Lessons from a Fenceline

Last week, I spent some time collecting data and thinking about next year’s plans for managing our Platte River Prairies.  While I was out, I made an interesting observation along the boundary of one of our properties and that of the neighbor.

About two years ago, we replaced a section of fence that separated our prairie from the prairie to the west.  The fenceline had become overgrown with shrubs – something that is great for some species of birds but really hard on a barbed-wire fence.  We ended up treating the shrubs with herbicide, pulling out the fence, and shredding the remains of the shrubs before re-building the fence.

This fenceline was cleared of shrubs two years ago so we could re-build the fence. The photo shows the vegetation that came in after the shrubs were removed (left side of the fence). Note the lack of flowering plants in our property to the right.

The above photo shows that fenceline as it looks now.  In place of the shrubs, there is now a stand of thick prairie vegetation, including grasses, sedges, and forbs.  Ok, there’s also some smooth brome and even the beginnings of a stand of Phragmites (the thick-leaved grass in the photo).  But the interesting thing to me is the species that are blooming right now.  If you look at our prairie – which is shown on the right side of the photo – you don’t see any flowers blooming.  That’s not a photography trick.  There really are very few plants blooming right now in that prairie.  Yet in the fence row, Maximilian sunflower and Canada goldenrod are abundant and showy, and there are a few other flower species blooming as well.

So what’s the deal?  Here’s what I think is happening.  Our prairie had a long history of annual summer haying – as far as we can tell.  I don’t think it’s been sprayed with 2,4-D, though I’m not 100% sure, because it has a pretty good abundance of spring and early summer flowers, including pale poppymallow, blue-eyed grass, violets, prairie clovers, Illinois bundleflower, and others.  However, I think many years of annual haying likely eliminated late-blooming flowers from our prairie.  If perennial plants aren’t allowed to bloom and complete their annual life cycle they don’t produce seeds.  Perhaps more importantly, annual defoliation while the plants are still actively growing removes the plants’ ability to produce food for their root systems that were, until they were defoliated, gathering enough resources to support tall vigorous plants.  If wildflowers are like grasses (don’t know if there is research that has tested this) that sudden loss of aboveground vegetation causes an abandonment of large segments of roots – because there is no food coming in to maintain them.  If those plants are defoliated at the same growing stage every year without a break, it’s easy to see how they would eventually die without replacing themselves.

The Maximilian sunflower and Canada goldenrod plants growing in the fenceline are not rare plants, or even plants that are particularly difficult to maintain in most prairies.  But they’re almost non-existent in our prairie.  We’ve begun to overseed some late-season-flowering plants into the prairie, and species such as Maximilian sunflower, stiff sunflower, wild bergamot,  and a few others are slowly establishing – and seem to be surviving well under our patch-burn grazing management.  I hope we can bring them back so that late-summer pollinators (for example) can have something to eat other than what they can find in the fenceline!

A closer view of some of the plant species growing in the unhayed/ungrazed portion of the prairie along the fenceline. The prairie to the left in this photo is our neighbor's prairie - which is annually hayed.

So, if the wildflower species that are missing from our historically-hayed prairie are common in the fenceline where they weren’t being mowed, burned, or grazed, does that mean we should manage (or not manage) our prairie by perennially idling it?  No, I don’t think so.  First, remember that although those flowers are blooming in the fenceline now, they weren’t two years ago because they were covered up by tall vigorous shrubs.  Prairies managed without fire – or something that sets back trees and shrubs – tend to grow quickly to woody vegetation, changing their very nature pretty dramatically.  In addition, though I haven’t looked carefully, I would guess that the fenceline “prairie” is missing many of the early season plants that are so abundant in our prairie because there is nothing that removes each successive year’s thatch along the fence to allow those small plants to get sunshine.  I think one lesson of these plants along the fenceline is that it’s important to provide a periodic rest period for plant species – especially when a site is being managed with the same treatment every year.

