The landscapes that characterize different places on the earth, and from which many people earn their livelihoods and their sense of place, and which support diverse flora and fauna, are often built with a mix of local and introduced plants. Sometimes, introduced plants succeed so wildly in their new home that people come to see them as weeds or pests, crowding out crops or native species, changing soil conditions, altering fire regimes, or affecting the water table. The field of invasion biology emerged over the past few decades seeking to document, understand, and stop such “alien invasions”. But the fervour of this effort has at times crashed head-on with alternative worldviews. One of South Africa’s top weeds, for example, is the Australian native silver wattle, also naturalized in France where it is celebrated for its winter flowers and as an ingredient for Chanel No. 5 and other perfumes . Such conflicting outlooks were on stark display at a workshop I attended in October 2010 at Stellenbosch, South Africa, on Australian acacias as a global experiment in biogeography.
The view of many workshop participants was that Australian acacias (i.e., wattles) were water-hungry, ecosystem-changing aliens requiring control. This comes not only from their field experience in places like the Western Cape, Portugal, Chile, or diverse oceanic islands, but also because most participants were trained in ecology and invasion biology. Metaphorically, the message of much invasion biology has long been that plants need passports, and that many should be denied immigration visas and those already present should be deported or at least kept under house arrest.
This view was also influenced by the fact that many participants came from South Africa – a country strongly attuned to issues of invasion – and particularly from the Cape Town area, where wattles are prominent colonizers of grassland and fynbos shrubland environments containing a prized local flora. The tone of the meeting might have been different had the workshop taken place in southeast Asia, a place where farmers and foresters widely use wattles such as Acacia mangium, and where a chief environmental concern is over plantations replacing natural forest, not over invasion. After the conference, one disgruntled invitee even formally urged organizers to consider a future fieldtrip to Vietnam for a different perspective:
“From my recent interactions with many of the stakeholders in the recent Acacia workshop held at Stellenbosch, I suspect that the widespread social/environmental/commercial use of acacia may be rather abstract to people who have spent their lives in landscapes where they are regarded as unwanted weeds. The reality in SE Asia is that populations are rising and there is a concomitant increase in the demand for wood and wood fibre. It is highly unlikely that native forests will be able to meet these needs and plantations will become the dominant source of wood and will remain an important and productive part of the landscape. I shared my thoughts with my Vietnamese partners who were puzzled at some of the very negative opinions on acacias….”
Yet the clairvoyant conference organizer Dave Richardson (see his overview paper) had also invited historians, geographers, agroforesters, and others who provided a different perspective. For instance, Rod Griffin outlined the commercial uses of Australian acacias overseas (link), Jane Carruthers and Libby Robin described the historical contexts and ideologies around wattle introductions (link), and I reviewed the uses and perceptions of wattles by rural households and communities around the world (link).
Richardson also encouraged the production of several multi-authored papers for a special issue of the journal Diversity and Distributions. The process of writing these papers was interesting and illuminative of the compromises necessary in collaborative science. In my paper on community acacia uses, I had several exchanges with co-authors who wanted a stronger emphasis on the damaging aspects of invasions (which I asserted was amply covered elsewhere) and the need for more public awareness about this (which is hard to disagree with, but who chooses what the message is?). I was also associated with a paper about acacia control and eradication, which made me somewhat uncomfortable. However, lead author John Wilson, who invited my contributions, was very accommodating to my concerns that the paper tended to be heavy-handed in its presumptions of introduced acacias as ‘guilty-as-charged’, therefore recommending control and/or and eradication. The result is that the crucial wording, like in IPCC reports, is very much worked over. While I still do not agree with everything, I respect it as a good negotiated outcome (link).
