December: Lessons from Collecting Fallen Leaves: Lignin, White-Rot Fungi, etc.

(English follows Japanese)

2026 New Year's Greetings

I was so busy at the end of the year that my December activity report spilled over into the new year.💧

Happy New Year.
Thank you to everyone who supported us last year.

In 2026, we will continue our activities to connect the care of land (watersheds) to the regeneration of the marine environment, not from a human-centric or human-convenience perspective, but by observing and proceeding through trial and error, one "chotto" (little bit) at a time. Thank you for your continued support.

Fallen leaves and branches are "resources"

In December, we continued to be busy with collecting fallen leaves and branches. Especially during this season when large amounts of dead leaves fall, we collect them before they are
cleaned up and disposed of as "trash" or flow from rivers into the sea, accumulate on the bottom, and turn into sludge. We collect and store them to effectively utilize them as resources.

I borrowed a light truck from an acquaintance to pick up pruned branches from another acquaintance's property.

Since cars cannot enter along the river, I had no choice but to carry them myself. I carried the thick, heavy branches by hand from where the car was parked, making several trips, and wrapped the thin branches in a sheet to transport them downstream.

Collecting fallen leaves

I do not take fallen leaves from the mountains or soil because they decompose naturally and turn into compost; I collect leaves that have accumulated on asphalt or concrete. When I visited the nearby
Jorakuji Temple for some business, I recalled that when the "Daichi no Saisei®" (Earth Regeneration) construction was carried out a few years ago—which I was also involved in—we drilled holes in the concrete gutters around the main hall to promote the movement of air and water. Since fallen leaves had accumulated in these gutters, I got permission from the temple staff to collect them. It was killing two birds with one stone, as it also served as maintenance work since the leaves were blocking the holes.

Pulling up fallen leaves accumulated in the river

To some extent, I think it is good for fallen leaves to accumulate in the river, creating dead water zones or areas where the flow slows down, as these become habitats for aquatic insects and small fish. However, because the shape of the river and its surroundings have been heavily artificialized, a phenomenon occurs where the accumulated fallen leaves turn black and become sludge, so I also pick up the fallen leaves accumulated in the river.

Continuing with the "Shigara" (wattle) retaining wall

The work was a continuation of increasing the height of the "Shigara" retaining wall, which only had one tier because we ran out of branches.
Even for a work area only 5 meters wide, I used up a whole truckload of branches in no time...
Ideally, it would be best to prune tall trees in the unmaintained mountains nearby and use those branches, but we currently lack the equipment and skills for that work. Also, there are many hurdles, such as the fact that much of the land is private property and requires permission from landowners or the government, so for now, we are using branches pruned in other places.

Cellulose, lignin, and white-rot fungi that help decompose fallen leaves

The people I am learning from who work on environmental improvement and restoration all unanimously say “Fallen leaves are treasure,” and in the autumn, they desperately collect fallen leaves, using them as an “indispensable material” by putting them into the soil, into compost, behind check dams, or using them as ground cover.

What is the process by which fallen leaves are decomposed to enrich the soil and ecosystem?

I looked it up, and to summarize it briefly, the process is as follows.

1. Fungi (molds/mushrooms) and bacteria begin the decomposition → [Bacteria]
   　・Pseudomonas genus
   　・Bacillus genus
   　・Actinobacteria (Actinomycetes: Streptomyces genus, etc.)
   　　I have absolutely no idea about this, it's beyond me...💧
   →
   
   [Fungi] (molds/mushrooms) 　 ・Molds such as the Penicillium genus
   　 ・Oyster mushrooms, shiitake mushrooms, etc.
   White-rot fungi of the mushroom family 　
   

2. Earthworms, mites, insects, and other small animals chew up the fallen leaves, making them easier for microorganisms to work on.
   

3. Microorganisms break down cellulose and lignin, transforming organic matter while absorbing nutrients.transforming organic matter while absorbing nutrients.
   
   →[Cellulose] (fibrous materials such as cotton, paper, and vegetables)
   ・The main component of plant cell walls.
   ・A polysaccharide consisting of glucose units linked in a straight chain.
   ・Provides strength to paper and wood by forming a fibrous structure.
   ・Cannot be digested by humans, but can be broken down by herbivores and many microorganisms.
   
