Assisted Migration or Assisted Colonization: What's In a Name?
Commentaries solicited by Torreya Guardians


From its beginning in 2004, the very loose-knit organization Torreya Guardians was formed to move ahead with "assisted migration" for one highly endangered species, Torreya taxifolia. The organization has its roots in a paper published in the Fall 2004 issue of Wild Earth, titled "Bring Torreya taxifolia North — Now," by Connie Barlow and Paul S. Martin. This article was published about a year after email debate and communications had been ongoing among a dozen naturalists, botanists, and ecologists, among them Barlow, Martin, Hazel Delcourt, Bill Alexander, Peter White, Mark Schwartz. Barlow and Martin decided that the group could not reach common ground and thus split off to publicly propose the radical end: assisted migration. Importantly, their published article established the rationale for such assistance not only in the plant's neediness, but also from a deep-time perspective that portrayed the plant as simply being given some assistance for moving back to what would have been its "native habitat" in prior instances of interglacial warmings over the past several million years.

In "Climate Change and Moving Species: Furthering the Debate on Assisted Colonization", by Malcolm L. Hunter Jr. (Conservation Biology Vol 20(5), 2007), the term assisted colonization was proposed as a replacement for the original term assisted migration (the latter likely to have been first used by ecologist Brian J. Keel). Hunter wrote:

"I have used the term assisted colonization in contrast to assisted migration used by McLachlan et al. because many animal ecologists reserve the word migration for the seasonal, round-trip movements of animals (Wilcove 2007) and because the real goal of translocation goes beyond assisting dispersal to assuring successful colonization, a step that will often require extended husbandry."

18 July 2008, marked a Policy Forum posting that furthered the term "assisted colonization": POLICY FORUM: ECOLOGY: "Assisted Colonization and Rapid Climate Change" by O. Hoegh-Guldberg, L. Hughes, S. McIntyre, D. B. Lindenmayer, C. Parmesan, H. P. Possingham, and C. D. Thomas, in Science 18 July 2008: 345-346.

This webpage has been created to support moderated discussion of the choice in terminology: assisted colonization v. assisted migration. The first posting is by webmaster and Torreya Guardians founder Connie Barlow.

  • July 19, 2008 / by Connie Barlow / Pro "Assisted Migration" as the term of reference

    Here are the reasons that I advocate for retention of the original term, "assisted migration":

    1. Unfortunately, for many of us, the term "colonization" has hegemonic overtones harking back to European "colonization" of the world. In contrast, "migration" has an immediate natural and organic cast to it.

    2. "Migration" has its emphasis on the movement itself — thus feeling less interventionist than a word that places emphasis on a desired end result, "colonization." Indeed, "assisted migration" evokes subsequent discussion of how much to assist the species in its success, once the act of migration itself is completed. For example, Torreya Guardians are now discussing whether or not to assist its rewilded T. taxifolia seedlings with soil supplementation/liming at the time of forest plantings (scheduled for July 30, 2008 in Waynesville NC). In contrast, the term "colonization" implies that the effort is incomplete unless management interventions continue after the transfer, toward the goal of ensuring successful establishment and eventual reproduction. (Note: If one provides soil supplementation or other assistance as a norm upon arrival, then there is less opportunity to "read" the response of the species itself as to whether the landing site actually meets all its needs, or whether, in fact, a better migration target might be attempted with a subsequent batch of immigrants.)

    3. "Migration" inclines one to think that either something has gone catastrophically wrong with the native home, or that the movement is part of recurring cyclic phenomena — seasonal in the case of Monarch butterflies, or in the case of genus Torreya (and presumably many other nonendangered plants), cyclic movement of plants upslope/downslope or north/south in sync with the pulses of glacial warming and cooling at the scale of geologic time. In contrast, "colonization" may indicate movement of an expansionist (opportunistic or hegemonic) cast, even while the home range is still quite viable for the species in question.

    4. "Migration" is suggestive of more localized and contiguous movements, whereas "colonization" often refers to human-led actions that can spot-move from and to anywhere on the globe — indeed, even interplanetary, as in "colonization of Mars" or establishment of a human "colony" on the moon.

