Climate Change, Carbon, and Clonal Shrubs

I’m not sure if you’ve heard about this climate change thing? Everyone’s talking about it, apparently.

Among the many impacts of climate change in Great Plains, one that has been weighing heavily on my mind is the increasing competitive advantage woody plants are gaining in grasslands because of increased drought frequency/severity and rising levels of atmospheric carbon. In Nebraska, eastern red cedar (Juniperus virgniana) has received tremendous – and well-deserved – attention in recent years as it continues to spread quickly across the state. However, while I’m concerned about cedar invasion, we have a viable strategy for dealing with it. We can kill it with fire. There is still lots of work needed to build our prescribed fire capacity in Nebraska, but there is strong momentum and I’m optimistic that we’ll eventually get on top of cedars across most of the state.

This photo shows a portion of the Niobrara Valley Preserve north of the river, where the 2012 wildfire swept through and killed huge numbers eastern red cedar and ponderosa pine trees. Under the current drought conditions, the green plants in this photo are primarily cottonwood trees, a few bur oaks, and (most prolifically) smooth sumac.

What’s getting much less attention is the growing scourge of deciduous shrubs and trees. Some of those, like Siberian elm (Ulmus pumila) and autumn olive (Elaeaganus umbellata) are nonnative invaders, but some native trees like honey locust (Gleditisia triocanthos) are also increasingly problematic. Those trees and many more can cause big problems for prairie managers on both public and private lands.

Most deciduous trees re-sprout after being top-killed by a fire or being cut down. Even multiple repetitions of those treatments won’t normally kill them, though frequent fires (every year or two over long periods of time) may eventually cause mortality and prevent new invasions. In most cases, once they’ve established themselves, those trees have to be dealt with one-by-one and treated with herbicide to kill them for good. That’s a tremendous challenge, especially when those trees become abundant.

However, while really scary, even the invasion of those trees isn’t the threat I worry about most. I’m much more concerned about the clonal deciduous shrubs – most of them native species – that are incrementally blanketing and smothering grasslands. These include species such as smooth sumac (Rhus glabra), dogwoods (Cornus sp.), and even wild plum (Prunus americana), among many others.

Because they grow in large colonies, connected belowground by rhizomes, clonal shrubs invade as massive cooperative armies, rather than as scattered individuals. This strategy gives them lots of advantages, including an ability to create ever-expanding canopies of leaves that shade out competition. Eventually, that shading-out process can fireproof those clones as grasses beneath the canopy become so sparse that fires won’t carry through them.

Here’s a closer shot of sumac clones and skeletons of dead cedar trees at the Niobrara Valley Preserve, surrounded by dormant prairie vegetation this week. This image, and others below, provides a frightening illustration of how drought conditions can help sumac and other clonal shrubs gain additional advantages over other prairie plants.

Increasing carbon dioxide in the atmosphere gives these clonal shrubs a leg up on many prairie plants. So does the increasing frequency and severity of droughts. While most prairie plants have deep roots, you may remember an earlier blog post that shared recent research showing that only shrubs and trees seem to be pulling water from deep in the soil, even during droughts. Many herbaceous (non-woody) prairie plants go dormant or dramatically slow their growth when the soil dries up. Shrubs like smooth sumac and dogwood just keep plugging away, drawing moisture from further down in the ground.

This week, while spending some time at our Niobrara Valley Preserve, I took some photos that help illustrate the varying impacts of drought on prairie vegetation. The Niobrara Valley Preserve and the surrounding area have received less rainfall this year than during the 2012 drought. The University of Nebraska-Lincoln’s drought monitor shows the area around the Preserve as being under severe drought conditions, but because of local rainfall amounts and distribution, it’s even worse than that across most of the property. As a result, much of the prairie is brown and crispy.

…except for clonal shrubs like smooth sumac and wild plum.

