Although noncrop woody plants in crop field landscapes serve multiple functions, the modernization of agriculture has threatened their preservation. In this study, isolated woody plants used as farmland boundary markers were investigated in Ibaraki Prefecture in the eastern Kanto region. A total of 2001 individuals of 50 species were found around 177 equidistantly spaced points. The most frequently used species was Deutzia crenata (60.7%), and the main subordinate species were Pourthiaea villosa (8.8%), Euonymus japonicus (7.7%), Camellia sinensis (6.8%), Morus bombycis (4.6%), and Celtis sinensis (4.2%). According to multiple kernel density estimation, all six species were estimated to have at least one core area of high presence probability. Spatial segregation analysis of those species observed more than twice indicated that the marker usage showed significant spatial heterogeneity in the region. According to managers at 32 farms, marker plants are seldom used for other purposes. Trimming frequency of markers varied among the managers, even for the same species. Most of the managers did not know the introducer, introduction year, and marker plant source, except four managers who introduced or restored the markers using D. crenata (n = 2) and E. japonicus (n = 2). These findings suggest that the regional diversity of markers reflects historic species selection. Therefore, preservation of woody plant markers must be planned based on the local characteristics of biocultural resource usage.
Although the value of noncrop vegetation for biological control has been extensively studied in agricultural landscapes, there are few reports on how it functions mechanistically. When focusing on the pest control function provided by noncrop vegetation, tritrophic interactions among a predatory natural enemy, its prey, and the prey's host plant need to be examined. In Japan, the multicolored Asian ladybird beetle, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), an aphidophage, serves as a natural pest control agent in agricultural production, although the species' introduction into Europe and North America for pest control has had a negative impact on native ecosystems. In the present study, 33 aphid-plant pairs from an agricultural landscape in the eastern Kanto region of Japan were examined experimentally for initial larval survivorship and development of H. axyridis. Significant differences were found among plant-aphid pairs with regard to these parameters. In addition, the larval survivorship of H. axyridis was not consistently determined by host plant or aphid species alone but was context-dependently influenced by the aphid-plant combination. Some alien host plants showed positive effects on the ladybird beetle. Others, however, served as hosts for unsuitable prey species, such as the competitive alien plants Solidago canadensis L. and Robinia pseudoacacia L., which are the host plants of Uroleucon nigrotuberculatum (Olive) and Aphis craccivora Koch, respectively. These findings suggest that various noncrop plants could be managed to promote ladybird beetle populations in rural landscapes.
Background Understanding the history of anthropogenic vegetation is often difficult due to the lack of tangible historical evidence. In this study, we examined chronological changes of farmland demarcation trees planted on alluvial plains along the Hijikawa River in southwestern Japan based on species distribution patterns, folk nomenclature, and multiple usage of the trees. Methods The species composition of demarcation trees was investigated at 47 sites in 13 villages. We performed hierarchical clustering using Bray–Curtis measures to detect groups of similar tree composition and permutational multivariate analysis of variance to test whether differences in species composition correspond to village units. To better understand the traditional knowledge of demarcation trees, we conducted interviews with 53 farmers, most of whom were over 60 years old. Results Clustering resulted in six tree composition groups. The group characterized by the most frequently planted species, Chaenomeles speciosa , dominated around lower reach villages. The group characterized by Euonymus japonicus dominated around middle reach villages, and that characterized by Salix pierotii was mainly located around upper reach villages. Chaenomeles speciosa was always identified with the standard Japanese name boke or similar names. Euonymus japonicus and several other species were also called boke by many farmers. Several elderly farmers stated that C. speciosa was pervasive in upper and middle reach villages in their youth, suggesting the prototypical use of C. speciosa in the study area. In addition, some minor species were likely to have been left after commercial crop production or subsistence use between the late nineteenth and mid-twentieth centuries, including Morus sp. and Celtis sinensis for sericulture, Salix koriyanagi for fiber production, and Gardenia jasminoides for food coloration. The name kōshin bana recorded for E. japonicus suggests that the species’ use originated from the folk faiths Kōshin-shinkō and/or Shōmen-Kongō. Conclusions The composition of demarcation trees in the region has not been stable over time, but instead changed to reflect the local livelihood, industry, and faiths. Despite the lack of tangible historical evidence, the spatial distribution patterns, folk nomenclature, and traditional knowledge of plants can provide clues to trace the chronological background of ecotopes in anthropogenic landscapes.
Field abandonment has increased over several decades under a long-term recession in Japanese agriculture. To support effective farmland management or reforestation, the patterns of tree recruitment in abandoned fields, which influence management costs, need to be clarified. We investigated tree seedling establishment and microsite variables along forest-field transects in 11 abandoned fields adjacent to secondary broad-leaved forests in the eastern Kanto region of Japan. Generalized linear mixed model analysis indicated that tree seedling establishment in abandoned fields was not correlated with the period of abandonment. Instead, it was positively correlated with vegetation openness. The dominance of a woody vine (Pueraria lobata), an annual liana (Humulus japonicus), and a dwarf bamboo (Pleioblastus chino) mainly explained low vegetation openness within the fields. In addition, the establishment of evergreen tree seedlings and tree seedlings dispersed by hoarding was negatively correlated with the distance from the forest edge. In the forest interior, taller understory vegetation at the edge correlated with lower seedling establishment. These results suggest that seedling establishment across forest-field ecotones is restricted by the dominance of competitive natives within abandoned fields and distance-dependent limitations in both abandoned fields and adjacent forest.
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