What’s the Best Time to Burn?

As I mentioned last week, prescribed fire can help meet many prairie management objectives.  It’s important, however, to match the timing of the burn to those objectives in order to avoid conducting a fire that is either unproductive or counterproductive.  For example, if you’re burning to set back trees or invasive plants, you’ll want to be sure to burn when the fire will suppress those species and encourage growth of competing plants.  Too many times, people burn to control smooth brome or another invasive cool-season grass but burn so early in the season that they end up helping the plants they’re trying to hurt.  Here are some examples of various management objectives for prescribed fire, along with examples of how to time those burns to meet those objectives successfully.

dormant

This early March burn (dormant season) will stimulate the growth of cool-season invasive grasses such as smooth brome or Kentucky bluegrass.  However, we brought in cattle to knock back the strong growth of those species.

In the Platte River Prairies, our biggest invasive species threat comes from smooth brome, Kentucky bluegrass, and other invasive grasses that grow early in the season.  They can monopolize space and moisture, reduce plant diversity and wreak havoc on habitat conditions.  When we target those species with fire, we try to burn when the targeted species is just about to bloom.  By doing so, we can knock the brome or bluegrass back after it has invested energy in growth but before it invests in reproduction.  At the same time, we create excellent conditions (lots of light and warm soil) for competing warm-season native species which are just getting ready to start their growing season.  Bluegrass blooms significantly earlier than brome, so we can’t get maximum impact on both species with one burn.  Instead, we have to decide which is the more dominant grass at the time.  Regardless, the timing of our burn is aimed at the growth stage of the plant, not a particular date, since plant growth rates vary by year.

One issue we’ve seen with using fire to control brome or bluegrass is that while we can suppress those cool-season grasses and facilitate growth of warm-season native grasses, we often just trade one dominant grass for another without encouraging overall plant diversity.  As a result, we often combine cattle grazing with fire to add a more selective defoliator (cattle) to the mix.  When we’re using grazing, the timing of the fire can be more flexible.  We can conduct a burn in the fall or early spring, and while that will stimulate strong growth of brome and bluegrass, we can use intensive spring cattle grazing to counter that strong growth and suppress those invasives.  Later in the summer, a fairly light stocking rate of cattle can help suppress major warm-season grasses and keep them from simply taking all the space left open by weakened invasive grasses.  This creates opportunities for wildflowers to flourish.  Since cattle prefer big bluestem and indiangrass over all other plant species in our summer prairies, that kind of grazing usually works pretty well.  There are too many potential combinations of fire and grazing to cover here, but suffice it to say we can burn at many times of the year when using cattle to complement the effects of those fires.

bluegrass

This fire was conducted at about the time Kentucky bluegrass was starting to bloom, so it should knock the vigor of that species back for a year or two.

If cattle aren’t an option but you find that fire alone just encourages dominant grasses of one kind or another (a more common result in the Great Plains than in the Midwest), one option could be a summer fire.  If you’ve never seen a summer prescribed fire, you might find it hard to believe that green prairie can burn, but as long as there is sufficient old growth from previous seasons that dead vegetation will carry a fire, regardless of how green this year’s vegetation is.  (That green vegetation does make summer fires extra smoky, however.)  If big bluestem is the dominant species you want to suppress, the best time to burn is when it’s just ready to bloom.  Remember that there are many other factors to consider with summer fires, including the various animals that are active in the prairie at that time of year.  It’s usually best to burn only a small portion of a prairie in the summer to avoid excess impacts on wildlife and invertebrates.  However, summer fires can be very good for encouraging wildflower growth, and the habitat benefits from added plant diversity help counteract short-term impacts of the fire on animals.  Another caution with summer fires is that if cool-season invasive grasses are a problem at a site, they will likely benefit from a summer fire, and could thrive during the following fall and spring without some other treatment.

