William W. Hargrove, Forrest M. Hoffman, and Jeffrey T. Morisette
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The National Invasive Species Council (NISC) is interested in gauging the impact of a Korea/US Free Trade Agreement on the potential for invasive species, both within the United States and globally. The United States Trade Representative held an initial meeting to discuss ways to address invasive species concerns in regards to the environmental review of the U.S./Korea (KORUS) Free Trade Agreement negotiations on February 9, 2007. The group will convene a representative group of Federal invasive species experts to identify questions to be addressed and appropriate sources of data. The final environmental review for KORUS will be prepared no later than May 2007.
This work illustrates a proof-of-principle, using a quantitative global ecoregionalization as a statistical basis for predicting areas that might be susceptible to plant (or animal or insect) invasion. The analysis is based on the degree of similarity between the types of environments found in South Korea and those found elsewhere in the world, calculated as the degree of multivariate similarity between the most-similar South Korean environment and environments found elsewhere in the world. This conceptual model assumes that transportation and transplantation of invasive insects and plants will occur between the U.S. and Korea, and, when it does, that the probability of establishment is directly related to the degree of similarity between the original and the destination environments.
These statistical tools have also been shown in to be useful for representativeness and network analysis, as well as network design, repair, and active management.
Environmental similarity was calculated on the basis of global maps of 14 climatic, soil, and topographic variables at 4 km resolution. Global landmasses were divided into the 5000 most-different ecoregions on the basis of these 14 environmental descriptor variables.
We began by identifying the 70 global ecoregions of the 5000 that occur within South Korea. The map below shows all quantitative global ecoregions that occur within the Korean penninsula.
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While coloring the ecoregions randomly emphasizes the borders between adjacent ecoregions, we might wish for a visual way to estimate the degree of environmental difference between the conditions found in two different quantitative ecoregions. By assigning the first three Principal Components to the red, green, and blue color guns, respectively, we can statistically create a unique color for each ecoregion whose hue indicates the predominance of the mixture of the 14 environmental characteristics within that ecoregion. Now ecoregions having similar mixtures of environmental conditions will be colored in similar hues, and the degree of similarity of environmental conditions can be judged by visual inspection.
The map below shows the quantitative ecoregions of the Korean penninsula shown using these Similarity Colors.
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Quantitative ecoregion numbers 18, 78, 107, 162, 199, 267, 322, 449, 475, 507, 510, 577, 600, 622, 785, 898, 913, 981, 1008, 1027, 1257, 1347, 1451, 1689, 1695, 1698, 1895, 1926, 2130, 2263, 2365, 2495, 2573, 2628, 2654, 2715, 2729, 2869, 2881, 3006, 3008, 3040, 3083, 3110, 3262, 3285, 3337, 3454, 3469, 3565, 3586, 3710, 3866, 3882, 3949, 4020, 4050, 4093, 4121, 4155, 4231, 4414, 4468, 4575, 4576, 4656, 4718, 4853, 4956, and 4992 all occur within South Korea. Many of these same "training" ecoregions, shown in red on the map, also occur extensively outside South Korea, and comprise the majority of North Korea, except for a few northern locations.
In the global map below, areas shown in red are ecoregions that are also found somewhere in South Korea. Black areas have environments that are very similar to some South Korean conditions, white areas have environments that are different, and gray areas are intermediate. Click on the global map below to open a full-resolution version in a separate window.
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Eastern China, Japan, and northern India and the Himalayas have environments that show a high degree of multivariate similarity to those found in South Korea. A broad band of similar environments also sweep across Russia into southern Europe, the northern Mediterranean, and Spain.
Most germane to KORUS, however, are the areas in the northern central United States and southern Canada having environments that show a high degree of multivariate similarity to those in South Korea. Click on the map below to open a full-resolution version in a separate window.
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Parts of the Yukon and Northwest territories of Canada show a high degree of similarity with South Korean environments. Southern Saskatchewan, a discrete spot in central Manitoba, and central portions of the province of Quebec also show high multivariate "Korea-ness." The southern slopes of the Brooks Range, and some southern portions of Alaska show similarity with South Korean environments.
Within the conterminous United States, South Korean environments are like much of the agricultural heartland of the north central "breadbasket" and "corn belt." The western and especially eastern slopes of the Sierras in California show similar environments to parts of South Korea. Finally, a portion of the mid-Atlantic seaboard also shows similarity. These areas are predicted to be the most susceptible to invasive species endemic to South Korea.
We selected as training areas *every* global ecoregion occurring within South Korea. Some of these ecoregions, while present in South Korea, are likely to be very small. A different approach would have been to use for training only ecoregions greater than some threshold of size for inclusion. However, since including fewer ecoregions for training would have decreased the areas highlighted as potentially susceptible to invasives, ours is the more conservative approach. We suspect that the alternative approach would have little effect on the large scale pattern of the resulting susceptibility map, differing only in details.
Invasive risks shown here are relative, not absolute. The threshold in graylevels that would define areas actually at risk from a particular invasive species will vary with the range of environmental tolerance shown by that species. But, since most invasive species are generalists, having a relatively wide tolerance for environmental conditions, the results shown here are likely to be useful for general predictions of relative risk.
Risks of invasion among red/black areas on this map are bidirectional. Species endemic to the northern central United States might show high invasibility in South Korea, and vice versa. Transplanted organisms endemic to any highlighted location are likely to establish in another, given the high degree of similarity of their two environments. Environmental similarity is measured here exclusively in terms of the mixture of the 14 characteristics considered here. Addition of conditions beyond those considered here might drastically alter the relative risks that this set of characteristics has produced. Similarly, the inclusion of conditions in this analysis that are not actually relevant or potentially limiting for a particular invasive species might alter the relative global susceptibilities for that species.