Illustration by Jesse Tarlton

“And we danced, on the brink of an unknown future, to an echo from a vanished past.”
~ John Wyndham, The Day of the Triffids

Unlike the the mobile, man-eating Triffids in The Day of the Triffids, our trees don’t crawl around and eat people, but they may come and go over time. The huge old apple tree that loomed over my patio and backyard blew down a few winters ago, the result of age and fire blight. I’ve had to take down a decades-old maple hollowed (out) by age and threatening our roof, but I’ve planted a few trees as well, taking something small and putting it some place where it can thrive (great oaks from tiny acorns grow).

Global warming, that misunderstood and oft-maligned theory, actually accounts for and predicts shifts in vegetation as a result of climate changes, but recent studies have identified shifts in tree growth that are unexpected. Climate change has elevated temperatures and significantly altered rainfall totals across the world. For example, temperatures in the eastern US are higher, with more precipitation in the northeast and less in the southeast. The Great Plains have received much more precipitation than historically normal.

However, current studies show that trees are moving at unexpected rates and directions. According to Robinson Meyer, “About three-quarters of tree species common to eastern American forests — including white oaks, sugar maples and American hollies — have shifted their population center west since 1980. More than half of the species studied also moved northward during the same period.” Ari Phillips quotes a study in Nature’s Scientific Reports, “Windmill palms have recently been found in the forests of southern Switzerland — the foothills of the Alps — after one such decorative palm escaped and spread “simply because frost is not as prevalent as it used to be”.

But, do these changes portend dire consequences, like invasion by the Triffids? Probably not, but different species react differently to change. In the eastern U.S., deciduous trees are moving westward following the moisture, and evergreens are moving north to chase lower temperatures. According to Loic D’Orangeville (in Meyer), “These results show contemporary proof of something we know has happened before and will happen again: that trees are highly dynamic organisms, constantly moving in response to climate shifts like recent glaciations or other disturbances.”

While these shifts are not intrinsically dangerous, Robinson Meyer points out, “Forests are defined as much by the mix of species, and the interaction between them, as by the simple presence of a lot of trees. If different species migrate in different directions, then communities could start to collapse.”

A forest community includes not only the trees and other vegetation, but a whole slew of animals from microscopic to huge. Forests make their own nutrients over time, changing the soil and the microclimate, leading to succession as a part of growth. Plant and animal interactions define the community, and are dependent upon all components.

Historically, shifts in communities, both human and ecological, have occurred over long time frames, possibly with the exception of world-wide extinction events. Current climate change science predicts relatively rapid change, affecting the whole world over the next few decades.

Since our ‘planetary boundaries’ include ‘biosphere integrity’, the health of our ecological communities is important to us all. We currently have only a semblance of an understanding of all the interconnections among and between ecological communities. And as we know, we have less understanding of the interconnectedness between human and ecological communities.

If Chaos Theory supposes that the flap of a butterfly’s wings can have global impacts, then what might rapid, widespread changes in our ecological communities cause? For examply, increased atmospheric CO2 appears to be increasing ocean CO2 and changing the health of coral reefs. This in turn effects the health of ocean biota, including the species that humans rely on for food. Given increases in human populations and climate change impacts on land-based agriculture, we may come to rely more on the oceans for sustenance. Then what?

Trees aren’t the only ones on the move. All of these effects will also cause human migration, which will have cascading effects on ecological communities as well. So, understanding what’s happening and why — and what we can do about it before it’s too late — is critical.

And don’t forget to keep an eye out for the Triffids.

Additional information:

Robinson Meyer, American Trees Are Moving West, and No One Knows Why, The Atlantic, 5/17/17

Ari Phillips, Palm Trees Are Moving North, Earther Newsletter, 3/20/18

Steffen, W., K. Richardson, J. Rockström, S. E. Cornell, I. Fetzer, E. M. Bennett, R. Biggs, S. R. Carpenter, W. de Vries, C. A. de Wit, C. Folke, D. Gerten, J. Heinke, G. M. Mace, L. M. Persson, V. Ramanathan, B. Reyers, and S. Sörlin. “Planetary Boundaries: Guiding Human Development on a Changing Planet,” Science:Vol. 347, 13 Feb 2015