Ants as landscape restorationists

The entire forest floor is covered with a magnificent population of wild leeks (Allium tricoccum) on an east-facing slope in a western MA “sugarbush” – a stand of Acer saccharum tapped for maple syrup production – note the tubing. This species is ephemeral…in mid-June the leaves will not be visible. A typical Allium flower stalk will then emerge, and ants will collect the seed. Photo © Ruth Parnall

Not only are there plants that are protected from herbivory by ants , there are plants with a mutualistic relationship to ants for their seed dispersal. Readers who live in the eastern deciduous forest may know some of the plants:  Erythronium americanum, Sanguinaria canadensis, Asarum canadense, Dicentra canadensis, Viola species, and Claytonia virginica. Many of these species are shade-tolerant, and their leaves persist in mature woodlands throughout the growing season. Several members of the rich woods flora are herbaceous plants called spring ephemerals. Their whole life cycle – from emergence to dormancy – is completed in the short span of time between the first weather for active pollinators to full leaf-out and canopy closure.

Within the sugar maple/white ash/basswood mesic forest association there are habitats with the favorable bedrock (limestone predominates), aspect (SE to NE), landform (slightly concave slope), soil (neutral to high pH and evenly moist), and land use history (no cultivation) . Because the growing conditions are so good here, plants thrive, resulting in more species richness than most other habitats. And in these rich woods 30 to 40 percent of the species will be myrmecochores – having seeds dispersed by ants. (Matlack 1994). The ant species doing this work are the foraging type: Aphaenogaster, Myrmica, Formica, and Lasius (Handel et al 1981).

The ants are interested in the tissue rich in lipids (eliaosome) which is attached to the outside of the seed. They harvest the seeds and carry them to the ant nest.

Bloodroot seeds with their white eliaosomes are collected by ants within about 6 hours of the pod splitting open, so you need to keep a sharp eye on the ripening if you are collecting for propagation. Photo used by permission of Jacqueline Donnelly http://saratogawoodswaters.blogspot.com/

After eating the eliaosome, they discard the intact seed into a refuse pile within the nest – a perfect environment that protects the seed from predation and fosters germination. No surprise that researchers have found the highest density of ephemerals near tree bases or decaying logs where ants prefer their nests (Thompson 1980).

Needless to say, seeds dispersed by ants do not move very far in any one year. Using historic records to determine whether a woodland was previously cultivated, grazed, or logged, Professor Henry Art and his biology students at Williams College have found that colonies of various myrmecochores expand at a rate of no more than 1-3 meters per year. Their research and my own has found that refuges within formerly cleared lands were important seed sources…places that were too steep to have been plowed, niches at the base of stone walls where grazers or mowers could not reach, strips of woodlands separated from pastures or hayfields by wetlands too soggy to cross. (Parnall 1998). Small colonies of ephemerals survived in these refuges long enough for an abandoned field to be repopulated. In the case of land that has been plowed, however, the seed bank has been destroyed and the soil profile disturbed, so recovery takes several decades.

Trout lily (Erythronium americanum) well camouflaged against lichen at the base of a tree. Photo credit: Kathleen Kerivan, www.bughillfarm.org

Dzwonko and Loster (1989) found that older woods had more ant-dispersed herbaceous species than young woods; that numerous patches of woodlands within agricultural uses had more richness than isolated patches; and that where there is more species richness, there is higher probability of finding rare species – meaning that the rare species they found were only in old or ancient woods.

South African myrmecochores:

The South African fynbos is an area of world-class floral richness within the Cape Floral Kingdom. Many species exist only in this area of the world, and some of these are only in very small populations. Researchers in this fire-adapted landscape reported myrmecochores in almost every plant genus in the Proteaceae family, resulting in the highest frequency of myrmecochores in the world. Seeds from these plants, stashed underground in ant nests, would have a better chance of surviving the natural ground fires. Of the shrub species they studied, they found that winged, fringed, hairy, and nut seeds were dispersed fairly far from the parent plant which could establish well-separated new populations after fire. The ant-dispersed seed, however, would not travel so far and would serve to fill in some of the gaps. Pierce and Cowling (1991) noticed that sometimes ants in the dune fynbos community do indeed eat the seeds and not just the eliaosome.  They suggest that this unreliability for restoring particular plant species from the seed bank after fire actually contributes to species richness, amounting to species taking turns with successful regeneration,resulting in no particular species able to dominate to the detriment of others.