Smooth sumac stands out as green vegetation against a backdrop of drought-stricken Sandhills prairie.
These smooth sumac plants look just as vibrant as always while most of the surrounding plants are either dormant or showing other signs of drought stress.

In the midst of that matrix of dried and dormant prairie vegetation, clonal deciduous shrubs are thriving. Those shrubs look perfectly healthy and happy while most other plants have shut down for the year. It doesn’t take a prairie ecologist to recognize what happens if some plants can keep growing and spreading while their competition is sidelined. If summer droughts continue to become more common, sumac, plum, and other clonal shrubs are going to be more and more difficult to deal with.

Dealing with clonal shrubs is a huge challenge, especially when those clones get big. It’s not hard to kill an individual sumac stem. You can cut it off at the ground and paint the stump with herbicide. The real issue comes when you’re facing tens of thousands of those stems. You can broadcast herbicide across a clone, but that will also kill many of the plants beneath. That, of course, is really bad for the productivity and health of the prairie we’re trying to save.

Scientists and landowners in places like the Flint Hills of Kansas or in many eastern tallgrass prairies have shown that burning annually or every other year can keep these clonal shrubs at bay. That, however, comes with its own consequences, including significant impacts to invertebrates and other animals. In addition, at least in the Great Plains, frequent fire can favor grass dominance and reduce plant diversity. It also greatly reduces the options available for grazing systems when you have to leave behind enough grass each year to carry next year’s fire.

More significantly, frequent fire is hard to envision as a feasible option to be applied across the entire Great Plains. Apart from the actual logistics involved in burning privately-owned grasslands at that scale, the smoke produced by those fires would be hugely problematic. Much of the Flint Hills landscape of Kansas is annually burned, and in addition to the aforementioned consequences to wildlife and plant diversity, that annual burning is causing significant human health concerns from smoke concentrations – even in neighboring states.

The Flint Hills is about 4 million acres in size and only about half of that is burned each year. Now imagine the impacts from smoke produced by annual fires across the Nebraska Sandhills (12 million acres) or the majority of all Nebraska’s grasslands (23 million acres). Even if spread across the year, that’s a tremendous amount of smoke, especially when multiplied across other grassland-heavy states like the Dakotas, Kansas, Oklahoma, and others.

Fire will probably be part of the answer, but we’re going to need more than just a significant increase in our prescribed fire work. Goats are being used in some places, and might be another partial answer in certain situations, but goats don’t kill shrubs, they just knock them back. They also eat lots of other plants besides just shrubs, so need careful management to prevent negative impacts to plant diversity. Goats also present a number of difficulties when it comes to managing them – especially in terms of keeping them in place and/or alive.

The point of all this griping is that we need to get serious about finding more and better ways to address the spread of clonal shrubs in the Great Plains. We already have a significant problem in some places – especially in the eastern portions of the Plains and in other specific locations (like the Middle Niobrara River Valley) where shrub invasions have been growing unchecked for a long time. If we don’t find ways to slow it now, the problem is going to overwhelm us.

We waited too long to start dealing with eastern red cedars and now we’re really racing to try to save places like Nebraska from being completely overtaken (some landscapes in the southern Plains are likely past the point of saving). That’s happening despite the fact that we’ve known for a very long time how to deal with cedars (fire). Now we’re facing another wave of invasions that we don’t yet know how to fight. Let’s not wait until our boats are underwater before we start bailing.

Ok, if you’ve made it this far and are feeling down, here are a few photos that might cheer you up just a little. While much of the prairie at the Niobrara Valley Preserve was dormant or heavily wilted this week, there were some plant species apart from sumac and plum that were still doing well. I spent a lot of time trying to document which species still looked happy, despite that drought, and there were quite a few – mostly wildflowers and forb-like shrubs.

