Facilitation of management plan development via spatial classification of areas invaded by alien invasive plant

Propagule supply and habitat suitability strongly influence the success of invasive alien plants. Thus, an invaded area is likely to have an adequate propagule supply, a suitable habitat, or both for species persistence. Based on this idea, we classified invaded areas into four categories as follows but with establishment still occurring in some cases: Class 1, adequate propagule supply and habitat suitability; Class 2, adequate propagule supply but limited habitat suitability; Class 3, limited propagule supply and adequate habitat suitability; and Class 4, mid- to low-level propagule supply and habitat suitability. We propose a framework for the classification of invaded areas into these four classes and present a case study in which this framework was applied. Classifying target areas in this manner could facilitate more efficient and practical management planning, thereby saving time and resources. We selected the alien shrub Leucaena leucocephala L. (Fabaceae) as a model species, which has invaded the Nakodo-jima Island in the Ogasawara Archipelago of Japan. We developed a species distribution model by incorporating proxy variables for propagule supply and habitat suitability as well as submodels for propagule supply or habitat suitability. Using these submodels, we estimated the levels of propagule supply and habitat suitability in each, and classified the current distribution range appropriately. Using these classifications, land managers could set priorities to concentrate their efforts to efficiently control target species.