Controlling trees with fire is a common objective for prairie managers, but timing is also important for that objective – and appropriate timing varies by the species of tree being targeted.  We’ve had some very good late spring burns that suppressed brome wonderfully but failed to kill small eastern red cedar trees.  I think the trees failed to die because there was insufficient heat created to make up for the increased moisture in the stems at that time of year.  The trees turned yellow-orange after the fire but then greened up again.  We’ve found dormant season fires to be far more successful when we’re targeting cedars.  On the flip side, it seems like we’ve had the best luck suppressing (but not killing) dogwoods and other deciduous trees and shrubs when we burn as those species are just leafing out later in the spring.  However, our success with deciduous plants has been inconsistent enough that I hate to make recommendations – and deciduous tree control with fire is usually temporary at best.  Dirac Twidwell, range ecologist at the University of Nebraska-Lincoln, has experimented with intense summer fires during drought conditions in the southern plains and has found that the combination of high temperatures and drought stress can be deadly on trees not ordinarily considered to be susceptible to fire.  Unfortunately, burning under those conditions takes much more training and preparation (and more trusting fire chiefs) than most of us can muster.

cedar

This cedar will probably survive this growing season burn.  It turned yellow but will likely turn green again and continue its growth.

Dormant season burns include any fires conducted after the prairie turns brown in the fall and before it greens again in the spring.  Impacts from late fall and early spring burns are pretty similar to each other, with the caveat that fall burned prairies have bare ground all winter long, which can dry out the soil somewhat and – obviously – provide very different winter habitat than prairies with standing vegetation for species that need that.  Drier soil and bare ground are not necessarily bad things, especially if there is other prairie habitat nearby.  In fact, some managers in northern parts of the United States have found that bare soil over the winter can help winter kill Kentucky bluegrass during particularly cold winters.  Fall or winter burning can also help extend the window needed to find the right weather to conduct a dormant season burn.  Depending upon your objectives, those fall burns could be just as effective as an early spring burn and you can relax all winter, knowing that your burn is already done.  One additional consideration with fall burns is that the day length (at least in North America) is considerably shorter in November than in March, giving you less time to conduct a fire during daylight hours.

There are many other possible objectives for prescribed fire, and examples of how to achieve them.  Those of us who harvest seed for restoration work, for example, use fire to stimulate seed production in some species (especially big bluestem).  In addition, because time since the last fire is linked to the amount of thatch and litter present in a prairie, burning can help manipulate habitat conditions for many wildlife species.  Speaking of wildlife, it’s critically important to remember how vulnerable some invertebrates and animals are to fire and to keep that in mind when setting burn objectives.  Burning an entire prairie (especially one that is isolated from others by roads or other obstacles) can completely eliminate some species of invertebrates that are aboveground during the fire – including many that overwinter in standing dead vegetation.  Depending upon your other objectives, you might consider not going into a burn unit to light all the patches of vegetation that didn’t burn initially – leaving those unburned areas can provide important refuges for vulnerable insects and other critters.  In addition to invertebrates, nesting birds, recently emerged reptiles in the spring, and other less mobile animals are all species to consider as you plan growing season burns.  There will always be negative impacts of any fire, but they should not be reasons to avoid burning.  Instead, they are examples of why it’s so important to have clear objectives so that you make sure you get the desired benefits from the fire and minimize the undesirable outcomes.

refuges

This growing season burn left behind numerous unburned patches, providing refuges for invertebrates and other small animals.

Fire is a powerful but dangerous tool for prairie management.  While it can be very useful for a wide range of objectives, there are too many risks (to people, property, and wildlife) to use it in a cavalier manner.  Setting specific goals for a fire and being thoughtful about the timing and tactics for that fire will help ensure that it is as productive as possible.

Be safe out there.

Report from the 2013 Grassland Restoration Network Workshop – Part 1

The Grassland Restoration Network’s annual workshop took place a couple weeks ago in Columbia, Missouri.  This year’s workshop was hosted by the Missouri Department of Conservation and included more than 90 people from around the country.  As always, the meeting was a mixture of presentations, discussions, and field tours, and was informal enough that we had plenty of time to get to know each other and catch up on what everyone has been learning at their own sites.  There were too many topics and discussions from the workshop to cover in a single blog post, so I’ll spread them out over the next several weeks or months.

