Risky Business

Imagine that you’re a seed produced by a milkweed, goldenrod, or some other plant species that relies on the wind to carry its seeds away. Attached to you are long fuzzy plumes (or similar structures) that allow to you ride along on the breeze after becoming detached from the pod or flower head where you developed. If you were able, you’d probably feel excitement about the potential journey you were about to embark upon.

Dotted gayfeather (Liatris punctata) is one of many wildflower species with wind-dispersed seeds.

Unfortunately, the chances of you taking a long trip aren’t actually that great. More importantly, the chances of you making any kind of trip that ends with successful germination and survival are even less good. Much less, in fact.

The majority of wind-dispersed seeds fly only a short distance from their parent plant. Most get caught on nearby plants or simply float down to the ground before getting picked up by the wind in any significant way. If those seeds were able to, they’d probably feel pretty disappointed by that.

All this, of course, assumes the seeds weren’t eaten by an insect, bird, or other animal prior to being released by the plant. It also assumes the plant was actually able to produce a viable seed in the first place. (Asters, blazing stars and many other similar ‘fuzzy-seeded’ prairie plants have notoriously low seed viability – they often create ‘seeds’ that don’t actually contain a live embryo.)

This common milkweed (Asclepias syriaca) seed got snagged on big bluestem plant just a few feet from its seed pod. Most wind-dispersed seeds end up landing close to their parent.

Ah, but the seeds that DO get picked up by the wind must have a marvelous time, right? They rise up into the air, borne by a breeze that carries them far away until they land in just the right place to germinate and grow into a new plant.

Except they don’t. Almost never.

Think for a moment about the incredibly specific criteria that need to be met to ensure the successful germination and survival of a wind-dispersed seed. Seeds that land close to their parent have a decent chance of remaining with the same soil type, light and moisture conditions, and plant community that allowed their parent to thrive. Seeds that travel further away, however, face the really strong likelihood that they’ll end up someplace completely unsuitable to their basic survival needs.

Just for fun, let’s assume a seed from a plant growing on the south-facing slope of a loamy mixed-grass prairie flies off for miles and somehow lands on another south-facing loamy prairie hill slope. It beat incredible odds by not ending up in a woodlot, crop field, or even a north-facing slope in a similar loamy prairie. By some amazing luck, it has found itself descending into a place that looks just like home. Hooray! It (probably) gets to die in a familiar-looking place.

Tall boneset (Eupatorium altissimum) seeds.

I say it will probably die because just landing in the kind of habitat it grew up in doesn’t mean it will automatically get to germinate and grow there. In order for that to happen, the seed needs to make contact with the soil. It then needs the right amount of moisture to trigger germination. Many seeds also need certain light conditions (light intensity and/or photoperiod) before they germinate. Lastly, they have to be able to successfully compete with surrounding plants for light, nutrients, and space as they grow from a tiny seedling into a mature plant.

If you’ve spent much time in prairies, you know that most grasslands don’t have a lot of exposed soil on the ground – at least not most of the time. That soil is usually covered by vegetation, both live and dead. A seed that falls on top of that layer of vegetation isn’t going to be able to germinate unless it can get through that mesh of plants and down to the soil. Rain and wind can help jostle and push seeds down to the soil, but even if that works, it might take a while.

In the meantime, the seed is vulnerable to being eaten by any number of invertebrates, being attacked by mold or fungus, or simply dying of old age. Many seeds, especially those built to be light enough to fly, don’t contain enough endosperm (starchy nutritious tissue inside the seed coat) to keep the embryo alive for very long. A few weeks or months is the limit for many wind-dispersed seeds.

Let’s say a seed lands in good habitat, makes it way to the soil, and gets the right combination of light and moisture to germinate before it dies. The last big obstacle is the competition from surrounding plants. Root systems in prairies tend to be pretty tightly-woven and neighboring plants are likely to grow fast and tall enough to canopy over a tiny seedling. Often, some kind of disturbance that weakens nearby plants (drought, growing-season fire or grazing, excavation by animals, etc.) is needed to create enough space for that little new plant to squeeze its way into a plant community.

Tall thistle (Cirsium altissimum) seeds.

So, to recap, in order to survive and grow into a new plant, a wind-dispersed seed has to be extraordinarily fortunate. If it flies very far from its parent, it will need to land in the appropriate habitat. Once there, it will need to somehow make it down to the soil and get the right light and water it needs to germinate. Then, it will probably need some help to reduce competition from nearby plants if it’s going to survive its seedling stage.

Why even bother? Why should plants even create seeds that can travel long distances if the risks are so high? It seems smarter to drop their seeds close by where at least the habitat conditions are most likely suitable.

