Grazing, especially by goats and/or sheep, is often promoted as a control method for weeds or shrubs. Depending upon the life strategy of the weeds being targeted, grazing can be effective, but it’s important to set realistic objectives. As you might expect, many perennial grasses, forbs, and shrubs have evolved strategies for surviving repeated defoliation. In those cases, grazing may appear to effectively control plants while grazers are present, but the plants bounce back right after grazers are removed.
One of my all-time favorite research projects showcases this exact phenomenon at a site in South Dakota owned by The Nature Conservancy. Back in the early 1990’s, an estimated 75% of the Conservancy’s Altamont Prairie Preserve was covered by leafy spurge (Euphorbia esula). In 1994, goats and sheep were installed in separate pastures and spurge was treated by using periodic high-intensity grazing sessions during both early summer and early fall. Both the goats and sheep were very effective at eating the spurge plants, and after five years, managers conducting walk-through inspections the site felt like excellent long-term control of spurge had been achieved. Inside small exclosures, spurge was still abundant and vigorous, but outside the exclosures, almost no plants could be seen. As a result, the goats and sheep were removed and everyone was happy.
…Until the next season when spurge plants popped right back out of the ground and the pasture looked essentially as it had before the grazing treatment had started. In dismay, the managers looked for another option and decided upon flea beetles (Apthona spp.), which ended up being a much more successful choice, greatly reducing the footprint of leafy spurge over the next several years.
You’d be excused for thinking the use of sheep and goats was a total waste of effort, but additional data collected at Altamont Prairie adds some interesting nuance. As it happens, mean Floristic Quality (a kind of qualified plant diversity metric) stayed relatively stable within the grazed area during the five years sheep and goats were present. During the same time period, mean Floristic Quality decreased significantly in exclosures. In other words, while grazing didn’t eliminate the spurge problem, it may have stabilized some of its negative impacts for a while.
This, to me, is one of the best attributes of many grazing-for-weed-control efforts. Even if grazing can’t eradicate many weeds/shrubs from a prairie, it might be a strategy that prevents further spread (eliminating flowers and reducing vigor for belowground reproduction) and/or reduces the weed’s ability to compete with desirable plants. In a large site where more effective long-term strategies (such as selective herbicide application or biocontrol releases) aren’t feasible across the whole area, using grazing as a suppression tactic in some areas of the site while you kill it in others can make a lot of sense. In other words, grazing might buy you time to work on a problem that would otherwise seem overwhelming in scope. (However, it’s also important to remember that grazers will also be eating and suppressing the vigor and reproduction of desirable species with similar growth strategies to the invader you’re targeting. If you do succeed in reducing populations of invaders, you might also reduce populations of those desirable plants.)
Grazing can sometimes provide effective control of short-lived plants if it prevents flowering and seed production and forces plants to die without reproducing. Just remember that more seeds are likely waiting in the soil, so it will likely take repeated grazing treatments to reach your goal. Here in Nebraska, we often use short-term intensive grazing as a tool to knock back the competitive ability of perennial cool-season grasses such as smooth brome (Bromus inermis) or Kentucky bluegrass (Poa pratensis). We don’t expect the grazing to kill those grass plants (and it doesn’t) but we can allow other plants a chance to flourish for a few years until the invasive grasses regain their vigor. By repeating the treatment periodically, we can maintain a more diverse plant community.
Personally, I’ve never used goats or sheep to help with a management challenge. In contrast with cattle, goats and sheep, feed preferentially on forbs, and I’m usually trying to suppress grasses and encourage forb growth. However, I do think goats, sheep, and cattle can all play important roles in controlling invasives as long as you don’t expect them to do more than they can. I worry that landowners and land managers can sometimes end up paying an exorbitant price to someone that brings animals in with the promise of weed control. It’s important to remember that if you do that, you’re providing food for that contractor’s animals, and that should be factored into whatever price one of you pays the other. When we use cattle for prairie management, the cattle owner always pays us. That seems not to be the case with many goat grazing operations. I’m not saying it’s wrong to pay someone to graze their goats on your land, I’m just saying it’s important to fully process what each party is getting from the transaction. That includes the forage provided to the animals from your land, the time and expenses incurred by the owner of the animals, and – importantly – the actual effectiveness of the treatment.
As long as you have clear objectives and a good understanding of the plant(s) you’re targeting, grazing may be a great tool for invasive species control. Just remember one of the biggest lessons from the South Dakota spurge experiment: just because you can’t see the invasive plant anymore doesn’t mean it’s gone!
Note to my son (and others who mainly follow this blog to see if there are cool pictures or pictures of them): This is a pretty long and involved post – sorry. The first picture is probably the best one, though there are a couple other decent prairie photos further down (though none with you in them). The other pictures are more instructional than aesthetically pleasing. Don’t worry, I’ll put up some better photos later this week.
Great Plains grasslands are more resilient than most of us give them credit for. Just recently, for example, they survived the drought of 2012, the worst single year drought on record in many places (including at our Platte River Prairies). In a post I wrote during 2012, I compared that drought to similar conditions described by famous prairie ecologist J.E. Weaver back in the 1934. In both cases, prairies recovered nicely. In fact, in a 1944 paper, Weaver and collaborator Frederick Alberts provided a detailed summary of how prairies in Iowa, Nebraska, and east-central Kansas persevered and recovered from repeated drought conditions between 1933 and 1943.