Attendees of the Grassland Restoration Network's annual workshop at Tucker Prairie, east of Columbia, Missouri.

Attendees of the Grassland Restoration Network’s annual workshop at Tucker Prairie, east of Columbia, Missouri.

One of the most intriguing discussions of the workshop was an extended conversation during our field trip to the 711 acre Prairie Fork Conservation Area, managed by Missouri Department of Conservation (MDC).  At several points during the trip, we talked about objectives for restoration projects and prairie plantings.  Here in the Platte River Prairies, our restoration objective is to use prairie plantings to enlarge and reconnect fragmented remnant prairies – hoping to increase overall ecological resilience and the viability of populations of plants, bees, etc.  At Prairie Fork, however, there are no remnant prairies to stitch together, and education is a major focus of their restoration project.  Their stated restoration goal is simply to rebuild natural communities and their processes.  Then they use those restored areas as platforms for their education work.

Although Prairie Fork Conservation Area is not far from Tucker Prairie – the last remnant of the once vast Grand Prairie that stretched across a large swath of Missouri – MDC staff are not trying to design their plantings to mimic Tucker Prairie.  Instead, they are harvesting seed from Tucker prairie and other small scattered areas of native prairie vegetation to create seed mixtures that are a composite of all of those sites.  As a result, prairie plantings are allowed to develop into communities as local site conditions allow – a very sensible approach.

Rattlesnake master is common at Tucker Prairie, the last sizeable remnant of the Grand Prairie that used to cover a large portion of northern Missouri.

Rattlesnake master is common at Tucker Prairie, the last sizeable remnant of the Grand Prairie that used to cover a large portion of northern Missouri.

The decision not to impose constraints on what each Prairie Fork planting needs to look like gives MDC considerable freedom in terms of evaluating success.  That freedom led to some great discussions about what success should/could look like.  There were three tour stops where the topic came up in some form, and each is worth discussing.

1. The first discussion occurred early in the tour when we were looking at a soybean field that was going to be converted to prairie vegetation within the next few years.  Around the edge of the field were “waste areas” of tall fescue with infestations of sericea lespedeza, autumn olive, and other invasive plants and trees.  Because of the trees and topography, it wasn’t feasible to put those areas into cultivation, which is the technique MDC (and most of us) would prefer as a way to create a clean seed bed prior to planting prairie.  The group starting talking about other ways those areas might be prepared for planting, until Bill Kleiman (with The Nature Conservancy’s Nachusa Grasslands in Illinois) abruptly shifted the discussion.

Bill made the excellent point that those difficult areas wouldn’t necessarily have to be converted to a diverse prairie planting, and that attempting to do so might prove to be overwhelmingly time consuming or simply impossible.  The seedbank of invasives in those areas is probably heavy enough that even multiple years of cultivation might still result in long-term fights with invasive plants emerging from that seedbank long after prairie vegetation was planted.  Instead, Bill suggested, why not implement an annual program of broadcast herbicide spraying in those waste areas – with the simple goal of maintaining them as a low diversity, grass-dominated, plant communities that won’t threaten nearby diverse plantings?  In other words, rather than trying to make those areas perfect, just make them harmless.  Down the road, when everything else is restored, MDC can always come back and spend energy trying to convert them to something diverse.  In the meantime, they can save a lot of time and energy by avoiding a (likely fruitless) battle to convert a very weedy area into a pretty prairie.  It was certainly an interesting proposal.

Rosinweed (Silphium integrifolium) was just beginning to bloom during the GRN workshop.

Rosinweed (Silphium integrifolium) was just beginning to bloom during the GRN workshop.

