File This Under “Unexpected”: Excess Trees in Japan are Harming the Environment

posted: 06/10/15
by: Danny Clemens
Japanese cedar trees

Can trees cause pollution?

Short answer: yes -- mismanaged forests can cause nutrient pollution. Cypress and cedar trees in Japan are causing massive amounts of nitrogen runoff into local streams, resulting in harmful algae blooms.

But, it's not exactly their fault. Said trees are planted in massive, commercial plantations, many of which have mostly fallen into a state of disrepair since their establishment half a century ago, during a period of high demand for wood within Japan. For a variety of reasons, Japanese companies began to increasingly import wood in subsequent decades. The shift in the market left in its wake an overabundance of humungous wood plantations, which are now causing major problems for adjacent wildlife in their sad state of ruination.

The older, slowly growing trees use notably less nutrients (namely nitrogen) than younger trees, which grow faster and require more nutrients. Very few new trees are growing in the plantations because the land has become so densely populated with older trees, which prevent sunlight from nourishing the shorter, nascent trees.

As such, there is an unusually high concentration of nitrogen in the soil on the plantations, which is left to run off into neighboring waterways. Algae blooms have begun to form in the highly nitrogenous marine habitats, and are problematic for existing wildlife: the algae sucks oxygen out of the water, and other marine wildlife are unable to survive (a process known as eutrophication).

According to the American Society of Agronomy, the problem is widespread: these large plantations account for up to 30% of forestland across Japan.

Kyushu University's Masaaki Chiwa, who penned a new study about the issue, says that the process can be prevented by adequate forest management. Chiwa is encouraging the owners of the large plantations to thin them out, creating room for new, smaller trees to grow and utilize the abundant nutrients in the soil. His team is already investigating the impact of recent trimming operations on local waterways.

"We have been measuring water quality to evaluate the effect of forest thinning on water quality including nitrogen loss," he says.

Click here to read Chiwa's research in the Journal of Environmental Quality

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