I am waiting for the leaves to start to fall from my trees. It is an event that occurs at the same time each year (sometime after Columbus Day and before Halloween) but it always seems to be late in coming. I am not sure why I am always so eager to get on with the Fall, it just means that winter is closing in on us and that the color green is going away for five months!
There are so many “truths” and “myths” about tree leaves and what you need to do with them after they fall. One lawn product company stated on their web site that you need to rake up and dispose of these leaves or else “you will get rats in your yard.” Yeah, right. One of my neighbors piles his leaves in a great mass on top of his cleaned out garden and sets them on fire (or tries to set them on fire, anyway). The resulting smudgy, smoky mess smolders for hours and hours and triggers asthma in everyone for blocks around. One of my other neighbors runs her riding mower over and over her yard to scoop any stray leaves. I am not sure what she does with the mower bag’s contents. Another neighbor runs his leaf blower from August to November pushing his leaves to somewhere out of sight. His hearing must be destroyed by the din of that blower!
I usually rake up my leaves into several large, strategically located piles around my yard and leave them to nourish the worms and beetles and other invertebrates that will shred and grind them up into food for fungi and bacteria. In the old days my kids and I would jump in the leaves and further accelerate their fragmentation. Now I just rely on the worms to do the job with less noise and vigor (and much less fun, too!). Through the next spring and summer birds (especially the robins and the cardinals) peck at and dig around in the leaf piles looking for insect larvae and earthworms. These leaf piles are a great source of nutrition for these hunters and gleaners. By the time the next fall rolls around, the piles are remarkably reduced in size and are ready to be renewed by the freshly raked up leaves. One pile down in my orchard was kept in this yearly equilibrium for over twenty years. The rich, humus that accumulated at the bottom of the pile eventually was raked up and added to the soil of my tomato patch.
In a forest, the fallen leaves spread out in a thin layer over a broad area. Often earthworms start working on these leaves right away, pulling them into their middens and burrows, grinding them up with their muscular mouth-parts and gizzards, mixing them up with ingested soil, and defecating them out in nutrient rich, erosion resistant pellets. In soils without earthworms, numerous arthropods of many sizes begin to slowly chew away the leaf materials making a fine powder of organic residues enriched with bacteria. Both the worms and the arthropods are setting the table for the bacterial and fungi that then steadily work away at the less resistant molecules in the leaves. Like in my leaf piles, by the time the next fall comes around what’s left of the old leaves serves as the base for the new and the decomposition process grinds on.
Another fate of some of the leaves that fall in my yard is my household compost bin and pile. I collect a couple of trashcans of dry, freshly fallen red maple and apple leaves each fall and store them over the winter in my garage. When I charge up my composting bin in the spring, I throw in a good amount of the dry leaves to serve as a carbon source for the brewing compost and to give the dense, wet kitchen materials (usually dominated by coffee grounds!) some structure and air spaces. After some weeks in the bin (with regular turning and weekly additions of fresh kitchen materials) I shovel out some of the compost and transfer it to my nearby compost pile. Then I add some more leaves to the bin. By the end of the summer I have a rich pile of compost ready to be used in my garden or Deborah’s flower beds.
My leaf piles decompose more slowly than the managed compost piles primarily because of an innate nutrient imbalance in systems made up simply of leaves. There is too much carbon on these piles and not enough nitrogen. In the compost bin and pile the kitchen materials (especially all of those coffee grounds!) need the extra carbon of the leaves to balance out their decomposition. On the forest floor the richness of the chewing and shredding and burying organisms add nitrogen to the leaf materials via their feces and accelerate and balance the decomposition of leaves.
Natural decomposition is best thought of as an ensemble effort of an entire community of organisms where the products of one group of species becomes foods of another group of species until the food energy in the decomposing leaves is exhausted and only humus is left.
An old friend and mentor of mine, Daniel Dindal, summarized this community concept of composting into a very visual diagram that he called the “Food Web of a Compost Pile.” Please look over this marvelous work of art and science!
Up on campus we have started a composting system for the materials generated in the Café. We have three fence-sided compost bins into which we are putting kitchen and post-use “waste” materials. We are monitoring the rates and directions of the composting process, and I have three students who are conducting experiments on various stages of the composting system. Hopefully, in the spring we will have some rich compost to add to the flower beds and tree plantings around campus.