China’s single-species commercial forests beset by tree-gnawing rodents

Source:Global Times Published: 2017/4/5 20:13:39

A squirrel enjoys a meal at Huanglong National Park, Songpan County, Sichuan Province. The rodents are plaguing the region's commercial forests. Photo: IC

Staring at Japanese red cedars that had been stripped bare by hungry squirrels, Gao Shunfu started to regret spending his money on planting so many of the trees on the hills of his native Leshan, Southwest China's Sichuan Province.

Gao, 50, started to grow Japanese red-cedars, a rapidly growing tree which produces wood that is particularly prized for its use in construction, on the barren hills of his hometown about eight years ago.

Following Gao's lead, many other local farmers also planted the trees around the village, hoping to see a healthy return on their investment.

But in the first half of 2015, Gao found that rodents had removed the bark from many of his trees. Since then, as the number of squirrels has grown, so has the amount of damage being done to his cedars.

Gao said nearly half of his cedars had been chewed on by the animals so far. "The trees might not survive the summer, and if they do, they cannot be sold for a good price."

The villagers have planted over 2,000 square kilometers of cedars, Wang Quanyou, the village secretary noted, adding that thousands of square kilometers of trees around the village have been damaged by squirrels.

Leshan is just one of many tree-growing areas that have been ravaged by hungry squirrels.

Ecosystem breakdown

Hongya forestry farm in Meishan, Sichuan, which is known around China as a cedar-growing region, did not escape the rodent onslaught.

"In the last 10 years, squirrels have run rampant and made themselves our biggest animal problem," a Hongya employee said.

Nearly two thirds of the forest has been damaged by squirrels, costing around 44 million yuan($6.4 million), according to the employee.

The squirrels are able to peel off strips of bark from a tree, which damages the plant's structure and hinders nutrition delivery. This damage can also lead to fungal infections which can kill trees.

Squirrels rarely eat bark in this way in untouched, natural forests where they  live on fruits, seeds, insects and bird eggs, Fu Yiqiang, a zoologist at Leshan Normal University said.

However, commercial forests, which are usually monocultures made up of one kind of tree, do not have a thriving ecosystem which can provide squirrels with a diverse diet, which leads to them mainly eating bark for sustenance, Fu said.

Fu added that these kinds of forests also lack predators, so the squirrel population often explodes in size.

Inter-species competition among plants is less effective in artificial forests, as is the pressure animals exert on each other, Luo Liqun, a botanist at Leshan Normal University said.

Luo explained that the other plant species which were common in forests before extensive human management always gradually die out and the new dominant specie cannot provide sufficient food and an appropriate habitat necessary for most animals, leading to one animal becoming dominant.

Bi Jun, a professor at the Hebei Agricultural Scientific Research Center, told the Global Times that China has the largest total area of artificial forests in the world - over 600 million hectares as of 2009 according to official statistics - which are the country's primary source of wood.

It's normal to see animals attacking trees in such forests, but there are regional differences, he noted. Forests in northern China, for example, usually face problems caused by rabbits, while squirrels are more prevalent in southern regions.

Defending the business

Hongya forestry farm has been suffering from an imbalanced ecosystem for more than 10 years, the employee of the farm said.

In order to stop squirrels damaging trees and to sustain their business model, the farm exterminated squirrels through multiple methods such as spreading poison bait, sterilizing them with drugs and setting lethal traps, he said.

"But the best way to solve the problem of excessive squirrels is to fix the broken ecology," the Hongya employee said.

Forests that only contain one kind of tree are able to produce a lot of resources at a low cost, because they are relatively easy to manage and maintain, said Bi, adding that mixed tree populations are more complicated.

Some areas of the Hongya farm have been turned over to other trees to recreate a natural forest environment, and they have also tried to reintroduce and nurture populations of predators to create a more complete food chain.

Chengdu Business Daily and Global Times


Newspaper headline: Bites are worse for bark

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