Life Webs


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Puzzling over earthworms

earthwormEarthworms were the superheroes of my elementary-school science class. They aerated the soil, added organic matter, created structures that held water, turned garbage into gold. Seeing them and their lovely, rich castings in my garden and in the compost pile, all these many years later, makes me feel proud and virtuous.

But there’s more to the story. Here’s what they didn’t tell us in school: In the parts of North America that were glaciated (including the northeastern and midwestern regions of the U.S.), the glaciers wiped out all the terrestrial earthworms. Over the next ten thousand years, as the glaciers receded, the ecosystems adapted to this wormless state. Leaf litter piled up in the forests, and trees and understory plants evolved to gather nutrients directly from the litter, with help from fungi and bacteria. They also evolved to plant their seeds directly into the leaf litter. These forests had little or no topsoil, just mineral soil covered by a “duff layer” – leaf litter, twigs, bark, and so forth.

Fast forward to the 1600s, when the Europeans who settled the area unknowingly brought worm eggs in their cargo. They cleared forests and planted (mostly European) crops; the worm eggs hatched; fields and pastures filled up with earthworms and their castings. Today, there are some 15 species of earthworms in the area, all from Europe or Asia.

Earthworms damage the forests – we think

The worms are great for lawns and gardens (I think they’ve been poisoned out of most industrial-type farms), but – according to today’s accepted wisdom – they are making a mess of forests. They eat the duff layer, making it hard for trees and other forest plants to gather nutrients and for seeds to sprout. They eat tree roots, which weakens the trees. They greatly reduce the amount of carbon that trees can sequester. Forest scientists think earthworms cause as much damage as deer overpopulation.

I read all this recently, while I was trying to research the deer problem (see Regenerating trees), and I was horrified. Our compost pile is at the edge of the woods, and it’s full of worms. (My guess is that the worms come from the hay that we use as food and bedding for the rabbits – much of which ends up in the compost pile – but who knows.) Not only the compost pile but also the area around it is rich with worm castings. Suddenly, that stopped being a source of pride and became a source of anxiety. Are we setting off a worm apocalypse in our woods? Will all our efforts to re-create native woodlands be for naught?

There’s no open area suitable for the compost pile, but we decided that, once the weather gets warm, we’ll move the pile up to the chicken coop. There, we can count on the chickens to eat the worms as fast as the worms can multiply. It will make the chickens very happy, too.

Confusion reigns

But the more I think about it, the more confused I become. The Northeast was largely reforested in the last century or two after farmers abandoned their fields and pastures. How did native forests arise successfully on these earthworm-infested lands? Do the trees or the fungi fight back with earthworm-inhibiting chemicals? Or are they evolving back to their pre-Ice Age, earthworm-friendly genetics? Or are the post-agricultural forests all inherently weak and unhealthy?

And then another question arises: How are agroforestry and permaculture possible in the once-glaciated regions of the United States? People are planting rows of canopy trees (oak, chestnut, hickory), understory trees (hazelnut, native and non-native fruits), berry bushes and vines, with alleys of grass and even annual crops such as squashes between them. (One person doing this type of agriculture is Mark Shepard, who describes his experiences in his wonderful book Restoration Agriculture. He’s in Wisconsin, and I was wondering how he managed this problem till I realized that he’s in the Driftless Region, a high plateau that escaped glaciation. So he probably still has native earthworms. However, people are using similar practices in once-glaciated areas.) Do these “artificial edge” communities have earthworms, or not? If the pasture/garden alleys have earthworms, what prevents the worms from getting into the wooded areas?

More research to be done….

And any insights welcome.

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Regenerating trees

trees in snowOn these cold, snowy, icy days, there isn’t much to do in the way of gardening, so I have been thinking about the woods. We have about five wooded acres here, but they aren’t as healthy as they might be.

A couple of years ago, a forester from the Department of Environmental Conservation came out and cast a professional eye on the woods. “You’re not getting enough regen,” he said, which is forester-speak for regeneration. “Too much deer pressure.” In other words, whenever a tree seedling pokes its head above ground, a deer munches it.

Let’s get rid of all the deer! we thought. We hate them anyway – they spread Lyme and other nasty diseases. But the only way to do that is to fence in our whole property, about twelve acres in all, which would be wildly expensive. And, as it turns out, having too few deer is as bad as having too many. Deer are a major transportation mechanism for seeds, good seeds as well as bad ones. Without deer, you lose a lot of biodiversity.

Is there any way to have just the right number of deer? Not without more predators, and that’s a problem too. People around here tend to shoot coyote, bears and whatever else might eat fawns, because they don’t want competition for hunting. But DEC doesn’t give out enough hunting licenses for humans alone to keep the deer population in check. Even their deer management assistance program, which is not available for small properties like ours anyway, wouldn’t begin to make a dent in the population.

So what’s to be done? The only option seems to be strategic deer management – that is, protecting the seedlings we want to keep until they are large enough to withstand the onslaught of the deer. There are several methods, including tree tubes, DIY cardboard caps, and small fences, which vary in difficulty, cost and effectiveness. We’re already using small fences for the fruit trees we’re planting at the edges of the woods. (You can see an apple tree enclosed in a small fence at the bottom of the photo.) There are also techniques, such as hinge cutting, for distracting the deer with saplings you don’t want to keep.

Which trees to protect?

Now the question is: which seedlings should we protect? The canopy trees we have, in order of prevalence (more or less) are Eastern hemlock, oak (several species), beech, birch, maple, hickory, ash, and a few specimens of white pine, sycamore, basswood, and possibly black walnut down by the creek. The trees regenerating most successfully seem to be beech and birch.

Here are the tentative guidelines I’ve come up with – and I would appreciate any comments on these:

1) Don’t protect species that are subject to heavy insect and disease pressure. That includes hemlock (woolly adelgid), beech (beech bark disease, which has been endemic here for half a century), and ash (emerald ash borer arrived about a decade ago). Saplings of these species are unlikely to become mature, healthy adults.

2) Don’t protect species that can’t regenerate in shade, unless the seedling is at the edge of the woods. That includes white pine, oak and hickory, which are early to mid-succession trees. An oak forest is sustainable only by means of continual logging or fire, neither of which are we going to do on any significant scale.

3) Don’t protect species that are doing all right without protection. That includes birch and sycamore, neither of which the deer seem to prefer. (And beech, of course, but we already ruled that out for reasons of disease.)

That essentially leaves sugar maple, not coincidentally the official state tree of New York. We have a few mature trees, so we should be able to find some seedlings to protect. There are problems with gypsy moths, but they don’t seem to endanger the whole population. Sugar maple regenerates exceptionally well in its own shade, as long as the deer aren’t eating it. On top of that, it is a beautiful tree that produces a valuable product.

If spring ever comes, I’m ready to start my maple rescue mission. Watch out, deer!