Co-ordinating Editor: Alessandro Chiarucci
Dealing with scarce data to understand how environmental gradients and propagule pressure shape fine-scale alien distribution patterns on coastal dunes
Article first published online: 31 MAY 2011
© 2011 International Association for Vegetation Science
Journal of Vegetation Science
Volume 22, Issue 5, pages 751–765, October 2011
How to Cite
Carboni, M., Santoro, R. and Acosta, A. T. R. (2011), Dealing with scarce data to understand how environmental gradients and propagule pressure shape fine-scale alien distribution patterns on coastal dunes. Journal of Vegetation Science, 22: 751–765. doi: 10.1111/j.1654-1103.2011.01303.x
- Issue published online: 1 SEP 2011
- Article first published online: 31 MAY 2011
- Received 13 October 2010, Accepted 20 April 2011
- Carpobrotus acinaciformis;
- Coastal dune vegetation;
- Exotic plants;
- Imputation of environmental variables;
- Natural stress and disturbance;
- Predictive modelling;
- Xanthium orientale;
- Zero inflation
Questions: On sandy coastal habitats, factors related to substrate and to wind action vary along the sea–inland ecotone, forming a marked directional disturbance and stress gradient. Further, input of propagules of alien plant species associated to touristic exploitation and development is intense. This has contributed to establishment and spread of aliens in coastal systems. Records of alien species in databases of such heterogeneous landscapes remain scarce, posing a challenge for statistical modelling. We address this issue and attempt to shed light on the role of environmental stress/disturbance gradients and propagule pressure on invasibility of plant communities in these typical model systems.
Location: Sandy coasts of Lazio (Central Italy).
Methods: We proposed an innovative methodology to deal with low prevalence of alien occurrence in a data set and high cost of field-based sampling by taking advantage, through predictive modelling, of the strong interrelation between vegetation and abiotic features in coastal dunes. We fitted generalized additive models to analyse (1) overall patterns of alien occurrence and spread and (2) specific patterns of the most common alien species recorded.
Conclusion: Even in the presence of strong propagule pressure, variation in local abiotic conditions can explain differences in invasibility within a local environment, and intermediate levels of natural disturbance and stress offer the best conditions for spread of alien species. However, in our model system, propagule pressure is actually the main determinant of alien species occurrence and spread. We demonstrated that extending the information of environmental features measured in a subsample of vegetation plots through predictive modelling allows complex questions in invasion biology to be addressed without requiring disproportionate funding and sampling effort.