Unsung heroes of the fall foliage season

The trees are on fire.

In a good year, they’ll burn for a solid month, and people will come from all over to watch it happen. The inferno will peak in October, with Carbon County awash in tourists, and the forests aglow. Fall foliage season is a predictable cause for annual celebration.

By Thanksgiving the whole matter is forgotten. Trees that commanded our attention just weeks ago in vibrant shades of yellow, orange and red will fade into a uniform shade of background gray.

Leaves once necessary for harvesting the energy of summer sunlight became a liability, paper-thin and subject to damaging frosts. Chemical signals told the trees to cut them loose, and they fell to the ground like so much used Kleenex.

At least, that’s how we tend to see things. What happens after the leaves fall is nowhere near as spectacular, so we fail to realize how important the next part of the process really is.

For the trees, those leaves were a costly investment, and recouping the energy that went into their production is of great consequence. It should come as no surprise that forests have installed a remarkably efficient, almost magical system of leaf litter recycling.

It starts long before the leaves begin to fall. Like salvage workers picking through a scrap yard, trees first pull out all the valuables they can.

The process, called retranslocation, takes out whatever nutrients might remain in the leaves and stashes them in branches or twigs. Trees are this way ensured a good head start on next year’s growth.

What’s left in the leaf after this is mainly a handful of compounds notoriously hard to break down: lignins, tannins and cellulose.

This is why no furry forest creatures such as deer or squirrels make a habit of eating dead leaves; there’s little nutrition left for mammals, and the acidic tannins tend to leave a bad taste in the mouth.

But somebody has to eat these things! Somebody’s got to recycle what the U.S. Forest Service estimates at roughly 2 tons of fallen leaves per acre, per year. Otherwise the whole system breaks down and comes to a screeching halt.

Enter the detritivores — an unsightly ensemble of unsung heroes who thrive on an otherwise unwanted resources.

By definition these things feed on detritus which, loosely translated, is waste or debris. Detritus is what’s left on the carpet of a frat house after a party; it’s the muck on the bottom of the stream. In this case, it’s everything dead and dying on the forest floor.

Detritivores eat notoriously tough-to-eat material. They’re a diverse group, led mostly by fungi and bacteria. “Fungi” include the familiar mushrooms, but also a host of similar organisms, all networking below ground in a massive and far-reaching system of weblike strands.

Fungi are often the first to act on fallen leaves, and you can see them at work for yourself. Scoop up a handful of leaves well on their way to decay, and you’ll see the cobwebby filaments of fungi at work.

Detritivores also include earthworms, millipedes, slugs, slime molds, beetles and other insects, all working to break down leaf litter and add nutrients to the soil — soil which can support more trees and shrubs, which produce more leaves, which feed more detritivores, which … you see where this is going.

What happens when this cycle is interrupted was evidenced years ago on the Blue Mountain, where emissions from zinc smelting operations poisoned the detritivores.

No fungi, no bacteria, no creepy-crawly soil critters, and you have no functioning forest, certainly no brilliant fall foliage either.

Once this year’s flames have become no more than dying embers, take a moment to consider the detritivores — the countless, nameless underappreciated things beneath your feet, working hard to ensure that next year’s fire will be all set to ignite.