“If you can't measure it, you can't manage it” is, as with all such well-worn phrases, only partly true. But to adapt
another such maxim, while we might be able to make progress without measurement, we do need proof to satisfy everyone else.
There are a range of methods, but surprisingly few consistent measures. In fact, international comparisons of invasions have been
hampered by inconsistent data collection. There is an urgent need to move beyond basic lists of invasive taxa, to reporting information
at a level that be used to identify problems and prioritise actions, and ideally at a level that will allow a mechanistic understanding
of the dynamics which might allow reliable predictions to be made. But as a fundamentally international phenomenon, one of the most
important goals in invasion science is to take the lessons learned in one place and apply them elsewhere. In fact, invasiveness
elsewhere is commonly cited as one of the most reliable predictors of invasiveness.
As part of a workshop held in September 2012 “Tree Invasions – Patterns & Processes, Challenges & Opportunities” in
Bariloche, Argentina, C·I·B core team member John Wilson lead a discussion on this topic. John and 13 colleagues from 8
countries reviewed different sampling methods used and reviewed a variety of metrics dealing with key dimensions of an invasion, from
simple and cheap to complicated and expensive. It was important to define some core aspects of invasions that are necessary to: provide
base-line statistics for biodiversity assessments; estimate impacts; estimate costs of different management strategies; estimate the
threats posed; and ultimately place species into management and legislative categories as part of a strategic planning process.
Based on this, in a paper published as part of a special issue in Biological Invasions, on tree invasions resulting from the
Bariloche Meeting, the authors argue that a set of metrics should provide information on status, abundance, spatial extent, and impact of
an invasion and how these characteristics change through time.
This culminated in six key metrics:
- Current status in the region
- Potential status
- The number of foci requiring management
- The area of occupancy (AOO) (i.e. compressed canopy area or net infestation)
- The extent of occurrence (EOO) (i.e. range size or gross infestation)
- Observations of current and potential impact
Based on these they developed and tested a standard reporting template for tree invasions.
Schematic representation of the six proposed metrics
The IUCN Red List is celebrating its 50th year in 2014. While research is on-going to develop a similar procedure for
biological invasions, the paper on metrics will hopefully improve the global exchange of information among researchers and managers.
Read the paper:
Wilson, J. R. U., Caplat, P., Dickie, I., Hui, C., Maxwell, B. D., Nuñez, M. A., Pauchard, A., Rejmánek, M., Richardson, D. M.,
Robertson, M. P., Spear, D., Webber, B. L., van Wilgen, B. W. & Zenni, R. D. (2014) A standardized set of metrics to assess and monitor
tree invasions. Biological Invasions, 16, 535–551
For more information, contact John Wilson at firstname.lastname@example.org
Attendees at the Bariloche meeting