Long-term vegetation transition on man-made slopes 53 years after construction in Central Japan

Currently, the quantitative assessment of revegetation is often limited to within a few years of vegetation construction. Thus, it is imperative to gather information regarding vegetation transition such as plant species composition and identify new indicators that can be applied to evaluate long-term vegetation restoration on revegetated slopes. To achieve this, the vegetation on the oldest expressway slopes in Japan and its transitions were studied 53 years after construction using the Braun–Blanquet method, cluster analysis, and indicator species analysis (INSPAN), and two vegetation successional patterns were identified. The first pattern, a vegetation transition dominated by deciduous broad-leaved trees, was observed on orthosere slopes. Despite a previous study predicting the establishment of a Pinus densiflora-dominant community by about 50 years after construction, no adult P. densiflora trees were identified in this study, and pine wilt disease was implicated. The second pattern, a transition to a plagiosere with Pueraria lobata as an indicator species, was observed on slopes where a P. densiflora-dominant community had been established 33 years after the construction. A plagiosere with a bamboo-dominant community was newly identified in addition to the previously reported P. lobata-dominated one. All the plagiosere slopes displayed single-peak community structures, in which the highest coverage was recorded for the lower tree layer, community height was less than 10 m, and P. lobata as an indicator species. It is suggested that these common features are indicative of the vegetation shift to a plagiosere and are useful as long-term revegetation evaluation criteria.