  • July 20, 2008 / by Chris Thomas (co-author of the July 2008 key paper on "assisted colonization" in Science journal / Pro "Assisted Colonization" as the term of reference
    NOTE: Chris Thomas (Dept. Biology, University of York, UK) sent this statement by email reply to Torreya Guardians in response to Connie Barlow's request for elaboration. It is printed with permission of the author.

    I was personally particularly keen that this issue be described as "assisted colonisation" rather than the more commonly used "assisted migration". This is my personal view, and other authors of our paper might possibly wish to add something.

    In common usage (outside pure science), "migration" is most commonly used in two major contexts.

    The first, and most common, is to describe the seasonal return migration of birds and other groups of animals. This is quite clearly NOT what is being discussed. There are already policy reports and published scientific papers on the potential consequences of climate change for these "true" migrants, so I believe that it will be very confusing to use "assisted migration" as the general term to describe the type of endeavour we are discussing.

    The second common useage relates to human migration, meaning the net flow of people from one region to another. The connection with this is also undesirable because (a) this already has a negative image in many people's minds, and (b) it usually represents the flow of individuals from one region to another, already populated, region, rather than establishment in an area without human populations.

    In a scientific context, the term migration is also sometimes used in ecology to describe the unidirectional movement of individuals from one location to another. However, migration in this context normally means the act of movement itself, and not the establishment of new populations in the locations where individuals arrive (although this may be the consequence). Assisted colonisation does not stop at moving individuals; it may also require preparation (and protection) of sites to receive the immigrants, and subsequent management of the establishing population until such time as a self-sustaining population has been achieved.

    My personal belief is that "assisted colonisation" avoids confusion with other types of migration, and identifies that establishing populations at the destination is the key goal (not simply moving individuals).

    best wishes,
    Chris Thomas

  • July 21, 2008 / by Malcolm L. Hunter (author of the June 2007 paper in Conservation Biology that proposed the terminology change / Pro "Assisted Colonization" as the term of reference
    NOTE: Malcolm Hunter (Dept. Wildlife Ecology, University of Maine, USA) sent this statement by email reply to Torreya Guardians in response to Connie Barlow's request for elaboration and Chris Thomas's reply to her. It is printed with permission of the author.

    Dear Connie et al:

    I understand that I am the person responsible for the proposed switch to "assisted colonization", and having read the four reasons you support continued use of "assisted migration" I have to stand by my original argument and agree with Chris' elaboration. "Colonization" is a perfectly acceptable word among ecologists, and your concerns about its "hegemonic overtones" will not worry most scientists who are primarily concerned with evaluating this management option in clear language rather than advocating it with the public.

    mac hunter

  • July 20, 2008 / by Hugh Possingham (co-author of the July 2008 key paper on "assisted colonization" in Science journal / Pro "Assisted Colonization" as the term of reference
    NOTE: Hugh Possingham (Centre for Applied Environmental Decision Analysis, University of Queensland, Australia) sent this statement by email reply to Chris Thomas, and cc-d Torreya Guardians. It is printed with permission of the author.

    I agree completely, and in one of my interviews I clarified this point also, although not as clearly as you have, Chris.

  • July 21, 2008 / by Jessica Hellmann (co-convenor of the August 2008 Working Group meeting on Assisted Colonization prior to annual meeting of the Ecological Society of America) / Agrees with need to address the naming issue at the ESA pre-meeting
    NOTE: Jessica Hellmann (Dept. Biological Sciences, University of Notre Dame, USA) sent this statement by email reply to Torreya Guardians in response to Connie Barlow's request for elaboration. It is printed with permission of the author.

    Dear Connie,
    Thank you for your email. I am sympathetic to your concerns, and we will discuss it at the ESA meeting. I also understand the authors' worry that "migration" tends to refer to seasonal movements, e.g., migratory birds. But I also think that the term "migration" is also well defined in the paleo literature with the definition that we intend in this modern context.

    My own concern about "assisted colonization" is the same that Chris Thomas raises in his email about "assisted migration." So, clearly, this needs more discussion. I tend to think of "colonization" in the way that it is defined by the invasion pathway — as the first step in population establishment. Instead, we might envision more conservation action than just establishment. But then, Thomas says the same about "assisted migration" and doesn't feel that "assisted colonization" has that problem. Again, I'll do my best to raise your concerns at the meeting.

