Analyzing about sixty years of land-cover change and associated landscape fragmentation in Shiretoko Peninsula, Northern Japan

The aim of this study is to detect and quantify the dominant land cover changes in a human dominated forest site in Northern Japan. Vegetation maps prepared from aerial photos and socioeconomic information were used to define three land cover change trajectories: the rapid cultivation stage (1947–1968), the abandonment stage (1968–1978) and the plantation/reforestation stage (1978–2004). The analysis revealed that in the rapid cultivation stage, the degradation from broadleaved forest to dwarf bamboo brush occurring in more than 3% of the landscape was the only dominant signal of change. In the abandonment stage, the pasture land-dwarf bamboo brush, dwarf bamboo brush-broadleaved forest, and broadleaved forest-conifer-broadleaved forest transitions covering about 18% of the landscape were the dominant change processes. In the plantation stage where the dominant signals of change affected about 27% of the landscape, these three transitions were also observed in addition to pasture and dwarf bamboo brush-conifer plantation transitions. Patch density (PD) increased in the rapid cultivation stage. In spite of natural revegetation and the large-scale reforestation project between 1978 and 2004, the mean patch size of the landscape in 2004 was only 24% of the pre-cultivation era. Mean proximity index (MPI) and interspersion juxtapostition index (IJI) showed contrasting trends, but the latter exhibited high values at extreme values of mean patch size (MPS). The relative ability of other pattern metrics to measure fragmentation of the landscape is highlighted. Prompt mitigation of adverse land change requires close monitoring by land use planners.

Research highlights▶ The strongest signals of landscape transition over sixty years were identified. ▶ The observed systematic transitions were sequential changes in old growth forest caused by human activities and natural revegetation processes. ▶ The fragmentation of natural forests was quantified using landscape metrics.