Decrease in Wetland Vegetation Area and Species Richness by the Growth of the Surrounding Trees in Hillside Seepage Bogs

We investigated changes in wetland vegetation area for approximately 35 years (1974-75 to 2010) and richness of the moor species for approximately 15 years (1995-96 to 2010) in hillside seepage bogs in the southern region of Hyogo prefecture. We found that the wetland vegetation area decreased in all the hillside seepage bogs during the 35-year study period. The moor species growing the wetland periphery disappeared in the 15-year study period. Our results indicate that the decrease in wetland vegetation area and the disappearance of the moor species depended on the growth of the surrounding trees. The number of the moor species correlated positively with wetland vegetation area. The results indicated that the decrease in wetland vegetation area in all the hillside seepage bogs influenced the disappearance of the moor species. In the future, decrease in wetland vegetation area by the vegetation succession, may continue to decrease the richness of the moor species in such hillside seepage bogs. The number of moor species on a biggest hillside seepage bog was approximately 50 percent of the total number of the moor species in this region. To conserve the moor species in this region, not only the large hillside seepage bogs but also the groups of hillside seepage bogs need to be conserved.