    Just previous to the ESA meeting, we're gathering a group of conservation biologists, invasion biologists, lawyers, ethicists, and economists to form a working group that we think will have something meaningful to contribute to this issue. (The working group is being convened by myself, Mark Schwartz, Jason McLachlan, and Dov Sax.) We'll talk about the naming issue with that group as well, and I'll let you know what they had to think.

    I've seen your site, and I've enjoyed watching it grow. Thanks very much for your efforts on this important issue — you guys started it all!
    Best wishes,

  • July 31, 2008 / by Connie Barlow (Torreya Guardian) / Acceptance of either terminology; advocacy of "rewilding" as a correlative term

    After reading all 4 comments (above), I now feel less squeamish about the terminology for this effort shifting from the original "assisted migration" to "assisted colonization". From my deep-time perspective (see my 2001 book, The Ghosts of Evolution), and having been inspired to begin the discussion that eventuated in Torreya Guardians after I read Forests in Peril: Tracking Deciduous Trees from Ice-Age Refuges into the Greenhouse World (2002, by palynologist and deep-time ecologist Hazel Delcourt), I still regard "migration" as the preferred term. This is because I regard our assistance today as mimicking actual migration patterns that likely played out as climate warmed during previous peak-interglacial periods — that is, episodes of climate change in which human interference in the natural world had not yet disrupted the continuity of natural corridors for long-term migratory movement, and when humanity had not yet undermined natural dispersal by extincting or extirpating seed dispersers of plants (such as tortoises and squirrels as dispersers of Torreya taxifolia).

    One other term I'd like to toss into the mix for discussion: rewilding. Rewilding was introduced professionally in the following two papers: (1) "Rewilding North America" by Josh Donlan and 11 other authors, Nature, 18 August 2005 (2 pages), and (2) "Pleistocene Rewilding: An Optimistic Agenda for the 21st Century" by Josh Donlan and 11 other authors, American Naturalist, November 2006, vol 168: pp 660-681. Yesterday, a group of Torreya Guardians, colleagues, and a writer and photographer recording the event for Audubon magazine undertook what we regard as the first rewilding of the highly endangered "Florida" conifer, Torreya taxifolia. Others have already intentionally or unintentionally planted this species northward into the Appalachian Mountains in ways that constitute "assisted migration" or perhaps even "assisted colonization", but such plantings in home gardens and institutional botanical gardens are not in wild, forested habitats — nor in great enough numbers to ensure long-term population survival and pollination in this dioecious species (male and female reproductive organs occurring on separate plants).

    Yesterday, we planted 10 seedlings on one property and 21 on a second property in the vicinity of Waynesville, NC. Elevations were 2600 and 3400 feet, respectively. We chose natural forested landscapes with fully deciduous canopy, on somewhat steep slopes. Deciduous canopy will allow this subcanopy evergreen conifer to have access to nearly full sun in the early spring and late fall (as well as winter). Significantly, at both sites where our potted seedlings of Torreya taxifolia were planted, dying hemlocks were evident. Perhaps this "deep-time native" of the Appalachians will be able to ecologically serve its forest community in ways similar to that of the beleaguered eastern hemlock.

  • October 23, 2008 / by Brian Keel / Posting of chapters from my "Assisted Migration" PhD thesis
    I have noticed the term assisted colonization showing up in several sources. I feel that assisted colonization and assisted migration are two similar but separate concepts. The attached document is part of chapter one of my dissertation that may help clarify the difference. [Editor's Note: Click for "Defining Migration" chapter or "Assisted Migration" chapter.

