This post was written by Alex Brechbill, one of our Hubbard Conservation Fellows. Alex hails from right here in Aurora, Nebraska. He has worked both in the policy arena and deep in the wilderness, and so brings a broad perspective to his thinking about conservation. You’ll hear much more from him during the coming year.
I must come clean before diving into this article: I love trees. Trees are one of my favorite things in the world. From the towering conifers of the Pacific Northwest to the vast overwhelming deciduous canopy in the Shenandoah Valley. So long as I have two boots on my feet and passion in my heart, I will always love trees. Out of all trees, I especially love (brace yourself, fellow prairie-folk) the eastern redcedar.
I love cedars, largely because of the time I spent up North, in Minnesota, on the water. The first canoeing paddle I carved was from a slab of western redcedar. I cut the profile with a bandsaw and spoke-shaved the shaft, throat, and blade, leaving the finesse of the handle to fine grit sandpaper. Walking into the woodshop, the pungent aroma of cedar fills the air. As someone who enjoys woodworking, there are few things as visually appealing as the aesthetic of a golden, polished cedar-strip canoe. At times I’m a little embarrassed at how much time I spend ogling canoes on the Internet. From the bow to the stern, they are charming and iconic. While camping, I spent hours sitting by the warmth of glowing hot firepit, from freshly split cedar. Even on a soaking wet, bitter-cold day, cedar will burn well. There is a reason that the cedar was known as the tree of life.
Redcedar invokes all five senses; from smelling it to feeling the warmth of a fire. However, seeing thickets of trees, cedar or otherwise, on the prairie is jarring. A majority of the land stewardship time I have spent so far in the fellowship has been dedicated to removing woody invasive plants: Eastern redcedar, Siberian elm, mulberry, and several others. Cutting down trees is bittersweet. I have an immense respect for trees as organisms, and each time I cut one down I have to remember why I am cutting it down: we will lose our prairies if we don’t do anything about encroaching woodlands.
Encroaching trees limit the ability of some plants to establish themselves, and they will choke other plants out. Trees decrease the amount of forage that can be produced on a prairie for grazing. I could go on, but the bottom line is that trees can be harmful to prairies. On the other hand, there are certainly places for them. Along stream banks, as shade trees, and in shelterbelts, trees can be very helpful for people and livestock. I love both trees and prairies, but not when they form a Venn-diagram.
Not only do we improve the quality of our prairies by removing invasive trees, we can also glean valuable products from their wood. Firewood is the first product that comes to mind. Sitting next to my fireplace on a cool night is one of my favorite ways to end the day, relaxing in the dry heat of the seasoned firewood. Milling logs into dimensional lumber is another great way to utilize problem trees. Sawing dimensional lumber is like breaking open a geode, the rugged exterior concealing a center of splendor. The freshly exposed grain of the wood is captivating, and it’s easy to get lost in the curvilinear waves flowing through the heartwood and sapwood. Currently, I am carving a flatwater canoeing paddle out of a milled slab of Siberian elm, another problem tree that we spend hours removing. I spend my evenings whittling black walnut, with its gorgeous dark heartwood, and cottonwood, which cuts like butter under the bevel of freshly honed edge.
For utility and beauty, trees give us a lot, whether they are the subject of a photo or some shade for a picnic. Unfortunately, as much as they give us, they can take a lot away from us, and if that means taking away our prairies, I better sharpen my saw and get back to work.
Those of you who have followed this blog for a while know about the big wildfire that swept across The Nature Conservancy’s Niobrara Valley Preserve back in 2012. One of the results of that fire was the death of almost all of the Preserve’s ponderosa pines on the bluffs north of the river. I’ve posted several times about the recovery of that portion of the site, which we are watching closely and learning from. We haven’t seen any new pines coming in yet, but grasses, sedges, wildflowers, and deciduous shrubs are all flourishing.
As new plants colonize the site, the old skeletons of pines and eastern red cedars are starting to break down. Some of those dead trees are tipping over completely, while others are breaking off further up the trunk. The result is a landscape that is a little more difficult to walk through (and dangerous on windy days), but one that is still very pretty. The gradual degradation of the tree skeletons is a necessary part of the recovery and transition of this area to a different ecological community. We think that pines will eventually recolonize the site, but it’s going to be many years before that happens to any great extent. In the meantime, there is a great abundance of wildlife, insects, and wildflowers living between the falling trees.
While up at the Niobrara Valley Preserve earlier this summer, I spent a little time wandering in, ruminating about, and photographing the area where the old trees are breaking down. Here is some of what I saw.
I’ve always enjoyed looking at the patterns I find in ponderosa pine park. It’s hard to resist photographing them. This last trip, I was seeing specific images in some of the patterns, so I photographed a few and present them here for your consideration. They are a kind of Rorschach test, I suppose. What images do you see?
This post was written by Evan Barrientos, one of our Hubbard Fellows.Evan is a talented writer and photographer and I encourage you to check out his personal blog.
