Number of cherry trees on the decline in Tokyo

A worker cuts down the last native Oyama-zakura cherry tree in Koganei Park on May 10.

TOKYO - The number of cherry trees in Tokyo parks famous for hanami cherry-blossom viewing has sharply declined, as many trees aged 50 years or older have perished from attacks by pests or been knocked down by strong winds.

In Koganei Park in western Tokyo, the only remaining native Oyama-zakura cherry tree died and was cut down on May 10. According to research by a citizen group, more than 300 cherry trees, or nearly 20 per cent of the park's total, died in the 13 years through 2012.

307 trees died over 13 years

"We never imagined the native tree would die. It's a relief that we planted subsequent trees that are already maturing," said Masayoshi Ito, 72, head of citizen group Koganei Koen Sakura-mori no Kai (Cherry tree guardians of the park). Ito and the group of volunteers work to maintain and help grow cherry trees in the park.

The Oyama-zakura was deemed native because it was the only tree of its kind that had been in the park since the grounds opened. It was about 10 metres tall and estimated to be 60 years old.

It took only 15 minutes to cut down the tree, a decision that was made to avoid the risk of it falling on its own. Most of the trunk was rotten due to bacteria, except for the outer ring, and it was impossible to count the growth rings.

Fortunately, grafted seedlings from the tree are doing well, and the tree's 16 "children" are growing around new playground equipment in the park.

About 50 kinds of cherry trees can be found in the about 80-hectare park, with varieties such as Oshima-zakura, Oyama-zakura, Koganei-usubeni-zakura and Someiyoshino, the last of which accounts for 80 per cent of the park's total.

Research in 1999 showed the park had 1,745 trees, but the figure had decreased to 1,438 according to a study the volunteer group carried out from 2011 to 2012. This means 307 trees, or 17.6 per cent of the total, died in the 13-year period. A previous record also shows the park boasted as many as about 2,500 cherry trees in 1981.

'Deaths' outnumber 'births'

Many of the park's cherry trees were planted 59 years ago when it opened. Forty-three trees died of diseases or pests and were cut down in the year through October 2012, but only 11 saplings were planted that year. Furthermore, about 100 saplings were planted in the 10 years through 2012, but far more cherry trees died during the same period.

"We expect 30 to 40 trees to die and be cut down every year. Professional tree-care skills are necessary to prevent diseases, and we can't keep up with the task only through the efforts of volunteers," Ito said. "If we don't accelerate efforts to transplant saplings, the number of cherry trees in the park will continue to decrease."

Ueno Park in Taito Ward, Tokyo, one of the nation's busiest parks during the cherry-blossom viewing season, is also suffering from a drop in its number of cherry trees.

According to the park's administration office, the park contains about 800 cherry trees, most of which were planted around the time of the 1964 Tokyo Olympics. But more and more trees have recently been knocked down by strong winds, typhoons and heavy snow. Despite the 10 saplings that were planted this year, the total number of cherry trees is still on the decline, the office said.

Hoping to maintain the new trees until they turn 100, the park is working to spread fertiliser and remove destructive shoots that can weaken trees, in cooperation with volunteers.

Kuniharu Ichita, 74, is the head of Tokyo Jumokui (Tree doctor) Project, a nonprofit organisation that participated in revitalising cherry trees at Asukayama Park in Kita Ward and other places. Ichita said the life of Someiyoshino cherry trees is believed to be 60 years, but this is a misconception that spread because many trees died around this age in the 1960s from air pollution. He added that there is at least one Someiyoshino tree that is 85 years old.

"In may cases in urban areas, trees have difficulty developing roots due to hardened soil or are unhealthy because of a shortage of sunlight resulting from obstruction by other trees," Ichita said. "[Park management] has to find [the reasons for the trees' short life spans] soon, and maintain them carefully in ways suitable for each tree."

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