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NATURE HAPPENINGS - September 2007

September’s Seed Migration
by Damian Fagan

Not only are animals and birds on the move in September, but so too are summer’s seeds. Unlike wildlife that uses their feet or wings to get around, seeds rely on a variety of other transportation options.

Many members of the sunflower family have long fibers or hairs attached to the seeds that enable the seeds to travel airborne. These hairs and bristles may form an umbrellalike structure that provides buoyancy from a slight wind. Sort of like Mary Poppins’ bumbershoot when she decides to fly. As the wind settles down so do the seeds, hopefully landing on an optimal growing site. The wind may continue to push these seeds along the ground like a parachutist trying to collapse their chute. As the structure starts to break apart, the seed’s transporting days are limited.

Tumbling tumbleweeds, the classic weed of western landscapes, also rely upon the wind, but with a different intent. As the plant matures and the seeds ripen, the roots of this annual plant release their grip on the soil. Autumn’s wind gets the lightweight plants rolling, literally, and the plants tumble and bounce across the landscape like an Olympian gymnast. This tumbling action scatters the minute seeds.

Lupines use a different method of launching their seeds away from the mother ship. As the pea pods dry out, they split along one edge and twist. The release of pressure within the pod catapults the large seeds. You may notice the curled and twisted shape of old pods - silent testimony to this “snappy” dispersal method.

Of course, wildlife also engage in transporting seeds via direct or indirect methods. Direct methods include ingesting berries or fruits and pooping out the indigestible seeds. Not only are the seeds carried away from the host plant, but also are deposited in their own fertilizer! One September while hiking in Seven Mile Canyon, I found numerous coyote and bear scats that were stained eggplant purple and loaded with the tiny black seeds of Fremont’s mahonia.

Another direct method is the carry-and-cache mode. Acorns, grasses and pine nuts seem to be the primary recipients of this process. Pinyon jays, ground squirrels, Clark’s nutcrackers, and small rodents collect the seeds or nuts and hoard them in underground burrows. Some of these caches are visited later in the fall or winter. Those that are either forgotten or left alone may sprout forming new plants in the spring.

The indirect method of seed transport is due to seeds or fruits clinging to the feet or fur of animals and becoming dislodged at some point along the way. Cockleburs, certain grasses, blazing stars, jimsonweed, and members of the borage family have projections or spines on either the seed’s coat or the fruiting capsule that enables them to hitch a ride. This attachment concept works so well, that cockleburs are given credit for the creation of Velcro®.

Although there is no guarantee that these seeds will land in a favorable spot to germinate, they do have an addition advantage – longevity. Many desert seeds will lie dormant hidden beneath the soil surface for just the right set of germination conditions. Even after many years, the seeds remain viable.

For a fun experiment with kids, collect some dandelion seeds and have one person release them from a standing point. The other person places markers – stones, Popsicle sticks, twigs – where they land and measure how far these seeds travel.

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