Meandering in the meadows

musings about seed dispersal

One fine day in late September—in between other days of slatting rain and wind, Parks and Rec hikers headed up the ridge behind Cropley Lake. It was a good day for that hike. However, I was feeling considerably less ambitious, so I chose another way to spend the lovely day. Oh, I started at Eaglecrest, all right, as did the main group, but I elected to meander about the mid-elevation meadows with a friend.

The first treat was a migrating red-tailed hawk soaring over the ridges, calling to another one half a mile away. This bird had very dark plumage, as is common in western populations, but the red tail was clearly evident.

That was a good start to our little explorations. We soon found another prize: a stand of alpine blueberries, which (maybe along with the other low-bush species) beat the tall-bush species for flavor. We browsed for a while and then figured out the best situations in which to look for more. Sure enough, the good ones were definitely concentrated in certain kinds of places (a secret, of course), so naturally we searched them out and browsed some more. Very satisfactory! We could have harvested a good bucketful, if we hadn’t eaten so many.

As we cruised around, we also encountered several stands of the high-bush blueberries, both the ‘early’ one and the ‘alaskan’ one, with good crops of berries still on the bushes. So all those folks who fussed about a poor berry crop maybe just did not go far enough.

We found the seed heads of leatherleaf saxifrage, with seed still in the capsules. I’m ashamed to say that I’d never looked closely at these before, but we did so now. And that led to a discussion of the various means by which seeds disperse from the parent plants. Here’s a quick synopsis with selected local examples:

Colorful berries are usually sweet (and a few are rich in oils), and both color and content are adaptations to attract vertebrate consumers that eat the fruit and pass the seeds through the digestive tract. The seeds survive gut passage and often germinate in a handy little pile of manure. If a bear is the consumer, the manure pile is quite sizable and competition among the hundreds of germinated seeds is fierce. When an urban human is the consumer, however, the usual dispersal pathway generally fails. I have seen animals eating all of our local kinds of berries except bunchberry (a.k.a. dwarf dogwood), which seems to remain in place until the berries just fall off (unless a mouse has opened the fruit and eaten the seed).

After a meal of Viburnum. Photo by David Bergeson

We’ve all seen the seeds of fireweed, cottonwood, and willow floating through the air on their fluffy, white ‘parachutes’. Lots of other plants disperse their offspring in similar fashion: goldenrod, aster, dandelions, to name a few. Still other plants put little wings on their seeds: all of our conifers, for example, and maples and alders. Both wings and parachutes are adaptations for wind dispersal.

The seed pods of lupine open explosively on warm, dry days, scattering the seeds. You can hear the pitter-patter of falling seeds if you listen for it. The dwarf mistletoe that parasitizes hemlock trees also disperses its seeds explosively. And the plant known as jewelweed or touch-me-not vigorously pops open its seed pods at the slightest touch.

Some plants make seeds with hooks that latch onto fur (or socks) and get carried some distance from the parent plant. Examples include bedstraw, avens, and some grasses. And plants that grow in water sometimes have flotation devices (but how do pond lilies and buckbean seeds get from one muskeg pond to another??).

There are many plants, however, whose seeds have no evident adaptation for dispersal; leatherleaf saxifrage is one such, and shooting stars, wild iris, and chocolate lily fit this category. In some cases, the stem that supports the seed capsule is moderately tall, and seeds may simply get shaken out at a short distance from the parent. In other cases, the entire plant may be eaten by a large animal and the seeds passed through the digestive tract. A few plants, such as the swamp gentian, put their seeds in splash-cups to await a raindrop that will wash them out. But in many cases, we are just left to wonder how the seeds get to new sites for establishment.

I have not mentioned a means of seed dispersal that occurs in other North American forests, namely dispersal by ants. The seeds of these plants have an oil body at one end of the seed; the ants collect and eat the oil body, and then dump the seed in their midden. Very neat! But, alas, I don’t know of any ant dispersed plants around here, and there may not be any, given our paucity of ants.

However, for many local species I do not know the most likely means of seed dispersal. Folks often go on walks to survey the variety of wild flowers that bloom earlier in the year, so why not try a walk to survey the variety of seed capsules and likely dispersal mechanisms?


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