A tracer shows how the flow is diverted around patches of vegetation. Credit: John Kondziolka

Some plants change their environment, engineering their habitat to make it more amenable to themselves and, sometimes, hostile to competitors. Through chemical emissions or symbiotic relationships with pests, or even by physically strangling each other, plants can eliminate the competition and carve out their own territory.

In some cases, a plant’s presence is enough to cause changes in the landscape. Using a controlled laboratory experiment, Meire et al. show how mock aquatic plants change the flow of a simulated river, driving the distribution of future growth.

A cluster of stalks poking up from the riverbed obstructs the fluid’s flow in a predictable way. The flow slows down in a small region upstream as it’s diverted around the stalks, and there is a long, thin region of slow flow that stretches behind. Slower flows are less able to transport sediment, so the obstruction causes a concentrated deposition of nutrient-rich material on and just behind the group of plants. If a solitary patch of vegetation were all that originally took root, this disturbance would eventually cause a long line of plants to grow parallel to the flow.

When there’s more than one region of vegetation at the start, however, the fluid dynamics become a little more complex. If the plant patches are close enough to each other and perpendicular to the flow, the slowdown zone (and the region of sediment deposition) doesn’t form directly behind either of the two patches but in a spot behind and right between them. Two clusters, then, will set the conditions for a third to grow.

Just as the river slows down ahead of the first two vegetated regions, however, it also slows down upstream of the third. As the authors found, this slowdown will actually cause a fourth grouping to grow right between the first two, explaining the previously unknown mechanism by which plant groups can merge together. (Geophysical Research Letters, doi:10.1002/2013WR015070, 2014)

—Colin Schultz, Freelance Writer

Citation: Schultz, C. (2015), How do aquatic plants direct where other stalks grow?, Eos, 96, doi:10.1029/2015EO022139.

Text © 2015. The authors. CC BY-NC 3.0
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