There’s a growing body of scientific evidence that trees share information, warning their neighbors about danger and nurturing nearby small trees. If you Google “trees communicating” you can get some notion of the traction that this idea is getting. Trees appear to communicate through their root systems and have measurable biochemical reactions to threats of stress. Much of the original work has been done in dense forests like those in the Pacific Northwest, but it may also provide some insights into little trees on the prairie.
This stand of cottonwoods is just down the Creek from our house and you can see it’s distinctive shape from our porch. The tallest and oldest trees tend to be toward the middle and the smaller younger trees are out at the edges. This gives the top of the grove an arch shape—-actually there are two arches shown on this photo. So, are the mature trees near the centers of the clusters providing information, protection, and nurture to the juveniles out around the margins?
Wild plum thickets in our Creek pasture show similar shapes, although the patterns are somewhat harder to see when the individual clusters are close together. The spring blossoms make the thickets look like a single mass. But, if there’s a smaller thicket standing alone you can see the same arched top. The elders toward the centers are providing care for the kids on the outside edges.
Inside the thicket, the trunks of individual plum trees seem to reinforce the pattern. Generally, in the internal tangle of trunks, you see the mature larger trees toward the middle and the immature smaller trees out at the margins. The left photo is a view from the center toward the margin and the right photo is a view from the margin toward the center. These are taken in the fall after the leaves have dropped so you can see the trunks easily. Actually, the individual plants at the margins are more like shrubs or bushes and the individuals in the middle are really only relatively small trees.
Looking down on the complex overall plum thicket from the perspective of these air photos (available online from Rock County), we can see that it’s actually a cluster of clusters. Single, sub-circular constituent clusters coalesce into a relatively continuous mass that makes it hard to distinguish the outlines of individual clusters. Some of the most obvious ones are circled. But, again a smaller, isolated thicket shows the distinctive sub-circular pattern: mature in the middle and juveniles at the margins. Walking through an isolated thicket, the perspective from “boots on the ground” usually supports the generalization.
We’ve got an experiment going in one of the paddocks. A single mature tree and her surrounding offspring are fenced off and protected from grazing. If this “exclusion” works and the little ones grow up to make a new thicket, this might be a way to expand the stands of wild plums along the Creek. That would be a good thing because in hot weather the cattle use the shade to get protection from the sun.
Here’s another example of an arched plum thicket, but this one also shows an emerging threat. Increased erosion of the steep channel bank has cut into the plum populations all through the pasture. In fact, the single small tree in the center of this photo is all that remains of a thicket almost completely removed by bank erosion. On a more hopeful note, the cottonwood monarch on the right is probably more safe than it was because the active bank erosion has shifted to the left farther away from the root system.
Although the idea of nurturing mother trees has a certain anthropomorphic appeal, there is an alternative interpretation. Maybe the canopy of the tall older trees cuts sunlight and moisture off from the short ones, so the young ones can only thrive out on the more bare margins. Like so many things in Nature, the reality is probably a dynamic between competition and cooperation (and probably many other variables). But, an over-emphasis on competition has apparently limited our understanding of the important lesson of cooperation among trees until recently. Maybe the mother trees on the prairie can provide some insights into what’s currently going on in the world of humans?