  • December 18, 2008 / by Connie Barlow / The working group website leans toward "Managed Relocation"
    I just learned about the url posted by the group of conservation biologists, lawyers, and ethicists that met just prior to the Ecological Society of America meeting in August 2008, and whose goal is to produce a document to guide others in these fields and governmental and private conservation managers on how to deal with this issue. Notably, the website is called "Managed relocation". However, right under the home page title appears this list:
    Working group on managed relocation
    Working group on assisted migration
    Working group on assisted colonization
    Here is a clip from the Info about MR page within that site:
    "Managed relocation" (also called "assisted migration" or "assisted colonization") is the purposeful translocation of species adversely affected by global change, particularly climate change. Goals of managed relocation include, but are not limited to, the reduction of extinction risk, the enhancement of evolutionary potential, and the enhancement of ecosystem services.
         The terms "assisted migration" and "assisted colonization" are terms that have been used to refer to the same basic strategy as "managed translocation." In Aug., 2008, this working group suggested a more comprehensive term, "managed relocation." We prefer "managed relocation" because it captures the concept of persistent intervention (if necessary) and emphasizes the geographical movement of organisms, a conservation or management concept particularly distinctive to the modern era of climate change. In several locations on this website, however, you will see use of "assisted migration" because it captures the essence of managed relocation in the sense of geographic movements that actors pursue in a helpful or beneficial sense.
    Connie Barlow speaking here, with Torreya Guardians, I find I prefer "managed translocation" to "managed relocation" for the same reason that I preferred "assisted migration" to "assisted colonization", as the former implies (to me) more of a boost to a species, giving it a chance, rather than a highly interventionist goal to have that boost succeed. For example, Torreya Guardians planted seedlings of Torreya taxifolia into a natural forest situation on private lands in the mountains of North Carolina in July 2008. If those seedlings do not survive and grow pretty much on their own here, then that will be an indication that (a) the troubles the species has in northern Florida is not just climate-induced, or (b) maybe we ought to try a north-facing slope, a higher elevation, or a more northerly latitude.

    Of interest, I have been receiving "Google alerts" for the terms "assisted migration", "assisted coloniz/sation" and the results are fascinating. About a quarter refer to precisely the issue we are dealing with, but check out some of these other usages of the term:

    1/12/08: "Rush University Medical Center will also be using the Acuo DICOM Assisted Migration (ADAM) to move data from the existing proprietary archive

    12/14/08: "Slow-moving cranesWeather has not cooperated with this year's ultralight-assisted migration of whooping cranes."

    12/08/08: "Displaced Darfuris response to joint Arab-African peace initiative for Darfur: SLM Nur's rebels in Darfur's Kalma Camp dismiss peace talks and demand more UN security or assisted migration out of Sudan."

    12/05/08: "Called the Assisted Migration Adaptation Trial, the long-term research project aims to better understand the climatic tolerance of all of B.C.’s tree species, then take that information to better refine the province’s reforestation strategies as it relates to climate change."

  • January 30, 2011 / by Connie Barlow / "Assisted Migration (Not Colonization) of Endangered Torreya
    Following the Shirey and Lamberti 2011 commentary in Nature, Torreya Guardian found Connie Barlow posted her strongest advocacy yet for choosing "assisted migration" as the term of reference: "Assisted Migration (Not Assisted Colonization) for Endangered Torreya".

  • 2011 / Juergen Kreyling et al. / Assisted migration, assisted colonization, managed relocation
    Assisted Colonization: A Question of Focal Units and Recipient Localities, by Kreyling et al., 2011, in Restoration Ecology distinguishes the 3 key terms:
    "We define assisted colonization as 'the intentional movement of focal units (ecotypes, species, taxa, functional types, life forms) to recipient localities, where these focal units are currently absent, and where they cannot be expected to colonize by natural means within a short time frame (i.e. years or decades).' We agree with Hunter (2007) that assisted colonization is a more appropriate term than assisted migration, because the final goal of this approach is not only to assist dispersal but rather the successful establishment of individuals and the subsequent development of self-sustaining populations, which is much more demanding. 'Managed relocation' or 'managed translocation' are further used as synonyms for this approach. However, these terms are not necessarily confined to the context of adaptation against climate change (Ricciardi & Simberloff 2009)."

