What was done
Based on a pollen analysis of a sediment core retrieved from Karikomi Lake in the border area between the Hida and Echizen regions of Japan in the Hakusan mountains, plus local histories of the region, the authors describe the historical development of a practice called hansaibai, whereby the local inhabitants encouraged the growth of horse-chestnut (Aesculus turbinata) trees as an important food source during cold-induced famines of the Little Ice Age.

What was learned
The mix of tree species comprising the local forest prior to the Little Ice Age was that of "a warm temperate forest," to quote the authors.  At about 1360, however, they say the warm-climate species "decreased, suggesting cooler climatic conditions," which point in time is noted by them as corresponding to "the beginning of the Little Ice Age as generally recognized in Japan (Sakaguchi, 1995)."

During this multi-century global cool spell, Kitagawa et al. report that "serious famines frequently occurred because of adverse climatic conditions," three of which were especially serious.  Quoting them again, "both the Kyoho famine in 1732 and the Tenmei famine (1782-1787) resulted in population decreases of about one million, and during the Tenpo famine (1823-1839) the population declined by ca. 290,000 (Nakajima, 1976)."

What it means
These diverse observations clearly reveal the existence of the Medieval Warm Period and Little Ice Age in Japan, thereby strengthening our contention that these distinctive climatic intervals were global as opposed to merely regional phenomena restricted to countries bordering the North Atlantic Ocean (as climate alarmists like to claim).  They also reveal the harshness of the Little Ice Age, which the authors say "caused serious famines in Europe, Argentina, and Mexico (Appleby, 1980; Cioccale, 1999; Post, 1984; Swan, 1981)," the latter two of which locations are also far removed from the North Atlantic Ocean.

References
Appleby, A.B.  1980.  Epidemics and famines in the Little Ice Age.  Journal of Interdisciplinary History 10: 643-663.

Cioccale, M.A.  1999.  Climatic fluctuations in the central region of Argentina in the last 1000 years.  Quaternary International 62: 35-47.

Nakajima, Y.  1976.  Kikin nihonshi.  Yuzankaku Suppan, Tokyo, Japan.

Post, J.D.  1984.  Climatic variability and the European mortality wave of the early 1740s.  Journal of Interdisciplinary History 15: 1-30.

Swan, S.L.  1981.  Mexico in the Little Ice Age.  Journal of Interdisciplinary History 11: 633-648.

Sakaguchi, Y.  1995.  Kako l man 3000 nenkan no kikou no henka to ningen no rekishi.  In: Yoshino, M. and Yasuda, Y. (Eds.), Koza: Bunmei to Kankyo. Dai 6 kan: Rekishi to Kikou.  Asakura Shoten, Tokyo, Japan, pp.l 1-23.