Wild lettuce seeds (Lactuca sp) poised to float away.

There are several ways plants can benefit from sending some of their seeds long distances. First, colonizers from far away can bring in new genetic information to otherwise isolated populations, helping to bolster genetic diversity and fitness. At the same time plants can send their “kids” off into the world to places where they don’t have to compete for space with all their close relatives. That can be especially important for plant species that live in specific and/or small habitats where there might not be a lot of space for continued population growth.

Plants can also use seed dispersal to make sure they don’t have ‘all their eggs in one basket.’ If something bad happens in one location, it’s helpful to have closely-related relatives living elsewhere to make sure your family line continues. As rapid climate change continues, that ability to send offspring far and wide can also help plants adjust to shifting growing conditions across broad geographies.

Sending seeds into the wind is a high risk strategy, at least for individual seeds. However, if even one seed manages to successfully establish in a new site, the parent plant’s efforts are justified. Sometimes you just have to throw caution, and your babies, to the wind and hope for the best.

This entry was posted in Uncategorized by Chris Helzer. Bookmark the permalink.

About Chris Helzer

Chris Helzer is the Director of Science for The Nature Conservancy in Nebraska. His main role is to evaluate and capture lessons from the Conservancy’s land management and restoration work and then share those lessons with other landowners – both private and public. In addition, Chris works to raise awareness about the importance of prairies and their conservation through his writing, photography, and presentations to various groups. Chris is also the author of "The Ecology and Management of Prairies in the Central United States", published by the University of Iowa Press. He lives in Aurora, Nebraska with his wife Kim and their children.

24 thoughts on “Risky Business

  1. Simply love the imagery and education in this post (and so many others). I scattered a bunch of milkweed seeds high into the wind this weekend, not fully realizing the significant challenge to their survival. Nature is mind-blowing in its intricacy and beauty!

  2. I had never really thought this through, but certainly spent lots of effort (as a child) trying to help the local dandelions spread their wind-borne seeds far and wide by blowing at the seed heads. Probably the only animal species that does that for dandelions. Milkweed seeds are fun too. Then there are the winged seeds like maples, elms, ashes . . .

  3. What timing – this will be perfect to share with the kids at my school. We just received a wildflower seed grant, and I’m trying to explain to the the staff and students (in an interesting way) why it is important to have bare ground for these seeds to land on. Thank you for this!

  4. Chris,

    I have enjoyed your blog for maybe four years but is been a while since I donated to your efforts and chapter of the nature Conservancy. Let me know how I can best support your efforts specifically.

    Jamie Jacob

    >

    • Thanks Jamie, that’s very nice of you. Whenever you donate, you can always be as specific as you like about where your money goes. Of course, from our standpoint, something fairly general (Nebraska Chapter, land management, science) is helpful because it gives us some flexibility – and any of those three categories would be great for me! But if there’s something specific we’re working on that you’d like your money to go to, we will certainly honor that and be grateful for your support. You can indicate your wishes in the check memo, on a note submitted with the donation or anywhere else you can leave us a note as you donate. Thank you again for your financial support. We’ll do our best to make your money count!

      • Jamie, you are doing a good thing. As a long time monthly donor, I am always happy to hear about other donating to The Nature Conservancy.

  5. Thank you for the thought provoking post. It is amazing to consider the resources a plant invests in seed production with so few seeds producing a new plant. But then you have to consider how long that seed might remain viable wherever it lands and if it can germinate and grow when conditions are right. Are there any general ideas of how long wind-dispersed seeds remain viable?

    • Hi Nancy, seed viability really varies a lot, and also depends upon heat, humidity, and other factors. Seeds stored in a dry, temperature controlled situation can obviously last a lot longer than seeds out in the heat and humidity. We frequently store seeds for more than a year before planting them, and generally have good luck with most species, but the wind-blown seeds tend to be the touchiest. Some research shows that planting many spring-flowering plants right after harvesting them greatly increases their establishment (compared to storing them until the winter or subsequent spring). There is research out there about the viability for other species too, but again, most of that is research on seeds stored indoors – not in real world conditions. So, I don’t know the answer to your question other than to say that it can vary from a few weeks to a few years.