Preservation and restoration implications:

As designers, foresters, and landowners in areas where ant-dispersed plant species, and especially spring ephemerals, can be found, there are implications for planning changes on the land. Since evidence of ephemerals disappears from the flora by mid-June, such a woodland might look very sparse and ‘uninteresting’ in the ground and shrub layer in other parts of the year. We would do well to pay attention to the tree species, bedrock, and soil type, which will predict for us whether there might be a trove of beautiful woodland ground flora worth preserving. Or have the patience to wait until spring to see what emerges. Where new home building is the project in rich woods, good site planning that ensures a small footprint of disturbance is essential. These plants are better preserved in situ, because replenishment from nursery stock is unrealistic (both unavailable and expensive).

Selective logging (not clearcuts) is not necessarily harmful to these populations, but the cutting must take place when the ground is frozen. For the educators among us, any displays showing pollinator gardens should contain more than the typical meadow wildflower species.  The spring ephemerals belong there too, since some are obligate to rare butterflies and many are essential to the earliest bumblebees and flies. And any landowner with rich woods would be well advised to leave fallen logs in place to decompose and favor ant habitat, encouraging ants to plant a forest garden unequalled in beauty.

References:

Bond, William.  South African National Biodiversity Institute, Kirstenbosch, Cape Town. protea.worldonline.co.za/watch.htm

Dzwonko, Z. and S. Loster.  1989.  Distribution of vascular plant species in small woodlands on the Western Carpathian foothills.  Oikos 56: 77-86.

Handel, S.N., S.B. Fisch, and G.E. Schatz.  1981.  Ants disperse a majority of herbs in a mesic forest community in New York State.  Bulletin of the Torrey Botanical Club 108 (4):  430-437.

Matlack, Glenn R.  1994.  Plant species migration in a mixed-history forest landscape in Eastern North America.  Ecology 75 (5):  1491-1502.

Parnall, Ruth. 1998.  Vegetation and land use history of nine mesophytic forest stands in western Franklin County, MA.  Masters thesis, Dept. of Botany, CT College.

Pierce, S.M. and R.M. Cowling.  1991.  Dynamics of soil-stored seed banks of six shrubs in fire-prone dune fynbos.  Journal of Ecology 79:  731-747.

Thompson, J.H.  1980.  Treefalls and colonization patterns of temperate forest herbs.  American Midland Naturalist 104:  176-184.

© 2012 – 2013, Ruth Parnall. All rights reserved. This article is the property of Native Plants and Wildlife Gardens. We have received many requests to reprint our work. Our policy is that you are free to use a short excerpt which must give proper credit to the author, and must include a link back to the original post on our site. Please use the contact form above if you have any questions.

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Comments

  1. Sue Sweeney says

    Nice article – I had no idea that the ants were doing this much of the work to conserve our wonderful spring wildflowers.

    • Ruth Parnall says

      Sue – I love the boney landscape in SE CT (tho your area might be different), but would expect the ground layer to be lowbush blueberry, little bluestem, oak leaf litter and not much in the way of wildflowers, especially ephemerals. Not so???

  2. says

    it is wonderful to find articles and people who i can feel connected to, who articulate the woods as i know them as a root digger, a non-timber forest worker.. i learn from you’ll. thank u

  3. says

    This is so fascinating, Ruth! The spring ephemerals are my most favorite wildflowers of all. But I had no idea those plant communities were maintained by ants. It’s funny how much we take for granted in our constant quest for development, but if we disturb these ants we’re going to lose these stunning spring blooms, and that would be a very sad loss.
    Carole Sevilla Brown recently posted..A Love Letter to Wildlife

    • Ruth Parnall says

      And there’s a whole team of other winged and crawling creatures that pollinate, aerate soil, decompose leaf litter to release nutrients, and keep the sheltering trees healthy. In the right growing conditions, I say who needs exotic bulbs as signs of spring. I know a lot of people like daffodils, but I get greater pleasure walking my woodland garden paths to look for each new species as it breaks dormancy in its quiet woodland way.

  4. says

    I think “Elaiosome” is the correct spelling, though you’re closer than others I’ve seen. Also I’m not sure Cardamine diphylla is dispersed by ants, do you have a source on that?

    A major group you didn’t mention is Trilliums which all disperse their by ants. Twinleaf also does but they only flower for 8 hours where as a Trillium is typically 2 weeks.

    Another strategy all these plants seem to use is holding off on germinating. Most of them don’t start growing until the second year. Also, at least for Trilliums, they start to produce a foul odor. I think the idea is to encourage the ants to move on. Of the genera mentioned Aphaenogaster, Myrmica, and Formica, all regularly move their nests as needed. Lasius don’t move as much, and a third of the species in this genus are mostly subterranean root aphid farmers.
    MrILoveTheAnts recently posted..Happy Valentines Day

    • Ruth Parnall says

      Good catch on the spelling…have corrected it – thanks.

      Have also changed Cardamine to Claytonia virginica, because the Thompson article lists Dentaria (Cardamine) as ant-dispersed, but two other authors say it is not dispersed by ants or others.

