In March Last year, I attended a seminar held by researchers for Kanagawa Natural Environment Conservation Center. One of the topics was about Japanese oak wilt, presented by entomologists. Japanese oak wilt is disease of oak trees caused by Raffaelea quercivora virus carried by insects called Platypus quercivorus. So, the presentation was by entomologists. Platypus quercivorus is monogamous ambrosia beetle. Platypus quercivorus has fashionable pockets on their back where they nurture Raffaelea quercivora. The bugs dig lots of tunnels within trunks of oak trees and mate. The female lays their eggs inside their home-sweet-home tunnel. While they are busy in their home, their back rubs the surface of the tunnel, and infects the tree with the virus. Viruses multiply rapidly, which is a good thing for the insect family as their diet consists almost solely of the Raffaelea quercivora. Her eggs soon hatch and the baby worms eat voraciously the virus as their parents. Happy insect-family life. It is a death knell for mighty oaks.
 |
| Fashionable back of Platypus quercivorus |
Platypus quercivorus is a beetle having a big family life. Their nest within an oak has several egg chambers for thousands of babies. i.e. The bug loves to dwell in a large, established oak. They need at least 30cm of diameter for raising their offspring. Once a parent beetle infests an oak with Raffaelea quercivora, the virus spreads within a body of the tree like cottony mold. It clogs vascular cambium of the oak rapidly, just like blood clots for heart attack, stroke, et al. Big tree has big cambium that can somehow keep a space for water and nutrition to flow if the amount of such liquid is not much, like during rainy season in Japan with moderate temperature. Though, when Japanese summer temperatures skyrocket to 35°C+ with 80%+ humidity, trees get thirsty at once and needs lots of fluid circulating within their body. If Raffaelea quercivora blocks such vital “endocrine system,” large oaks dehydrate and become starved to death rapidly. The researchers for the Centre warned us, “With severe infestation, very large and tall oaks can be blasted within few weeks, even if they looked healthy and vigorous with rich green leaves during rainy season. Japanese oak wilt attacks a tree drastically.”
 |
| This photo was taken in
Koajiro Forest on August 1st, a bit early to observe autumn leaves in Kanagawa Prefecture. The tree was blasted by oak wilt. |
Worse, the story does not end here. Tiny worms of Platypus quercivorus with lots of tasty Raffaelea quercivora grow briskly and leave soon parents’ home in masse as adults. A young male immediately tries finding a mate and emits pheromone to attract partners of different DNA. It calls for another flock of Platypus quercivorus to this forest, and move to another oak to build their new nest in droves. Japanese oak wilt would spread rapidly within the forest when the place has lots of established trees of Quercus family, like Quercus serrata, and Quercus acutissima. It is said that the first massive infestation inJapan was recognized in the western part of archipelago around 1990. Since then, the disease devastated the forests in the western Japan, including Kyoto 京都. It now marches to the east.
 |
| Another example from Koajiro Forest |
Basically, Platypus quercivorus is common in the jungle of South-East Asia, like Vietnam. They are comfortable in tropics. Japan may have had home for Platypus quercivorus for centuries, but within a limited area. It’s no more. The climate change with warmer Japanese winter and lots of rain during spring (like this year) may have provided ideal conditions for the bug to proceed further north. And/or, it would be the result of our neglect of forests. For Platypus quercivorus to have nests, they need large oak trees. When our ancestors used firewood as household energy to cook, to warm, to prepare bath, etc. they coppiced oak trees every 10-15 years to harvest their logs. It was rare to find an oak tree of 30cm of diameter in Japanese villages. In colder places, it could take 50 years for a tree to be that big. Yeah, maybe Platypus quercivorus has lived in Japan for ages, but it was not easy for them to find a suitable home to multiply. Now, no more. When fossil energy replaced firewood in the 1960s, traditional usage of forests was abandoned. An oak forgotten in a forest since the 1960s is nearing 60 years old in 2019. They are big and tall enough for Platypus quercivorus to make holes for thousands of baby worms. Platypus quercivorus of the 21st century Japan find themselves living in a gorgeous place to procreate. The stage is ready for a forest of oaks to die massively. As the disease is caused by virus, once a tree is infested hopelessly, we have to
1. Cut the tree and uproot it entirely to remove the infested body completely.
2. The logs, leaves, etc. must be moved from the site promptly to be incinerated perfectly.
3. The soil where the tree stood should be sanitized entirely.
You see? Once the affected area becomes large, it’s impossible for humans to control the situation.