   →[Lignin] (the hardness of wood, the stiff texture of fallen leaves)
   ・An aromatic polymer derived from phenylpropanoids.
   ・A highly complex structure with irregularly linked aromatic rings, lacking fixed repeating units.
   ・Due to this complexity and strong bonds, lignin is harder to decompose than cellulose, and only limited microorganisms, such as specialized white-rot fungi, can fully break it down.
   ・Binds cells together, hardens wood, and makes it resistant to falling and decay.
   
   (For details, see the site below)
   https://katosei.jsbba.or.jp/view_html.php?aid=1764
   
   I thought the functions of lignin—'making wood hard and resistant to decay' and 'causing fallen leaves to decompose'—were contradictory, so I looked into it and found that:
   ・white-rot fungi and others cleave and oxidize the lignin structure, and rather than completely breaking it apart, they destroy the chemical structure.
   ・Bacteria and other fungi utilize the decomposed plant components and release metabolic products.
   ・Lignin-derived fragments and other organic matter recombine, which exposes cellulose and makes it available to other microorganisms (while being decomposed, it is simultaneously converted into a stable form).
   

4. As decomposition progresses, black, nutrient-rich, stable organic matter (= humus) is formed, becoming leaf mold.

＊Which fungi dominate varies greatly depending on the tree species and soil environment (altitude, soil type, etc.), and the 'microbial flora unique to a specific location' is the key to leaf litter decomposition.

* Decomposition proceeds well when conditions are moderate: moderate moisture and temperature (around 15°C to 30°C), slightly acidic soil (around pH 5–6), and in semi-shaded to shaded areas away from direct sunlight.

Recalling the talks by Shogo Arai, a seaweed proliferation expert who has visited us about four times, I remember the terms "recalcitrant substance lignin" and "fungi" coming up. At the same time, I was reminded once again of "why air circulation in the soil and rainwater infiltration are so important."

I understand that when government agencies or companies carry out construction, it is inconvenient if they cannot quantify things like "material costs per square meter" or "durability in years." However, even if the goal is disaster prevention or human convenience, when dealing with nature, I believe it is desirable to consider the workings of the ecosystem, including small organisms and adopt a collaborative approach. Since we see signs of a shift in that direction among some government agencies and companies, we will continue our work this year, learning as we go and observing the progress, even though our efforts are small and experimental.

If you are interested in participating in our activities, please contact us by email at the address below.chottojapan@icloud.com

We look forward to your continued support this year.

(Organizer of the Water Cycle Connection Activities: Mariko Miki)

December Work Report

Lessons from Collecting Fallen Leaves: Lignin & White-Rot Fungi

I was busy at the end of the year, so my December activity report ended up crossing over into the new year.

Happy New year and wishing you a bright, fresh start!

This year as well, we will continue our activities with the aim of “connecting care for the land (watershed) to the restoration of the marine environment.” We’ll move forward —"chotto", little by little, by observing carefully and learning through trial and error, without putting human convenience or a human-centered viewpoint first.

Fallen leaves and branches are “resources”

Throughout December, we kept busy collecting fallen leaves and branches. This time of year especially, huge amounts of leaves fall. If they are simply cleaned up and thrown away as “trash,” or if they flow from rivers into the sea and accumulate on the seabed, they can turn into sludge. So we collect them beforehand, store them, and make effective use of them as materials.

We picked up pruned branches from a friend’s property, borrowing a mini truck from another friend.

Since cars can’t enter the riverside areas, everything had to be carried by hand. From the nearest parking spot, we made several trips carrying thick, heavy branches in our arms, while thinner branches were wrapped in sheets and transported downstream.

Collecting Fallen Leaves

We don’t collect fallen leaves in the mountains or on soil, where they naturally decompose and become compost. Instead, we focus on leaves that accumulate on asphalt or concrete surfaces.

When I visited Joraku-ji Temple located 5 minutes drive from our activity site for an errand, I noticed fallen leaves piled up in the concrete drainage channels around the Main Hall. A few years ago, large-scale "Daichi no Saisei® " (Regeneration of the Earth) work which I was involved, was carried out there, and holes were made in the concrete drains to encourage the movement of air and water.

With permission from the temple staff, we collected the leaves that had built up in the channels. Since the leaves were blocking the holes, this also worked as maintenance.

