Coutts, S.R., van Klinken, R.D., Yokomizo H. & Buckley, Y.M. (2011). What are the key drivers of spread in invasive plants: dispersal, demography or landscape: and how can we use this knowledge to aid management? Biological Invasions. DOI: 10.1007/s10530-010-9922-5
Author: Shaun Coutts
Stopping the spread of an invasive plant to new areas is the only cost effective management strategy for many invasive plants, but few general guidelines are available to managers and policy-makers on how to achieve this aim. We simulate plant spread using a model that included demographic, landscape and dispersal parameters, run with different life history strategies. We used the output of this model to train boosted regression trees, a relatively new technique in the analysis of simulation outputs. Boosted regression trees allowed us to find which parameters most affected spread and for the first time how spread reacted to those parameters over their whole range, while taking into account non-linear responses and higher order interactions common in simulations.
Our results indicate several management relevant guidelines:
1) Manage dispersal if possible, however this is often impractical.
2) If dispersal cannot be managed then the next most useful target will depend on life history strategy, dispersal opportunities and the way spread was measured. However two processes were important in driving spread under a wide range of conditions. If the species is short lived then target fecundity, but because there were generally many more seeds than vacant spots for new plants to establish in, the number of seeds produced per plant had to be reduced to low levels before spread was reduced. If the species is longer lived then target survival, or age of first seeding if the species has limited dispersal ability.
3) Different types of spread are driven by different processes, thus, managers must decide if they are more concerned about short bursts of rapid range expansion (which is more strongly affected by fecundity), or more usual year on year range expansion (which is more strongly driven by age of first seeding).
This is the first study to produce general guidelines for managing spread that take into account life history strategy, dispersal ability and the metric of spread used.