they are making their way through the mountains of nagano.isitors may be bringing tit on their shoes. >> the plant grows like crazy. >> toshiyasu aruga has been involved in mountaineering and rescue missions for some 30 years. in recent times, he's seen invasive species asserting themselves. >> translator: the native plants will probably die if their sunlight is blocked. these outside species grow rapidly and harm the ones that belong here. >> reporter: another change is the direct result of human activity. >> translator: these holes were all made by hiking poles. they stab at roots and push them further into the ground. the roots are exposed. eventually that will affect the trees. >> reporter: the mountain sides are now pitted with evidence of sharp-pointed hiking poles. nagano prefecture is trying to make climbers mindful of their actions. they include an event with examples of how the environment may suffer. visitors are asked to sign a note to protect the environment that includes staying on the trails and not harming plants. >> translato