Present and potential distribution of invasive garlic mustard (Alliaria petiolata) in North America

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Abstract
This paper demonstrates the use of a bioclimatic model mapped over geographical regions as a tool for spatially refined risk assessment for the establishment of non‐indigenous plants with invasive behaviour. Drawing on the relationship between plant distribution and climate, the approach uses gridded spatial interpolated monthly means of temperature and precipitation linked with accurate maps of general native distribution ranges to predict the long‐term potential of a plant species to invade a certain region. The ascertained potential for establishment is illustrated by the example of garlic mustard (Alliaria petiolata[M. Bieb.] Cavara & Grande) in North America. The first step is to calculate and visualize the number of populated grid cells along climatic gradients in frequency diagrams for the general native distribution range. Interpretations of the response curves recorded are used for assessing apparent climatic range boundaries. Modelling was gradually optimized based on the results of experience‐based interpretations and by examining omission and over‐representation errors. The obtained climatic model of the range of A. petiolata shows considerable congruencies with its mapped, native Eurasian range. Degrees of climatic similarity between North America and the native range of A. petiolata were calculated with the help of GIS methodology and were used to assess the regionally different likelihood of establishment in North America of the invasive species under consideration.