Kochi’s Sika deer population caught in the crosshairs

The forest is rather bright. It appears to be in the middle of winter as there is not a leaf left on the tree. But wait, this tree doesn’t seem right. The bark of the lower trunk is gone. It’s obvious as there is stony bark on the upper trunk, but nothing stony on the tree trunk below about 1 m high from the ground. It’s completely smooth with a woody creamy color. What is going on?

That was a picture of an evergreen Nikko fir shown in our Conservation Biology class and taken by Prof. Shingo Isikawa on Mt. Sanrei, one of the highest mountains in eastern Kochi prefecture. The tree, which is not supposed to ever shed all its leaves, looked to be another victim of the nihonjika, or Japanese Sika deer. (Pictures of typical damage can be seen here.)

The deer eat all the bark they can reach, interuppting water and nutrient transportation and leaving the trees for dead. In the mountains of Kochi, trees are dying en masse and birds are losing their home.

Before the trees started having their bark stripped, several particular species of grass community had been the deer’s favorite food. Now these grasses are gone. As a result, exposed bare soil is being eroded away into the Kochi’s rivers during the heavy rains. The rivers turn black, and fish populations crash.

The deer have also overgrazed on running bamboo, especially Suzudake and Miyakumazasa, which are some of the most important members of Japan’s plant communities. Instead of making flowers and seeds, which they do but once in several decades, they reproduce quickly and asexually through underground shoots. These shoots spread horizontally to form a kind of underground net which serves to stabilize the topsoil. It is essential for many forest and grass community in Japan to survive heavy and abundance rainfall.

Since 2003, Japan has officially recognized that sika deer are creating several environmental problems: deforestation, soil erosion, habitat loss for many species, and heavy damage to agriculture. The damage was reclassified as “serious” in 2005. And in 2009 it became clear that the larger ecosystem could no longer restore itself.

The deer are merely one member of an ecosystem which is supposed to be perfectly balanced. The continuous increase in deer population implies that the ecosystem has been broken. We can see drastic impact of this on other members of the ecosystem, including us, human beings. But did the deer jump out of the ecosystem all by themselves, and gain control over other members so well that they are now at least 5 times more numerous than they should be?

Beginning in 2009, Kochi has held semi-annual public conferences on deer-related issues. People from various organizations gather and give presentations about the issue.

“They destroyed all the corn in my farm after only one night”, said one local attendee to the conference held this past June 24th.

“Hunt the deer!” “Here are the recipes!” Speakers from different organisations expressed encouragement towards deer-hunting and deer-consuming, after giving numbers and charts related to deforestation, habitat loss, deer population, endangered plant species, etc. It might sound dreadful but local residents are really in a panic.

“The top wild predator of Japan went extinct a long time ago,” explained Prof. Isikawa from the plant-ecology laboratory of Kochi University. “The only wild predator that preyed on the sika deer was the Japanese wolf,” he said, “but they were all gone by the late 19th century due to excessive hunting. After that, human beings became the only factor that controls the deer population. Several rules towards hunters to prevent the deer from extinction was even made that time.” he continued.

Now, after a century, they are rushing to gather hunters in order to reduce the number of deer.

“I haven’t seen what the deer are doing to the forest,”said Emi Ohmori, a Kochi University student from Kubokawa town, Kochi. “But I have seen how destructive they can be to our local neighborhood farms in only a single night.”

In response to the serious disruption of agriculture, communities are taking action.

“Two years ago, the town paid for the fences to protect the farms so we are fine now,” Emi explained. “The town spends good money on it for the people. They also pay a bounty for every single deer hunters kill.”

A team of professors and students lead by Prof. Isikawa has been making attempts to protect the vegetation and soil in Mt. Sanrei. They are covering exposed soil with sedge mats to protect it from rainfall, and have enclosed several area with fences in the mountains to protect the community. According to a Nishinihon Institute of Technology last year, 34 indigenous plants species were recognized as endangered species and put onto the protected-object list.

In years past, the deer population was brought under control by hunters. One big problem this time is that the number of hunters has decreased dramatically, keeps on decreasing.

“72% of hunters now have reached the age of 60.” said Mr. Mawaki from Wildlife Division of Kochi prefecture. “The proportion of the youngest listed hunters between the age of 20 and 29 was too small to be recognized in the chart. People have been leaving mountains for the city life after the end of WWII.” The deer are then gradually being left out of control.

In order to understand fully, now we need to put in the scene the member who jumped out of the ecosystem first, which is us, human being. This series of environmental destructions all results from human activities.

Unexpectedly, global warming also has something to do with the deer. According to the data from the prefecture, Kochi’s average temperature has increased from 15.6°C, in the late 19 century, up to 17°C now. According to the same report, number of days with temperature below 0°C has decreased from 47.4 to 21.8 in 70 years up to now. Warmer winter causes the significant decrease of infant death rate.

There is nothing which can keep the deer population in balance. They will keep increasing until there is nothing left for them to eat, and every member of the ecosystem is killed directly or indirectly.

Humans caused the extinction of the keystone species, the Japanese wolf, and have left the mountains for the unbalanced city life. Humans initiate global warming. They also plant secondary forests by cutting away the primary forest community. Consequently, after the timbers are harvested, lots of food for the deer grow due to abundant light supply. These are the 4 reasons Prof. Isikawa explained in our class.

“We don’t have any other choice but culling as a temporary solution to protect the forest community.” said Mr. Mawaki to the audience during Q&A session in the latest conference. “We hope to coexist with the deer without any of such problems, but everything has become too serious now.” he continued.

–by Ain Đỗ Ngọc