An Imperfect Analogy

I love a good analogy.  I find analogies can help me express ideas in ways other people can relate to. At the same time, I’m definitely guilty of sometimes fighting too hard to make an analogy fit, or relying too much on analogies to make a point that doesn’t need help being made. It kind of reminds me of when you go shoe shopping and the shoe you really want is only available in the half size below what you usually wear. It’s really tempting to just buy that smaller shoe, even though it doesn’t quite fit. Is there enough upside to getting that particular style of shoe to offset the costs of buying it and being uncomfortable? Also, how did I end up talking about shoes?


This week, as I was putting the final touches on a presentation, an idea popped into my head and I’ve been wrestling with it ever since.  The presentation is about plants that are often labeled as weeds but are actually crucial role players in the recovery of prairies from disturbances.  Those ‘opportunistic’ plants are always poised to respond quickly when fire, grazing, drought, or some other force temporarily weakens the dominant grasses and other vegetation in a prairie.

Curly cup gumweed is a native annual plant, but considered a weed by many because it appears quickly in high abundance after disturbances. That’s it’s job, and it provides tremendous resources (including for pollinators) when it makes that kind of appearance.

My objective for the presentation is to point out that these plants aren’t aggressive or in need of control.  They are responding to a disturbance, not causing it.  In a way, I realized, the process is similar to the way our body reacts when we cut ourselves.  There’s a built-in response (blood clotting) that prevents the wound from continuing to bleed or get worse.  Eventually, a scab forms and holds everything together while the wound heals. Those opportunistic plants are kind of like a scab…

Wait a minute, I thought.  I’m trying to make these plants sound positive.  Is equating them to a scab really the way to shine a positive light on them?  It’s not like scabs are something most people celebrate.  In fact, people tend to pick at them and pull them off…  Oh. Oh!  That’s even better!

Some landowners, when they see part of their pasture become ‘overrun’ with ragweed, annual sunflowers, or something similar, are tempted to try to kill off those ‘weeds’.  Often, that involves something pretty drastic like broadcast herbicide spraying.  It’s a counterproductive strategy because it removes the plants that were helping the plant community recover from the disturbance. 


When you pick a scab, you reopen the wound, causing the pain and bleeding to restart.  It’s better to just let the scab be and let the body do what it’s set up to do – heal itself.  Besides, you’re not getting rid of the scab.  It’s just going to re-form for the same reason it formed in the first place.

When you spray the ‘weeds’ that are stabilizing a disturbed plant community, you restart the disturbance.  And what plants are going to respond best to that disturbance?  The same ‘weeds’ you just killed – or other species that play the same kind of role.

That’s a pretty good analogy, if I do say so myself.  There’s only one major flaw.  Equating a flush of opportunistic plants to blood clotting and the formation of a scab makes it sound like disturbances like fire, grazing, or drought are somehow hurting the prairie, which is an idea I’ve tried to push back on.  Those disturbances, including extended periods of grazing or drought, can be an important part of maintaining prairie diversity, both by keeping the plant community diverse and by providing a full range of habitat conditions for animals.  Disturbances define prairies, they don’t harm them.

This prairie is in the early stages of recovery from intensive grazing. All the plant species present before grazing are still present, but those grazed hardest are reduced in size/abundance while others (‘weeds’) are taking advantage of the reduced competition to flourish. Two years later, this same site was dominated by big bluestem and perennial forbs like stiff sunflower (Helianthus pauciflorus).

Over the years, I’ve legitimately angered some prairie people – especially botanists – by advocating for management that includes cycles of fairly intensive disturbance, followed by recovery.  They disagree with my stance that those cycles bolster the biodiversity and resilience of prairies and argue that they degrade the quality of the plant community. It’s a healthy discussion and I’m not going to try to recap that whole argument here.  Let’s just say that me equating prairie disturbances to injuries isn’t going to help my case.

…But it’s such a good analogy otherwise!

Just for fun, I went to Wikipedia and found a description of four basic stages of wound healing.  Here they are (heavily paraphrased and simplified), along with some possible parallels from prairies and their recovery from disturbance:

Stage 1 – Hemostasis.  This is when blood clotting starts to plug the break in the blood vessel and stop the bleeding.  The resultant scab also covers the wound and facilitates the next steps of healing.

