Studies on spatial distribution of two invasive alien species spreading and conservation of vegetational landscape in a warm-temperate evergreen forest of the Kasugayama Forest Reserve, a World Heritage of Ancient Nara, Japan

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We studied the spatial distribution of two alien species, Podocarpus nagi (Podocarpaceae) and Sapium sebiferum (Euphorbiaceae), in the Kasugayama (Mt.Kasuga) Forest Reserve (KFR), a warm-temperate evergreen forest designated a Special Natural Monument of Japan and a UNESCO World Heritage Site. We conducted field surveys and distribution mapping of these species with the aid of geographic information system (GIS) technology from 2002-2004 field data, to determine their distributions and characterize the likely invasion patterns. We recorded the locations of ca 10000 S.sebiferum plants and ca 10000 P.nagi plants (including current-year seedlings) at, respectively, using a global positioning system (GPS) in an approximately 120-ha site. Most S.sebiferum plants were aggregated in canopy gaps, whereas P.nagi tended to occur in closed canopies. High densities of P.nagi in the western part of KFR near Mt.Mikasa indicated the development of P.nagi stands. Sapium sebiferum showed no remarkable … More directional tendency in its distribution. The spatial distributions of saplings of these two alien species differed, but few differences were observed in the spatial distributions of these two species. Our results suggest that these two alien species, which originated from Mt.Mikasa and Nara Park adjacent to KFR, have expanded abundantly because of their unpalatability to deer, although they differ greatly in invasion history and spreading behavior.Additionally, we investigated bark-stripping by sika deer (Cervus nippon) in the forest at Nara Park, which is inhabited by >1200 deer. We found bark-stripping in 33.8% of 1041 trees >1.3 m in height. Among the 39 tree species recorded in 10 areas, 31 species were found to suffer various degrees of bark-stripping. Bark-stripping by sika deer depends on bark preference rather than DBH. In each plot, the proportion of tree species of low electivity increased with increasing distance from the Kasugayama Forest Reserve and/or Wakakusayama Hill. The relationship between the spatial environmental gradient and bark-stripping by sika deer suggests that regional conservation is necessary for the management of vegetation and the high-density sika deer population in Nara Park. Less