Biohazard II: Japanese Oak Wilt in Niiharu Citizen Forest, update

Homo sapience is in extreme ado about COVID-19 these days. But it’s not only we with infectious diseases. Do you remember I posted the problem of Japanese Oak Wilt last summer (on August 23, and September 6, 2019)? At that time, the City had not decided yet what to do with this infectious disease for mighty oaks in Yokohama. Here’s the update. In the end, they cut the tree standing on the popular strolling way in Niiharu Citizen Forest 新治市民の森. Now there is only a stump where I first found the infection.

There was a lot of wood powder for the infected tree …

At that time, I’ve heard it costs fortune to protect forest from the rapidly spreading disease. (It sounds familiar, doesn’t it?) Once infected, it’s hopeless to rescue the tree. The only possible way for humans to guard the rest is to vaccinate them, with the cost of 10,000 yen (USD 100) per tree. (In this regard, oaks are luckier than we with COVID-19 without vaccine.) For 67ha of Niiharu Forest with countless number of trees in oak family, it’s a fortune. My seniors murmured that the City did not have money to do that (,of course). “Well, they cannot leave the tree situated on the most popular road in the forest, can they?” “No, no.” Ultimately the Office has settled in felling the dying tree, but they did not have money to excavate the roots and sanitize the soil. (It is the standard way to treat this disease. Please see my post on August 23.) Having said that, we are not sure if it is wise to take such a complete measure especially for the area in question.

The stump of an infected oak.
 Inside the oak infested with Raffaelea quercivora,
 the virus spreads like cottony mold
 to clog vascular cambium rapidly,
 just like blood clots for heart attack, stroke, et al.
 Could you see the difference between
 the whitish core and the reddish rim?
 Cambium is the outer part of a trunk,
 and here, they have almost entirely changed the color.
 This is an evidence the tree was infected by the disease.
 It was dying …

Near to that point, there is a place where people could find a plant nearing the extinction and on the red list of IUCN. My seniors told me they have not spotted it for more than 10 years already. But hope springs eternal. If we treat the area chemically, perhaps the probability for us to meet that plant again in Yokohama becomes almost zero ... Though, what would happen this summer in Niiharu without complete treatment against the Oak Wilt? Will we have sudden tree deaths spreading to the entire forest? “Huh, no one knows.” It’s just like us with COVID-19. Who can say for 100% sure Tokyo Olympics and Paralympics will be held in the next year free of global pandemic? Never underestimate viruses …

Still, spring has come … Viola keiskei

If you find environmental issues 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/

Still Rhapsody in (spring) Blue: Cherry Blossoms in Yokohama, this year

Spring has come, no matter what COVID-19 is doing for our community. Although the City of Yokohama is not yet under lockdown, the Governor of Kanagawa Prefecture is asking us self-restraint to go out except for absolute necessity. Schools enter spring recess after 2 weeks of closure. People are telecommuting ... The saving grace is our parks and gardens are not yet closed off. And as every spring in Japan, we are now in the season of cherry blossoms. Having said that, this year’s flowers are somewhat strange.

Cerasus ×yedoensis (Matsum.)
 Masam. & Suzuki 'Somei-yoshino'

Local Meteorological Agencies in Japan declare opening of cherry blossoms for their prefecture when more than 5 buds open in the benchmark tree.  People are eager to know when it would be. So, the Agency forecasts the arrival of the flowers. They have complicated formula to deliver the date based on scientific studies by botanists (; we can find related academic articles here). The abbreviated version of this math is to calculate the sum of average daily temperature from February 1^st. The benchmark is the day when the total becomes more than 400°C for a location. The forecasted date is plus or minus from the date when the sum reaches to 400. This year in Yokohama, it is like

8.9*29 + 12.3 + 7.9 + 11.4 + 9.7 + 9.6 + 9.7 + 7.7 + 7.4 + 13.3 + 14.9 + 16.2 + 11.4 + 13.1

= (Average daily temperature of February 2020 in Yokohama)*(29 days)+(Sum of daily average until March 13)

= 402.7

i.e. The Yokohama’s arrival date of the flower was plus or minus from March 13th.

Somei-yoshino in Niiharu this year

Actually it was March 18th this year when more than 5 flowers were observed in the benchmark tree planted in the campus of Yokohama Meteorological Observatory. This itself was super-early, 8 days earlier than the average of last 30 years. Yeah, we have had very mild winter. No wonder cherries have flowered this quick. But that’s not all.

Cerasus jamasakura, aka wild cherry

Normally, cherry blossoms burst into open almost at once. It seems to me, this year it’s not that simple. One part of a branch is fully open, but not the other sections. Trees have jumbles of flowers, half-open blossoms, and still very young buds. When we see them from afar, they are often not a familiar pink clouds, but wispy smokes with lots of holes. Hmmmmmmmmmm … Cherry trees complete forming their buds before winter comes. Then, they sleep under cold weather until an occasional warm spell in February kicks them out of dormancy. Just like we jump out of bed with alarm clocks every morning for morning java, they wake up and burst into the flowery frenzy. But, if winter is not chilly enough … it could be like a morning for us after insomnia. I’ve found an academic bibliography here that discusses this issue. Maybe, this year’s frail blooming is something of global warming …

A confusion … I hope it won’t be an epitaph
 … (Yes, Naomi loves King Crimson!)

By the way, the forecast date of full-bloom in Yokohama is 27th, i.e. today. Yes, facing COVID-19, we are good boys and girls of self-restraint!

If you find environmental issues 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/