One plant that seems to be doing well despite the dry soils is hairy goldaster (Heterotheca villosa).
Lead plant (Amorpha canescens) is also thriving, despite the dry conditions.
Many annual plants like this prickly poppy (Argemone polyanthemos) and plains sunflower (Helianthus petiolaris) seem to be weathering the drought very well.
Prairie clovers, including white prairie clover (Dalea candida), purple prairie clover (Dalea purpurea) and the species shown here, silky prairie clover (Dalea villosa) are all looking good.

Below is a partial list of plants that were still green and vibrant in the drought-stricken prairies of the Niobrara Valley Preserve this year. I’d love to partner with someone who has the interest and capacity to look at the strategies these plants are using to weather dry conditions. Are these outliers in terms of the deep-roots-to-pull-water conundrum? Or do they have other strategies that allow them to be more efficient with water or effective in dealing with dry soils? So many fun things to think about.

Some of the still-green plants in the droughty Sandhills prairie this week:

Missouri goldenrod (Solidago missouriensis)

Prairie clovers (Dalea purpurea, D. candida, D. villosa)

Cudweed sagewort (Artemisia ludoviciana)

Hairy puccoon (Lithospermum caroliniense)

Lead plant (Amorpha canescens)

Scaly blazing star (Liatris squarrosa)

Hairy goldaster (Heterotheca villosa)

Green sage (Artemisia campestre)

Sand milkweed (Asclepias arenaria)

.

One of the nice things about the prairie plants that are still actively growing and flowering is the habitat they provide for animals that need to keep eating and living during drought conditions. Despite the severe drought, there is still a lot of animal activity in the prairies at the Niobrara Valley Preserve. I caught a little evidence of that with my camera this week, but not enough to be representative of the full spectrum of activity and sound going on around me while I was there.

I’ll end this with some optimism. Despite my real and serious worries about clonal shrub invasion and the facilitation of that by climate change, prairies are still very resilient. That resilience gives me a lot of hope for their future and gives us a lot to work with as we struggle to manage and restore them. Prairies have been through a lot and they’ll survive a lot more if we can continue to give them some help.

This western bush cicada (Megatibicen tremulus) was glad there are still some green plants around to feed on, including this plains sunflower.
This bee (and a grasshopper behind it) were also glad to have some green and flowering plants to feed on.
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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.

21 thoughts on “Climate Change, Carbon, and Clonal Shrubs

  1. Thank you for this post about aggressive shrubby perennials. I have a small (but beloved) acreage in southeastern Iowa. Much of it was grazed before I acquired it but over the years both the grassland and woodland have developed nice patches of natives. But, dogwood and sumac are starting to win the war. I will keep on keeping on, but fear I am losing ground. Literally.

    A. Burnside

  2. I read through all the way trying to find an answer to my initial question as I read this post….
    In all earnestness, please tell us why the evolving landscape is a terrible thing? Are we stuck on the idea of maintaining our grasslands whol Nature itself is doing what it must to navigate us? Not a flip question. Truly trying to grasp all of this change/plant species migration/secession…

    • Thanks for this thoughtful question, Genevieve. It deserves a longer answer than I can give here and I’ve been considering a full blog post on the topic so maybe this will spur me to do it sooner than later. For now, here are a few thoughts. First, most of the thousands of plant and animal species living in prairies need open habitats (free from the shade and visual obstructions created by trees and shrubs). So allowing prairies to transition into another habitat eliminates those species.

      Second, you’ve separated people from Nature in your question, and I’ll argue against doing that. Again, I need more space to do that well, but especially in tallgrass and mixed-grass prairies, people have been managing those prairies for about 10,000 years. In fact, as the last glaciers receded from the Midwest and Great Plains, prairies arose because of the management actions of indigenous people – especially their frequent and intentional use of fire. That fire management led to a transition away from savannas and woodlands and into more open prairie habitats. We’ve seen what happened when fire was later suppressed by Europeans – prairies started transitioning into woodland.

