Continuing the topic of forest green tree frogs, the place in Yadorki Water Source Forest we’ve found their frogspawn is above a concrete gutter that can dry up easily. When we met the adult frogs, the only water available in the gutter was in water collecting basin. The idea of the engineer who built the road would be
1. The pavement is slightly sloped towards the mountain, not valley, side. Rainwater poured over the paved forestry road first run down to the mountain side of the road. It could mitigate rapid erosion of the road to the side facing to Yadoriki stream and so the landslide, when it rains hard. And Yadoriki Water Source Forest has lots of heavy rain for its name’s sake.
2. Rain drops gathered on the mountain side of the road goes down as a stream and buckets in the catchment basin.
3. When the small basin reaches to the full, water is discharged to the gutter that is connected to the Yadoriki Stream. In this way, the power of water is so-so weakened and delayed the collapse of the forestry road.
4. For tree frogs, such design of the gutter means they can expect certain water level even the forest is in a dry spell. It would be OK for their babies, aka tadpoles, drop down from the bubbly cradle on the treetop into the 50cm * 50cm concrete pond and stay there for about a month until they become tiny frogs.
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| There! |
Forest instructors found a problem in this childcare strategy. Yeah, catchment basin could keep the water longer, but there is no guarantee that it holds suitable water long enough for tadpoles to be a young frog. As a matter of fact, the connected gutter dries up easily and frequently. In general, one bubble of frogspawn has 300-500 eggs. If all tadpoles hatched in the bubble drop down to the tiny basin, the place is VERY congested. Granted, cannibalism is a part of growing process for any tadpoles to be a frog. But once the gutter becomes dry and the babies are trapped in a small basin, the continuation of the family of forest green tree frogs should be in danger.
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| This
is last year’s frogspawn. At that time, the gutter was completely dry. |
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| And if
the torrential rain brought lots of soil, the gutter can be buried instantaneously. |
A week later after we’ve met 3 adult frogs near the gutter, the water collecting basin had more tadpoles including larger, i.e. growing up, kids. And above us there was another bubble of frogspawn. The gutter kept some water here and there. i.e. It rained for Yadoriki Water Source Forest for that week. But we knew. Strange movement of Trade Winds blew up the monsoon atmospheric pressure to the north far earlier than for an average year. Summer could start 2-3 weeks earlier than for the regular year. “Look, this pond could desiccate before the tadpoles are ready.” “Yeah. And newer ones may be waiting in the bubble.” We thought what to do. “OK, let’s dig a simple small biotope next to the gutter on the mountainside. We hope the tadpoles find it convenient as a nursery.” “In any case, they won’t stay in water more than 2 months. The structure does not have to be sturdy.” “Yep. Let’s work!” We dug a shallow 50cm * 100cm hole next to the gutter, line it with plastic garbage bags, fasten the sides of plastics with rocks, and add river water into the instant pond. “From now on for a while, let’s check it whoever of us visits Yadoriki forest.” “Roger.” The next day, strong sunshine of summer dispersed clouds completely for Kanto Region and the highest temperature in megalopolis Tokyo shoots up beyond 35 degrees of Celsius. We keep crossing our fingers as the frog place is in a deep mountain, harsh summer day in downtown means regular evening showers for tadpoles.
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| There is another bubble to the left of bigger one … |
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| Our emergency measure |
Later I happened to meet Dr. Tamotsu Kusano 草野保 for Tokyo Metropolitan University who is a specialist of Population Ecology, especially for Japanese amphibians. According to him, in Kanagawa Prefecture until the late 2010s, forest green tree frog was only identified in the north of Lake Sagami 相模湖. The frog itself has been more widely spotted in Tokyo’s Okutama 奥多摩 region that is next to the north forests for Lake Sagami. Reasonable. Basically, any amphibians are not so good to adapt to rapid changes in environment. They have soft skin = can be dried easily and need both lots of water and so-so dry land. The population distribution of them tends to be stable as long as climate allows them to stay put. Then, since 2020, several news started to appear for frogspawns of forest green tree frog around Lake Miyagase 宮ケ瀬湖, Lake Tanzawa 丹沢湖, and Hakone 箱根. He said for a forest green tree frog to be adult enough for breeding it takes several years. But, once tadpoles become frogs, this species could have relatively large mobility, say 5km radius in their birthplace. One possible scenario is, several years back global warming allowed the frogs to cross higher, (before-)dryer, and (before-)colder mountains like Mt. Hiru 蛭ヶ岳 (ASL 1673m), Mt. Tanzawa 丹沢山 (ASL 1567m), et al from Lake Sagami to find new frontier for their family. The young adults eventually have become moms and dads to have babies around 2020, and thus the news, including from Yadoriki Water Source Forest. Oh … is that so?
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| Lots
of tadpoles. Could you figure out there are several in the upper part of the photo? |
Whether those pioneer forest green tree frogs shall establish their family depends on nice combination of good water and land, in addition to now warmer climate. I’m not sure such things are reliably available in Yadoriki Water Source Forest. The water there is basically ravine. Instructors are now thinking to build semi-permanent pond at the place where we expanded the plastic garbage bag. That’s not for this year, but possibly for the next? Let us see if our improvised pool becomes some help for the frogs … Reebeep, reebeep, reebeep …
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| The frog needs lots of tree, for sure. |
p.s. This year, here in Yokohama, we had only 3 weeks of monsoon season. Worry about water level for the instant frog pond (and water supply in general) aside, Naomi is currently at loss about pickling schedule for salty plums (my post on July 16, 2021). The traditional standard dictates we can start drying the pickled plums in late July, which is the time when the average monsoon period ends. BUT, this year we completed our rainy season a month earlier, and I don’t know how to reschedule pickling process. In Google search, some say as long as the salted fruits yield vinegar they are ready to be dried. Some other say better wait until the average date for the end of the monsoon. And the other recommends better wait for more than 1.5 months whenever the monsoon ends as waiting makes the pickles softer … Hmmmmmmmmm. It sounds like laziness could make the treat softer. I’ve decided to wait till the end of July. 😊 Come to think of it, global warming is affecting such seasonal tradition of food preparation of humans, just like for the life of forest green tree frogs. *Sigh*
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/
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