      Handel did not list Trillium as ant-dispersed, since “its dispersal mechanisms is untested in the field…it is not known if ants themselves can liberate diaspores from the pulpy berries of this species. Vertebrates may be the actual dispersers of the fruit in natural populations…” So I left Trillium out – the examples at the beginning are not an exhaustive list anyway. More recent research may have tested this.

      And I did not mention that some of these plants – Asarum canadense, for one – also spread vegetatively, once established.

      The ant-plant relationship is fascinating to me and reading about it always leads deeper and deeper into wanting to know more…like details about nest locations. Thanks for the information.

      • says

        I’m not sure I agree with the Claytonia virginica as ant dispersed. I don’t think their seeds have elaiosome on them. Even so that’s not to say they aren’t distributed by ants. Lots of granivore ant species regularly fill up stores with extra seeds even when they don’t have elaiosome. The ants rarely eat all of their stores and many seeds inevitably get lots in the nest. Seeds that benefit from this the most typically don’t require direct sun to germinate, and aren’t dispersed by the wind.

        Vertebrates transporting Trillium seeds seems unlikely to me. I’d go as far to say anyone wishing to witness ant seed dispersal should start with Trilliums. I’ve had Hepatica and Twinleaf both produce seeds with the elaiosome on them but for some reason ants don’t take much interest in them. I believe the size and quality of the elaiosome is effected by the quality of pollination. Some of the Violets also produce an abundance of seeds that have elaiosome on them but I rarely see ants collecting them. Not that Violets ever have trouble spreading around, the following year I typically find a mass germination of them all around the adult plants.

        I did a video on Myrmecochory (Ant Seed Dispersal) with Trilliums as the focus. Generally it’s just me having way too much fun with seeds for a day. I found wasps take an interest to them as well. One plant had a pencil sized hole cut into it where the wasp had entered and hollowed out and taken all the seeds. Apparently people who study Trillium seed dispersal also note this. Once the seed pods are damaged it’s not long for ants to find them though I found species of a certain size (roughly 4mm long or greater) are ideal for transporting the seeds around. My garden has been invaded by a nonnative tramp species, Nylanderia flavipes, (formerly Paratrechina flavipes) and they are so tiny they remove the elaiosome from the seed without transporting it anywhere.
        http://www.youtube.com/watch?v=ysB3gYv9-3Y&list=PL92E5B07C148999B2&index=11&feature=plpp_video

        When it comes to Trilliums I’ve noticed gardeners focus more on how decadent these plants are and generally glance over the ant seed dispersal part. The fact your $7 to $45 plant seeds can start walking away can be a nuisance. It’s never a good idea to have such plants coming up in the lawn or undesirable places. Should that be the case it’s okay to open the seed pods after they soften and “change color” and plant in the ground as normal. These plants are sensitive to chemical fertilizers and even time released will slowly cause them to diminish with time. It’s best to let nature do it’s thing with these plants. They benefit from organic matter in the soil as well as a reasonable amount of leaf mulch.
        MrILoveTheAnts recently posted..Some Valentines Left Overs

  5. says

    Thanks for this interesting information. I knew about ants as seed dispersers; but didn’t know that some familiar plants like the mentioned spring ephemerals are among the ones serviced by ants. Now, I will look at them with renewed interest. I will also look at the possible seed dispersers nearby.
    This is another example of the intricate web of life. Everything seems to be intertwined in multiple ways. Another reason for favoring native plants. They have been co-evolving with other members of the community for a very long time.
    Beatriz Moisset recently posted..Pine Barrens, plants and their pollinators

    • Ruth Parnall says

      Donna – I hope everyone reads your post to get more information on trout lily. To answer a few questions in the comments collected there – the corm does indeed look like a dog’s incisors…hence dog-tooth violet; apparently only about 10 percent of a colony will flower–just the ones with two leaves–tho occasionally I see a colony with much higher percentage. One really unusual characteristic is that the plants can increase by “droppers.” This is true of other Liliaceae as well. It’s a white fleshy stem-like appendage, that has a corm-producing tip. It originates in the corm and grows up about 1″, then bends over to plant itself. Trout is tricky to transplant, because sometimes the roots are 6″ deep…

  6. says

    Wonderful article Ruth! Your excellent essay only further highlights how important our soil is and that we manage our forest well. There is such intelligence within every inch of our living earth. Thanks for teaching us how important ants are. I will never look at a trout lily the same way again. I am lucky to have a lovely rich wood and do leave it to ‘be’ naturally . . . except for maintaining paths.
    Carol Duke recently posted..Flower Hill Farm BUTTERFLIES OF 2011 ~ Favorite Fritillaries Part Two ~ Surprise Ending!

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