Spatial analysis to evaluate the effects of soil sand content on the progress of the invasive process of G. triacanthos in riparian forests

Abstract Riparian systems are highly threatened by alterations in its hydrological regimen and biological invasions. To guide its conservation is important to understand the relationships established between biological invasions and abiotic conditions affected by the hydrological regimen. We analyze the relationship between the distribution pattern of soil sand content and the invasive process of the woody invasive Gleditsia triacanthos in riparian forests of the Esteros de Farrapos and Islands of Uruguay River National Park, zoning the study area according to the type of relationship between both variables. We integrate the use of regression trees and geographic information systems to zone this relationship. This is a novel approach to study the relationships between an invasive species and its environment. Areas with lower sand content were found to be favorable for the development of the invasive species, and areas with higher sand content were found to limit its spread. No relationship was found between the intermediate sand content and the progress of the invasive process. This work highlights the complexity inherent to the definition of causal relationships in highly heterogeneous systems such as riparian ecosystems. Spatial analysis techniques are a useful tool for this approach.