Removing Leaves Accumulated in the River

To some extent, collecting fallen leaves in a river can be a good thing. Slow-flow areas and small pools made from the piled fallen leaves can become habitats for aquatic insects and small fish. However, in this river, the channel shape and surrounding area are highly artificial, and the accumulated leaves were turning black and muddy which is negatively affecting living organisms here.

Because of this, we also pulled out the leaves that had built up in the river.

Continuing the "Shigara" Retaining Fence Building Work

We continued working on the "shigara", soil retaining structure, which had only been built to one level because we were short on branches last month. Even for a stretch just five meters wide, we quickly used up a full mini-truck load of branches.

Ideally, we would prune tall trees along the river, which makes the area too dark, however, at the moment we don’t have the equipment or skills for that kind of work. Many areas are also privately owned, so permission from landowners or local authorities would be required, so it's not work that we can do at the moment.

Cellulose, Lignin, and White-Rot Fungi: Helping Fallen Leaves Break Down

People involved in environmental improvement and restoration work—especially those I follow closely—often say, “Fallen leaves are treasures.”

In autumn, they eagerly collect leaves and use them as essential materials: mixing them into soil, adding them to compost, packing them behind "shigara" structures, or using them as ground cover.

So how exactly do fallen leaves break down and enrich soil and ecosystems?

After looking into it, the process can be summarized like this:

Microorganisms such as fungi (molds and mushrooms) and bacteria begin decomposition.

→ Bacteria
・Pseudomonas
・Bacillus
・Actinobacteria (such as Streptomyces)

Honestly, those terms are a bit overwhelming for me… 💧

→ Fungi (molds and mushrooms)
・Molds such as Penicillium
・White-rot fungi like oyster mushrooms and shiitake mushrooms

Small creatures such as earthworms, mites, and insects chew and break down the leaves, making them easier for microorganisms to work on.

Microorganisms then decompose cellulose and lignin, absorbing nutrients and transforming the organic matter.

→ Cellulose (fibers found in cotton, paper, vegetables)
・The main component of plant cell walls
・A polysaccharide made of straight chains of glucose
・Its fibrous structure gives strength to paper and wood
・Humans can’t digest it, but herbivores and many microorganisms can

→ Lignin (what makes wood hard and fallen leaves stiff)
・A complex aromatic polymer derived from phenylpropanoids
・Made of irregularly bonded aromatic rings, with no repeating pattern
・Because of this complexity and strong bonding, lignin is harder to decompose than cellulose
・Only certain microorganisms, such as white-rot fungi, can break it down effectively
・It binds plant cells together, making wood tough, resistant to decay, and less likely to fall over

• 
  Lignin’s role in making wood hard and resistant to decay seemed contradictory to the process of breaking down fallen leaves. So I looked further and learned that:

  • White-rot fungi partially break and oxidize lignin’s structure, not simply shredding it but chemically altering it

  • Bacteria and other fungi then use the decomposed plant components and produce metabolic byproducts

  • Fragments of lignin recombine with other organic matter, exposing cellulose and making it accessible to more microorganisms
    (In other words, while decomposition continues, the material is also reorganized into a more stable form.)

As decomposition progresses, dark, nutrient-rich, stable organic matter—humus—is formed, eventually becoming leaf mold.

Which microorganisms dominate depends greatly on tree species and soil conditions (such as elevation and soil type). Local, site-specific microbial communities are key to leaf decomposition.

Decomposition proceeds best when oxygen and moisture are balanced, temperatures are moderate (around 15–30°C), soils are slightly acidic (pH 5–6), and the area is in partial shade to shade rather than direct sunlight.

I was reminded that terms like “lignin” and “fungi” had been taught by marine algae researcher Shogo Arai, who we have invited to give us a lecture four times so far. At the same time, it reinforced my understanding of why air circulation in soil and rainwater infiltration are so important.

When governments or companies carry out construction projects, I understand that they need measurable figures—such as cost per square meter or expected lifespan—to make decisions. However, even when the goal is disaster prevention or human convenience, working with nature means considering ecosystems, including small organisms, and treating the process as a collaboration.

Some local governments and companies are beginning to move in this direction, but it still seems in the stage of “experimental.” In the same spirit, our work is also small-scale and experimental. We will continue observing, learning, and adjusting as we go this year.

If you’re interested in our activities, please feel free to contact us by email to chottojapan@icloud.com .

(Text: Mariko Miki, organizer)

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