      Climate change happens to support that same kind of transition, but again, that climate change is also being driven by people. This isn’t just a prairie thing either. Woodlands in most of the eastern U.S., for example, were managed by cultural burning for thousands of years, helping to prevent dense undergrowth of shrubs and small trees that was bad for wildlife, bad for herbaceous plant diversity, and bad for seedling generation of trees like oaks. People managed that way for those reasons, but also because more open woodlands are easier to travel through, better for hunting, and more comfortable in terms of temperature (cool and breezy). Does that make prairies and woodlands un-natural? It gets tricky, right?

      I think it’s better to connect nature to our actions and accept the responsibility of continuing the thoughtful stewardship that has been going on for thousands of years – around the globe. Taking that approach, I think, is more respectful to those who came before us, but is also better for nature. It also forces us to make decisions about what we want to see in ‘natural areas’ and how to promote both species diversity and the welfare of the individual plants and animals living there. Letting ‘nature take its course’ is a European invention, as is the concept of ‘wilderness’ as something separate from or better off without people. It’s probably time to re-think those notions and embrace our role in nature.

      I hope that helps. Again, I’ll try to write this up in a longer form sometime when I have time and space to better flesh out these ideas. Thanks again for the question!

  3. Would it work to use a forestry mower on the sumac and plums?
    For what it’s worth, here in SW Wisconsin it seems like fall burns are more effective against the woody shrubs like honeysuckle, multiflora rose and prickly ash. My (unproven) theory is that the fire damages their bark, which is then subjected to freeze/thaw cycles that do even more damage. (Though that hasn’t been enough to actually kill many honeysuckle.)
    Love your posts, I learn a lot and you get me thinking about my property in different ways. Thanks for sharing your knowledge!

    • Hi Peggy, Yes, I think mowing can be a helpful piece of the puzzle, though it becomes more difficult in steep terrain and on larger scales. At the Niobrara Valley Preserve, we currently have thousands of acres of these shrubs, which makes mowing seem pretty daunting. Some of that is also on steep bluffs where no equipment can go. In both cases, fire is easier to imagine as a tool to defoliate the shrubs. However, I do think mowing makes a lot of sense, maybe in combination with fire or even herbicides in some cases, at many sites. Timing is something we still need to understand better, as well as frequency and the number of times it needs to happen before it makes a significant difference. Thanks for the info and question!

  4. We’re dealing with the same issue here in southeastern Oklahoma. For a place that averages 45 inches of rainfall per year, we’ve had .05 inches since back in early June. The daily highs during the intervening time have been 97-110 degrees. By the end of June, even the black eyed Susans were burned up and done for the year. The Monarda, which usually covers these pastures in high summer never came up. Ragweed is wilting. Of course the million little trees invading our prairie areas are lush green and continuing to expand while most of everything else is paralyzed. I’ve heard that warm season burns are effective at killing re-sprouting trees, putting them under additional moisture stress. We managed to get in a burn right before the burn ban started. That was a month ago. So far, with the exception of the persimmons, not many of those little trees are showing signs of re-sprouting. We’ll see how it goes longer term. Interestingly, after the burn, the eastern gamagrass is resprouting and continuing to grow even in the really dry areas. Any observations on the effects of summer burns on woody vegetation in your area?

    • Oof. I do think fires in all seasons can be helpful. I’m not sure yet what role summer fire might play for us here. Our big wildfire at the Niobrara Valley Preserve was in late July during the big 2012 drought. Sumac popped right back in the prairies after that fire and exploded in the formerly-wooded areas where it had been crouched beneath cedar and pine trees, suppressed by their shade. So one single summer fire during drought isn’t a magical answer, but that doesn’t mean summer fires can’t play an important role in a larger scheme. We’ve done some summer burning in the Platte River Prairies, and have seen similar things – it bangs the shrubs back but certainly doesn’t kill them. One additional piece of the puzzle for us is that fire plus cattle grazing seems to do a pretty good job keeping dogwood short because cattle like to eat the new year’s growth off the dogwood. If cattle are out there every year, they keep dogwood knee high or so. If cattle aren’t there for a season, the dogwood grows 6 inches taller (or more) but fire can reset the dogwood back down to the ground. For that particular species, both fire and cattle seem to help, and I think the same works for plum, but not for sumac. Lots to learn, still. Good luck down there!

