Integration of ecological impacts by invasive exotic plants: a methodological approach

Abstract

Castro-Diéz, P., Alonso, A., Gutiérrez-López, M., de las Heras, P., Medina-Villar, S., Pérez-Corona, E., Trigo, D., Vázquez de Aldana, B.R.  2015. Integration of ecological impacts by invasive exotic plants: a methodological approach. Ecosistemas 24(1): 12-17. Doi.: 10.7818/ECOS.2015.24-1.03

In Spain as in Europe there are too many invasive alien plants to address their management, so it is necessary to give priority to the most harmful species. But this requires the use of quantitative, systematic and comparable impact measures. The information available is uneven in terms of the criteria and variables to measure impacts and, therefore, difficult to integrate. We propose the following method to integrate measures of impacts from different studies: 1) search for case studies, 2) calculation of effect sizes; 3) classification of cases by level of organization, 4) integration of all effect sizes for each species and level of impact with meta-analysis techniques, and 5) estimate a consistency index (based on the heterogeneity among cases) and of reliability (based on the number of cases). We apply this method to estimate the impacts in Spain of three invasive trees (Ailanthus altissima, Robinia pseudoacacia and Ulmus pumila). We found 50 cases for A. altissima, 39 for R. pseudoacacia and 15 for U. pumila. The impacts at the ecosystem level (fertility) were the most studied, while the community or the individual level are less documented. Robinia pseudoacacia tends to increase fertility, while A. altissima does not alter this property. The proposed methodology has the advantage of allowing an impact assessment using data from disparate studies, but its application is limited by the availability of case studies.