Warning: This post contains images of fluffy, baby animals.
Along the edge of one of our prairies there is a road lined with mature cottonwood trees. Although I appreciate the wide-open prairie environment, I like to take a walk once a week in the shady security of this miniature forest. The rustling leaves are soothing, shade is a novelty, and the trees bring back memories of hiking in New York’s forests. I also happen to see a lot of interesting wildlife behavior when I go here. One morning in July I was jogging down this road when I spotted an Eastern Screech-Owl being mobbed by Baltimore Orioles and American Robins. I sprinted back to my house, grabbed my video equipment, and hurried back before the action was over.
For several minutes I filmed as the orioles and robins viciously pelted the seemingly harmless owl (click here for a previous post I wrote about this behavior). It amazed me that the owl could withstand such harassment so patiently. Despite several painful-looking beak-jabs to the back of the head, the brave little owl outlasted the assault and was finally left in peace. Only then did I realize why she had refused to leave; she had babies to look after!
In a nearby branch I finally noticed three owl fledglings trying to sleep. In addition, there was a second adult screech-owl who seemed equally intent upon sleeping unnoticed. I don’t know which adult was which gender, but I like to imagine that it was the mother who bravely endured blows from the angry songbirds in order to let her family sleep in peace while the lazy dad took a nap. Either way, I always find it touching when I see animals put such great effort into protecting their young.
On another subject, all three birds in this post are species that used to be much less common in Nebraska. Before Europeans arrived, trees were hard to come by in central Nebraska. Over the last century, however, trees from the East have spread into the state as people have planted them around their crops for windbreaks and around their homes for shade. With trees leading the way, many forest species from the East, such as Eastern Screech-Owls, have ventured into Nebraska and the Great Plains. The ecological effects of this tree march are more complex than I’ll go into here, but overall they’re detrimental to grassland plant and wildlife populations. Here are just a few examples:
Trees provide perches for aerial predators (such as owls and hawks), which increases predation rates of prairie grouse and mammals.
Tree corridors provide safehavens for woodland nest predators (such as skunks and opossums) as well as brood parasites (i.e. Brown-headed Cowbirds), who venture into the prairies for prey/hosts. Thus, wildlife in small prairies bordered by trees experience abnormally high rates of nest depredation and parasitism.
If uncontrolled, trees form dense canopies that shade out prairie plants, which are adapted to full sun. This makes it harder for prairie fauna that rely on prairie plants for food and shelter to survive. The result is a positive feedback loop: the presence of trees encourages more trees to grow.
So what’s the takeaway? Our relationship to nature is complicated. Nothing is simply good or evil. On one hand, trees may seem like a existential threat to prairies, but on the other, I value them for their soothing shelter and the species they harbor. I think the key to this dilemma is diversity. Although I appreciate woodlands, I also appreciate prairies. But healthy prairies are so much more scarce in eastern Nebraska than wooded roadsides, and grassland species are generally in decline, while most woodland species are stable or even increasing.* Therefore, I would choose to cut down trees that are encroaching upon prairies. This does not mean that I think all trees in Nebraska are evil and must be destroyed, just that we need to keep them in check in order to maintain a balance between the two habitats.
*To make things even more complicated, while tree invasion is a real problem, cottonwoods are actually failing to reproduce in Nebraska. To germinate, cottonwoods need floods to scour vegetation and deposit sediment. Now that Nebraska’s rivers are regulated by dams, these floods happen much less often. As a result, we’re seeing very few young cottonwoods taking their parents’ place.
We spent a long day at our Rulo Bluffs property last week. The site is at the very southeast corner of Nebraska, and includes about 450 acres of mostly oak/hickory woodland with prairie and savanna habitat on steep ridge tops. I’ve written before about our work to burn and thin the woodlands to open up the understory layer as a way to encourage higher plant diversity and better wildlife habitat. Last week, Nelson, our land manager, spent the entire day in a rubber-tracked skidsteer, shredding brush along ridges because we didn’t manage to get a fire done last fall or this spring. I got a few overhead photos of his work with our drone.
The second image above, taken with our drone, was interesting because it and others from the day showed a surprising number of large dead trees scattered across the property. We knew we were reducing the number of smaller diameter trees with our thinning and fire work, and that a few bigger trees were also dying, but couldn’t see the real scope of that without being in the air. (Couldn’t see the forest for the trees…) While we’re not trying to kill off a large number of big trees, losing some provides space for new oak trees to get started, and provides a number of other benefits – including habitat for the many species that live in standing dead timber. So, it wasn’t a shock or disappointment to see all the dead trees, it was just an interesting observation we couldn’t have gotten without the ability to get eyes up in the air.
My main job last week was to be on site in case Nelson ran into trouble with the skidsteer. (That makes it sound like I was there to help fix the skidsteer – nothing could be further from the truth. Nelson has more mechanical ability in his little finger than I could dream of. I was just there to go for help in case he rolled the thing down the hill or something.) While he was doing the real work, I tried to stay productive by pulling garlic mustard, scouting for invasive honeysuckle, and killing small trees with herbicide. I also managed to find a little time for some photography. Here are a few of the photos I took.