        • Although these plants do not have wind born seeds, I have had two species whose seed was kept outside in pots that did not germinate for at least five years after the seed was sown. Both have small or very small seeds. The first is Phemeranthus teretifolium, which germinated in a pot under the over hang of my roof. The location of the pot kept it rather dry until one very wet spring that must have triggered germination to occur. This pot had nothing growing in it for the previous five years. The second plant was Castilleja integra, which germinated in a pot with a sandy mixture five years after the seed was sown. I also sowed seed of this species in my garden hoping it could use Penstemons as a host, but so far only the one Castilleja integra plant in the pot has developed. This plant is in a pot I keep outside next to my garage door. I roll this pot into my garage during the winter. My garage is insulated but not heated. I do put some snow on the pots in my garage so they have some moisture during the dry winter months. The only other plant in this pot is Erigeron compositus, which the Castilleja could be using as a host. Possibly, the germination of the Castilleja was triggered by the growth of the Erigeron in this pot.

          These are both species of dry habitats, which might explain the longer than normal dormancy I observed.

          • I should also mention that species have been observed to grow from what appears to be a seed bank in wetland situations after agriculture has stopped and drain tiles are removed. These species do not categorically have wind dispersed seed but are of interest since these areas were previously in agriculture for many decades. Stephen Packard first pointed this observation out to me.

  6. I often talk to my groups about the difficulty seeds would have actually hitting bare ground without a regular fire regime. I hadn’t taken it the extra step to corelate it with the risks windblown seeds will face finding optimal conditions for germination.

    That got me thinking about wind pollination. I’m having a hard time coming up with plants that “double down” by having risky wind pollination and seed dispersal via the wind.

    I love these posts that give answers, but also promote even more questions!

  7. Wow. Wind pollination is very tricky business. Really had not thought about it to this extent but it is pretty fascinating and really involves some serious luck for success.

  8. Hello Chris –

    I loved the post, and the way you put the reader into the dynamic.
    I do think that the property owner’s management strategies would also be a factor – do they burn? If so, is it a fall or spring burn? How do these practices affect the ability of wind blown seeds to
    germinate. Does winter sowing (especially over snow) help the seeds to come into contact with the soil, as the snow melts?
    In spite of the difficulties encountered by some wind blown seeds, we had too much success with pale Indian plantain. Eventually it was spreading all over our prairie gardens. They are reasonably mature, having been planted in 2005, 2006 and 2007. They are respectively 1/6 acre, 1/3 acre, and 1/8 acre. We do burn in the spring. We have had to reluctantly remove the species from our plantings. How much difference is there in the management approaches that are dictated by the size of the prairie. Even though our gardens are large compared to conventional gardens, they pale in comparison to the properties you are managing.

    • Yes, all of that matters. Fire is a great way to get seeds to hit the soil (depending upon the relative timing of the fire and seed dispersal, of course) and yes, snowmelt can help draw seeds down to the soil. Of course, there’s still the competition issue. A dormant season fire doesn’t usually have much impact on the vigor of the plants surrounding where a tiny seedling might try to start – a growing season fire does, however. In eastern tallgrass prairie, moisture seems less limiting than further west, and seeds that fall into burned areas seem to have a reasonable chance of establishing. Further west, we often seem to need something else to help reduce competition (fire, drought, or other disturbances).

      And it’s interesting to see which prairie plant species are better and worse at being able to spread into surrounding prairie. Many times, seeds that are bigger/heavier than most wind-dispersed seeds are more successful because they can survive long enough to take advantage of delayed opportunities to germinate and compete.

      • It is interesting how pale Indian plantain (Arnoglossum atriplicifolium) is infrequent at a lot of remnants and the land managers wish they had more of it. Whereas, in prairie reconstructions, like Indian Ridge Marsh (Chicago Park District), it occasionally becomes super abundant. A true case of one land managers weed being another land manager’s treasure.

  9. Excellent lesson (and reality check) accompanied by similarly excellent images–as always. Asters and liatris produced prodigious amounts of seeds this year along the roadsides in the semi-rural subdivision where I live in northern Colorado on the edge of the shortgrass prairie. So, I collected as many seeds as I could and spread them in my yard to see if I could establish new colonies in locations that I deemed similar to where they were already growing. We’ll see what happens. After all, a supermajority of the seeds were doomed, anyway, right, and I did help disperse the seeds naturally as I collected some for my yard because many got carried away on the wind when I disturbed the plants.

  10. Excellent lesson (and reality check) accompanied by excellent images–as always. Asters and liatris produced prodigious quantities of seeds along the roadsides in the semi-rural subdivision where I live in northern Colorado near the edge of the shortgrass prairie. So, I collected many of the seeds and spread them in my natural yard in areas where I deemed the conditions were similar to the locations where the plants were already growing in order to establish new colonies. After all, most of the seeds were going to fail to produce new plants anyway, and I did help to disperse the seeds “naturally” since many floated away as I disturbed the plants during my collecting.

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