Date Published: March 29, 2017
Publisher: Public Library of Science
Author(s): Christian Leipe, Elena A. Sergusheva, Stefanie Müller, Robert N. Spengler, Tomasz Goslar, Hirofumi Kato, Mayke Wagner, Andrzej W. Weber, Pavel E. Tarasov, John P. Hart.
This paper discusses archaeobotanical remains of naked barley recovered from the Okhotsk cultural layers of the Hamanaka 2 archaeological site on Rebun Island, northern Japan. Calibrated ages (68% confidence interval) of the directly dated barley remains suggest that the crop was used at the site ca. 440–890 cal yr AD. Together with the finds from the Oumu site (north-eastern Hokkaido Island), the recovered seed assemblage marks the oldest well-documented evidence for the use of barley in the Hokkaido Region. The archaeobotanical data together with the results of a detailed pollen analysis of contemporaneous sediment layers from the bottom of nearby Lake Kushu point to low-level food production, including cultivation of barley and possible management of wild plants that complemented a wide range of foods derived from hunting, fishing, and gathering. This qualifies the people of the Okhotsk culture as one element of the long-term and spatially broader Holocene hunter–gatherer cultural complex (including also Jomon, Epi-Jomon, Satsumon, and Ainu cultures) of the Japanese archipelago, which may be placed somewhere between the traditionally accepted boundaries between foraging and agriculture. To our knowledge, the archaeobotanical assemblages from the Hokkaido Okhotsk culture sites highlight the north-eastern limit of prehistoric barley dispersal. Seed morphological characteristics identify two different barley phenotypes in the Hokkaido Region. One compact type (naked barley) associated with the Okhotsk culture and a less compact type (hulled barley) associated with Early–Middle Satsumon culture sites. This supports earlier suggestions that the “Satsumon type” barley was likely propagated by the expansion of the Yayoi culture via south-western Japan, while the “Okhotsk type” spread from the continental Russian Far East region, across the Sea of Japan. After the two phenotypes were independently introduced to Hokkaido, the boundary between both barley domains possibly existed ca. 600–1000 cal yr AD across the island region. Despite a large body of studies and numerous theoretical and conceptual debates, the question of how to differentiate between hunter–gatherer and farming economies persists reflecting the wide range of dynamic subsistence strategies used by humans through the Holocene. Our current study contributes to the ongoing discussion of this important issue.
Barley is the fourth most important cereal cultivated in the world today, after maize (Zea mays ssp. mays), rice (Oryza sativa), and free-threshing bread wheat (Triticum aestivum) . Domesticated barely evolved under human selective pressure from a two-rowed, hulled, narrow-grained, and brittle-rachised wild form (Hordeum vulgare ssp. spontaneum). While there has been a longstanding debate over the origins and spread of barley, the currently accepted view suggest that it was morphologically domesticated multiple times, but that all of these domestication processes took place within the Fertile Crescent of Southwest Asia. The fixation of the tough-rachis mutation, the first phenotypical trait of domestication, into the cultivated barley population took several millennia and occurred in farming communities across the Crescent in parallel. As Willcox  and others have recently pointed out, there is roughly contemporaneous evidence for the gradual domestication of wheat and barley at several different sites spanning from the southern Levant to western Iran , dating to the early Pre-Pottery Neolithic, i.e. more or less simultaneous with the end of the last glacial period and the onset of the Holocene interglacial.
The people of the Okhotsk archaeological culture are regarded as a hunter–gatherer society with an economy that strongly relied on marine resources. They occupied a widespread maritime environment, mainly along the southern and eastern littoral margins of the Sea of Okhotsk including northern and north-eastern Hokkaido (see Fig 1C for archaeological site distribution), Sakhalin Island, and the Kurils (Fig 1A). In the Hokkaido Region, the peak of the Okhotsk cultural occupation dates from the 6th to the 8th century AD (see  and references therein). Based on pottery style, the “Okhotsk cultural sequence” in northern Hokkaido is divided into three chronological stages comprising the (1) Susuya culture (2nd–5th century AD), which is often referred to as incipient or Proto-Okhotsk, (2) the Towada, Kokumon, Chinsenmon, Haritsukemon, and Somenmon cultures (6th–8th century AD) regarded as the main stages, and (3) the Motochi culture (9th–10th century AD) as the final stage . While Okhotsk cultural traits persisted through the Tobinitai period in eastern Hokkaido until the 12th century AD, replacement or assimilation of the Okhotsk culture in northern Hokkaido by Satsumon/Proto-Ainu populations originating from the central and southern areas of Hokkaido was completed by the end of the 10th century AD .
