The number of trees on Jeju infected with disease or forest pest insects was the lowest it has been for the past eight years, according to insect and disease expert Kim Hong Lim of the Environment and Park Division Clean Environment Bureau Jeju Special Self-Governing Province of the Republic of Korea. Out of 88,000 hectares of forest on Jeju, only 1,622 hectare (1.8 percent of the island’s forests) were affected by disease or insects in 2011.
“I analyzed the average from 2001 to 2010, and the average was 3,785 hectares, so this is less than the 10 year average,” Kim said.
According to the “Jeju Statistical Yearbook 2010,” 2004 was the worst year within the past eight years for forest infestations and disease with 4,100 trees infected, followed by the year 2008 with 3,088.
According to Shin Chang Hoon of the Jeju Special Self-Governing Province Hallasan Research Institute — an organization that conducts forestry research and develops preventative measures against diseases — the pine moth caterpillar (100 hectares), witches’ broom (3,000 trees), phalera flavescens moths (500 trees), and pine wilt disease (195 trees) caused the most damage to Jeju’s forests in 2011.
The reason for this downward trend, Kim said, is that prior to 2007 the previous system in place to deal with forest diseases and pest insects lacked focus and structure. “The preventative measures weren’t solid, but [since 2007] we are more focused and know what we are doing.”
Kim said that currently the greatest threat is pine wilt disease, which is spread by the Japanese pine sawyer beetle, and was introduced to Jeju through Busan from Japan in 2004. According to the Forestry Commission of Great Britain, pine wilt disease “kills huge numbers of pine trees every year in Japan, Korea and China.” The Environment and Park Division Clean Environment Bureau spent 2 billion won in 2011, on preventative measures like medical injections to control the spread of disease.
Before 2007 though, there were no preventative measures in place, Kim said, and their only method to stop the spread of pine wilt disease was to cut down and burn infected trees. “But with research [The Korea Forestry Research Institute] invented the injections, chemicals, and to experiment with the chemicals … Right now, the [injection] technique is being exported to Japan and Portugal.”
Along with the use of injections, they also use helicopters to spray insecticides to kill the Japanese pine sawyer beetle. Also, he said, approximately 10 employees from the Hallasan Research Institute routinely scavenge the forests of Jeju acquiring samples for testing to uncover which trees are infected. If such a tree is found, it is completely destroyed to prevent the spread of the disease.
He continued that even with these preventative measures in place there are several issues that make forest diseases hard to control. For instance, like the pine wilt disease, many diseases are transmitted through insects which have a five to six-year cycle meaning that the insect only appears in large numbers every half decade or so. This is the reason why the number of infected trees was so high in 2008.
Also, diseases don’t necessary infect an entire area; a sick tree may not infect those surrounding it but rather another tree much further away. This makes it harder to located infected trees, but allows for effective infestation, Kim said.
The current system of calculating infestation is by hectares he said, which might cause some miscalculation of the severity of the diseases on the island. If there is a single tree with a disease, the entire surrounding hectare is designated as being infected. “Starting now we are trying to calculate the trees and not the area,” he said.
The next preventative measure being taken is to stop diseases and pest insects from entering Jeju. Shin said that the mainland is suffering from oak wilt disease, and matsucoccus thunbergiana (the separation of inner tree skin below the bark) and “to prevent those from coming to Jeju we’re constantly monitoring.”
Kim said that oak wilt disease and black pine scale “are doing major harm on the mainland,” and though they have yet to reach Jeju’s shores the island needs to be extra cautious. Diseases and insects are “usually transferred from bad trees … but people try to make houses out of them, and if it comes to Jeju” it will cause severe problems for the island’s forests.
“We are trying to [put in place] more restrictions,” Kim said.
(Interpretation by Angela Kim) <Jeju Weekly>