Because of its long distance from our shop and field headquarters, we never feel like we spend enough time working at Rulo Bluffs. It’s a beautiful site, and one of the best examples of oak woodland remaining in Nebraska. As with other oak/hickory woodlands, however, it requires active management in order to survive and regenerate. Without frequent fire, or substitutes such as thinning and shredding, the understory at Rulo Bluffs would become choked with small trees and shrubs, such as ironwood, dogwood, paw paw, and others. Those woody understory species block light from hitting the ground, prevent the establishment of new oaks, and choke out most grasses, sedges, and wildflowers. Eventually, if older oaks die without being replaced, these woodlands change into new communities, dominated by trees such as ash, hackberry, and others that don’t create leaf litter that can carry fire. At that point, restoring the oak/hickory woodland community, which supports a much larger diversity of plant and animal life, is nearly impossible.
…and that is why we keep trying to find time to head down to Rulo Bluffs. That, and it’s such a beautiful place.
Trees are great, but trees in and around prairies can negatively impact habitat quality for many grassland plant and animal species and provide points of introduction for invasive species. Encroachment by trees has become a major threat to prairie conservation in many landscapes.
A few months ago, I cut across the courthouse lawn on my way home from the office (I was walking – it’s a small town). On the west side of the courthouse, there are a number of statues and other monuments memorializing veterans of various wars. In the midst of those, however, is a very different kind of memorial (pictured below). This plaque-on-concrete memorial got me thinking – yet again – about our relationships with trees, our desire to plant and care for them, and how that affects our former, current, and future relationship with prairie.
I live in Nebraska, home of Arbor Day. Early European settlers of Nebraska were enthusiastic tree planters for both practical and aesthetic reasons; our legislature even designated us as “The Tree Planters State” back in 1895. There were good reason for all that tree planting. It’s certainly nice to have shade around one’s house and yard, and a grove of trees provides a valuable shield from strong winter winds for both homes and livestock. In addition, early settlers found the open prairie lacked adequate wood for fuel and building materials. However, despite the numerous practical uses for trees, I think most tree planting was and is done primarily as a way to make the landscape more visually appealing. People just like trees.
This brings me to my contemplation of tree planting and prairie conservation. Research has shown that when given a choice, people seem most attracted to the aesthetics of a savanna-like landscape – one with scattered trees and short grass. That mindset is evident in the way we design our yards and parks. Not only do we enjoy having trees, we really like to plant them ourselves. We gain immense satisfaction from the simple act of digging a hole and plopping a seed or small seedling in the ground, knowing that we and future generations will be able to watch that tree grow skyward. The trees we plant often become almost family members in the way we celebrate their growth and mark time by how big the trees were when such and such happened.
This brings up two issues for those of us working to conserve prairies. First, we’re starting from a handicapped position when we advocate for prairie conservation because prairies are not what most people visualize when they think of natural beauty. Given the choice between a treeless grassland and a park-like landscape dotted with trees, most people would choose the wooded park as a site to photograph, hike or picnic, or build a house. In fact, there are countless examples in which people buy a small patch of prairie for a recreational property and immediately plant numerous trees to make it “look nicer.” We really haven’t changed much from our European settler predecessors in that regard.
Second, we haven’t yet found a prairie-related analog to tree planting; a simple activity that creates something people can take ownership of, love and nurture. Planting trees is so easy a child can do it, and with very little investment of time or money, someone can establish a couple trees that become treasured landmarks or memorials – – which further reinforces people’s love of trees and wooded areas. In contrast, planting prairies is fairly complicated and requires more space. It also takes a few years for a planting to grow out of its weedy phase and start to look like a prairie. Prairie planting can certainly be rewarding, but it’s not nearly as simple, accessible, and instantly gratifying as tree planting.
So how can we help people connect with prairies in the same way they connect with trees and wooded landscapes? I don’t have all the answers, but here are a few ideas.
1) We need to encourage more people to spend time in prairies and make sure they enjoy themselves when they go. It can be a definite challenge to convince someone to take a walk in a prairie. Even worse, when people do step foot in a prairie, many are unimpressed because they don’t really know what to look for or how to appreciate what they’re seeing. As a result, they often walk away with an even less favorable opinion than before they came. “It was just a lot of grass! And I was pulling ticks off myself all night!”
A good naturalist and interpreter can lead someone on their first prairie excursion and make it a positive and thought-provoking experience. There is no substitute for the expertise and enthusiasm of a good leader, but there aren’t enough of those people to go around. Several Nebraska Master Naturalists approached me last year with an idea to create a “Prairie Exploration Guide” – a pamphlet/booklet designed to help newcomers to prairie see the beauty and complexity they might otherwise miss. The guide is still in the development stage, but I have high hopes that it will be a useful tool when it’s done.