  • 2011 / Laura K Gray et al. / Assisted migration v. colonization word preference
    A 2011 issue of Ecological Applications titled, "Assisted migration to address climate change: Recommendations for Aspen Reforestation in Western Canada" includes:
    We find it useful to differentiate the movement of species far outside their range for conservation purposes (assisted colonization), and population movement within a species range or somewhat beyond the leading edge (assisted migration). Under this definition, assisted migration would usually apply to common and wide-spread species for the purpose of maintaining ecosystem health and productivity, whereas assisted colonization aims at conserving endemic or range-restricted species. Although there are exceptions, this definition largely reflects previous usage of terminology in conservation biology (e.g., Hunter 2007, Hoegh-Guldberg et al. 2008, Ricciardi and Simberloff 2009) and forest resource management (e.g., Millar et al. 2007, O'Neill et al. 2008b, McKenney et al. 2009).

    EXCERPTS FROM THE "NAMING" SECTIONS of this review paper in Nov/Dec The Forestry Chronicle, by Catherine Ste-Marie et al., "Assisted migration: Introduction to a multifaceted concept":
         An Emerging and Rapidly Evolving Concept. Deliberate movement of species outside their natural range is an established practice in human culture and history, with long traditions in both agriculture and horticulture. However, the concept of moving species with the explicit intent to accommodate climatic changes is in its infancy; clear terminology has not yet been established and assisted migration still encompasses a broad range of practices (Seddon 2010). Three terms are used, somewhat interchangeably, in the scientific literature: assisted migration (the primary term in 51 percent of the documents examined), assisted colonization (41 percent) and managed relocation (9 percent).
         Interest in assisted migration, in the scientific and forest management communities as well as society at large, is growing rapidly, as shown by the increasing number of published documents covering the subject matter. To measure and depict this interest, an examination of research and media literature was conducted in January 2011. Peer-reviewed research publications on assisted migration were quantified by searching "assisted migration", "assisted colonization" and "managed relocation" in SciVerse Scopus (2004-2010), which is a comprehensive abstract and citation database. This search yielded over 100 articles, of which only 47 addressed the movement of species in response to the threat of climate change (Fig. 1). Assisted migration peer-reviewed literature has increased rapidly since 2007, with a peak in 2009 largely caused by the number of published letters responding to the strong statements against assisted migration made by Ricciardi and Simberloff (2009) in "Assisted colonization is not a viable conservation strategy."

       The Many Definitions and the Scale of Assisted Migration. News media reports (from established news sources such as newspapers, magazines and newswires) were found using Factiva (2010), searching the same three assisted migration terms. Of the hundreds of documents found, 203 addressed the movement of species, of which 124 directly referenced climate change. "Assisted migration" remained the most common term, with 82 percent of the 124 climate change media documents containing this term. Media coverage of assisted migration closely followed the temporal pattern of scientific publications (Fig. 1), with a steep increase in the number of documents starting in 2007, once again, followed by a peak in 2009.

    Despite the growing body of literature addressing the issue, assisted migration still does not have an established definition; instead, it has multiple interpretations and therefore can be applied to a broad range of practices. In Table 1, definitions are provided from scientific publications, demonstrating that despite the use of different terms to describe assisted migration, the concepts are complementary and overlap substantially. The term "assisted migration" is the most commonly used term, and it combines the concepts of "assisted" (human intervention) with "migration" (movement of biological units).

    Attempts to clarify the terminology have been made in recent years. Seddon (2010) proposes a "standard framework and terminology for discussing translocation option" and ranks conservation translocation practices along a gradient based on the reliance on documented historical distribution, ranging from species reintroduction to assisted colonization (his synonym for assisted migration), and then one step further to community construction (introduction of novel species assemblages). In Canada, Sally Aitken (in Johnston et al. 2010) also proposed an alternative terminology based on the potential risk of the translocation, from "assisted population expansion" (low risk) to "translocation of exotics" (high risk), with "assisted range expansion" posing moderate risks.

       The following discussion provides an overview of the potential scale of assisted migration, including the terminology that has been introduced to differentiate between assisted migration practices. Our proposed terminology, developed following a review of the literature, and selected for its effective communication, is outlined in Table 2... Because of the interest in assisted migration as a potential adaptation option and because of the complexity of the issue, the need to develop a comprehensive review of assisted migration as a forest management option to adapt to climate change in Canada is addressed in this special issue of The Forestry Chronicle.

