Choosing Your Destination Before You Choose Your Mode of Transport

Last week, I attended a science and stewardship conference of The Nature Conservancy in Madison, Wisconsin.  It was an inspiring and thought-provoking week.  There were a lot of topics that will provide fodder for future blog posts, but I wanted to start with an issue that came up in several sessions.  The topic had to do with setting appropriate objectives for conservation strategies, and for land management in particular.  In short, it’s really important to make sure we’re not setting objectives that are focused on strategies rather than outcomes.

This mixed-grass prairie is managed with both prescribed fire and grazing.  However,  neither fire nor grazing is the objective, they are tools that are strategically employed to create desired outcomes.  Gjerloff Prairie – Prairie Plains Resource Institute

Here’s an illustration of what I mean.  If I was planning a vacation for next summer, I probably wouldn’t start with the following question: “What mode of transportation should I take on my vacation next year?”

Clearly, it’s tough to answer that question without knowing more about the ultimate objectives of the vacation.  Where do I want to go?  What time of year am I going?  How many people are going with me?  If I’m planning to travel from Nebraska to Ireland, I probably won’t be able to do that by bus.  I could conceivably travel by motorcycle (if I had one) to the Rocky Mountains, but probably not if I was going during the winter or planning to take little kids with me.

It seems silly to start by thinking about how to get somewhere before deciding where to go, but as land managers, it’s easy to fall into exactly that mindset.  We sometimes set objectives about using fire or grazing, for example, instead of first defining the outcome we want and then thinking about what tools and strategies might get us there (which may or may not include fire or grazing).  In this post, I’ve provided examples of how this trap can present itself, both to managers of conservation land and private landowners, and some thoughts about how to avoid the trap.

Significant research has helped us understand the kinds of fire and grazing patterns under which North American prairies developed.  For example, in many places, we have a pretty good idea how often a particular site burned, on average, before European settlement.  We also have reasonably good information on the presence, abundance, and behavior of historic grazers.  Based on that information, a land manager could decide that the best management for their prairie would be to reinstate, as closely as possible, the timing and intensity of historic fire and grazing that site likely evolved under. 

Historically, prairies in this region probably burned on an average of every 4-5 years.  However, within that average range, there would have been wide variation.  More importantly, this prairie sits within a very different landscape today, with challenges not faced by those historic prairies.

Patch-burn grazing is often described, for example, as “mimicking historic fire and grazing patterns.”  Mob grazing advocates trumpet (though I’m skeptical) that their system replicates the way bison moved across a landscape.  Some in the Upper Midwest region of North America point to research showing high populations of indigenous people and scarce evidence of abundant bison and argue that their prairies should be managed only with fire.  We can argue about all three of those examples – and many more – but the bigger point is that none of those arguments should determine our management strategies.  Again, we shouldn’t be setting objectives about the strategy we want to use without first identifying the outcome we want.

To make a clunky return to my vacation travel analogy, it would be silly of me to choose horseback as my preferred mode of transportation across the Great Plains to the Rocky Mountains just because it’s what worked several hundred years ago.  Today’s landscape is broken up into countless fenced off private land parcels, which would make cross-country horse travel difficult, to say the least.  In addition, there is a pretty nice set of modern opportunities (roads and vehicles) I can take advantage of nowadays.

Likewise, our prairies exist within a different world today, with a new set of challenges and opportunities.  Mimicking historic disturbance regimes won’t necessarily keep prairies in good shape in a world with habitat fragmentation, massive invasive species pressure, climate change, nitrogen deposition, and other factors.  And speaking of good shape, our first and primary concern should really be to define what “good shape” is, right?  Are we managing for plant diversity or a few rare plants?  Are we trying to sustain diverse bird populations?  Habitat heterogeneity? Is ecological resilience the goal?  If so, what are the factors driving resilience, and how to we sustain those?  There are countless reasonable goals for land managers to choose from, many dependent upon scale, but those goals should be based on the outcome we want.

This annually-hayed prairie maintains high plant diversity but provides only one type of habitat structure for nesting birds and other wildlife species.  Depending upon the objectives for the site, that could be fine, but it very much depends upon what the manager wants to accomplish.

I feel it’s important to say this here:  I am a big proponent of both fire and grazing as management tools – you can find myriad examples of that by searching through my previous blog posts.  However, while I think combining fire and grazing can create some fantastic results, those strategies/results don’t fit all objectives.  More importantly, your particular site may or may not respond well to those kinds of fire and grazing combinations.