2) Using native prairie plants in landscaping is becoming increasingly popular. The public’s concern over population declines of bees and monarch butterflies is helping to spur the movement, as are issues such as water conservation. There is no question that getting the public to buy, plant, and appreciate native prairie plants in their backyards is a major step toward building a prairie conservation constituency – and backyard prairie gardens also make real conservation contributions on their own. Significant obstacles still hinder the movement, especially our cultural norms about what yards and gardens are “supposed” to look like, but I am optimistic about the future.
3) One successful method for engaging people in prairie conservation at our Platte River Prairies has been through seed harvesting. People identify with both the value of seeds and the idea of restoring lost habitats. Harvesting seed is a tangible way people can contribute toward something important; they can measure that contribution by the amount of seed piling up in their buckets. Ideally, harvesters come back and help plant the seed they picked, and then visit regularly to watch the prairie planting develop over time.
Along those lines, one of the most inspired strategies I’ve seen to engage people in prairie restoration was being done by Wayne Pauly in Dane County, Wisconsin. I went on a tour of some of his prairie restorations back in 2004 and was very impressed with both his plantings and his involvement of volunteers. Most particularly I liked Wayne’s strategy of having volunteers “paint the prairie” with seeds during prairie plantings. He’d give each volunteer a bucket of seeds of one prairie wildflower species and let them decide how and where to plant those seeds – allowing them to create a pattern or design of their choice (thus the idea of “painting”). That is a brilliant idea, and one that should not only be fun on planting day, but should also draw those volunteers back in subsequent years to view the results of their work.
Humans have a long and strong relationship with trees, one that is likely embedded within our DNA. Tree planting is an easy, accessible, and tangible way to contribute something to the natural world. Unfortunately, tree planting doesn’t do anything to help prairies, and can sometimes be counterproductive if trees are planted in or near open grassland. If prairie conservation is to succeed, we need to get the public excited about grasslands and combat the perception that prairies would look a lot prettier if they just had some trees growing in them. More importantly, we need more strategies that actively connect people with prairies and give them the same sense of fulfilment they get from planting trees. I think we’re getting better, but we have a long way to go.
A couple years ago, I wrote about some work from Kansas State University related to woody plant expansion in prairies. Many of us who work with prairies constantly wrestle with questions about trees in prairies. Why are they encroaching so quickly these days? What prevented them from doing that in the past? During our recent trip to Konza Prairie, we got to discuss this topic more in-depth with Jesse Nippert and other researchers at Kansas State.
Clearly, a combination of factors influences how quickly trees and shrubs enter and spread in grasslands. One big reason is the increase in “seed rain” in some of today’s prairies. Prairies in fragmented landscapes with numerous trees and shrubs in nearby woodlots, road ditches, shelterbelts, etc., are deluged with seeds from those woody plants. The vast majority of those seeds fail to establish, but the high number of seeds coming in means that some will find opportunities to grow.
Other factors may include the higher rates of carbon dioxide in today’s atmosphere and higher amounts of nitrogen deposition (from industry and agricultural facilities, for example), both of which tend to favor woody plant establishment. In addition, we are in a relatively wet climatic period if you look at the geologic record. While there have been droughts, including severe ones, in recent years, those droughts are nothing like the multi-decade severe droughts that can be seen in the relatively recent geologic records for the central United States. Long and/or frequent droughts favor herbaceous plants (such as grasses and wildflowers) over trees.
However, Jesse Nippert’s research into the way trees, shrubs, grasses, and forbs (wildflowers) compete for water belowground provides some additional insight into the march of woody plants into prairies. As we started talking about roots, Jesse confirmed something I’d heard from Dave Wedin at the University of Nebraska; even though grasses can have very deep roots, most of their water use is actually very shallow – within the top 25 cm of soil. Jesse says the reason those grasses persist during very dry periods is not because of their deep root systems, but because they can continue to grow and function when available soil moisture is very low. Forbs also pull a lot of their moisture from shallow roots, but utilize slightly deeper roots (50-75 cm deep) during droughts because they can’t compete well with the ultra-efficient fine-rooted grasses at the upper levels.
It turns out that understanding root competition might help us better understand woody plant encroachment as well. In many parts of Konza prairie, clonal shrubs such as rough-leaved dogwood and smooth sumac have expanded rapidly over the last several decades. As Jesse and his students have studied this phenomenon, they have concluded that an important factor behind this expansion is the strategy those shrub clones use to acquire water. While grasses and forbs are mostly using water from the top 1/2m of the soil, shrubs pull much of their water from deeper in the soil profile, allowing them critical access to water not being utilized by their competition – especially in years when the upper soil layers are dry.
The clonal form of dogwood and sumac gives them another advantage. As clones expand, the tillers (aboveground stems) on the outer edge of the clones have very small roots. However, by studying the isotopic signatures of the water in those shallow-rooted tillers, Jesse can tell that they are also accessing water from deep in the soil profile. He says this is almost surely because the older, deep-rooted plants in the center of the clone are sharing the water they acquire with the younger stems on the outside. Not a bad strategy.
