INFLUENCE OF FERTILIZATION ON NATIVE PLANTS AND EXOTIC PASTURE GRASSES ON THE FASCINED LANDSLIDE SLOPES IN MIKURA-JIMA ISLAND, JAPAN

Abstract

Typhoon 9512 hit Mikura-jima Island, Izu Islands, Japan in 1995, producing many landslide slopes. Torino-o No.3 landslide slope was fascined with fallen trees and planted with seedlings of native species (Alnus sieboldiana tree and Miscanthus condensatus grass) as part of vegetation recovery efforts, and was subsequently seeded by helicopter in 2002 with exotic pasture grasses. To elucidate the influence of fertilization on the growth of transplanted seedlings of native species, exotic pasture grasses and newly invading trees and herbs, we designated seven plots in 2004, and surveyed vegetation every summer until 2013: four fertilized plots (fowl manure applied at 0.2 g/m 2 ) and three non-fertilized plots. The native species seedlings grew steadily irrespective of fertilization, but with self-thinning in A. sieboldiana. Exotic pasture grasses decreased gradually and almost disappeared in 2013. Fertilizing temporarily enhanced the growth of some species, but seemed to induce species competition, judging from the delay of invading of native trees and the increase of climbing plants in herbaceous layer in fertilized plots.