A massive new study of Japan’s native plants reveals an extinction crisis in the making. The study examined 1,618 threatened Japanese vascular plant species, most of which can be only be found in extremely limited ranges and many of which already face shrinking populations. According to a paper published June 12 in PLoS ONE, the rates of habitat loss and population loss are so great that between 370 and 561 of those species will not survive another 100 years.
The data in the paper comes from two nationwide surveys conducted by 500 lay botanists in 1994–95 and 2003–04. For those surveys, Japan’s Ministry of the Environment and the Japanese Society for Plant Systematics divided the country into more than 4,000 parcels of 100 square kilometers each (“cells”) so the plant species present in each location could be counted and mapped. According to the paper, Japan’s plants are particularly at risk because so many of them have such limited ranges. For example, a grassland flower called hanashinobu (Polemonium kiushianum) can only be found on Mt. Aso on Kyusyu Island. The people there traditionally raised cattle, which grazed on and maintained the grassland. Now that the cattle are mostly gone the habitat is being overrun by forests, limiting the habitat for the flower. All told, nearly 300 of the plant species could each only be found in a single cell. Another 374 species grew in only two or three cells.
Between the two surveys 437 different species experienced notable population declines. The authors of the new paper, from the National Institute for Environmental Studies in Japan and 13 other institutions, used this rate of decline to calculate future risk. In addition to the change in a particular species, they also factored in how all of the plants in a particular cell had fared over the course of 10 years. Cells that experienced greater overall plant loss indicated a higher risk of extinction for plants in those locations. The researchers also considered a “what happened here may happen there” hypothesis—if a plant was disappearing in one location, it could disappear in another as well.
The biggest risk for all of these plants, according to the authors, is the fact that only 0.91 percent of the country’s land is strictly conserved from any human disturbance. The authors wrote that protecting these plant species from extinction would require the establishment of protected areas representing 17 percent of Japan. They note that the 10th meeting of the Convention on Biological Diversity (COP 10), held in Japan in 2010, endorsed setting aside 17 percent of the world’s terrestrial and inland water as protected areas by the year 2020. According to the International Union for Conservation of Nature, protected areas currently represent about 11 percent of the planet.
Lead author Taku Kadoya of the National Institute for Environmental Studies says the next stage of this study “is to incorporate effects of possible future environmental change like land-use change and climate change.” Additional plant distribution censuses, which take place every five to ten years, will also enhance their predictions.
Japan has only catalogued 42 plant extinctions over the past 60 years. The next century could exceed that many times over.
Photo: Polemonium kiushianum, courtesy of Taku Kadoya