  • August 2012/ by Mark W. Schwartz and 30 coauthors / "Managed Relocation: Integrating the Scientific, Regulatory, and Ethical Challenges", in BioScience 12 pp PDF online
    "We prefer managed relocation to alternative terms because it is value neutral and emphasizes all of the steps that one might take in adaptation, including source extractions; establishment; performance and affect monitoring; and, possibly, the control of established populations. Because managed relocation is the intentional introduction and maintenance of populations for a specific conservation-focused outcome, it includes ethical, social, and policy concerns (Camacho et al. 2010, Minteer and Collins 2010, Sandler 2010)." Table, below, is drawn from this 2012 paper.

  • July 2013 / by Connie Barlow / Journal of Forestry Review Article opts for "assisted migration"
    A Review Article in the Journal of Forestry not only consistently uses the term "assisted migration" but demonstrates how and why foresters are far more comfortable with this adaptation strategy for maintaining the productivity of populous trees than are the conservation biologists who nurture endangered species. See: "Preparing for Climate Change: Forestry and Assisted Migration", by M. I Williams and R.K. Dumroese, July 2013

  • April 2014 / by Connie Barlow / e-conversation with staff of SUNY "Move It?" website for evaluating species-specific needs in climate change
    To: Andrew Neil Stillman (Fr: Connie Barlow): . . . You call the action "assisted colonization", which the IPCC now has shown is not the primary term of choice. Working Group II of the IPCC, its updated report of 31 March 2014, uses the term "assisted migration." I have attached a pdf of the key figure from the IPCC summary report, along with its caption and the single para in the 44 pages that referred to "assisted species migration." I like to quibble on terminology because it is not a quibble. "Migration" lands on concerned citizens as natural — and thus humans are merely helping the geological time-scale N-S and upslope movements that plants in particular have been handling on their own for tens of millions of years as the glacials waxed and waned and also climate changes before then. "Colonization", in contrast, makes human help sound so artificial, hegemonic, indeed "colonial" — far from natural. We're gonna need all the help we can get in evolving citizen conservation attitudes away from static assumptions of native range and thus concerns for invasiveness. In my view, the below paper is crucial in this regard: "An Assessment of Invasion Risk from Assisted Migration" by Jillian M. Mueller and Jessica J. Hellmann, Conservation Biology, 28 June 2007.

    Response fr Andrew Stillman: Thank you for completing the survey and offering such helpful advice. Your time and effort is greatly appreciated. The Moveit program was developed by graduate students at the SUNY College of Environmental Science and Forestry in 2010, and our "Resources" page has not been updated since then. Thank you for pointing that out — it is never a good idea to let more than a year go by without updating it. I will also take into account your suggestion for changing our terminology. We have been using "assisted colonization" and "assisted migration" almost interchangeably, but I agree that "assisted migration will ring better in the public ear. I am pleased that you found the program helpful, and I hope that the Moveit website can assist in informing future assisted migration dialogues.


  • May 2014 / by Connie Barlow / Many forestry articles use term "facilitated migration"
    Since 2013 when I began searching seriously for assisted migration topics within forestry journals, I have been noticing that "facilitated migration" is often the term of choice. Googling, the first significant paper I have found using this term is "Adaptation, migration or extirpation: climate change outcomes for tree populations", by Sally N. Aitken et al., 2008, Evolutionary Applications. Comment by Connie Barlow: I think "facilitated migration" is an excellent choice for the forestry professionals to distinguish themselves from conservation biologists discussing this controversial issue. "Facilitated" is even more intentional and structured than "assisted" implies; yet both terms agree on "migration" as preferable to "colonization."

  • June 2014 / by Connie Barlow / Forester in 1997 writes of the need to "assist migration" of trees
    EXCERPT (pp. 198-199): "Adverse effects of a changing climate would then result from (1) changes beyond the plastic capability of the physiologic system, or (2) changes so rapid as to preclude migration. Several autecological characteristics (see Wolf, 1948) thus place taxa of the C. arizonica complex in precarious positions: a nearly wingless seed that inhibits migration; reproduction that is fire dependent in an age when wildfires are suppressed; delayed sexual maturity that demands migrant populations to occupy a site for a prolonged period before abundant reproduction can be expected; and habitat demands that conflict with human demands for ranching, housing, and recreation.
         Because of this, perpetuation undoubtedly will require human intervention, particularly in the face of rapid climate shifts (see Wigley and Raper, 1992). The two primary human roles most likely will be to assist migration by maintaining the appropriate habitat and providing the genotypes appropriate to those habitats. As demanded by the genetic structures, the first of these roles would be appropriate for all taxa, while the second would partic- ularly appropriate for C. glabra."

