The Risks of Managing Prairies Exclusively for Plants

Prairies are often defined as plant communities dominated by grasses, sedges, and wildflowers.  However, prairies are also home to thousands of animal species, not to mention countless varieties of fungi, bacteria, and other microbes.  Animals are just as much part of the prairie as plants, and they can have immense impacts on the plant community and overall prairie function.

Mixed-grass prairie managed with periodic fire and intensive grazing. Gjerloff Prairie - Prairie Plains Resource Institute.

For most of us, prairies are characterized by the plants we see when we walk through them. Gjerloff Prairie – Prairie Plains Resource Institute. Nebraska mixed-grass prairie managed with periodic fire and intensive grazing.

Despite the importance of animals, many prairie managers and biologists focus largely on plants when evaluating the quality of a prairie or when making management decisions.  Interestingly, many ranchers do the same thing, though they tend to focus mostly on dominant grasses while biologists often look more at plant species diversity and/or rare plant species. Regardless, it is rare that the needs of harvest mice, leafhoppers, or smooth green snakes are incorporated into management plans or evaluations of prairie quality.  (A major caveat is that some prairies are managed primarily for bird habitat – either song birds or game birds – a practice that has its own set of ramifications.)

Deer mice and other small mammals are rarely considered during management planning. Small mammals and other animals have specific needs for habitat structure, however, and are also vulnerable

Deer mice and other small mammals are rarely considered during management planning. Small mammals and other animals have specific needs for habitat structure, however, and their populations can decline or disappear after several years of unfavorable habitat conditions.

To be fair, there are good reasons to give plants primary consideration in management planning.  Cattle ranchers correctly recognize that cattle feed mostly on grass, so maintaining robust stands of grasses is critical for a successful ranching operation.  For biologists and conservation land managers, plants are often good indicators of prairie health.  Plant communities are easier to assess than insect or small mammal communities, and they provide the foundation for many ecological processes.  Pollinators, for example, rely on plant diversity and abundance of flowering plants.  Many other insect species need particular plant species or groups of plant species for food and/or living quarters.  A diverse plant community also provides a consistent supply of vegetative growth and seed production for plant-eating animals.

Bees and other pollinators rely upon plant diversity to provide a consistent supply of flowers throughout the growing season. This bee (Svastra sp) is on a native tall thistle (Cirsium altissimum) in September.

Bees and other pollinators rely upon plant diversity to provide a consistent supply of flowers throughout the growing season. This bee (Svastra sp) is on a native tall thistle (Cirsium altissimum) in September.

Not only are plants helpful in assessing prairies, every plant species is also significant and worthy of conservation for its own sake. However, the same is also true for animal species.  A prairie without birds, ants, butterflies, or grasshoppers just wouldn’t be the same, and not just from an aesthetic standpoint.  The complex interactions between all the various organisms in prairies are difficult to study, but absolutely critical to ecological function.  Studies that have excluded or suppressed populations of small mammals or insects have documented tremendous changes to the plant community – usually resulting in lower plant diversity and dominance by a few species at the expense of others.

Animal communities are vital to prairie communities and ecological function, and conserving healthy animal communities relies on at least two broad factors: plant diversity and a variety of habitat structure. As mentioned earlier, most pollinators and herbivores rely upon a wide range of plant species in order to be able to find food at all times of the season, and many insects depend upon particular plant species for survival.  However, habitat structure is also critically important for animal communities, and because every animal has its own unique habitat requirements, prairies need to provide a wide variety of habitat conditions.

Habitat structure for animals is driven by factors such as the amount of plant litter covering the ground and the height and density of the vegetation.  Some animals depend upon short vegetation with lots of exposed bare ground, some need tall dense vegetation, and still others prefer something in-between – or combinations of several habitat types.  The size and distribution of habitat patches is also important.  For example, some animal species need fairly large areas of a particular habitat structure, while others thrive best in situations where small patches of short and tall vegetation are intermixed.

A variety of habitat structure types across a prairie helps ensure a diversity of animal species, including invertebrates, will thrive.

A variety of habitat structure types across a prairie helps ensure that a diversity of animal species, including invertebrates, will thrive.  This area of intensive grazing is adjacent to other patches of taller and thicker vegetation.  Restored prairie in The Nature Conservancy’s Platte River Prairies, Nebraska.

This is the same restored prairie as shown above, but in a diffrent yet

This is the same restored prairie as shown in the previous photo, but in a year when management provided different habitat structure.  Cattle have grazed much of the grass, but have left behind a diversity of blooming plants, including Canada milkvetch (Astragalus canadensis), compass plant (Silphium laciniatum), black-eyed Susans (Rudbeckia hirta), bergamot (Monarda fistulosa), and many others.  Platte River Prairies, Nebraska.