  5. Very interesting. I understand the issue of colonial established shrubs, but I would think established grasses and perennials would outcompete germinating shrubs in drought. We are seeing similar phenomena this year in the little pocket habitats we work on the city. We have some spots where a few species look to have died or gone dormant mid season, which is rare: Liatris ligulistylus (not actually native here, so perhaps couldn’t take the heat), and Pycnanthemum sp. However, in their stead has been mulberry shrubs and Siberian elm that seem to be newly germinated and thriving. These are not encroaching colonial shrubs (not so much of a problem in pocket habitats in cities surrounded by concrete), but they do appear to still have an advantage in the drought (anecdotally).

    • That’s interesting. I think a lot of woody plants are built to establish themselves in harsh situations, including under the shade of other trees or plants. Sumac definitely does that, as does white mulberry, because I see them sitting beneath large eastern red cedar trees, alive, but small, and just waiting for that tree to die so they can quickly spring up and take its place. I think the large seeds of many of these trees probably help them survive as seedlings too, providing enough food to get their roots big enough to compete more effectively with surrounding plants. That’s just speculation, of course, based on observation and guesswork.

  6. I’m looking forward to your researched opinion on prairie vs woodland ‘invasion’. Burning woody plants would seem counterintuitive from a carbon producing perspective.

    • Margy, It’s a complicated topic for sure! Burning through shrubs doesn’t have much of an impact on atmospheric carbon because it is simply returning carbon (through smoke) to the air that was pulled out over the last year or two. That carbon is part of the active cycle that has always occurred. Carbon is traded back and forth between the ground and air. What causes big problems for us is when we dig carbon out of deep in the ground and release it, adding it to the atmosphere on top of what’s already in the active cycle.

      At the same time, burning can help prairies (and some woodlands) increase or optimize their carbon storage because a healthy strong-growing stand of plants pulls carbon out of the atmosphere and puts it into the soil. Land that sit idle has less vigorous plant growth, which slows carbon storage.

      To make it even messier, though, sites in good shape have kind of topped out on their carbon storage. So, some of our grasslands and woodlands can’t store more carbon than they have now. The key in those situations is to make sure we don’t release the carbon that’s stored. With grasslands, that’s easy because as long as you don’t plow them up, the carbon is safe. Trees store a lot of their carbon aboveground as well as below ground, so if those trees die, they release that aboveground carbon into the air – especially if they are burned. But in fires that help suppress trees and shrubs without killing them shouldn’t really release a significant amount of carbon unless those trees are pretty big.

      Oof. Lots to think about and a lot we still don’t understand.

      • I understand the complexity! I live in the Alberta hail corridor and all claims about climate change and hailstorms are highly speculative because hail has not been studied enough to understand!

  7. Chris,

    Do you really think it’s practical to try and reverse the consequences of a warming and drying climate when it comes to preserving prairie in particular locations, or do biologists/ecologists need to concede the loss of prairie in some places and perhaps plan for its spread elsewhere?

    • Hi Gary, it’s an important question. I think it’s likely going to be a little from column A and a little from column B. In terms of brush suppression, I think we’ve got a reasonable chance of maintaining the openness of much of the northern Great Plains grasslands if we come up with strategies soon. Then it becomes a question of how resilient they are in other ways and trying to be adaptive in our stewardship/restoration work.

      In places to the east and south of the northern Great Plains, I think there might be examples of landscapes where we need to accept some major ecosystem transitions and work with the new systems. That might include landscapes where brush encroachment is just too overwhelming to protect more than a few examples of prairies into the future, but also places where habitat fragmentation is going to make it impossible to rebuild viable prairie landscapes unless there are some major shifts in societal priorities and policies around restoring land around and in-between those tiny isolated remnants.

