted migration, representing (1) future range that will keep apace with climate change, (2) recovery of historic, near-time, or deep-time range or life communities, or (3) a suitable range justified by nothing more than compatibility with the ecological requirements of an imperiled plant and low risk factors of the recipient life community.

* Plant guardians - A network of individuals who have jointly and publicly stepped forward to advocate and act in behalf of a particular plant, including the possible need for assisted migration. The group may or may not include credentialed botanists, horticulturalists, or other scientists.

  • "Assisted Migration" chapter of 2007 PhD thesis by the scientist who coined the term: Brian Keel.
    The full title of Keel's thesis is "Assisted Migration as a Conservation Strategy for Rapid Climate Change: Investigating Extended Photoperiod and Mycobiont Distributions for Habenaria repens Nuttall (Orchidaceae) as a Case Study". The link above connects to a PDF of his chapter 3.

  • "Defining Migration" chapter of the Brian Keel thesis, above.
    This short chapter will be useful for those engaged in considering whether "assisted migration" or "assisted colonization" is the best term for the kinds of conservation actions now beginning to be considered.

    Connie Barlow speaking in 2004
    in favor of assisted migration
    for Torreya taxifolia

       Download in PDF articles pro and con assisted migration
       for Torreya taxifolia, which appeared as the featured
       Forum in the Winter 2005 issue of Wild Earth:

  • FOR assisted migration, by Connie Barlow & Paul Martin  

  • ANTI assisted migration, by Mark Schwartz

  • FORUM (both articles for wide screen)
  • "Taking Wildness in Hand: Rescuing Species" article by Michelle Nijhuis, Orion Magazine, May/June 2008.
    A feature article that explores the human side of the controversy over assisted migration, with Torreya taxifolia providing the focal point and actions by the citizen group Torreya Guardians stirring the brew. Comments page accessible through the foregoing link to Orion magazine.

  • "When Worlds Collide" by Douglas Fox, Conservation Magazine, Jan-March 2007 (cover story).
    This is an article exploring the debate about assisted migration of plants in an era of global warming. The work of Torreya Guardians is mentioned.

  • "A Radical Step to Preserve Species: Assisted Migration" by Carl Zimmer, New York Times (Science Times), 23 January 2007 (lead story).
    Content: References a forthcoming paper to be published in the journal Conservation Biology that encourages debate on the topic, by Mark Schwartz, Jason McLachlan, and Jessica Hellman
  • Click for a CURRENT LIST OF HOTLINKS for assisted migration and rewilding news and commentary.

    2013 ADDENDUM: Three essential papers for understanding how to minimize the risk of invasiveness in evaluating species prospects for assisted migration are:

  • "An Assessment of Invasion Risk from Assisted Migration" by Jillian M. Mueller and Jessica J. Hellmann, Conservation Biology, 28 June 2007.
    Content: Distinguishes history of inter- v. intra-continental invasive species in assessing the risks. Concludes that fish and crustaceans may pose a high risk. "We conclude that the risk of AM to create novel invasive species is small, but assisted species that do become invasive could have large effects."

    EDITOR'S NOTE: For suggested standards for translocations of aquatic species, see "Challenges and Opportunities in Implementing Managed Relocation for Conservation of Freshwater Species" by Julian D. Olden et al., Conservation Biology, February 2011.

  • "Translocation of Species, Climate Change, and the End of Trying to Recreate Past Ecological Communities" by Chris D. Thomas, Trends in Ecology and Evolution, May 2011.
    Abstract: Many of the species at greatest risk of extinction from anthropogenic climate change are narrow endemics that face insurmountable dispersal barriers. In this review, I argue that the only viable option to maintain populations of these species in the wild is to translocate them to other locations where the climate is suitable. Risks of extinction to native species in destination areas are small, provided that translocations take place within the same broad geographic region and that the destinations lack local endemics. Biological communities in these areas are in the process of receiving many hundreds of other immigrant species as a result of climate change; ensuring that some of the 'new' inhabitants are climate-endangered species could reduce the net rate of extinction.

  • "Climate Change and Forests of the Future: Managing in the Face of Uncertainty,", by Constance I. Millar et al., Ecological Adaptations, 2007.
    EXCERPT: Establish 'neo-native' forests. Information from historical species ranges and responses to climate change can provide unique insight about species responses, ecological tolerances, and potential new habitats. Areas that supported species in the past under similar conditions to those projected for the future might be considered sites for 'neo-native' stands of the species. These may even be outside the current species range, in locations where the species would otherwise be considered exotic. For instance, Monterey pine (Pinus radiata), endangered throughout its small native range, has naturalized along the north coast of California distant from its present native distribution. Much of this area was paleohistorical range for the pine, extant during climate conditions that have been interpreted to be similar to expected futures in California. Using these locations for 'neo-native' conservation stands, rather than removing trees as undesired invasives, is an example of how management could accommodate climate change. (p. 2148)

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    Annotated List of Papers/Reports Online re Assisted Migration