One could, I suppose, make the argument that we should manage some portions of the prairie for late-season plants and other portions for early-season plants, and everything will be fine.   Unfortunately, by doing that, we would be reducing the plant diversity – and ecological resilience – of those individual portions by not facilitating the full range of biological diversity and ecological function.  As a result, the entire prairie would be weakened.  This is, by the way, why I disagree with biologists who promote leaving portions of prairies permanently unburned in order to protect insect species that are vulnerable to prescribed fire.  I completely agree that small isolated prairies should not be completely burned (or hayed) in any one year, helping to ensure that refuges are left behind for those species that might be harmed by the management treatment.  Shifting the location of management treatments from year to year should allow species to find appropriate habitat, especially if (as in small isolated prairies) the distance between one management treatment and another is short.  If that’s insufficient, it might be that the real issue is not management, but size and isolation of the prairie – something that can only be solved by strategic prairie restoration of surrounding land parcels.  Reducing the ecological resilience of small prairies by managing them for a small suite of species is certainly not a good long-term solution for those species or the larger community.  (Baby with the bathwater…)

There is one more observation that’s too important not to mention.  The plants that are blooming in these photos somehow survived being covered by dense shrubs for at least a couple decades, and also survived the foliar herbicide application that removed those shrubs.  Plants are tough.  Granted, the wildflower species we’re talking about are species that have a reputation for toughness anyway, but I still think their survival is worthy of note.

I’m not completely sure I’m right about why those flowers are in the fenceline and not my prairie, but even if I’m wrong, just going through the thought process is valuable!  If nothing else, it gives me a hypothesis I can test (and sufficient fodder for an entire blog post).  Isn’t it amazing what we can learn just by looking around us?

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About Chris Helzer

Chris Helzer is an ecologist and Eastern Nebraska Program Director for The Nature Conservancy. He supervises the management and restoration of approximately 4,000 acres of land in central and eastern Nebraska - primarily along the central Platte River. Chris is also the author of "The Ecology and Management of Prairies in the Central United States", published by the University of Iowa Press.
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13 Responses to Lessons from a Fenceline

  1. Dan Staehr says:

    Chris,
    Back around 1980 or so, I remember going to a grassland management field day in Johnson county where they had used a combination of Atrizine and disking to increase warm season grass growth. Don’t know if that is still something that is done, but it was interesting to see the effect in that particular prairie parcel. It would be interesting to see what it looks like today.

    Dan Staehr

    • Chris Helzer says:

      Dan, I’ve seen where Atrazine was used on native prairies to control smooth brome – with some apparent success, though it’s not labeled for that as far as I know. It’s not something I have any personal experience with.

  2. James McGee says:

    Chris,

    The stand of dominating warm season grasses in your photo reminds me of the effect from another management plan — annual burning. Any burning reduces the level of soil nitrogen. I’m sure haying similarly decreases soil nitrogen. I think the increase in warm season grasses from annual burning is likely linked to reduced levels of soil nitrogen. A similar effect could be expected from annual haying. This may be what you are observing. A soil test should be able to tell whether there is a difference in the amount of soil nitrogen in the hayed prairie versus the fence row. I am sure a difference will be found. I am also sure this is not the only mechanism causing change. However, the effect is probably significant.

    I find it hard to believe that mowing alone could have such an impact on prairie. I have seen prairies recover with a rich forb component after having been mowed as a lawn for decades. This is a common observation from settler cemetery prairies. The difference is the mowing does not remove nitrogen from the system to the extent of haying or burning. This is the reason I am thinking soil chemical changes may be more important than direct impacts on individual species from the cutting.

    Love the Blog,

    James

    • Chris Helzer says:

      James – thanks for the comments. Interestingly, Kansas State University has actually shown no impact on soil N after years of annual burning at Konza prairie. Annual haying, in contrast, does tend to reduce soil N, but low soil N typically favors forbs over grasses (all other things equal). This could help explain why some hayed prairies have such nice forb diversity. On the other hand, even some (most?) of those annually hayed prairies are short on late-season forbs – but it all depends on the season of haying, regularity of haying, and probably many other factors. I had someone else reply to me about this post – not through the blog, though, who said that he’s found October mowing to greatly reduce Canada goldenrod. Interesting – have not heard anyone have success with that before. Hard to know how to tell what’s chance, what’s due to local factors, and what is broadly applicable…

      I, too, have seen good forb response after years of intensive mgt as you mention in cemeteries. Don’t know for sure what the answer there is, but I wonder if prairie plants have a different response to that kind of continual defoliation. Because they don’t get a lot of growth before they’re defoliated, they may not suffer the kind of root and tiller growth and then sudden shrinkage of both – and maybe that helps prevent as much stress to the plant. Wild speculation, really.