      I think it’s too early to give up right now, but I also think (and have written in prior posts) that we should be thinking about possible strategies so that if/when we’re faced with insurmountable odds we have some backup strategies ready to go.

  8. Chris,

    Thanks for sparking this discussion.

    A question and some rambling thoughts:

    Why does additional atmospheric carbon favor woody plants?

    Reading about the response of sumac to the wildfire at NVP brought to mind your ‘ball in a bowl’ analogy (or whatever you prefer to refer to it as).

    In my mind the wildfire pushed the ball out of the “woodland” bowl occupied by the ponderosas and cedars. But, where is the ball now? It’s not quite in the prairie bowl and it’s certainly not in the woodland bowl. It’s either teetering on the edge of the two awaiting a push or occupying some sort of intermediary shrubland bowl, right?

    How did the wildfire impact clonal shrubs that were located in open grasslands vs. wooded areas?

    We often focus on bison when talking about prairie herbivores, but in Iowa at least, elk played a major role as well. I don’t know much about NVP or elk, for that matter, but is it possible their absence (or greatly reduced range and density) in the Great Plains and Midwest has contributed to woody encroachment?

    A lot of speculation there, I know, just curious what your thoughts on those might be.

    • Hey Aric! To your first question, added carbon helps C3 plants, including shrubs, for some reasons that are too complicated (and somewhat beyond my full comprehension) to share here. You can find explanations online though.

      At the Niobrara Valley Preserve, there are definitely some differences between the way the 2012 wildfire affected sumac, especially, in the former woodland versus the prairie. I would say sumac came out of both sites looking good, but it expanded its footprint much more in the woodland. Observationally, I think that’s largely because of two factors. First, it must have been sitting underneath cedar and pine trees as small shoots, waiting for some light to be able to flourish. The fire provided that light and the sumac shot up and filled in the circular areas those trees had formerly controlled. But then second, it spread pretty rapidly out of those circles into surrounding areas that I think had pretty low competition because the dense woodland had limited the vigor of the surrounding herbaceous community. Meanwhile, in the prairies, the sumac has been slowly expanding for many years and just continued that without seeming to be bothered by the 2012 drought or wildfire – it popped right back up after the fire and I didn’t see evidence of any decrease in stem density.

      I do think elk and other browsers are an important part of the brush story, but I don’t think they’re the sole cause or potential answer. After this post, Jesse Nippert from K-State reached out and pointed me to a recent study they did (O’Connor et al. 2022) showing that a combination of defoliation (simulated browsing) and fire had a pretty significant impact on stem density and cover of dogwood in the Flint Hills. That provides some hope, I think, for exploring various combinations of treatments to shrink and thin existing stands. He also said that recent work in that area shows that even annual fire (alone) isn’t enough to get rid of shrubs once they’ve established. That also points us toward combination treatments.

      Lots of work ahead of us but I think we’ve got some options to explore. We just can’t afford to sit around while the shrubs thicken up too much more.

  9. Pingback: Synthesizing the 2022 Conserving Fragmented Prairies Workshop Part 2 – Trees, Shrubs, and Plant Genetics | The Prairie Ecologist

  10. I’m late to this discussion but wanted to pass along conversations that were had in Minnesota earlier this month. The manager at the USFWS New London Wetland Management District related having excellent luck controlling both sumac and buckthorn with a program of twice yearly defoliation (the WMD used goats in some cases and mowing in others) for three years in a row. The first defoliation took place once the new spring growth had reached its maximum (June) and the second was in late summer to remove any regrowth prior to root reserves being replenished before dormancy. The results were impressive. The scale they were working on was measured in the tens of acres, so I’m not sure how well this could be scaled up, but I think the main thing is that the root reserves need to be exhausted, and that will involve a long term effort and will most likely need to be repeated periodically.

  11. Pingback: Drought Flowers | The Prairie Ecologist

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