Alien Species.vp - IUCN

R. Arthur Chapman, David C. Le Maitre, and David M. Richardson
impact on water resources, every 15 years. This is a critical issue for a country that has limited
and unevenly distributed water resources and whose economic growth is already constrained
by water shortages. In this paper we have focused on invasive woody plants because they are
the best documented and their invasion ecology is relatively well understood (Richardson et al.,
submitted). Although the focus is on a limited group of invaders, the processes and forces
which we analyse are applicable to all biological invaders.
As a nation, we need to anticipate and understand the possible trajectories of invasions
through time if we are to take decisions now that will result in the best possible outcome in the
future. We cannot achieve this by concentrating only on the biology of invaders. We cannot
understand the intricate interactions that lead to invasions only by modelling. We need to
address this in an all-inclusive manner which takes into account: (a) the extraordinary
complexity of the human enterprises and human-dominated systems; (b) the ways in which
these systems facilitate and hinder invasions; and (c) yet provides a logical and tractable
approach to identifying and understanding the main factors that drive invasions. Scenario
planning is a tool that can be used to achieve this and, at the same time, present the results in a
way that is comprehensible to the general populace. We begin with some brief background on
scenario planning and then illustrate the steps involved in developing scenarios using invasions
by woody plants in South Africa as an example.
Scenario planning and the problem of
invasive alien species
Scenarios are stories of the future that are plausible and are meaningful to their intended
audiences. They help explain why things happen in a certain way and offer multiple
perspectives on a complex problem. Scenario planning has roots in the Second World War
where it was used to develop new tactics for the military. The methodology later became
prominent when the Royal Dutch/Shell oil company used the technique to successfully
communicate the likelihood of an oil shortage and to anticipate the 1973 “Oil Shock”
(Leemhuis, 1985; Wack, 1985; De Geus, 1988; Kahane, 1992).
A well-known South African use of scenarios is the “High Road” and “Low Road” scenarios
developed by Sunter (1987). These names have now passed into everyday language of a
significant portion of people concerned with high-level decision-making. They enabled many
people in South Africa to see a range of possible futures for the country and themselves, and
allowed them to develop alternate views about what was needed to avoid a descent into
economic and social chaos (Esterhuyse, 1992). The High Road and Low Road scenarios were
extended to address possible environmental trajectories by Huntley et al. (1989). The resulting
scenarios emphasized the inter-connectedness of the economic and social dimensions with the
environment. A strong socio-economic trajectory, in conjunction with a strong environmental
management ethic plausibly results in a sustainable future, while a weak environmental
management ethic invariably results in unsustainability.
As a result of the Shell success story, scenario planning has become a technique for
anticipating major shifts in the business environment (Wilkinson, 1995). It differs from
forecasting because the emphasis is on highlighting and understanding the effects of the largescale
forces that push the future in different directions rather than the details of that future
(Wilkinson, 1995). The range of possible future worlds described in a set of scenarios is thus
defined by the outcomes of the important elements at work now that could create those worlds.
The key strength of successful scenario planning is the ability to deal with uncertainty
explicitly. Invasion is a process that is inherently uncertain – it is very difficult to predict which
species will invade, when and how fast they will invade, and what and how severe the impacts
will be. Invasions are also often characterised by lag periods followed by very rapid increases
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