The archaeobotanical samples presented in this paper were collected from the archaeological site of Hamanaka 2. This shell-midden site is located on the coast of the Funadomari Bay on the northern part of Rebun Island, which lays 45 km east of the northern tip of Hokkaido Island (Fig 1C–1E). For nearly a century, archaeologists have recognised the abundance of archaeological remains dating to the Okhotsk cultural period in the Funadomari Bay area . Archaeological excavations started in the region in 1949, focusing on the Hamanaka 2 site complex and unearthed pottery, hearths, shell-middens, marine mammal remains, human burials, and house pits, suggesting residential activities at the site during the Okhotsk period . The most recent excavation campaign at Hamanaka 2 was conducted by the BHAP starting in 2011. The site deposits constitute a well-stratified shell-midden on top of a sand-dune formation roughly 100 m south of the current coast line. So far, archaeological finds include human and dog burials, pig remains, ceramic and lithic artefacts, and abundant remains of sea mammals, fish, and shellfish spanning the occupation periods of the Late, Final, and Epi-Jomon as well as Satsumon, Okhotsk, and Ainu cultures  between the 2nd millennium BC and mid-19th century AD (see  and references therein).
Okhotsk occupation at Hamanaka 2 is represented by a sedimentary succession, which is divided into eight stratigraphic units (IIIa–V, Table 1) defined on the basis of lithological characteristics and pottery typology. Based on pottery characteristics, the archaeological assemblage comprises the Okhotsk stages of the Susuya, Towada, Kokumon, Chinsenmon, and Motochi. To the best of our knowledge, the use of the water flotation technique at Hamanaka 2, as presented in this paper, is the first use of this archaeological method on Rebun Island. A total of 54 flotation samples from Okhotsk cultural layers were collected during the BHAP summer field excavations of 2013, 2014, and 2015 were analysed. Since the present study focuses on domesticated plants, we exclusively consider samples, which contain seed remains of cultivated cereals (n = 25).
There is evidence that human migrations from the north have played an important role in the prehistory of Hokkaido and other parts of the Japanese archipelago. This includes the intrusion of Siberian Palaeolithic hunter–gatherer groups around the Late Glacial Maximum (ca. 20,000 cal yr BP; ) and immigration ca. 15,000 cal yr BP, with the latter introducing microblade technologies on Hokkaido and Honshu [61, 62]. While they have not been taken into account for a while (e.g. ), recent anthropological studies (e.g. ) stress the role of migration from northern regions via Hokkaido also in view of the origins of the Neolithic Jomon culture. The most recent southward movement of prehistoric populations into the northern and north-eastern coastal areas of Hokkaido was that of the Okhotsk culture around the middle of the 1st millennium AD . Though, the Okhotsk groups inhabited a large area along the southern and eastern margins of the Sea of Okhotsk, most of our current knowledge has been derived from archaeological materials recovered in the Hokkaido Region. The archaeobotanical record from the Hamanaka 2 site presented in this study allows for greater insight into the use of plants by the Okhotsk people on Rebun Island (Fig 1D). Calibrated ages (95% confidence interval) of directly dated barley remains from five archaeological layers (IIIa–e) suggest that the crop was used at the site between 430–960 cal yr AD (Table 2) or at a 68% confidence interval between ca. 440 and 890 cal yr AD. This time period roughly corresponds to the late Susuya through mid-Motochi stages spanning between the 5th and 10th century AD , thus covering the Okhotsk culture settlement phase in northern Hokkaido as indicated by previous archaeological studies. Given the age of the oldest barley seed F2014-037-003 (440–600 cal yr AD, 68% confidence interval; Table 2), the Hamanaka 2 layer IIIe, together with the single dated grain (428–573 cal yr AD, 95% confidence interval; ; S3 Table) from the Oumu site (no. 29 in Fig 1C) represents, the earliest well-documented record of domesticated barley in the Hokkaido Region. The only carbonised barley grain recovered in Hokkaido was collected from the Epi-Jomon level of the K135–4 Chome site within the city of Sapporo . This single barley seed has not been directly dated and its proposed age of ca. 200–400 cal yr AD should be viewed with caution.
The archaeobotanical assemblage from Okhotsk cultural layers at the Hamanaka 2 site (northern Rebun Island, Japan) contained charred grains of compact naked barley. Direct radiocarbon dating indicates long-term use of barley at the site over a period of about 500 years. Together with the finds from the Oumu site, the data that we present marks the oldest well-documented evidence for the use of barley in the Hokkaido Region. Due to the broad error ranges of the calibrated radiocarbon dates of the oldest seed remains (428/440–573/600 cal yr AD, 68% confidence interval), more precise ages cannot be defined at this time. However, it is conceivable that the people of the Okhotsk culture were using this crop since they first arrived in the Hokkaido Region (ca. 500 cal yr AD). Accordingly, barley introduction by the Okhotsk culture would pre-date its adoption or introduction by Satsumon populations by at least a century, which may speak against the hypothesis that barley was introduced to northern Hokkaido by the more agrarian south.