  • October 2014 / by Connie Barlow / Two foresters define three distinct forms of "assisted migration"
    "Assisted Migration: What It Means to Nursery Managers and Tree Planters" is an excellent short introduction intended for landscapers and their clients, urging that planting for climate change become integral to the profession.

        LEFT: The authors (Williams and Dumroese) distinguish 3 types of climate assistance: (1) Assisted population migration, (2) Assisted range expansion, and (3) Assisted species migration. (Florida Torreya is the illustrated example of type 3.)

  • February 2015 / by Connie Barlow / Classic paper by Mary B. Davis & Ruth G. Shaw (2001) refers to post-glacial range extensions of trees as "migrations"
    "Range Shifts and Adaptive Responses to Quaternary Climate Change", 2001, Science 292: 673-679.
    EXCERPT (p. 673): "Range shifts are the most conspicuous, and best documented, response of woody species to Quaternary climate. As the climate warmed at the end of the last glacial interval, tree populations became established at higher latitudes. These range extensions are called "migrations," although individual plants, unlike animals, cannot move to follow changing climate. Rather, occupation of new regions occurs through passive seed dispersal and establishment of seedlings in sits where conditions permit. The patterns of migration during the past 25,000 years are individualistic, with the entire range of some tree taxa displaced to new latitudes, e.g. spruce. In contrast, others expanded from glacial refuges, e.g. oak. Migration rates and the routes of migration also differed among taxa."

  • December 2015 / by Connie Barlow / Paper lists range of terminology/citations, yet "assisted migration" is their choice in title
    "Alpine biodiversity and assisted migration: the case of the American pika", 2015, Biodiversity by Jennifer L. Wilkening et al.
    EXCERPT: "Assisted migration can be defined as the intentional movement of a species outside of its current range to areas predicted to be favourable under future climate projections. Related terminology is still under debate, and this process is also currently known as assisted colonisation (Hunter 2007), facilitated migration (Hoegh-Guldberg et al. 2008), managed relocation (Richardson et al. 2009), assisted range expansion (Hayward 2009) and species translocation (Heller and Zavaleta 2009). As a conservation strategy, assisted migration can be used to prevent populations of some species from becoming functionally extinct and/or to mitigate expected biodiversity losses resulting from climate change or other anthropogenic disturbance. Within the conservation community however, assisted migration remains a controversial topic due to its highly manipulative nature and the potential social and ecological consequences. Additionally, this is not a viable conservation strategy for some species affected by climate change (e.g. cold-adapted large mammal species such as polar bears), and therefore selection of appropriate candidate species is also important."

        Considerations for restoring temperate forests of tomorrow: forest restoration, assisted migration, and bioengineering, by Dumroese et al. 2015, sorts through the plethora of terms in conservation biology, forestry, and restoration ecology that refer to new management tools for climate adaptation.

    Notice that the 3 columns of bright green at the bottom of the chart offer nuances for the 3-category scheme depicted in the image directly above.

    This chart provides the key definitions for one of the three management tools specified in the title: assisted migration. This paper also deals with ecological restoration and bioengineering (genetic manipulation).

  • December 2015 / by Connie Barlow / Paper aggregates terms and establishes "assisted migration" as the term most linked to climate change adaptation measures
    "Reconstructing a deconstructed concept: Policy tools for implementing assisted migration for species and ecosystem management", 2015, Environmental Science and Policy by Roxane Sansilvestre et al.

