May 2023 – Tree Weaver

Whether a standing snag or a rotting log, dead trees play an essential role in sustaining life around them. It’s important for anyone who cares about the planet’s health to understand why a fallen tree found in nature is so essential to maintaining the delicate balance of the ecosystem around it.

Tree Lifespans
The lifespan of North American trees varies greatly depending on their species and circumstances.

For example, the grey birch has a lifespan of only 30-50 years and is among those with the shortest lifespans. On the other hand, Great Basin bristlecone pines can live for thousands of years. In fact, the oldest living individual organism in the world is a Great Basin bristlecone pine still living in the White Mountains of California that is over 5,000 years old! The exact location is protected.

While trees can live for tens, or hundreds, or thousands of years because they continually produce new tissues and adapt to their surroundings, the reality is that most succumb far earlier due to injury and disease (and sometimes both).

What is Tree Decay?
Decay is simply the process of rotting or decomposition.

The terms tree decay and tree decomposition can be used interchangeably to describe a biological process where wood’s cellulose and lignin convert to carbon dioxide and water, and the remaining nutrients are simply released into the soil.

Conditions that Cause Tree Decay

Wounds
Tree wounds occur when a tree is injured, and they can limit the tree’s ability to take in water or food properly and protect itself from infection, infestation, or disease.

The two basic types of tree wounding are stubs and scars.

Stubs
A stub is created when tree branches or tops break off or die. They can stick out from the stem and prevent the wound from closing and healing or leave a giant hole, both of which invite decay.

Storms with intense winds commonly knock tree branches off and cause stubbing.

Scars
When bark is removed or dies off, scars can leave the inside of the tree exposed to decay.

Animals and humans can cause tree scarring. Bucks rub their scent on trees to attract does during the mating season. Black bears shimmy up against trees to remove their winter coats and communicate with other bears by leaving their scent-marks along trunks. If you have ever seen someone’s “Harry loves Sally” declaration carved into a trunk, this is yet another form of tree scarring that leaves a tree more prone to decay.

Wherever wood is cracked open, insects like sugar maple borers or bark beetles can come in and weaken the tree further. Birds like sapsuckers and woodpeckers also drill into wound sites and deepen cavities.

Root Damage
When roots don’t get enough oxygen or the right amount of water or break off, this sets the stage for decay to begin underground or on another part of the tree linked to the affected roots.

What Does Tree Decomposition Look Like?

Many fungi, like the Armillaria, make their way onto decaying wood and other organic matter using microscopic spores that can drift in the air for long distances.

Fungi will often inhabit a tree, living within them their whole life, only becoming active later, when the tree becomes old or stressed. Other fungi form symbiotic relationships with trees, like the fly agaric, the classic white-spotted red toadstool, that grows around the roots of birch or pine and protects them against parasitic species.

However, most often when we see a fungus on the side of a tree it spells some level of trouble for the tree, like heart rot in an aspen.

Fungi can commonly spread by extending their networks of microscopic branches (called hyphae). As fungi spread their hyphae along a dying or dead tree, it releases enzymes that break down wood and, at the same time, allows the fungus to feed on it. Mushrooms later pop up from the hyphae as the fruiting bodies of the fungus.

As decay advances, more organisms come along to assist, such as bacteria and invertebrates, including slugs, beetles, woodlice, and millipedes. Organisms that feed on decaying organic matter are called detritivores. As these creatures feed on the wood, they open it up to increased moisture, causing it to get wetter, which helps it fall apart and decompose even faster. Mold also grows on wood – another example of a detritivore.

Once rotten wood starts mixing in with the soil, springtails and earthworms show up to feast on it. Fungi convert the wood’s cellulose and lignin into softer tissues that then decompose as the fungi’s fruiting bodies die.

Other Signs of Tree Decomposition
Live trees can also rot from the inside out, making signs of decay trickier to spot. Besides the signs of wounding mentioned earlier to look out for, here are some tips for spotting a tree that might be rotting internally:

White, Brown, or Soft Rot
There are three types of tree rot brought on by fungi: white rot, brown rot, and soft rot. Each causes the wood of a tree to appear differently and can often be observed in sticks and logs on the ground.

