A political ecology of weeds

How do plants that move and spread across landscapes become branded as weeds and thereby objects of contention and control? In a chapter recently published in the International Handbook of Political Ecology, Priya Rangan and I outline a political ecology approach that builds on a Lefebvrian understanding of the production of space, identifying three scalar moments that make plants into ‘weeds’ in different spatial contexts and landscapes.

Acacia farnesiana in southern Europe

by Priya Rangan

Acacia farnesiana, a plant native to Mesoamerica and the Caribbean, had already arrived in Australia prior to British settlement of the continent. How did it get there? We thought it might have been via the Portuguese, who may have brought the plant to southern Europe and then spread it to their trading forts and settlements in Asia. Manuel decided to pursue his doctoral studies in Geography and Spatial Planning (CEGOT), at the University of Porto, and focus his thesis on the history of how A. farnesiana arrived in southern Europe. See the outline of his research presentation at the 4^th International Symposium on Weeds and Invasive Plants held in May 2014 at Montpellier, France.

Reflections on invasion biology

By Christian Kull

Invasion biology has been a remarkably active branch of the life sciences in the past two decades. My itinerary first crossed this field when I noticed, at the time of my move to Melbourne, that the ‘precious’ mimosas (acacias, wattles) of the Madagascar highlands were called ‘green cancer’ in South Africa, and in both cases were introduced from Australia. It was quite surprising to discover that this shrubby tree, so appreciated by Malagasy farmers (as a resource) and environmental managers (as ‘regreening’ barren lands), was seen so negatively across the Mozambique Channel. This observation led to a research program that (1) opened a window for me to learn about and consider the field of invasion biology, and (2), serendipitously, to collaboration with ecologist Jacques Tassin at the French research institute Cirad. I comment on some of the recent fruits of both in this blog.

The South African approach to alien plants. Cartoon from environmental education material collected in 2006 (thanks to Rémy Kinna).

Acacias as weed or miracle plant?

By Christian Kull

Are Australian acacias planted overseas miracle plants for rural development, or are they the worst kind of environmental weeds? The battle lines appear rather stark at times. At least when one reads environmentalist Tim Low’s rebuttal to a critique that Jacques Tassin and I wrote of his views. We thought our statement to be tempered and tried to build a reasonable case for responsible use of exotic agroforestry trees (see also previous blog). But Low calls us “in denial about dangerous aid”, flogs a misplaced example about mesquite in an argument about acacia, all the time preaching his argument to the converted in the journal Biological Invasions.

Do plants need passports?

By Christian Kull

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 [1][2]. 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.

Picture 1: Do plants need passports? Who should control plant movements, and on what basis? Silver wattle (Acacia dealbata), native to Australia, invasive and assimilated as mimosa in the Côte d’Azur, France.

Picture 2: Do Australian acacias need passports? Australian passports specify “free passage without let or hindrance”…