      So much to learn! Thanks again for the comments.

      • James McGee says:

        Chris,

        Do you have a reference for the research from Konza regarding annual burning not impacting soil nitrogen? Their website has statements that are contrary to the ones you made above.

        http://www.k-state.edu/media/webzine/konza/maintain.html

        Thanks,

        James

        • Chris Helzer says:

          James M. – and James T,

          I get out of my comfort zone very quickly when we start talking about soil chemistry… My impression is that the answer to almost any question is “it depends.” For example, below is an excerpt from “Evolution and origin of the Central Grassland of North
          America: climate, fire, and mammalian grazers” by Roger Anderson (2006 – Journal of the Torrey Botanical Society). It indicates that although annual burning does decrease soil N, there are factors that somewhat compensate for that. Don’t know how to figure the total impact, but I was probably wrong on my statement about annual burning. I’m actually with some former K-State folks today and will ask.

          In terms of James Trager’s question about fertilization and grasses, I think the answer there is “it depends” too – but again, I’m not an expert by any means on this. I know timing is important, though. Fertilization is recommended in Nebraska for people who want higher quantities of cool-season grass hay in meadows, and that fertilization favors those grasses – but I think it’s carefully timed to do so. On the other hand, I”ve heard some of the same range scientists argue against fertilizing “native range” because it favors “weeds” over grasses. I don’t know. I do know Sara Baer (and others) found that adding carbon to soil helped reduce available soil N and that favored a much more diverse prairie planting because WS grass dominance was much lower… I’ve also been told that in some soils (Missouri, for example) phosphorous is much more limiting than N! To wrap up the confusion, I’m told by soil guys that annual haying has been used in European grasslands to reduce available N as a way to recapture and sustain plant diversity because higher N favors grasses. I’ll stop now… (and will probably refrain from future statements on soil N!!) Thanks very much for the comments and questions – keep ‘em coming! Here’s that excerpt from Anderson…

          Litter removal and inorganic nutrients. The presence of a litter layer reduces the availability of inorganic nutrients, especially nitrogen,
          which is thought to be the most limiting nutrient in grasslands. Annual burning of litter on prairies due to volatilization will
          reduce available nitrogen by about 1.0–4.0 g m22 yr21. This represents about twotimes as much nitrogen as the amount input
          by rainfall annually (Knapp and Seastedt 1986). Long-term there is a net loss of nitrogenfrom grasslands that are burned annually
          (Risser and Parton 1982, Ojima et al. 1990,Blair 1997), despite biogeochemical pathwaysto replenish nitrogen lost by burning.
          In prairies, both living tissue and detritusabsorb annual rainfall, with each absorbing about 20% of the annual deposition (Gilliam
          et al. 1987). Inorganic nitrogen in rainfall provides nitrogen equal to about 25–50% of that required by living foliage (Risser et al.
          1981, Risser and Parton 1982). Nitrogen absorbed by microbes is converted to micro-bial protoplasm and is unavailable to plants.
          As a consequence, more inorganic nitrogen in precipitation is available to plants on burned prairies than unburned prairies because there
          is no microbial sink for nitrogen in litter layers (Knapp and Seastedt 1986). Litter has high C/N and C/P ratios and microbes remove
          nutrients from the soil to carry out decomposition, which also reduces the availability of nitrogen to support plant growth (Seastedt
          1988). The input of nitrogen into prairies from nitrogen fixation by free-living Cyanobacteria is higher on burned prairies than unburned
          prairies because more light reaches the soil surface on burned prairies than unburned prairies (Eisele et al. 1989). In addition,
          ignition of the litter releases phosphorus and an increase in available phosphorus enhances nitrogen fixation (Knappand Seastedt 1986,
          Eisele et al. 1989).

  3. We’ve had some small-scale here in eastern MO experience with mowing tall goldenrod during flowering reducing its vigor for a couple of years thereafter.

    Also, with regard to James M’s comments on nitrogen, isn’t it the case that fertilizing prairies favors grasses over forbs? I know there is documentation for this in the species-rich, traditional hay meadows of Europe.