Let’s say your primary objective is to provide habitat for as many species of grassland birds as possible.  First, you’ll need a pretty big swath of land – many bird species have minimum habitat size requirements.  Assuming you’ve got sufficient land, the major factor grassland nesting birds respond to is habitat structure.  Some birds prefer tall thatchy structure, others like short/sparse vegetation, and others want something in-between.  A reasonable outcome-based objective might be that you want to provide all three of those habitat types across your prairie each year (and you’ll want to make sure the habitat are being successfully used by a diverse bird community).  Perfect.  Now, how will you create those habitat types?

 Grasshopper sparrows tend to nest in prairies with relatively short structure, but with some thatch (which they use to build nests) along the ground.  Some of the highest abundances of grasshopper sparrows around here are found in relatively heavily-grazed prairie.

Fall or spring fires can create short habitat structure that some birds really like to nest in.  However, some bird species (e.g., grasshopper sparrows) usually like short habitat with a little more thatch in the ground layer than is usually found in recently burned prairies.  Also, while burned areas are short and unburned areas are tall, it’s difficult to create in-between height/density habitats using only fire.  This is where other tools such as mowing and grazing might be helpful.  Mowing can reduce the height of tall vegetation and create short or mid-height structure that grasshopper sparrows, meadowlarks, and other species prefer.  Grazing can do the same and can have the advantage that cattle or bison are selective grazers, eating some plants and leaving others.  This can create structure with both tall and short vegetation mixed together and can also help suppress grasses and allow for greater expression of forbs (broadleaf plants) – something birds such as dickcissels often prefer.

Upland sandpipers prefer to nest where vegetation structure is short, but often move to sites with strong forb cover and a little patchier structure when their chicks become active.

If we’re trying to create optimal bird habitat, then, fire, mowing and grazing might all be useful tools to consider.  It’s important to understand how each tool can be used to affect habitat structure, as well as the potential risks of using each (fire can sometimes kill aboveground animals and stimulate invasive plants, grazers can sometimes target vulnerable plants and create issues via trampling).  With all of that information, you can start putting together strategies that employ the right tools, and then test those strategies against the OUTCOMES you desire.  Notice that the process I’ve just described is independent of the kinds of historic fire returns for your area or whether or not you think grazing was a significant factor in the evolution of regional plant communities.  Define your objective by the outcomes you want and test/adapt strategies based on that objective.

Other examples: At my family prairie, we aren’t using prescribed fire because we’ve been able to use grazing to meet our objectives of habitat heterogeneity and increasing plant diversity, and we use loppers/herbicide to successfully control woody invasion.  In small prairies where preserving particular plant species is the objective, a strategy using only fire or mowing could be most appropriate.  If that small prairie has rare insects or reptiles that are especially vulnerable to fire, maybe mowing is the best tool.  Regardless, the right tools and strategies depend upon the outcome-based objective.

This photo was taken in the burned patch of a patch-burn grazed prairie at Konza prairie, near Manhattan, Kansas.  The grazing created varied habitat structure because of the selective grazing by cattle.  Leadplant and other ungrazed forbs contrast with surrounding short grasses.

For ranchers and farmers who manage prairies, this same objective setting process should apply, but of course those prairies also have to help provide sufficient income to keep a family or business thriving.  Even in those cases, however, it’s still important to start with outcome-based objectives.  Those objectives can include a certain amount of needed income but should also include specific habitat or other ecological objectives.  Once you’ve decided, for example, that you really want to manage in a way that provides a certain amount of quail habitat or provides consistent pollinator resources through the season, you can look for ways to accomplish that while still providing the needed income.  When a conflict between income and habitat objectives arises, you can make the decisions that make sense to you, but at least you’re making those decisions with all the information needed to fully consider the options.

Prescribed fire can be a great tool for accomplishing some objectives, but it can also be difficult to implement for some managers.  While it is an important ecological process in prairies, employing prescribed fire should still be seen as a tool/strategy, rather than as an objective in and of itself.

There are plenty of reasonable prairie management objectives to choose from, but they should be based on outcomes rather than on tools and strategies.  Employing more frequent prescribed fire is not a good objective.  However, using more frequent prescribed fire might be a great strategy to reach a particular outcome.  (It could also be a terrible strategy, depending upon your objective.)  Don’t fall into the trap of choosing your transportation method before you know where you want to go. 

P.S. I’m sure some of you are thinking it, so let me address what might appear to be a weakness of my vacation transportation analogy.  Yes, it’s perfectly fine to start vacation planning by deciding that you want to take a cruise ship or motorcycle if the OUTCOME you really want is to ride on a ship or motorcycle.  If you don’t care where you go, the destination isn’t the outcome, it’s just a by-product of your mode of travel.  Fine.  But I think you understand what I was trying to say, right?  Sure, you could argue that conducting prescribed fires could be your objective if all you want is a legal way to light things on fire and watch them burn.  If that’s your objective, though, you’re not managing prairies, you’re lighting things on fire – and there’s a big difference.  Ok?  Ok.

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