2. The next site we visited had been planted to prairie vegetation several years earlier, but had a chronic infestation of sericea lespedeza.  While MDC staff was controlling the lespedeza through spot spraying, there was enough lespedeza (and enough spraying) that the area’s plant diversity had become fairly limited and dominated by a few grass and wildflower species.  Chris Newbold, who had been in charge of the restoration work at the time the site was seeded, said that if he had to do it all again, he would have left the area in cultivation a few more years to get better control of the lespdeza population prior to planting.  The more pressing question now, though, was how to deal with the site going forward.  Options included starting over by returning it to cultivation, trying to overseed the area to establish better plant diversity, or just leaving it alone.  An additional proposal was to overseed with plant species that are resistant to a selective herbicide that controls lespedeza, allowing the site to be broadcast sprayed without eliminating all plant diversity.  I don’t think the question was resolved through our discussion, but we built upon our earlier conversation by posing the question, “Does every part of a restoration project have to be ‘perfect’ in order for the project to be successful?”

This portion of Prairie Fork Conservation Area was seeded with a high diversity mixture but has lost plant diversity , at least in part because of years of herbicide spraying for sericea lespedeza.  The lespedeza is spot sprayed, but is abundant enough that herbicide impacts are evident on the plant community.

This portion of Prairie Fork Conservation Area was seeded with a high diversity mixture but has lost plant diversity , at least in part because of years of herbicide spraying for sericea lespedeza. The lespedeza is spot sprayed, but is abundant enough that herbicide impacts are evident on the plant community.  Mike Arduser, of MDC, pointed out that the site looks really nice from a bee habitat standpoint, bolstering the idea that although it had lost some of its plant diversity, it was still an important contributor to the landscape around it.

I appreciated the discussion because it forced me to reflect upon our Platte River Prairies, and areas that I wish looked better than they did.  In both my prairies and at Prairie Fork, it’s really the big picture that’s important.  Within the mosaic of natural communities that make up any sizeable prairie, it’s probably ok to have areas of low diversity vegetation.  At least at the scale of Prairie Fork, it’s really the mosaic that’s important, and variation in plant species composition between individual portions of the landscape is not only acceptable, but preferable.  Coming to terms with the idea that it’s ok to have portions of our prairies/properties that are less diverse than we think they could be is an important part of being a successful land manager.  The alternative probably entails driving ourselves to exhaustion!

.

3. The last site we looked at was a 2004 prairie planting that was very diverse and full of big showy wildflowers.  From an aesthetic standpoint, the planting was a big beautiful success.  I asked the MDC staff how they might judge the success of such a planting according to their objectives.  Clearly, one part of the answer is that a showy prairie is useful in terms of getting people to appreciate prairies – so that fits well into education/outreach objectives.  However, Jeff Demand, the current site manager, had another interesting perspective.  Jeff said that he appreciated the planting because it required very little maintenance.  There were no real invasive species issues to deal with, and nothing else about it that screamed out for attention.  The planting was clearly of value to wildlife, pollinators, and other prairie species, but it was particularly nice to have an area that just needed some period burning or similar management.  Especially when budgets and staffing are tight (and when are they NOT?) a site that is attractive and low maintenance can seem like heaven.

This 1994 seeding at Prairie Fork is an aesthetically-pleasing site.  Most people would be very happy to have this kind of establishment success from a prairie planting.

This 2004 seeding at Prairie Fork is an aesthetically-pleasing site. Most people would be very happy to have this kind of establishment success from a prairie planting.  However, aesthetics is not always the best measure of success.

There are no right or wrong answers when it comes to objectives.  Every site has its own, and they almost always change over time.  The important thing is to know what the objectives are for a particular site, and to be measuring whether or not you’re moving in the right direction.  It’s always nice to hear about other people’s objectives and measures, because it makes us re-examine our own.

I tend to worry more than I should about portions of our site that aren’t as “nice” as I think they should be.  The field trip discussion was a great reminder to sto obsessing about small areas and keep the big picture in mind.  It’s important to deal with areas that might negatively influence the surrounding landscape (e.g., by providing a foothold for invasive species that can spread into nearby areas).  Otherwise, however, variation between portions of a prairie or prairie landscape just adds to the diversity – and resilience – of the ecosystem.  I think that’s a good thing.

I guess I just have to be reminded of that now and then.