Anthropogenic legacies shaping the present composition of demarcation trees in a temperate upland field landscape in Japan

Mosaics of land uses in agricultural landscapes conserve biodiversity [1]. One important element supporting mosaics is a variety of vegetation maintained under human influence, including sacred groves, hedgerows, isolated trees, and farmlands under extensive management [2,3,4]. The aesthetic beauty of these kinds of vegetation is another important aspect contributing to improving people’s well-being [5,6,7]. Renes [8] expressed the concern that the history of these types of vegetation is often mischaracterized as being uniform. For example, recent research on the Amazonian landscape has suggested that the dynamics of plant use histories by ancient human groups determined current biodiversity patterns [9, 10]. To reconstruct the vegetation history, various types of evidence are available, for example, archaeological and botanical remains, literary records, old maps and photographs, written descriptions, and oral history [11]. However, the need for cross-disciplinary evaluation of information that is dispersed in various media and places has hindered research progress. Nonetheless, exploring the dynamics of non-crop vegetation under human influence is important to add heritage value, and motivate their conservation.

The dynamic history of European hedgerows has been well-documented [8]. The associations of plant composition and site types have been evaluated using multi-faceted information from archaeological features, written records (e.g., old census data), maps, photographs, plant distribution data, testimony of older people, and historical information on the origin of plants and chronological transformation of hedgerows [12]. The plant compositional characteristics of British hedgerows were intensively surveyed on a national scale [13]. Because of their historical value, the management, removal, and introduction of hedgerows has been regulated by the government [14, 15]. Trees other than hedgerows also contribute to shaping regionally unique agricultural landscapes, and the socio-economic and ecological importance of these trees has been evaluated in various countries [e.g., 1618]. However, the evaluation of the planting history has often been limited to relatively short periods because there were often few materials available for verification.

During the ritsuryo period, which began in the seventh century, the imperial government of Japan adopted a land demarcation system using various features such as topographic landmarks and roads to outline the surrounding environment of a piece of land [19]. Such features indicating the surrounding environment were called shiishi and the local features identifying the boundary lines were called bouji; the local features were important for land demarcation at least since the medieval period, when land disputes over the private lands of nobles and temple and shrine territory had become common [19, 20]. Examples of such features in the shiishi-bouji system are the hedges, often called kakiuchi, kaito, kaichi, and kakitsu, that can be found in ancient and medieval documents [21, 22]. There is some folk nomenclature indicating that Deutzia was used for demarcation purposes, as well as for agricultural, medicinal, and ritual uses [23]. Toda [23] also pointed out the strong linkage between people’s religious beliefs during the ritsuryo period and the multiple functions of Deutzia, particularly D. scabra Thunb. var. scabra. The use of D. crenata for hedges in the gardens of nobles and peasants was also depicted in some Japanese waka (poetry) and essays in the ancient and medieval periods [24]. Although these fragmentary records provide a glimpse into the livelihoods of people at that time and help to partially reconstruct the historical landscape, details of the customs of peasants were seldomly recorded, including the use of demarcation trees in the upland field landscape.

Some of the demarcation trees in Japan were planted as hedges, but others were isolated or in the form of sparse hedges on boundary lines or at corners. Isolated planted trees in farmlands, generally known as sakaigi, are widely found in the Tohoku, Kanto, Chubu, and Shikoku regions in Japan [25]. Such use of isolated demarcation trees of D. crenata was recorded in Musashino in the Kanto region in the early modern period [26]. A novel by Nagatsuka [27] realistically describes many D. crenata in bloom in the southwestern part of Ibaraki Prefecture in the modern period. The spatial distribution patterns, folk nomenclature, and folk tool use of demarcation tree species were recently evaluated in several studies [28,29,30]. These studies indicated that the demarcation tree composition varied regionally and changed gradually over time. Species turnover was governed by various factors, such as ease of acquisition and transplanting, local horticultural or aesthetic preferences, historical trends of commercial crop and subsistence plant use, and a possible linkage with folk faiths. However, these studies primarily depend on oral histories, which constrained their ability to examine the dynamic history of demarcation tree transition across centuries.

In this study, in accordance with the history of land development, we hypothesized that different types of demarcation trees were introduced in each period, and that they remain as demarcation trees in upland fields to this day. To evaluate this hypothesis, we examined the following for Ibaraki Prefecture: (1) the relationships between demarcation tree species and land use recorded in land disputes between the seventeenth and nineteenth centuries, (2) the association between present-day demarcation tree distribution and past land use depicted in maps created in the 1880s, and (3) the results of interviews with older residents on local methods of defining forest demarcation and demarcation tree use.

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