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.

Prairie Word of the Day – Habitat Heterogeneity

Do you know what time it is?  It’s time for another PRAIRIE WORD OF THE DAY!

Today’s Prairie Word of the Day (fine, it’s actually two words) is:

Habitat Heterogeneity

Heterogeneity is really just a longer word for Diversity, which is another way of saying “lots of different things”.  So why use the word “heterogeneity” instead of just saying “lots of different things”?  Well, for one thing, using big words makes a person sound smart, and when you’re a prairie ecologist and no one really understands what it is you do for a living, it’s good to at least sound smart.

More importantly, there’s a nice alliterative (another big word!) feel to the phrase Habitat Heterogeneity, which happens to be one of the most important phrases in prairie ecology.  In fact, I would argue that the foremost objective of any prairie manager should be to create habitat heterogeneity within the prairie(s) they manage.

Habitat heterogeneity simply means diversity or variety in habitat types.  Habitat homogeneity is the opposite – a lot of habitat that is all the same.

Every organism in a prairie has its own unique habitat requirements, so the number of different habitat types in a particular prairie is correlated with number of species that can live there.   Let’s use prairie birds as an example.  Birds such as upland sandpipers like to nest in large patches of relatively short-stature grassland.  Around here, a big hay meadow is great habitat for them, especially if it was cut fairly late in the previous year and is still short in stature when the subsequent breeding season starts.  On the other hand, Henslow’s sparrows want to nest in prairie habitats with relatively tall and dense vegetation.  It would be highly unusual to find Henslow’s sparrows and upland sandpipers nesting in the same patch of prairie because their habitat preferences are very different.  So, if you want both species in your prairie, you have to provide both short and tall/dense habitat.  Other birds have their own unique habitat requirements, including nearly bare ground (e.g., horned lark), relatively short, but with abundant thatch (grasshopper sparrow), tall with lots of tall/weedy wildflowers (dickcissels), tall and nearly impenetrably dense vegetation (sedge wrens), and many others.  Only if your prairie provides all those different habitat conditions will you attract all those different bird species.

Dickcissels prefer
Dickcissels prefer habitat with lots of tall wildflowers or weeds.  They often weave their nest into the stems of a tall clump of vegetation.

The same diversity of habitat preferences exists in other groups of prairie species as well.  Among small mammals, for example, voles tend to prefer habitats with abundant thatch, while pocket mice are more often found where bare ground is abundant – and there are many others.  Insects and other invertebrates have the same kind of diversity in habitat preferences

Scale is important.  While a bird, mammal, or insect might have a broad preference for a certain kind of habitat structure, it is likely to need some heterogeneity within that habitat too.  A mouse, for example, might prefer patches of prairie with fairly sparse vegetation, but it is likely to need a few clumps of vegetation dense enough to hide in when predators are near.  Insects and reptiles are ectothermic (cold blooded) and need to regulate temperature, so while a snake might like to hide in tall dense so it can bite your ankle as you walk by (I’M KIDDING!), it also needs some places to bask in the sun.  All of this means that habitat heterogeneity is important any many different scales.  Heterogeneity at a fairly large scale (acres) helps provide places for many different animals to live in a prairie, but heterogeneity within the home range or territory of each animal (square meters, or even centimeters) can be important too.

Some habitat heterogeneity occurs simply because soil texture, nutrients, and moisture, along with topography all vary across a landscape.  A prairie is likely to have areas of more productive soils where vegetation grows tall and thick, and less productive soils where vegetation is more sparse, for example.  In addition, water will pool in some areas of a prairie more than others because of topography, altering the habitat for both plants and animals.  However, despite this “naturally occurring” heterogeneity, it’s still important for prairie managers to look for ways to provide more.

This landscape at The Nature Conservancy's Broken Kettle Grasslands in northwest Iowa shows the kind of natural heterogeneity that occurs in many landscapes.
This landscape at The Nature Conservancy’s Broken Kettle Grasslands in northwest Iowa shows the kind of natural heterogeneity that occurs in many landscapes.  Topography, soil variability, and other factors create a diverse set of conditions for plant growth and habitat structure.  Land management can add to that heterogeneity and improve it even more.

Prescribed fire and haying/mowing do a great job of altering habitat structure at a fairly large scale (acres).  By applying those treatments in different parts of a large prairie each year (and varying the timing of each from year to year), a manager can create a shifting mosaic of habitat patches that supports a wide diversity of animals.  However, both fire and mowing are pretty non-selective – most or all of the vegetation within a burned or mowed area gets the same treatment.  Leaving unmowed patches of grass here and there and varying the height of the mower as it moves across the site can help leave more heterogeneity behind.  Designing prescribed fires so that not all vegetation burns (e.g., mowing around some patches ahead of time, burning on days with lower temperatures or higher humidity, etc.) can also help with habitat heterogeneity – though those kinds of fire might also be less effective at killing trees or accomplishing other objectives.

In prairies where livestock grazing (cattle or bison, for example) is feasible, it is much easier to create small scale heterogeneity because grazers pick and choose which plants, and how much of each plant, to eat at any one time.  By controlling grazing intensity, and varying it across both time and space, managers can create prairie patches that are ungrazed, almost completely grazed, and in various stages of partial grazing – with a mixture of tall vegetation and nearly bare ground.  The uneven application of “fertilizer” from the rear ends of grazers contributes even more to habitat heterogeneity by temporarily altering soil productivity in lots of little spots across the prairie.

These cattle at Konza Prairie in Kansas
These cattle at Konza Prairie in Kansas have created a nice example of small scale habitat heterogeneity by grazing many of the grasses short while leaving leadplant, purple prairie clover, and other wildflowers ungrazed.

Whether it’s fire, mowing, grazing, herbicides or various combinations of those, creating habitat heterogeneity may the most important job of a prairie manager.  We still have a lot to learn about how the scale and configuration of habitat patches affect wildlife and insect populations.  What we do know, however, is that the prairies thrive when they have a lot of different types of habitat.  …When they have habitat heterogeneity.

And that, folks, is your Prairie Word of the Day.