Starting with trees

Trees growing from a cliff wall on the New York State Thruway

We’ve all learned the stages of ecosystem succession: bare earth, annual grasses, perennial shrubs, pioneer trees, climax forest. In my part of the country, that’s what happens if you clear-cut a forest and walk away from it – the land will pass through all the stages and you’ll eventually end up with more forest. The reforestation of New England, following the abandonment of farming, has been one of the most talked-about ecosystem changes of our time.

But does it make sense to regard soil as the starting point? Soil is a complex living ecosystem and took a long time to develop.

On a recent trip to Boston, as we drove past mile after mile of rock walls – much of the highway was created by blasting through hills – I looked at the trees growing directly from the rocks and started to think differently about succession.

Trees live on minerals, water and sunlight, all of which are available on rock. (To be fair, lichen probably colonized the rock before the trees began growing, dissolving enough of the rock to make the minerals available to the tree roots.) Leaf litter from the trees then breaks down to become soil, making trees a more logical choice than soil as a starting point.

Annuals rush in where angels fear to tread

Does any of this matter? I think it does, if only as a matter of perception. If we regard trees as the starting point, it’s easier to see annuals as the anomalies they are – the ephemeral, opportunistic species that rush in after a disturbance (fire, windstorm, disease, timber harvest) to take advantage of a briefly unoccupied niche. They’re not a necessary step in creating the forest; they’re just fastest off the mark when there’s a niche to colonize.

Seeing annuals as anomalies helps us see exactly how bizarre the idea of annual agriculture is. Here are these fragile species that jump in for a brief moment when the forest is cut down and then get crowded out almost immediately – and we depend on them for our livelihoods? Talk about unsustainable!

And just as I was thinking this, I came across Janine Benyus’s comparison of human beings to annual plants in her book Biomimicry. Our strategy is to jump into a niche, reproduce as fast as we can, gobble up everything in sight, take up all the available space and resources, and then crash when there’s nothing more to eat. We’ve survived so far because our numbers were small and there were always new spaces to move to. But as we know, that’s no longer true.

To survive as a species, Benyus says, we have to become perennials. We have to dig in for the long haul, increase at a more reasonable rate and cooperate with the other species around us instead of trying to dominate them. We have to learn to be part of a sustainable ecosystem, as we were for so many years before the invention of annual agriculture.

Puzzling over earthworms

Earthworms 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.

Regenerating trees

On 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!

Changes in the Land

The brilliant book Changes in the Land, written thirty years ago by the historian William Cronon and said to have launched the field of environmental history (though Cronon modestly demurs), set me thinking about  what we mean by sustainability. Specifically, were Indian practices sustainable?

Cronon describes the land management practices of the New England Indians as of the time the English colonists began to arrive in the early 1600s, as well as the colonists’ practices, and the changes during the colonial period as the Indians dealt with the colonists and the colonists dealt with reality.

The outcome was horrifying. The Indians were largely exterminated, and the once-bountiful region was stripped and depleted of its resources. By the early 1800s, agriculture had moved west and New England was shifting to an industrial economy. Where the Indians had lived off the land for thousands of years, the English made it unproductive in a mere two hundred years. People still lived (and live) there, of course, but only as a part of a complex, global economy that is based on depleting resources in other, once-bountiful regions.

The colonists did not intend these results. The first settlers wanted to improve their own lives a little and not have to work quite so hard as they did in England. Early explorers’ (overstated) reports described the land as fantastically rich. Colonists imagined they could sustain themselves easily and make extra money trading with the Indians for furs and other commodities they could ship back to Europe.

Instead, they killed most of the Indians with germs they didn’t know they carried. (There was no germ theory of disease. Pasteur was not born until the nineteenth century.) They devastated the land because they tragically misunderstood how the Indians had managed it and what effects their own practices would have. In fact, they believed their industrious habits would improve land the Indians had neglected out of sheer laziness. This belief, as Cronon points out, sustained their ideology of conquest.

How the Indians Lived

Saying that the Indians lived off the land is somewhat misleading – it suggests that, as the English believed, the Indians simply feasted at the banquet that nature served up. But New England was not a wilderness. Even the tribes in what is now Maine, who did not practice annual agriculture, managed the land by burning the forest understory in their hunting grounds. (They also managed themselves by moving around in an annual cycle to the places that offered the greatest abundance in each season – something the English, with their fixed habits and household-level property boundaries, could not do.)

Tribes in southern New England, in addition to hunting and gathering, grew the famous Three Sisters – maize, beans, and squash. Contrary to the legend, they did not plant fish to fertilize their crops. They also had no draft animals, which typically fertilized fields in European agriculture. So even with legumes adding nitrogen to the soil, fields were exhausted in eight to ten years. Indian women would simply clear new fields and allow the forest to regrow in the old ones.

Indians throughout the entire area burned vast numbers of trees for warmth, in both winter and summer. Even the colonists were amazed by this – one of them wrote that the Indians used fire the way they used bedclothes. In fact, the Indians assumed that the English had crossed the ocean because they had run out of trees for fuel in their own land (which, as Cronon points out, was not far from the truth).

Sustainable or Not?

In several important senses, Indian practices were sustainable: The tribes had apparently occupied the same land for many years before the English colonists arrived. By late winter, they would be hungry, but outright starvation was rare. They apparently had no historical memories of things having once been better (as they did after the English began despoiling the landscape). Though Indian land management altered the ecology – for example, trees that regrew from their roots after girdling or burning, such as chestnut and oak, were favored, and some areas became deforested altogether – the levels of biomass and biodiversity, the two standards of ecological health, were both high.

Yet Indian practices – though they depended only on living resources, not on fossil resources – were far from energy neutral. If you keep open fires burning year-round, day and night, you take far more energy out of the environment than you can put back in. Exhausting fields every decade works only when you have plenty of land. So what made these practices sustainable is that the Indians kept their population density low (by what mechanism, Cronon is not sure) and didn’t even think of accumulating material goods, which their nomadic habits would have made impractical.

Today, with 7 billion people on the planet and little room to move, sustainability has to meet a higher standard. Humans make up such a large proportion of the ecosystem – and we take so much more than we give – that we can’t simply depend on the land’s ability to heal itself after we move on. We can look to indigenous practices for inspiration, but only for inspiration. We have to be way smarter than anyone had to be in the past.