Of course, as these clones of dogwood and sumac use their water acquisition and sharing strategy to advantage and spread into the prairie, they also shade out their competition – especially beneath the tall/dense tillers toward the centers of clones. Suppressing the growth of grassy undergrowth not only removes that competition for resources, it also helps make the clones fireproof. Since dried grasses are the primary fuel for prairie fires, the absence of grasses beneath shrub clones means that fires can’t burn through them. It’s not hard to see how the processes of deep water acquisition/sharing and fire-proofing can create a positive feedback loop that helps drive an inexorable expansion of shrubs into the surrounding prairie.
We didn’t talk about this in Kansas, but my experience is that fire-proof shrub clones are an important avenue for the establishment of trees as well. Many tree seeds are deposited into those shrub patches by birds that see those shrubs as convenient and prominent perching sites. If those seeds are able to germinate and establish within those clones – and they often can – the resulting trees can grow without fear of the fires that would otherwise threaten them. Hiding in the middle of big shrub clones also gives those trees a chance to grow in relative safety from marauding prairie land managers…
Because much of Konza prairie has been managed under a variety of long-term fire regimes (1,2,4,10, and 20 year frequencies), Kansas State Researchers have some pretty good data on how fire frequency affects shrub expansion as well. Essentially, prairies burned every year or every other year do not have encroachment by dogwood or sumac, but prairies burned less often are being gradually overtaken by shrubs. Interestingly, the fastest expansion appears to be in prairie watersheds managed with a fire frequency of every four years (which is also about what the estimated average fire frequency was for that landscape during pre-European settlement). While it might seem counterintuitive that a four year fire frequency allows for faster woody encroachment than a 10 or 20 year frequency, the explanation appears to lie in the way shrubs respond to fire. Fire seems to stimulate radial growth in dogwood and sumac, meaning that the plants put an emphasis in growing horizontally rather than just vertically after they are burned. Under very frequent fire, this is apparently immaterial, probably because the shrubs never get enough rest between fires to take advantage of that radial growth. However, when they are given 3 years to recover between fires, that radial growth response after each fire means that burning actually stimulates faster expansion of shrub clones. Under a 10 year fire frequency, that extra radial growth only occurs once every 10 years, so the overall expansion is actually slower than in under a four year fire regime.
Before you jump to the conclusion that burning every year or two seems the obvious best strategy for shrub control, remember that woody plant suppression is only one of many objectives for prairie management. I’ll address some of the other, less positive, effects of frequent fires at Konza in an upcoming post.
As I said earlier, there are multiple factors that affect the rate of tree and shrub encroachment on prairies. Seed rain might be as important as anything, and climatic conditions, increases in nitrogen and carbon dioxide levels, and fire suppression are all likely contributors as well. However, the way plants compete belowground, particularly the deep water use strategy of clonal shrubs such as dogwood and sumac, also seems to play an important role. Frequent fire application can be one way to prevent encroachment, though it comes with other baggage (see upcoming post…) and may not help remove shrub patches once they’re established. At Konza, they took some of the every-20-year-fire-freuency watersheds and started burning them annually to see if they could get rid of the shrubs and trees. Thirteen years later, those patches are still there, though the individual stems are much smaller. It seems that while frequent fire might help prevent woody plant establishment, frequent fire alone might not be able to reverse it – at least not on a very fast timeline.
Woody plant encroachment is one of the biggest challenges we face in prairie management today. A solid understanding of the mechanisms behind that encroachment should help us design more effective strategies to combat it. Shredding, burning and herbicide application are all useful tactics, but figuring out the timing, frequency, and intensity of those applications will be critical. We need to use the various competitive strategies of grasses, forbs, and shrubs to our advantage. As an example, some recent work by Dirac Twidwell (University of Nebraska-Lincoln) seems to indicate that burning under more extreme heat and drought conditions than we typically feel comfortable with might be one way to really tip the scales away from woody plants. The feasibility of that will be limited in some landscapes, but surely there are other innovative tactics that can help. If we work together and aren’t afraid to try some new ideas, we can figure this out.
It’s been a very mild winter in Nebraska. We took advantage of the warm weather on Tuesday to burn a small island in the middle of a stream/wetland restoration project area. The day was sunny, and it was 55 degrees F with light winds when we started the fire. (Quite a contrast with Wednesday, which was in the 30’s with winds gusting to 40 mph.)
The objectives for the fire included clearing most of the vegetation from the island to create feeding and roosting habitat for migratory cranes, shorebirds, and other species in the early spring. We also wanted to burn through the willow trees that were establishing on the island and set them back before they started to crowd out the grasses, sedges, and other herbaceous wetland plants beneath them. The fire worked out just right, removing most, but not all, of the vegetation.