Prairie parallel: Seeds of annual and biennial plants germinate and quickly become established, taking advantage of the extra sunlight and reduced competition from surrounding plants. Some opportunistic perennial plants also respond positively to reduced competition, growing larger and blooming more prolifically than in previous years.  All those plants create a canopy over bare soil and also spread their roots belowground, helping to prevent soil erosion, carry on nutrient cycling and provide important habitat for animals.

Stage 2 – Inflammation.  White blood cells rush to the site and engulf/destroy bacteria and other pathogens, along with damaged cells.

Prairie parallel: High numbers of invertebrates are drawn to the disturbed site.  They are attracted by both the habitat structure (sparse ground cover with a diffuse overhead cover of opportunistic plants) and the abundant resources (pollen, nectar, seeds, and more) provided by that copious new plant growth. 

Stage 3 – Proliferation.  The tissues damaged in the wound begin quickly re-growing.  The wound is also contracted as the edges are gripped and pulled back together by myofibroblasts (there’s a word!).

Prairie parallel: The perennial grasses weakened by the disturbance begin quickly re-growing.  The process starts slowly because the plants have depleted roots and energy reserves, but as their leaves grow they can pull in more energy, which allows for even faster growth.  Spaces between perennial grasses contract as those plants send out rhizomes and re-expand their footprint.

Stage 4 – Maturation (remodeling).  The structure of the tissues is re-established and cells that are no longer needed are removed by programmed cell death.

Prairie parallel: Competitive perennial plants re-establish their dominance and opportunistic plants fade away.  Annuals and biennials die after they complete their life cycle (‘programmed cell death’?) and less competitive perennials hunker down and try to conserve energy until their next opportunity to thrive.


It’s good, isn’t it?  The analogy fits well with the way prairies respond to disturbances, especially extended periods of drought or grazing that really set back dominant plants.  I’m particularly happy with the ‘pulling off the scab’ part because it reinforces the idea that those opportunistic plants are doing an important job.  They aren’t an injury, they’re a sign of healing from an injury caused by something else.  Let them play their role. (Also, here I go again equating prairie disturbances to injuries…)

The prairies I’m most familiar with thrive under a management approach that includes extended periods of intensive grazing, followed by even longer periods of recovery.  We have data that shows our plant communities are maintaining their diversity and we (and many others) have shown how animals benefit from the heterogeneous habitat created by that approach.  You can read more on this topic here and here.  Prairies are incredibly resilient.  We just have to make sure we give them the opportunity to adapt to and recover (if that’s even the right word) from the periodic disturbances that created and have sustained these diverse, dynamic communities.

This photo and the one below are from the same prairie. This photo shows the prairie in the middle of a season of pretty intensive grazing after a spring fire.
This image of the same prairie shows what it looks like after a couple years of recovery from fire and intensive grazing. Grasses have regained their vigor and plants like Canada milkvetch (Astragalus canadensis), which is heavily favored by cattle is blooming.

At the same time, that approach isn’t right for every prairie or situation.  Smaller prairies and prairies that have rare populations of plants or other species need to be managed more carefully.  The best long-term solution is to make those prairies bigger and more interconnected through restoration, but that’s easier said than done.  In the meantime, management of those small prairies is fraught with difficulty, though trying to create some degree of habitat heterogeneity is probably still worth the effort.  There is plenty of legitimate discussion to be had about how to balance all of that.

Regardless, when a prairie experiences a disturbance that temporarily reduces the vigor of dominant plants, it has an intrinsic process for responding.  As it happens, that phenomenon has some similarities to the way our bodies respond to being wounded.  In both cases, the best response is to let the process play out.  Instead of fretting about ‘weeds’ or scabs, we should celebrate the roles they play within complex and beautiful systems that keep both prairies and humans healthy.

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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.

17 thoughts on “An Imperfect Analogy

  1. Chris, I love the way you think — and write! Your essay is interesting, funny, thought-provoking, and it makes good points. Kids (especially boys) would relish this kind of learning, comparing a scab to a disturbance of plant life on the prairie. Please keep writing this kind of stuff — adults enjoy it, too.

