Dispersal

Gliders, dogs, tennis balls, crossbows, inviting packages, blowguns: just a few of the mechanisms devised by the M Groupers to meet the annual Seed Dispersal Challenge.  After the class studies different means of dispersing seeds through wind, water, animals, and propulsion, students create their own way of getting a bean seed to travel at least 3 meters away from themselves.  Use of their own muscles is restricted to one small movement of the fingers – as in, drop a seed or glider, or release a trigger. The seed has to land on a surface where it could potentially grow, and a logical argument must be made for how the next and future generations could use the same technique to disperse their seeds as well.  Attaching a seed to a ball and letting gravity roll it down a hill, for example, only works for one generation, as the next will not have the same gravitational benefit. maggieOver the years, I have witnessed countless ingenious solutions, including loosely taping the seed to the top of a 3-meter long pole, then letting it topple over to release the seed.  This seed would then ostensibly grow into another tall pole-plant, which would disperse its seed in the same way. Or there was the seed attached to a soccer ball, which was left on the grass and eventually kicked away by a passing child who was unaware of the challenge, but who couldn’t pass up the obvious invitation.

During aftercare today, I noticed a dozen or so familiar-looking saplings growing under the canopy of the pines: golden rain tree.  A large, non-native ornamental now considered invasive, a single tree had been planted about fifteen years ago, succumbing to an unknown disease just last summer.  In those fifteen years, it had produced prolific pods bearing wind-borne seeds, but until now I had never seen its offspring.  So many inadvertent plantings, and these were only the visible ones. The saplings were just beginning to reach above a thick growth of other introduced, invasive plants: garlic mustard, wine berry, and burdock. Osage orange and yellow buckeyes, prized in the Jemicy fort culture, are not native to this region either. They join the golden rain tree and other introduced plants in that enormous pantheon of species that humans decided, for one reasonparkerseeds or other, to bring here.  And once established, facing no native controls, most take over dispersal responsibilities with the utmost success.

“Are all introduced species bad?” “Are all native species good?” “But don’t we want more species for biodiversity?” These are questions from students that I can’t definitively answer. What I can say is, “Look around you. Which kinds of plants are there the most of? Which kinds are there very few of? Does it seem like some are growing “out of control”? And then we look for the stories of how certain species got here – why humans decided they wanted them, and the effect that they have on others. I hope from this they will take away at least one message: dispersal doesn’t end with the single seed that we successfully launch; it is just the beginning.

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