It’s not often we can get a burn done in January. Even when it’s warm enough, the days are too short. By the time the day warms up enough to dry out the grass and support good fire behavior, it’s usually after lunch – and by mid-afternoon, the sun has dropped low enough that fire stops burning well and smoke stops lifting. Most of our burn units are big enough that it’s difficult to complete them during that short window of time. The island we burned this week, however, was less than an acre in size and we didn’t have to do anything but light it and let it go. A great way to do prescribed fire!
Here’s a question I get asked occasionally: “At what point will my prairie become self-sustaining?”
There are lots of ways “self-sustaining” can be defined, of course, but usually the person is hoping that at some point they can just step back and let the prairie do its thing with very little or no human input. In other words, they hope the prairie will function like a machine. Once you have it tuned up correctly, it’ll hum along just fine with only occasional inputs of fuel or maintenance.
Ah, that it would be so easy. Unfortunately, there is a short answer to the question, and it’s a disappointing one. The answer is, “It just doesn’t work that way.”
Here’s the short explanation of that short answer:
A prairie with no management at all accumulates thatch from each successive year of plant growth, and if not removed, that thatch eventually builds up to the point at which only a small number of plant species can survive. Unfortunately, the most dominant of those surviving species tend to be either trees/shrubs or invasive plants. In the eastern half of Nebraska, smooth brome tends to be a primary winner, along with tree species such as Siberian elm and eastern red cedar.
Besides the issue of thatch build-up, there are just too many threats, particularly from invasive species and trees, for prairies to maintain their species compositions and ecological functions without human management. This is particularly true with tallgrass prairies in an agricultural matrix. The degree of vulnerability to invasion depends upon soil type and the surrounding landscape. Some soil types seem favor invasives more than others – oftentimes, high soil nitrogen levels can favor exotic grasses, for example. The degree of invasive species pressure on a prairie is also influenced by the abundance and proximity of those invaders in the neighborhood around the prairie . However, all prairies (that I’m aware of) have some degree of vulnerability to invasive species.
That’s the short answer. A longer and better answer is that tallgrass and mixed-grass prairies are not “climax communities” in the classic sense. In my early ecology classes, I learned that terrestrial plant communities move through a process called succession from bare ground to some final stable state – usually a forest. Bare ground is colonized by opportunistic species, which are eventually pushed out by longer-lived grasses and wildflowers. Those grassland species are then replaced by various generations of tree species, each topping out the other until a final set of tall long-lived trees becomes dominant and creates a stable community. Disturbances such as fire or severe weather events might set back succession temporarily, but the process keeps moving toward that climax community.
Prairies don’t fit that successional model very well. Prairies are maintained (and defined?) by disturbances such as fire, grazing, and drought. Without some combination of those ecological processes, prairies turn into woodlands. Because of that, some might argue that prairies are simply an ephemeral stage of the longer successional process, and not really a stable ecosystem. Others might argue that the whole idea of ecological succession is overly simplistic and not representative of the way all ecosystems function.
Without getting into that larger argument, the real point is that if we agree prairies are important, and we want to maintain them, active management is necessary. Some people point to expansive prairies in Great Plains landscapes and wonder if those prairies could maintain themselves without humans if given the chance. After all, lightning-caused fires and roaming herds of bison should be able to take care of things without interference from people, right? In reality, we don’t have any historical precedent to back that up. Today’s prairies have only been around since the last ice age – about 10,000 years (less in the east, more in the west.) During that entire time, people have been active managers of those prairies. Fires set by Native Americans were much more abundant and extensive than lightning-caused fires. Bison herds, and many other herbivores, responded to those fires by focusing grazing in those recently burned areas. That intensive fire/grazing disturbance interacted with and compounded the impacts of long droughts, floods, and other weather-related events. Cumulatively, those major disturbances maintained the integrity of prairies.
There’s really no way (and no reason) to separate people from prairie. Regardless of the intent or motivation of the people who manage prairies – historically or now – their actions have tremendous impacts. Similarly, inaction by people who control prairies has tremendous impacts as well. In the natural resource management world, the phrase “No management is still management” is well-worn but nevertheless true.
Of course, defining the need for continual human management – even in the absence of today’s new challenges such as invasive species – doesn’t solve the problem. What kind of management is needed? How do we know when to do what? The answers to those questions are complex, still being debated, and the primary subject of this blog, my book on prairie management, and myriad discussions among prairie managers around the world.
Some people who agree that prairies require some level of active management still search for a relatively simple management recipe to follow. Annual haying or burning or two to three-year rotations of fire or grazing are examples of management regimes that are commonly used and advocated for. This is really just a small step up from the idea that prairies should maintain themselves. In this case, the argument is that prairies should be able to maintain themselves if we just provide them the right basic disturbance framework.
