Life Webs


Starting with trees

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

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.