April lab discussion (Shaun’s pick)

Lab discussion 6th April 2010

Discussion lead by: Shaun Coutts

Background paper:

Magee, T.K; Ringold, P.L; Bollman, M.A. & Ernst, T.L (2010).

Index of Alien Impact: A method for Evaluating Potential Ecological Impact of Alien Plant Species.

Environmental Management 45: 759-778


Magee et al. (2010) developed an interesting mechanistic based index, referred to as Index of Alien Impact (IAI), to quantify and compare the impact of invasive plant species across sites. The aim was to develop the IAI to help make more informed decisions on how to prioritise management efforts when faced with the task of restoring multiple sites, affected by multiple invaders. IAI used the following three types of species traits to estimate how damaging the species is: life history traits, eco-amplitude (traits that allow a species to survive disturbance) and eco-alteration (key ecosystem functions changed by the invader). Once developed, the IAI was used to assess the impact of invasive plant species at different sites across the John Day River basin, Oregon, USA. Overall they found reasonable agreement between the species specific I scores generated with the IAI and two species specific indices of alien impact (NatureServe Impact Rank and Cal-IPC rank), as well as, interestingly, the simple state noxious weed classifications.

Despite the novel way in which key invasion theories are incorporated into this new index, as the authors acknowledge, there is much work to be done before IAI can become a common index of alien plant impact. For example, it needs to be tested in other systems to see how generally it applies and it needs to be correlated with indexes or proxies of ecosystem disruption to check that the aspects of alien plants included in the index are in fact affecting ecosystems negatively.