I’ve given my opinion on simple, repetitive management regimes often within this blog (see my Calendar Prairies post as an example). I think repetitive management threatens plant diversity because there are always some plant species that are favored in a particular management regime and others who are not. Over time, those species not favored will inevitably fade out of the community if the same regime is applied over and over. Perhaps more importantly, animal species – including insects – with fairly specific habitat structure requirements are similarly affected. Some species thrive under repetitive management if that management consistently favors them. However, those animals that don’t find what they need in that management system can’t normally survive for many years in suboptimal habitat like many perennial plants can. Animals without appropriate habitat either move or die – and in fragmented landscapes, or in landscapes where the same management is in place across the entire landscape, moving may not be a viable option.
All of this adds up to one conclusion. Diverse, functioning prairies require active, constant, and thoughtful management by humans. There’s no getting out of that responsibility. If we choose not to be active thoughtful managers, we are choosing to let prairies degrade, and we’ll have to live with the consequences (“No management is still management”). Hopefully, though, most people with influence over the management of prairies will embrace their role, and be active managers – as well as active participants in ongoing discussions about the impacts of various management techniques and systems.
Though active prairie management is time-consuming, and often expensive, it’s also extremely rewarding. Whether it’s a small backyard prairie garden, a 20,000 acre grassland, or something in-between, every year is a chance to try new things, see what happens, and learn from the experience. More importantly, the diversity of plant, insect, and invertebrate species in well-managed prairies – large and small – is its own reward. Who could ask for more than that?
It’s bad enough that invasive species are taking over our prairies and other natural areas. Why do we insist on helping them do it?
When my dad was in high school in the 1960’s, he planted trees and shrubs behind the pond in my grandpa’s pasture as part of a 4H conservation project. The species he planted – Russian olive, eastern red cedar, honeysuckle, and multiflora rose – were all promoted as conservation trees at the time but considered to be invasive species today. The honeysuckle and multiflora rose didn’t make it, but we’ve still got a strong population of Russian olive and cedar trees today, and now that I’m taking over the management of the pasture, I’m making plans to eradicate them. I give my dad a break on this one because it was a long time ago. Unfortunately, less has changed in the last 50 years than you might hope for. (See my earlier post on invasive trees in prairies)
Eastern red cedar trees are native to Nebraska, and so should probably be labeled as “aggressive” rather than “invasive” – though they can certainly take over grasslands, they’re only a problem where fire has been removed from the ecosystem. Russian olives, on the other hand, are clearly invasive species. Many thousands of dollars are being spent trying to remove them from riparian areas around Nebraska and many other states. Why, then, are we still planting Russian olives?? They are still listed and sold as conservation trees in Nebraska, and several agencies have long been providing cost-share dollars and promoting both the planting AND eradication of Russian olive trees (a situation that is just starting to change).
Siberian elm is another species that is being both promoted and controlled. The species was first introduced to the United States in 1860. When Dutch elm disease started wiping out American elms in the 1930’s, Siberian elm gained popularity because it was much less susceptible. It was also promoted as a substitute for privet (another introduced invasive species) in hedge plantings. Today, Siberian elm is widely recognized across the country as an invasive species (it is an official noxious weed in New Mexico) and is one of the most aggressive trees invading prairies in Nebraska and other states. Its abundant wind-dispersed seeds allows it to quickly overwhelm grasslands (and grassland managers) with numerous small saplings. They are common urban trees – but largely reviled because of their brittle branches and unattractive crown shape. Notwithstanding its record, however, this ugly aggressive non-native tree is still being promoted as a conservation tree in Nebraska and elsewhere, and the U.S. Department of Agriculture’s Plant Materials Center in Kansas is actually developing an “improved” cultivar for use in the western Great Plains (see page 82 of this report for details).
Unfortunately, Russian Olive and Siberian elm are only two of many examples of introduced species that are simultaneously viewed as useful and invasive by different constituencies. Nebraska’s newest official noxious weed is Japanese Knotweed, which has numerous hybrids (most of which are invasive) that can still be purchased through garden catalogs. Sericea lespedeza, a horrible invasive plant in the southern prairies (and a noxious weed in Kansas and Colorado) is still promoted as a forage and wildlife plant by Auburn University. In fact, sericea’s status as a “crop” is preventing the development of biocontrol agents that may be the only hope of controlling its spread.
Invasive grasses such as smooth brome, tall fescue, and reed canarygrass are being promoted as forage crops for livestock at the same time that huge amounts of money and effort are being spent to keep them from overrunning prairies. Perhaps most frightening, Monsanto and Scotts have developed strains of Kentucky bluegrass and creeping bentgrass (both invasive grasses in prairies) that are resistant to glyphosate herbicide (aka Roundup) for use in turfgrass applications. The possibility (probability) that those Roundup Ready species will either escape from planted areas or hybridize with naturalized populations is apparently being ignored – in spite of the fact that the bentgrass has already escaped from test plots in Oregon. There are plenty of other examples of introduced ornamental or agricultural plants that we’re assisting with their invasion of natural areas, but the list is too long and depressing to present here.
