One of the main questions that has driven the research on biological invasions is what are the traits that confer some non-native species their ability to invade new ecosystems. This question should be solved by analyzing the different stages of the invasion process: introduction, naturalization, invasion and impact. This information is useful to improve risk analyses and to avoid the introduction of new species able to cause ecological and socio-economic problems. For each invasion stage, we will explore the interaction between the traits of non-native trees and the ecosystem properties at different spatial scales, using exhaustive and highly representative databases (at regional, biome and global scales).

The project focuses on non-native trees because of their ecological, economic and social interest; because of the wide variability of invasion the success and of ecological impacts that they cause, and because the great amount of available -but dispersed- information. In the case of the introduction stage, we will identify which traits have promoted the selection of non-native trees for ornamental use in the main urban parks of Spain. In the case of the naturalization stage, we will rely on a database with the established non-native trees in different areas of the mediterranean biome. For the invasion stage, we will analyze the relative importance of different drivers of the nonnative tree expansion in Spain (species invasion risk, environmental and anthropic factors). Finally, for the impact stage, we will assess the determinants of the impacts at global scale relying on a previous meta-analysis on the effects of non-native trees on ecosystem services; and at local scale, we will quantify how non-native trees alter the functional structure of riparian forest of the Jarama watershed.

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Given the biogeographic amplitude of these databases, we will explore whether there are spatial differences in invasive species traits that can be explained by environmental, geographic and socio-economic factors. The scientific-technical implications of this project are that it will provide information on: (1) which ornamental trees planted in urban parks possess the highest invasion potential; (2) which are the most frequent traits in the naturalized trees in Mediterranean areas; (3) which anthropogenic and environmental factors determine the spread of the invasive trees in Spain; (4) which non-native tree traits influence their effect on ecosystem services, and (5) how non-native trees alter the functional structure of riparian trees. Doubtless, EXARBIN will compile the most comprehensive database of functional traits and impacts of introduced, naturalized and invasive non-native trees so far. This information will be useful to avoid conflicts between the introduction of exotic trees to fulfill our needs, and the environmental and social problems that they can generate, both in urban and natural areas.