Less in the spirit of dialogue and negotiation was the keynote speech by Tim Low, author of Feral Future and The New Nature. Low implied that invasion biologist are the unchallenged, all-knowing authority and proposed a categorical end to the movement of acacias. No more passports, no more visas, for these very useful trees. He framed the debate as one between ‘bad invaders’ and ‘good miracle trees’, and painted perceptions of the tree as the latter (by development workers and agro-foresters) as absolutely misguided.
I was incensed enough to prepare a reply to the published article version of Low’s speech, proposing an alternative to his blanket condemnation of plant transfers, emphasizing the importance of the regional socio-ecological context, taxon specificity, and participatory political process (official link to my article; author version pdf). I was heartened that the journal (Biological Invasions) allowed this response, despite a sometimes rather partisan editorial attitude. Together with Jacques Tassin, I argued that it was false of Low to frame things so starkly between ‘good’ and ‘bad’. We wrote that “the uncritical promotion of an alarmist view of introduced plants misses a chance to see introduced plants as important elements of dynamic human-shaped landscapes, important elements that may achieve various utilitarian aims and also may provoke ecological change, and whose place in those landscapes may be viewed differently from different social and temporal vantage points…. Instead of using an a priori judgement to call for a blanket ban of a wide array of plant species, the focus should be on the processes that societies (communities, governments, agencies) use to anticipate and debate the changes to landscapes and human lives that are possible outcomes of the introduction and diffusion of specific plants in specific places. Who are the winners and losers, now and in the foreseeable future? What tradeoffs can be expected? Who has the right to decide, and the might to enforce? What is the evidence that can inform these decisions? Human societies are usually well equipped to deal with such decisions, even in polarized debates in which compromise appears intractable. That is what the political arena is for.” It is a rather geographical view, seen through the lens of political ecology.
At a wider level, my debate with Low is but a small contribution to a wider shift in thinking about biological invasions. The science of invasion biology has been evolving rapidly in the past decade to accommodate internal and external critiques. Mark Davis, in a textbook titled Invasion Biology, proposes the disestablishment of that field, and its reconstitution as “species redistribution ecology”. Numerous social scientists and humanities scholars have dissected problems of labels, ideologies, and even nationalistic xenophobia in discussions of “alien invaders” (see also the Million Trees blog). From what I can tell, the discussion at the cutting edge of the field is evolving, with spirited debates in Science and Nature, and a variety of reflective new books like Emma Marris’ Rambunctions Garden or Brendon Larson’s Metaphors for Environmental Sustainability). This does not mean that concern with problem plants is lessened, but that the link between ‘alien’ and ‘pest’ is no longer automatic, and the fetishism of ‘native’ is seen as a social preference, not a scientific fact.
One interesting part of the evolution of invasion biology is recent research that shows that introduced plants are rather quickly becoming quite distinct from their overseas ancestors, moving towards speciation (in a biological sense) or acquiring native status or new roots (in a metaphorical, social sense). There is genetic evidence for this, for example, in the ‘formerly Australian’ Acacia saligna in South Africa [links]. University of New South Wales biologist Angela Moles provides botanic evidence for such a pattern in a large variety of newcomers to Australia, which, as she elaborates in a wonderful TED talk, might imply that it is time to grant Australian citizenship to introduced species.
So, do plants need passports?  And if so, who should have the authority to stand at the border and let plants in or not? I advocate that we stop judging plants on their origins, allow the responsible diffusion of plants, and focus management efforts on problem plants and noxious weeds (as defined by local or regional social negotiation) irrespective of origin. As Jacques Tassin and I wrote in our response to Tim Low, “as opposed to Low’s all-out ban, we suggest an evidence-based, context-specific, socially-negotiated approach. Instead of advocating a ban on planting all Australian acacias, for example, we would suggest that people be forbidden to plant particular acacia species or cultivars in particular environments (like in fynbos riparian areas) ifthe political consensus across interest groups in that area is that the value of those acacias (as a resource, or as an ecological restoration tool) is less than the potential damage now and in the future to aesthetics, flora, fauna, and other resources like water.”