    • James McGee says:

      Chris,

      A significant amount of the soil nitrogen lost through burning is returned by the increased growth of microbes and algae. The increased growth of microbes and algae is the result of warmer soil temperatures and increased sunlight reaching the soil surface. Although soil nitrogen levels are reduced by annual burning, I think there is actually a more limiting input. Burning and haying both reduce, or eliminate, the insulating thatch layer. The resulting increased soil temperature and incident sunlight increase the loss of water. Soil moisture is frequently more limiting to plant growth than nutrients in prairies. Grasses are better adapted to heat and drought than forbs. It should not be surprising that periodic management activities which increase soil temperature and evaporation would lead to the dominance of grass species over time. The reason the diversity of forbs in cemetery prairies would not be as affected by mowing is the thatch was not being removed. The reason your hay field would have a good diversity of Spring / Early Summer forbs is moisture is typically not as limiting at that time.
      It is true that fertilization could increase weedy species in prairies. The annual weedy species grow faster than the long lived prairie plants. If the weedy species are able to colonize then they would reduce the light available to the more conservative plants. One would expect that an increase of weedy species after fertilization would be the largest in prairies that have been degraded.
      Phosphorous limitation is usually due to a high or low pH. The following link explains the chemistry.

      http://books.google.com/books?id=OOH1H779-7EC&pg=PA218&lpg=PA218&dq=High+pH+ecosystem&source=bl&ots=q_NgnK6yTv&sig=EMoryNDd0DX42Jr3pqE4Ript3po&hl=en#v=onepage&q=High%20pH%20ecosystem&f=false

      You will see phosphorous limitation being most significant in soils derived from limestone (high pH) or silica based materials (low pH). These ecosystems frequently have unique plants. Some plants have even evolved to be carnivorous to survive in low phosphorus environments. In addition to releasing phosphorus from organic matter, fire increases the pH of the soil. Since phosphorus becomes less available as pH is increased above 6.5, the result of fire can be to make phosphorous temporarily less available to plants.
      I have noted that Reed Canary Grass dominates flood plains which receive large amounts of salt and nutrient pollution from upstream Suburban areas. This may be what is happening in European hay meadows.

      http://www.springerlink.com/content/q7g20484815jg235/

      In contrast, areas within the flood plain that receive spring water from hillside seeps have continued to maintain high quality sedge meadow vegetation. The addition of nitrogen rich fertilizer increases the ability of soil micro-organisms to consume organic matter. The loss of the microbe-rich organic layer would lead to a warmer average soil temperature and a reduced soil water holding capacity. The flood-drought extremes created by increased surface runoff and destruction of soil water holding capacity seem to be what has lead to the invasion of tolerant grasses like Reed Canary and Phragmites. Excessive fertilizer and salt can also be directly toxic to plants. This is another mechanism that could be causing the loss of forbs in European Hay meadows.
      I do not believe haying is necessary to reduce the soil nitrogen level. This argument has likely been presented by those who would like to see an economic return from these grasslands, which can be justified without ancillary arguments. De-nitrifying bacteria quickly brings the level of soil nitrogen back into balance. The real problem is reducing the continuing pollution. Soil organic matter and soil organisms may recovery if they have not been extirpated. However, if recovery does occur it usually takes a long period of time.

      Sincerely,

      James

  4. David says:

    We have found (Wisconsin) that mowing Canada goldenrod at the onset of flowering produces shorter plants (but often more stems per clone) for a year or two after the mowing.

    We also use annual fire (dormant season) to weaken smooth brome and open up the sod for interseeding. Works well on dry to dry mesic sites unless sweet clover is present in large numbers (I think the nitrogen fixation from the sweet clover is much larger than the nitrogen reduction from the fire) . It may work on moister sites but it may take more time?

    David

  5. Karen Hamburger says:

    Chris
    Where did you take this pic?
    Karen

  6. Dawn Littleton says:

    This post brings me hope for the dense overgrown areas within my “circle of influence”, These areas are on public park land that have been overgrown for decades with invasives, and are being considered for restoration grants. It would be great to know what is there just waiting for a bright, sunshiny season in which to grow. Hopefully we’ll know soon. Thanks for the positive outlook- Dawn

  7. REALLY enjoyed this post, Chris. Thanks.

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