Hello, and welcome to the fifth edition of the popular series, “Prairie Word of the Day.” This is the series that has previously brought you such inspiring words/phrases as Tiller, Habitat Heterogeneity, Disturbance and Shifting Mosaic of Habitat. Thank you for the many cards and letters expressing your gratitude for the explanations of these words, and suggesting future topics.
Today’s featured word is Phenology. In short, phenology is the study of the timing of various events in the lives of plants and animals and the factors that influence that timing. Phenology should not be confused with Phrenology, which is the long discredited study of how the shape and size of the human skull supposedly correlates with character traits and mental capacity. Phrenology has been used to bilk people of their money, support racist and sexist stereotypes, and bolster Nazi eugenics. Let’s not talk about that today.
Phenology, without the “r”, is a complex and important topic in ecology. You might hear someone talk about the phenology of plants related to when they begin emerging from the ground, when they flower, and when they begin to wilt and senesce at the end of the growing season. Additionally, however, phenology includes the timing of the emergence of insects from dormancy or their final molt into adulthood. It also includes the timing of animal migrations and hibernation, as well as many other events in the lives of myriad organisms.
The factors that influence a species’ phenology often include temperature, light, and moisture – in combination with genetic signals. We still have a lot to learn about the phenology of most prairie species, especially in terms of how they might adapt to changing climate. In fact, rapid climate change has brought much recent attention to phenology because changes in the flowering time of plants, for example, have already helped illustrate the occurrence and impacts of climate change. In addition, there is great concern that species may not be able to adapt the timing of their lives quickly enough to match the changing climate, and/or that timing of interdependent species might not remain synchronized. For example, flowers might start blooming before or after their particular pollinators are active, or birds or insects might migrate to breeding areas before food is available at those sites. A couple years ago, monarch butterflies arrived in Nebraska way ahead of schedule, but fortunately they were still able to something to eat and lay eggs on.
Here in Nebraska, we got some interesting insight into the phenology of plants during 2012. The year ended up giving us the most severe single year drought in recorded history and it started out as a year of extraordinarily warm temperatures. In fact, spring and summer temperatures arrived so early that we recorded many plant species blooming weeks or months ahead of their typical schedule. I wrote a short blog post about this back in May of 2012 and a number of people from around North America responded with their own sightings. The observation that stood out most to me was the blooming of asters in May. I had never seen heath aster (Aster ericoides) or New England aster (Aster novae-engliae) bloom before late August or September.
Phenology is also important to land managers trying to sustain biological diversity in prairies. For example, around here, we are constantly fighting cool-season invasive grasses. The growth period for those species starts earlier and ends later than that of most native prairie plants. That gives us some opportunities to use herbicides to kill or suppress smooth brome, Kentucky bluegrass, or other invasive grasses when the chance of harming other plants is very low. In addition, we can use prescribed fire, grazing or mowing to target those grasses when they are most vulnerable. For example, we might try to burn a prairie right as those species are starting to bloom because it wipes out those plants’ entire season of energy investment in growth and flowering. The fire doesn’t kill those grasses, but it can knock them back enough to allow other plants – especially those just starting their growth periods – to flourish while the vigor of the invasive grasses is low.
Timing of burns can also be aimed at suppressing many other kinds of plants. For example, we sometimes try to burn prairies when encroaching trees are just leafing out and highly vulnerable. Alternatively, burns can be timed to limit impacts on animal or plant species. That might include strategically scheduling a fire based on the emergence of rare insect species or before sensitive reptiles become active in the spring. Prescribed grazing can be employed in much the same way – strategically moving livestock in and out of an area to suppress the growth of particular plants or to create desired habitat structure prior to the arrival or emergence of particular animal species. In all these cases, land managers are acutely aware of the phenology of the species they are trying to suppress or assist.
If you’re someone who enjoys keeping track of when things happen each year, you might enjoy joining a citizen science effort to document changes in the phenology of many different phenomenon. You could start at the National Phenology Network and peruse some of the options they provide. Or, if you already have years of field notes that document when you see your first bumblebee, prairie clover flower, or grasshopper sparrow each year, I’d encourage you to contact a local expert on that/those particular species and let them know about your data. You might have information of great value to conservation.
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.
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
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.
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.
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.
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.
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.
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?
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.
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.
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.
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.
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.