The wolf and the wild boar

An ecological parable from the beech forests of northern Japan

Reading Brett Walker's book on the Japanese wolf led me to the case of another vanished beast. You won’t find any wild boar in Japan’s snowy Tohoku region today. With their short legs and their need to dig up fodder from the forest floor, the animals can’t live through winters where deep snow lies for seventy days or more.

In the past, those northern winters must have been even colder and snowier. Yet records from the Edo period show that wild boar once roamed as far north as Aomori, right at the top of Tohoku. In fact, so many of them were raiding farmers’crops around Hachinoe in 1749 that they caused a famine during which 3,000 people starved to death.

Despite all efforts to wipe them out, wild boar continued to thrive in northern Japan until the nineteenth century. Then, at some point in Meiji times (1868-1912), they went into decline. The last Tohoku boar was hunted down in 1907. This was just two years after the demise of Japan’s last wolf.

Was there some link between the fates of wolf and boar? The question had to go unanswered until the 1990s, when ecologists in Poland made studies of the country’s Carpathian mountains. This region resembles Tohoku in its rolling beech woods, cold winters, and deep snow cover.

Lynx, wolves and wild boar still roam the Polish forests. Unsurprisingly, the researchers found that the wild boar often furnish lunch for the wolves. So much so, that when the wolf population grows, the number of boar shrinks, and vice versa.

What was less expected is that the wolf returns this favour. During the winter months, the boar can't dig through the snow and frozen ground to get fodder. So how do they survive? Seemingly, by foraging on the leftovers from wolf and lynx kills.

That might explain how the wild boar of Tohoku endured the long winters. It also suggests why they died out in the north country. Traditionally, the boar’s disappearance was explained by swine cholera, a disease brought into the country with imported pigs when Meiji Japanese acquired a taste for tonkatsu.

Disease can't be the full story, as wild boar have survived in warmer parts of Japan. In Tohoku, however, the boar suffered a double whammy. First, they lost their winter food supply when the wolf went extinct –then the absence of their main predator meant that sick or weak wild boar continued to spread the swine cholera unchecked.

The secret liaison of wolf and boar is just one of the web of dependencies that makes up a forest. Pull on one thread, such cases suggest, and the ecosystem may unravel somewhere completely unexpected. What hidden connection will those northern woods next reveal?

References

Hito wa naze yama ni noboru no ka?, Volume 103 in the Taiyo Bessatsu: Nihon no Kokoro series (Heibonsha, 1998) - chapter on the Japanese wolf

Picture of wild boar from Wikipedia

And see Sapphire Sky for an update on the urban wild boars of Kobe ...