    EXCERPT: Among the many conservation strategies developed to lessen the impacts of climate change on plant and animals assisted migration (AM) is one of the options receiving increased attention. The rationale behind is a compensation for the dispersal limitations and potential lack of adaptive capacity of a given species resulting from the speed of current climate change. This concept encompasses several overlapping definitions (Ste-Marie et al., 2011) generating a great deal of debate (Hunter, 2007; McLachlan et al., 2007). Most of the time, AM refers to the movement within or outside the natural species range to mitigate the impacts of climate change (Aitken and Whitlock, 2013). In addition to this general notion, we find two other closely related concepts: assisted colonization (AC) which describes a movement beyond the range of species to limit human-induced threats (Seddon, 2010), and recently, assisted gene flow (AGF) which describes a movement of individuals (genes) inside the range of species to facilitate adaptation to anticipated local conditions (Aitken and Whitlock, 2013). Here, we consider AM to be a general technique corresponding to a human-assisted movement of biological entities (seeds, other propagules, individuals or populations) from a region where their survival is mostly threatened by climate change to a region where they could survive and maintain ecosystem services under current and expected future climates. On a more general perspective, AM would belong to actions seeking to repair the environment and ecosystems like in restoration or ecological engineering programs that have been recently dubbed "manipulative ecology" (Hobbs et al., 2011).

  • January 2016 / by Connie Barlow / 2010 American Journal of Botany paper opts for "assisted colonization"
    "Projections of Suitable Habitat for Rare Species Under Global Warming Scenarios", 2010, American Journal of Botany by F. Thomas Ledig et al.

    EXCERPT: Management strategies to accommodate the expected adap- tational and dispersal lags created by rapid global warming may include an active program of relocating genotypes as the environments to which they are adapted move in time and space. This will mean planting with seed or seedlings of nonlo- cal sources, often assumed to originate from populations to the south or from lower elevation (Ledig and Kitzmiller, 1992; Rehfeldt et al., 2002; Tchebakova et al., 2006). Such manage- ment is known as assisted colonization or assisted migration (Rehfeldt et al., 2002; Tchebakova et al., 2006; McLachlan et al., 2007). We will use the phrase assisted colonization to avoid confusion with the use of the term migration, which refers to intragenerational movements in animals, and also because more than dispersal of propagules will be needed to assure survival of translocated species. Because the environment to which species are adapted is, and will continue to be, a moving target, more than one generation of assisted colonization may be necessary. Delay or inaction is not an option (McLachlan et al., 2007; Aitken et al., 2008) because the gradual increase in stress will eventually exceed the limits of adaptability afforded by phenotypic plasticity (Rehfeldt et al., 2001; del Castillo et al., 2009). A point would be reached where seed production was at such a low level that establishing ex situ populations would be impossible. Therefore, early action is needed, and the first step is to project where threatened species might find suitable habitat in future decades.

  • February 2016 / by Connie Barlow / "Migration" is the standard term for plants tracking climate change.
    See, for example, "Estimating Population Spread: What Can We Forecast and How Well", 2010, Ecology by James S. Clark et al. (Note: the word "migration" appears 16 times in this paper.)

    EXCERPT: Abstract. Recent literature on plant population spread advocates quantification of long-distance dispersal (LDD). These estimates could provide insights into rates of migration in response to climate change and rates of alien invasions.

    See also, "How fast and far might tree species MIGRATE in the Eastern United States due to climate change?", 2013, Global Ecology and Biogeography by Louis R. Iverson et al.

    See also, "Predicting Plant Migration Rates in a Changing World: The Role of Long-Distance Dispersal", 1999, American Naturalist by Steven I. Higgins and David M Richardson.

  • March 2019 / by Connie Barlow / Whitlock and Millspaugh 2001 write "human-assisted migration".
    Thanks to Don Maier for pointing me to: "A paleoecologic perspective on past plant invasions in Yellowstone", by Cathy Whitlock and Sarah H. Millspaugh, 2001, Western North American Naturalist.
    EXCERPT: ...human-assisted migration may be a necessary conservation strategy for the survival of some native plant species. Climate will determine the potential limits for plants and animals, and current biogeographic barriers, like oceans and mountain ranges, may not be significant. The rapid rate of future climate change exceeds anything seen in the Holocene, and simple calculations suggest that native species will have to move or disperse at rates 40-50x faster than those observed in the paleoecologic record if they are to maintain equilibrium with the climate.



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