Talking with Soil Creatures: counting soil animals in Yadoriki Water Source Forest やどりき水源林

 

Every July, we Forest Instructors for Kanagawa Prefecture do field research in Yadoriki Water Source Forest やどりき水源林. The main theme of this occasion is what kind of soil animals live underground of the Water Source Forest. We employ two approaches to collect tiny animals in the ground. One is collecting roughly 10cm deep dirt from 50cm*50cm square soil, sifting it by large sieve over a white plastic table cover, and inspecting the soil spreading over the cover to find out what comes out from the sieve. Another is using pitfall trap. 3 days before the research, we bury three medium-sized plastic containers with wide mouth. Each container has bites inside; chicken meat to lure carnivorous creatures, a banana for vegetarians, and for everybody crumbled kitchen paper drenched in brown sugar syrup. The opening of the boxes is at the surface level of the ground. It is covered by a lid with legs to shield the trap from pouring rain, but with wide enough gap for small living things visiting for bites. We make such instalments for two observation sites and go to see what’s inside 3 days after.

Collecting soil from 50*50

Three traps

Retrieved trap with chicken meat

This year, the team I joined was to check the soil creatures inside the fence before the toilet at the corner of the open space. The place is a mound made about 30 years ago when the water source forest was a commercial camping site. At that time, people made the heap there and planted seedlings of broad-leaved trees. They then enclosed the area by a fence in order to prevent deer came in and devour the baby trees. Now in 2024 surely we do not find droppings of deer inside the fence. But the trees remain lanky, and the entire ground is always dark as it is surrounded by tall coniferous trees. By simple guessing, we may expect there are lots of soil animals which in general do not like baking sun or drier soil condition … er, wait. Not so fast.

Surely, inside the fence is deer-free,
and rarely hosts vampire leech.
It’s a good place to install hammocks for nap.

First of all, there was an accident. We started our research from collecting the buried 3 boxes. In the box of chicken, there were lots of Anisodactylus signatus (in beetle family). Fine. In the box of syrup, there was not many bugs trapped. Syrup 3 days ago was almost dried up. The problem happened in the box of banana. This box was also almost empty, and above all, there was no banana, or the remnants of it. “Hmmmmmmmm. There must have been at least one thief.” “Indeed. It seems to me the thief came here early. May be immediately after we left this place. The box is so empty and clean.” “Wow.” “But how did it do it? The gap between the lid and the box is not wide, and it must have dug deep inside the box.” “No trace of pecking …” “It means the culprit was a mammal.” “But there is a fence!” “Somebody which is good at climbing up fences ...” Last year when we checked DNA from the water of Takigoh Fall 滝郷滝, near our soil study site, there were DNA bits of masked palm civet. It is a foreign species devouring commercial produce from farm fields. Also, the animal is good at climbing high, trees, roofs, etc. For it, penetrating inside the fence won’t be much problem. ***Sign*** We discussed how to make a lid of the trap from mammals. We have not reached the conclusion, but we must improve the design of the trap, for sure.

Empty bananas

Takigoh Fall.
Somewhere up there, masked palm civet is roaming.

Having said that, when we checked the number of families in the soil brought from the front forest for the toilet, it also was not much. Another location for the research was near the garage for forestry monorail. The number of creatures identified there this year was 53. The number we could identify from the artificial mound near the toilets was 45. Actually, such difference has been observed for several years.

Carrying collected soil for study

What’s there?

For example, here!
Geophilomorpha and earthworm.
Geophilomorpha can be found only in non-contaminated environments.
It’s good news we could encounter it.

Come to think of it, inside the deer fence in front of the toilets shows only a small number of fungi either. According to Dr. Taizo Nakamori (2022) for Yokohama National University, fungi is like a sweet shop for soil animals. People often misunderstand soil animals like worms make fallen leaves or twigs on the ground into nutrients for soil, like nitrogen. Nah. That’s the job done by bacteria, not soil animals. Of course, tiny bugs eat such leaves to survive. But they eat them and simply poop them afterword, which makes the fallen leaves into a smaller bit for bacteria to digest. Their contribution for soil creation is in this way. Fallen leaves are litter after the plants stopped supplying sugar et al from their photosynthesis. The level of nutrients in it is inevitably low, consisting of mainly cellulose = hard to chew. The soil creatures make do with this poor diet. However, if the soil has lots of fungi which will become mushrooms when the climate is right, the story is different. Fungi decompose plant litter with their enzyme and recompose the nutrients to become fungi. For soil animals, eating fungi allows them skipping their hard labor of chewing cellulose. When mushrooms come out, the soil animals swam such “candy” which is a mass of fungi hypha. They will move to the ground of mushroom. i.e. When there are lots of mushrooms on the ground, there will be lots of soil animals. If not much mushrooms found, the number of soil creatures would be smaller. 

* Taizo Nakamori, Soil Animals and Fungi, in Tomoyuki Shimano; Motohiro Hasegawa, and Yasuo Ogiwara (eds.) “The Topics of Soil Creatures,” 39-56, Asakura Publishing, Tokyo, 2022.

A mushroom we found in a previous fall inside the deer fence.

“Is it because the place is made of artificially brought soil?” “Possibly. But the construction was tens of years ago, wasn’t it?” “Yeah, the effect still continues, maybe.” “Oh, … hmmmmmmmmmm …” “Why?” It’s a mystery. There would be an explanation why the shady artificial mound does not show the same level of biodiversity as the next door natural soil. Curious.

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/