Prairie management regimes that don’t consider animals’ needs can lead to problems.  For example, prairies with relatively uniform vegetation structure provide limited options for animals, regardless of whether that structure is uniformly short, tall, or somewhere in the middle.  A subset of animal species will thrive in those prairies, but other species can experience significant population declines.  If those same conditions persist for too long, some animal species can disappear completely.  Whether or not those species return depends upon the mobility of the animals and the degree of habitat fragmentation around the prairie.

Some management tactics can also cause animal populations to disappear or decline dramatically.  While it is an important part of prairie management, prescribed burning can be particularly dangerous to animals, especially if an entire prairie is burned at once. Fire can directly kill animals, including insects overwintering or living inside plants, but animals can also suffer from the sudden loss of habitat.  These impacts are especially severe in fragmented landscapes where there is nowhere for animals with limited mobility to go for better habitat, and no way for recolonization by species wiped out by fire.  Uniform haying and intensive grazing can have some similar impacts to fire, although both tend to leave a little more habitat for at least some species.

Snakes like this red-sided garter can be vulnerable to fires that occur during the growing season. However, dormant season fires can also be very damaging for insects and other species that overwinter in grass litter or in aboveground stems of plants.

Snakes like this red-sided garter can be vulnerable to fires that occur during the growing season. However, dormant season fires can also be very damaging for insects and other species that overwinter in grass litter or in aboveground stems of plants.

Plant diversity and the survival of rare plant species are important objectives for prairie management.  However, the same can be said for animal diversity and rare animal species.  In some cases, well-planned management can largely account for the needs of both.  Providing a shifting mosaic of habitat patches across big prairies can usually facilitate plant and animal diversity, and accommodations can be made for rare species or species sensitive to particular management tactics such as fire or grazing.  Understanding the needs and evaluating responses of various groups of plants and animals, however, is crucial to successfully adapting management strategies over time.

Conserving all species is much more difficult in small and/or isolated prairies.  A single prescribed fire can potentially wipe out animal species, and repetitive use of any management tactic, including fire, grazing, haying or rest risks eliminating species as well.  Read more about the challenges of managing small prairies here.

In both large and small prairies, setting clear objectives for management is very important.  Ideally, those objectives will accommodate the needs of most or all animal and plant species and sustain ecological resilience.  In reality, it’s more likely that the needs of some species will have to be sacrificed or given less priority than others.  As an example, frequent burns might sustain high populations of many plants (including some rare species) and help suppress invasive trees or grasses, but are likely to eliminate some species of butterflies and other invertebrates, and potentially some snakes and other vertebrates as well.  Alternatively, applying periodic patchy grazing and rest treatments in the same prairie could increase habitat heterogeneity to the benefit of many animals, but could reduce the relative abundance of some sensitive plant species while stimulating higher populations of more grazing tolerant plants.

These kinds of management decisions can be extremely difficult, and there are no easy answers.  The disappearance of any species from a prairie is a big loss, particularly at isolated sites, and we don’t yet know how to predict the ripple effects of losing most species.  Even when management decisions don’t directly eliminate species, reducing population sizes can make species more vulnerable to diseases or other factors that could eventually wipe them out.

Regal fritillaries are

The regal fritillary butterfly is one of many prairie animals that has been shown to be vulnerable to disappearing from prairies because of incompatible management.  Even for fairly mobile species like butterflies, recolonization after local extinction is far from assured, especially in fragmented landscapes.

No matter what management decisions are made, it’s crucial that land managers consider the needs of as many species as possible – including both plants and animals.  It’s not necessarily wrong to manage a prairie primarily for plant diversity or to sustain populations of rare plants.  It’s also understandable that a cattle rancher would want to sustain consistent vigorous stands of grass.  However, in both cases, managers need to acknowledge and accept that optimizing conditions for a particular suite of plant species will lead to negative consequences for other species, including both animals and plants.

Hopefully, continuing research and experience will help us better understand the inescapable tradeoffs that come with these kinds of difficult decisions.  For now, the impacts of losing plant or animal species and the potential for those losses to affect ecological resilience are still very unpredictable.  The best we can do is to be clear and honest with ourselves and others about why we’re making decisions, and do our best to evaluate the results and learn as we go.

 

If you’re interested in learning more about how excluding or suppressing animal populations can lead to unexpected and complex reactions in grassland communities, here are a couple example research papers.

Herbivory and Plant Species Coexistence: Community Regulation by an Outbreaking Phyotophagous Insect.  Walter P. Carson and Richard B. Root.  2000.  Ecological Monographs 70(1):73-99.