 |
| Also in Koajiro on 1 August 2019, damned hot summer. |
In 2017, the Office of Kanagawa Prefecture started to receive reports of Japanese oak wilt attacks in Hakone 箱根 and Miura Peninsula 三浦半島. And so, there was an urgent seminar topic in early 2018. Recently, I’ve been to Koajiro Forest 小網代の森 in Miura Peninsula, aghast to find extensive oak wilt. (More for my adventure in that Forest next week!) When I first posted my blog about Koajiro Forest (on July15, 2016), there was a talk to nominate such royally-loved forest for the 35th National Park of Japan. (It is said that the former Emperor and Empress 上皇 are planning to visit there again with their grandkids before long). I’m not sure if such ambition has any progress now with lots of died oak trees standing here and there. According to a person from the Koajiro Activities Coordination Council NPO法人小網代野外活動調整会議 who guided us at that time, the Prefecture hastily came to the forest and cut the infected trees along the board walk and brought out the logs, leaves, etc. for incineration. There remained rather sorry scenes very near for the visitors to observe. The typical evidence of disease was clear. The remained roots have lots of holes whose mouth is covered by wood powders. Peeled off barks of dying oaks are scattered without mercy. I presume the scientists are caught in a dilemma there. To stop infestation they have to sanitize the place. But Koajiro Forest is proud of its biodiversity and extensive natural underground water system within its tiny 70ha area. If humans chemically treat the soil, even if a bit, what would happen for the creatures, other than Platypus quercivorus, living in the entire forest? It’s a serious problem.
 |
| A killing field for oaks |
Then, few days later, I found a Quercus acutissima with wood powder in none other than our be-loved Niiharu Citizen Forest 新治市民の森. EMERGENCY. I panicked. I consulted with my seniors of Niiharu Lovers, and called the City Office for my sighting. The chairman of Niiharu Lovers has officially requested the municipality to tackle the problem promptly … Compared with the remnants of oaks in Koajiro Forest, the Niiharu’s oak has, it seems to me, fewer holes, and powder. The crown of the tree was still alive at least a week ago. I hope, I really hope, we have yet time to stop the disease to spread …
 |
| Niiharu’s sick oak. But it still has green crown. We may well be able to save it … |
 |
| A typical sign of
infestation. Lots of holes at the bottom of large tree covered by frass. |
If you find an environmental issues, like Japanese oak wilt, in Kanagawa Prefecture, please make a contact with Kanagawa Natural Environment Conservation Center 神奈川県自然環境保全センター
657 Nanasawa, Atsugi City, 243-0121 〒243－0121 厚木市七沢657
Phone: 046-248-0323
You can send an enquiry to them by clicking the bottom line of their homepage at http://www.pref.kanagawa.jp/div/1644/
If you sighting is in the northern part of City of Yokohama, the office you may call is
Office for Northern Parks, City of Yokohama 環境創造局公園緑地部北部公園緑地事務所
Phone: 045-353-1166
FAX： 045-352-3086
ks-hokubukoen@city.yokohama.jp
Or for the southern part, the address to call is
Office for Southern Parks, City of Yokohama 環境創造局公園緑地部南部公園緑地事務所
Phone： 045-831-8484
FAX： 045-831-9389
ks-nambukoen@city.yokohama.jp
We Really thank you, for your kindness to rescue our forest!
No comments:
Post a Comment