Why do we have such trouble agreeing whether species are helpful or harmful? A big part of the problem is the diversity of organizations and entities that work to introduce, promote, evaluate, and/or control plant species. There is no single clear controlling entity that can designate species as being invasive or not. Because of that, an internet search is not usually an effective way for a member of the general public to find out whether or not a species is invasive. While there are excellent sites like the USDA’s PLANTS database that list whether the species is considered to be invasive or a noxious weed in any states, a general search for species like sericea lespedeza brings up some websites that promote it as a wonder plant and others that denounce it as a nasty weed. What’s a person to believe? (In this case, it’s a nasty weed…)
To further confuse things, those who continue to promote the use of invasive species often claim that the species aren’t invasive in the habitat type or geographic area they’re promoting them for. I often hear that Russian olive trees are safe to plant as long as you only put them in uplands, and not in lowlands where they become invasive. This argument appears to rely on the assumption that the wildlife species eating the Russian olive’s “wildlife friendly” fruits don’t move between upland and lowland habitats. Considering a species safe in one state when it’s demonstrated to be invasive in a nearby state is equally illogical. True, it can be difficult to predict whether a species will be able to thrive in one area or another without actually testing it, but given the cost of controlling invasive species, why take a chance?
How Do we Fix the Problems?
One part of the solution to these issues is to make the general public more aware of which species are considered to be invasive in their area. Nebraska is currently building a set of lists that will identify known and candidate invasive species, and will rank them by severity and the appropriate response needed (e.g. – prevent their introduction, eradicate current populations, or contain the spread of current populations). It’s surprising that lists such as this are not more widely available across the country, but they’re actually difficult to find. Of course, while lists of invasives are helpful, they only work when they’re used. It’s difficult to imagine many homeowners taking the time to cross check their annual garden catalog wish list against an invasive species list before ordering. Most consumers assume that if they can buy it, it must be safe – something that is far from true – and the conflicting information found on the internet and in other sources only serves to further confuse and frustrate people.
Educating the general public about the value of using native species for both urban and rural plantings – thus avoiding the risk of introducing species that may become invasive- is another important approach. I’m a big fan of using native plants, but I’m also realistic about both the difficulty of marketing natives and some of the complications associated with “native” plants. One of those complications is that it’s very difficult for the public to know which plants are actually native. For example, mixtures of wildflower or wildlife habitat seeds that are commonly sold in Nebraska and other prairie states include both native wildflower species (though often with genetic origins from far away states) and non-native species, some of which are invasive. Invasive species that are often included in wildflower mixes include oxe-eye (shasta) daisy, damesrocket, baby’s breath, bouncing-bet, birdsfoot trefoil, red clover, chicory, common St. Johnswort, Queen Anne’s-lace, sweet clover and many others. It’s not reasonable to expect consumers to be able to determine which species are safe and which aren’t. (What could be dangerous about wildflowers?)
The demand side of the equation (consumers) is an important place for us to focus attention, but the only way we’re really going to solve the problem is by also working on the supply side. Somehow, we have to build consensus and understanding between those who are fighting invasive species (e.g. conservation and agriculture groups and landowners) and those who are introducing and promoting new plants (e.g. some agencies, universities, and nurseries). It’s certainly not going to be a quick or easy process, and it’s not going to solve the problem completely – but the only other option is to continue fighting an ever-growing list of invasive species.
Rather than sniping at each other across fences, we need to build partnerships that bring together nursery organizations and noxious weed control agencies, tree advocates and prairie biologists, and forage specialists and native plant enthusiasts. The initial partnerships don’t have to be (can’t be?) built around the sources of greatest disagreement. For example, nursery owners and noxious weed agents might come together because they both see the need for improved influence over nurseries that purposefully (or neglectfully) sell plants that are clearly illegal to sell – nursery owners might be concerned about reputational risk of the nursery industry as a whole, and noxious weed agents would want to prevent introductions of dangerous plants. More difficult discussions about how to handle the sale of plants that are potentially, but not definitively, invasive can wait. Once a rapport has been established, it’s much easier for both sides to see and appreciate the point of view of the other – and both have a stake in maintaining the relationship by finding ways to compromise. In some cases, it might not be possible to build partnerships right away, but important first steps toward building relationships can include things as simple as inviting each other to attend meetings, join field trips, or give presentations on current and future projects. Anything that gets people into the same space so they can see each other as people rather than adversaries is likely to be productive.
Invasive species are one of the biggest threats to prairies (maybe the biggest) and the issue is much bigger than simply attacking species as they appear. If we can work to prevent the next leafy spurge or sericea lespedeza from being introduced or released in the first place, just about any level of effort would be worthwhile. It’s up to all of us to raise awareness about the risks of introduced species and the benefits of native species. Even more importantly, it’s up to us to work with those who see things differently than we do to establish relationships and common understanding. While it’s tempting to go around with a rolled-up newspaper and whack those who appear to be acting irresponsibly, that’s not likely to be very productive. Maybe we should start by sending them (carefully vetted) flowers instead!