For example, white rot is present when wood appears lighter in color because the fungi feed on the lignin. It can also look fibrous since cellulose remains intact longer. The paper industry occasionally uses this natural, sustainable phenomenon to brighten sheets of paper by introducing white-rot fungi that feed on the lignin of wood chips before it’s processed into pulp, a process referred as biobleaching.

Likewise, brown rot can make wood look crumbly and browner in color when greater amounts of lignin are left behind.

Not as much is known about soft rot, but it occurs when a fungus uses enzymes and nitrogen in the soil to break down cellulose. It can appear similar to brown rot since it also does not target lignin and causes wood to take on a crumby, cubic appearance. Soft rotting logs are often partially buried in soil, giving fungus access to nitrogen from the soil.

Development of Fungi and Mushrooms
There are an awful lot of fungi and mushroom varieties that feed on wood.

Soft or Brittle Wood
When a tree is in a weakened state, soft wood can easily fall apart, and brittle bark or branches tend to crack or tear off easily.

Discoloured Leaves
Out-of-season, off-color leaves can be a sign of many things, including water or nutrient shortages, fungal or insect infestation, or mechanical damage to the branch, trunk or roots. In all cases, it is a sign of stress, and could lead to decay.

The Rate of Decomposition
Since trees are woody, their fibers are tougher to break down than non-woody plants, so they take longer to decompose.

There are countless factors that can determine the rate at which a tree decomposes. It may be affected by tree characteristics (species, age), climate (temperature, precipitation), and other circumstances. The tougher the species of tree, the longer the decay process. The wetter its surroundings, the faster a tree can rot. If surroundings are dry, fewer fungi and insects are active to break down wood, so the process can take far longer.

How a Fallen Tree Provides Life

Nutrients and Food Sources
The nutrients a tree used to build itself during its lifetime are spread into the soil and make it richer for other plants around it to use. These nutrients are essential for small trees to grow and replace the dead ones.

Fallen trees also sustain the many detritivores that feed on the decaying wood, like fungi and beetles, earthworms, etc. This means that other animals that prey on those detritivores also benefit, like the robber fly that eats beetles. In turn, the predators of those predators can also find food (like birds and bats) and so on.

More Light and Space. The space left by a fallen tree allows more light to reach the forest floor as well as space for other vegetation to take root and flourish. If a tree falls and takes others down with it, this helps the plants around it even further.

Shelter
Hollow logs are used by bears and smaller animals like foxes for making their dens. Also, a great variety of detritivores make their home in decaying wood, like millipedes and slugs.

https://www.plt.org/educator-tips/what-happens-trees-fall-forest

I spend a lot of my day looking down, as I think many of us do. We look down at phones, computer screens, and books. We direct our gaze toward the sidewalk as we rush to our next destination, smile at dogs walking by our feet, or stop to observe the wildflowers on our path. Even on beautiful hikes through the forest, I’ve caught myself fixating on the ground as my feet navigate rocks and roots, trying not to trip. It’s easy to go a whole day without really looking up. But when I do, I’m always impressed by what I see.

Day and night, the sky offers a constant, everchanging gift. The clouds shift into all sorts of shapes, some bright and buoyant, others dark and looming. The sun colors all around it with shades of pink, red, purple, and orange as it rises and sets. The moon changes each day — sometimes it’s barely visible, a tiny stroke of light, other times it shows up full, bright, and round. The stars glow like little lights left on to help us find our way home.

When I’m really caught up — in a thought, emotion, or situation — I like to remind myself to look up. However the sky has chosen to appear, looking up always offers a reminder that there’s more to this world than me and my own problems. The three pieces in this Weekend Reader draw inspiration from that same sky, reminding us that we all exist under this vast and wonderful canopy. May they remind you, when your head hangs down, to simply look up.

—Lilly Greenblatt, associate editor, LionsRoar.com