  2. Thank you for this blog, Chris. I too love the accessible and common sense way you write. You’ve kind of reassured me about relatively unwanted plants (heath aster and Western ragweed) that are thriving in the pasture, especially after a controlled burn in 2017 and early last spring on 400+ acres. I’ve spent a lot of time cursing and hand spraying them. But both plants seem to be getting thicker and heartier over time — especially the heath aster, which becomes shrubby. It seems really abundant after the burns and fairly large-scale ground slippage over the past few years (the earth looks like frosting rolling down a collapsed cake). Can heath aster and ragweed eventually choke out the grasses if there is too much of it? Buck brush and smooth sumac also seem to be increasing after the fires. I worry that I am doing more damage than good out there with my attempts at control.

    • Thanks James. One of the truisms with prairies is that each one is a little different, so it’s hard to extrapolate confidently from site to site. That said, I’d be surprised if the heath aster or western ragweed are serious competitors with the grass. There are likely other factors at play that are encouraging them. It might be helpful to build a couple small exclosures (wrap a 16 ft cattle panel around three t-posts?) in the middle of those weedy patches and see what happens after a few years. If the grass/ragweed/aster ratios change, that’ll tell you something about how important grazing might be to the story. It’s very possible that those areas just aren’t getting enough rest for the grasses to get their feet back under them – but I have no idea what your grazing looks like, of course. Nutrients could also be a big player, but without knowing the site or the neighborhood, I can’t give you many clues about that. Getting some local advice would be helpful.

      Buckbrush (assuming you’re talking about Symphoricarpus) has never bothered me much here because prairie plants seem to grow well between the stems, but smooth sumac can definitely become problematic and a 3-4 year burn frequency is likely to encourage, rather than discourage it if our situation is at all similar to yours. It might be interesting to experiment with some more frequent burning in a portion of the site, if that’s feasible, and see how the woodies respond. Is your 400 acres isolated or connected to other grassland? If it’s isolated, you’ll want to be cautious about burning the whole thing at once, and especially doing that too frequently (impacts on invertebrates and other animals) but maybe you could try burning patches at different frequencies and see what happens. You might have to burn every two years or more to suppress sumac with fire alone, and that might not be feasible or desirable. If so, you might have to switch some of your hand spraying efforts from ragweed/aster to sumac!

      Let me know if you’d like help finding someone in MN (I’m assuming?) who might be more of a local expert. I can ask around, if you like. Good luck!

      If you’d like to email me with more details (and photos) I’d be happy to brainstorm some more too.

      • Chris, thank you for your very generous reply. I’m actually living in Boyd County, NE, but I used to teach at the University of Minnesota, which is where my email address is from. After I retired, I’ve been learning to take care of 600+ acres along the Missouri River — some days I’m am very excited about it, but other days I lose heart. I was reminded yesterday of the problem I described above when I was out walking in the pasture and kept scratching my jeans on woody stems and branches, especially of the heath aster. Having two large burns so close together happened because my renter could get the Lynch Fire Department to help — I probably won’t be doing any more burning in the rest of my time here. I will, however, continue to spray sumac when I am not overwhelmed with spraying the Canada thistles along the deep draws.

        I’ve been following your blog for a number of years. I first learned about it from my brother in North Carolina, whose wife is a childhood and current friend of Renee Mullen — they visited her and Bob Moseley in Hong Kong when Bob was working there for the Asia-Pacific Cities program of The Nature Conservancy. I’ve also watched several of your Zoom presentations, and learned a lot from you about prairies and photography. You’ve probably been my most important teacher as I try to make sense of the wonderful complexity and aliveness of things out here.

        Probably the most important thing I’ve learned from you is to really, really, really pay attention. And so I thank you for both your artistry and for your science. I don’t have the resources to do a lot of experimentation, but I have been able to make a lot of art about the place (, and I am finishing up a book featuring 200 different plants I’ve found on the property (“Wildflower Prayers: Plants along the Missouri National Recreational River”). Again, thank you for your response and for your work!

  3. Well then….if all these analogies are workable. It should work as well in reverse? Maybe even better? So present this to staff at the nearest med school. They, or you, can explain “healing”, so even a country bumpkin ( like me) could totally comprehend? Hey! It’s cold here in northern wisc. And you gave the day a kind lift. Harold.

  4. Great imperfect analogy! Besides appreciating where this analogy does work well, on the part that doesn’t, I find a lot of similarities with ecologists’ discussion of fire in Western US forests like in the Sierra Nevadas (book I’m thinking about in particular listed below). The framing they use is that a fire event is just one stage of a healthy forests’ life, no different from the old growth stage or the shrub stage after a major disturbance. In fact, there are many species (birds, plants, etc.) that have evolved to rely on specific “lifecycle” stages of forest existing near each other. Without geographically-mixed forest of varied lifecycle stages made possible by fire or other disturbances, these species would go extinct and biodiversity would plummet. My impression from the article and in the context of your biodiversity articles is that this is also true for prairies.