 Secondary plant succession: how is it modified by insect herbivory?  V.K. Brown and A.C. Gange. 1992. Vegetatio 101:3-13

Massive and Distinctive Effects of Meadow Voles on Grassland Vegetation.  2006.  Henry F. Howe, Barbara Zorn-Arnold, Amy Sullivan and Joel S. Brown, Ecology 87(12):3007-3013

Effects of Coyote Removal on the Faunal Community in Western Texas.  1999.  Scott E. Henke and Fred C. Bryant.  Journal of Wildlife Management 63(4):1066-1081

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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.
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10 Responses to The Risks of Managing Prairies Exclusively for Plants

  1. Jeff from Minnesota says:

    This is a bit of a tangent but I think a lot of the emphasis on plants, at least in my experience, is that prairie “grading” systems are based exclusively on plants (whose more conservative than whom, and where). Evaluations that take insects into account (and snakes? rodents?) when defining “high quality” prairie may end up showing some big differences from those that take only plants into account. For example a “small” prairie with graded by plants can be ranked high but its ranking might plummet if animals are taken into account. And turning that around, a large prairie with more invasives and fewer “rare” plants may have robust populations of rarer insects. The trick of course is that those animals don’t sit still very well to be identified and counted. Long and short, plants are getting the attention because at the moment that’s how most humans determine their relative conservation “value” (my personal view is that with so very little prairie, especially tallgrass, left, ALL prairies have value.

    BTW, I loved hearing a bobwhite calling from the “weeds” in one of your beat up paddocks at the Network meeting last month.

    • Chris Helzer says:

      Thanks Jeff. I had a paragraph much like what you wrote, but cut it for space… But yes, I agree completely. It’s easier to use plants to evaluate prairies because they’re always there (relatively speaking) and don’t require capturing and sending things out for ID before being able to see what you have. Of course, I’m doing a lot of plant monitoring/evaluation, so I’m not saying it’s a bad idea, but as you say, it would be really helpful to include some other taxa as well. I’m hoping that tracking plant diversity/floristic quality and also tracking the available habitat types we have each season gives us a pretty good overall feel for how prairies are doing. We’re trying to figure out how to test that assumption… Oh, and I’m glad our bobwhite made you happy!

  2. Paul says:

    As one famous biologist/ecologist once said, “This isn’t rocket science – – it is a lot more difficult than that!!!

  3. James McGee says:

    The difficulty of management is it really needs to be expertly tailored to the site. A good example is grazing. In certain prairies bison grazing was likely a rare event. This could depend on both geography, as where I live in northeastern Illinois, and habitat conditions. I expect given a choice bison would avoid wet prairies, climbing very steep slopes, or travelling through densely forested areas. It should not be surprising that imposing grazing in a place not adapted to this selective force would likely cause undesirable changes. Likewise, excluding grazing from areas that have developed with it, like the prairies Mr. Helzer manages, would likewise cause undesirable changes (i.e. grass dominance). I think great consideration needs to given before drastic changes are made to any management regime. It should be remembered that many prairie animals are quite happy in a hay field full of Eurasian grasses whereas rare plants often have complete fidelity to undisturbed prairie.

    • Jeff says:

      Many prairie vertebrates can be quite happy in non native veg if the structure is appropriate, but the rarer insects (ottoe skippers, Dakota skippers, etc.) are dependent on native plants and thus native ecosystems. I would argue that not only does the management need to be tailored to the sites, it needs to be tailored, and adapted as needed, to the ultimate goals of the site (which can/should include conservation of any rare faunal components).

  4. Gary Gerth says:

    This is completely on a tangent but since this article is generating considerable interest I will pass on some of my own personal experience regarding plant succession after 100 years of small grain and row cropping in the Northern Tallgrass Prairie in Deuel County, SD. In 2003 I converted a previously cropped soybean field to a monoculture, Badlands Littlebluestem, from the NRCS plant materials center at Bismarck, ND. Since 2003 the field was burned once, straight combined or cut for straw about 4-5 times, stripped for seed-left standing a few times. Now it is in the CRP. Easily observable native plants observed re-occupying the site include milkweed, smooth blue aster, goldenrod, ( I would bet there is some wild bergamot) and to my surprise purple prairie clover and prairie coneflower. The latter would seem not to be easily spread by wind. The persistence and resilience of native species may be more significant than imagined.

    • Patrick says:

      May I ask why you decided to plant it to a monoculture of little bluestem? Was it simply a matter of cost, or seed availability, or desire to use it for grazing land, or something else?

  5. Patrick says:

    I had a crazy idea Chris…one thing I would like is an easier way to identify insects. I have used BugGuide.net and it’s ok, but it takes quite awhile to track things down. With advances in facial recognition software, I wonder whether someone has ever thought of adapting this technology to develop a searchable bug guide so that you coukd upload a photograph, and it could search a database for nearest fits based on key bug profiles. What do you think?

  6. Pingback: Best of 2016 – Stories and Photos From This Year | The Prairie Ecologist

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