    The concern is if there are too many disturbances too close together, the current ecosystem will be forced to shift into a new state and may never be able to return to the original without help. I’m curious on thoughts or a future article regarding this!


    The Ecological Importance of Mixed-Severity Fires: Nature’s Phoenix
    DellaSala, Dominick A., Hanson, Chad T., Elsevier

    • Thank you, Matt. Yes, I think that example from forests is very similar to prairies, in that there are species that rely on the kinds of habitat created by ‘major disturbances’, though it’s harder to say whether they’d go extinct in the absence of those disturbances. They might – I just don’t have data to back that up. Regardless, there are lots of species that respond very positively to each of the stages in a fire/grazing-recovery cycle.

      Prairies are adapted to a higher frequency of disturbances than forests, though, and in fact that kind of frequency is what helped them form in the first place (indigenous use of fire helped thin and eventually hold back trees, opening woodlands/savannas into large grassland habitats). That said, they’re not immune to negative impacts of overly frequent disturbance. That’s especially true where prairies are only found in small isolated fragments because the loss of a species from those fragments is unlikely to recolonize from elsewhere. Repeated intensive grazing without rests, overly frequent burning, or annual haying can all have potential consequences if they don’t include both rest periods and undisturbed refuges with each treatment. On the flip side, climate change, habitat fragmentation, and other factors mean that NOT doing those kinds of frequency disturbances – especially fire or haying – can lead to prairies being taken over by woody vegetation. It’s difficult! Lastly, prairies are even more vulnerable to state changes when disturbances are too infrequent rather than too frequent. The buildup of thatch and encroachment of trees that happen in an idled prairie can very quickly flip it to something that is difficult to recover.

  5. Thank you so much. I don’t have adequate words, so just please know that these illustrated educational posts mean so much to me.

  6. I will never look at a weed in the same way. I will see scabs everywhere in my garden and wonder what sort of wound it is covering or trying to heal. As to wounds I will be wondering what is going on under that scab. Also do I scratch it off if it begins to itch??? Or let it be and hope all heals as I wish.

  7. Chris, thanks for posting this. Very good information. I may have missed it in your post, but another important attribute of the opportunistic native and often temporary “weeds” is that they are armour against aggressive, non-native plants that can be persistent. As far as disturbance/rare plants/botany goes, I think it is important to keep in mind that original, unplowed prairies and other native grasslands differ throughout the continent. Many original prairies in Missouri, for example, are much more floristically diverse than many others, and certainly more diverse than many degraded grasslands that I hear people refer to as “prairie.” There is also a difference between “species diversity” and “diversity of remnant-dependent species.” Many conservationists, myself included, feel it is much more important to pay attention to the latter term when stewarding original natural communities–in terms of not allowing anything else to go extinct or become even more rare. Generalist species can usually co-exist with remnant-dependent ones, but the reverse is not always true. I know many botanists and ecologists who are not at all against cattle grazing, but they are right to insist that grazing and any management tool be very carefully considered before use, and monitored while in use. Also, another term to consider using instead of “disturbances” is “stressors.”

  8. I’ve used the same analogy in forest communities, talking about early successional species like aspen coming in (or being encouraged) after a disturbance. So it works for me, and I enjoyed the breakdown of the analogy!

  9. One of the tropes in school is the “Balance of Nature” and the examples given make you think that there is a finely tune set of feedback mechanisms that when one aspect gets out of line, there are forces that quickly bring it back.

    My observations of my 15 acre wood an 65 acre pasture returning to prairie is that instead of a finely tuned balance it is much more like two clowns on a slack wire, constantly lurching about, and almost falling off.

    A lot of my forest understory seems to depend on the winter. How much snow we get, how cold it got before it snowed. Some years we have tons of bishops cap. Sometimes northern bed straw.

    There are longer cycles too. Raspberries hit a peak a few years ago. Currently there is a boom in black gooseberry (R. lacustre) A few wet years in a row and we have a small surge in our native bracken fern. Normally this is rare to uncommon, only found on north facing slopes being the only spots consistently wet enough for them.


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