Nebraska prairies have also shown resilience to intensive fire and grazing – historically by bison and currently by cattle. Chronic overgrazing, of course, can decrease plant diversity and cause cascading negative impacts on prairie animals and critical ecological processes. However, most prairies can easily withstand periodic bouts of intensive grazing followed by comparable rest periods. We’ve been tracking plant community responses to this kind of fire/cattle grazing management in our Platte River Prairies since 2002 and have seen plant diversity remain stable. Even grazing-sensitive plants such as rosinweed (Silphium integrifolium), Canada milkvetch (Astragalus canadensis), prairie clovers (Dalea sp.) and others have maintained their populations. Likewise, at our Niobrara Valley Preserve in the Nebraska Sandhills, prairies managed with more than 25 years of periodic fire and intensive bison grazing are still healthy, diverse, and full of wildlife.
Since coming to dominance in the Great Plains after the last ice age, prairies have survived and thrived through long droughts (some lasting multiple decades), severe fires, and intensive grazing episodes. Yes, we’ve managed to destroy and degrade many prairies through tillage, herbicide use, and chronic overgrazing, but those are departures from the kinds of stresses prairies have evolved with over time. The more time I spend in Nebraska prairies, the more important I think it is to run prairies through their paces now and then. That includes beating them up with periodic intensive grazing.
Not only can prairies rebound from droughts and intensive grazing, some aspects of prairies seem to depend upon those patterns of disturbance and recovery. As we’ve experimented with variations of patch-burn grazing over the years, I’ve observed a consistent response pattern from plant communities. We burn a patch of prairie, let cattle or bison graze it hard all season and then provide a different burn patch for the grazers the following year. In the year following fire and grazing, prairie patches get a weedy look to them because dominant grasses are weakened by the previous year’s grazing and there is open space for new plants to establish. Often, I see an increase of roughly 25-30% in the number of plant species found at the 1 m2 scale in the year after grazing.
Many of the plants that fill spaces left by weakened grasses are opportunistic (‘weedy’) species that grow, bloom, and produce copious amounts of seed within a year or two – and most of those plants disappear within a year or two as grasses reassert their dominance. In addition to those short-lived plants, however, I also see expansion of long-lived perennial plant populations that are taking advantage of weakened competition. Prairie clovers, leadplant, perennial sunflowers, and many others spread via both rhizome and seed during those periods when grasses are weakened. What I don’t see is the death or disappearance of plants following intensive grazing bouts that last a year or two. Even plants – both grasses and forbs – that are cropped close to the ground and kept that way by repeated grazing regain their vigor within a few years of rest.
Prairie animals also seem to benefit when prairies go through periods of severe stress and recovery. For example, many of the plant species that flourish following intensive grazing (and/or severe drought) are very attractive plants for pollinators. Annual sunflowers, hoary vervain (Verbena stricta), black-eyed Susans (Rudbeckia hirta), and biennial primroses (Oenothera sp.) are just a few examples. The prolific seed production by those opportunistic plants also provides a bonanza of food for insects and wildlife species.
Animals also benefit from habitat structure created by patterns of intensive grazing and recovery. Because every animal has its own individual habitat preferences, the highest diversity of animals are found in prairies with patches of intensively grazed vegetation, patches of recovering vegetation, and patches of tall/thatchy vegetation. Mobile animals can move to their favorite habitat structure and less mobile animals need only wait a few years for conditions that allow them to prosper.
Vegetation recovering from intensive grazing can provide particularly unique and valuable habitat. Habitat structure consisting of short, weakened grasses and tall ‘weedy’ forbs provides wonderful brood-rearing habitat for birds such as grouse, quail, and pheasants, for example. The low density of grass leaves and litter at ground level makes it easy for young birds (and other wildlife) to move around and feed beneath a canopy of protective cover. Coincidentally, insect abundance also skyrockets under those same conditions, which is good for insects and also for the wildlife that eats them.
What are we afraid of?
I’m more and more convinced of the importance of putting prairies through periods of stress and recovery, especially when those stresses are applied in a way that provides a shifting mosaic of stressed, recovering, and full strength vegetation patches across a prairie. No matter how hard we have grazed prairies, even during severe and extended drought periods, the plant communities have always bounced back during the recovery periods that follow. In addition, my own observations and data collected by many researchers have documented benefits to wildlife and invertebrates that come from the variety of habitats provided by this kind of management. (You can read more about patch-burn grazing here and the way I manage my family prairie here.)
While I’m confident that it’s valuable to beat prairies up now and then, I’m having a hard time convincing others to try it. Both ranchers and public land managers tend to have strong visceral reactions when I walk them through patches of really intensively grazed prairie. Ranchers are often convinced that I’ve killed the grasses and created weed and erosion problems that will never go away. Conservation area managers worry about potential weed invasions too, and some also wonder if sensitive wildflowers will survive the stress. Many of those land managers also flinch at the lack of habitat structure for wildlife species they care about.
Walking tour participants from an intensively grazed patch into a nearby area of recovering vegetation doesn’t usually help things. Ranchers tend to see the flush of opportunistic plants as validation of their fears about dead grass and weed problems, even when I next show them patches where the grasses have regained dominance after a few years of rest. Some wildlife managers recognize the value of the weedy vegetation as habitat, but worry about the perceptions of neighbors and the public who just see weeds, not habitat. Others see the weedy vegetation as a sign that the plant community has been degraded, despite the fact that the plant species they like better haven’t gone away.
To be clear, I’m not suggesting that all prairies would benefit from the kind of periodic intensive grazing I’m talking about here. Some prairies, for example, are simply too small and isolated. There are big logistical challenges associated with fencing and providing livestock water in small prairies. More importantly, there just isn’t space to graze some portions of small prairies while leaving other areas to rest and recover. (Small prairies have a number of other challenges that make any kind of management difficult. If you’re interested, I tried to address some of those in a blog post several years ago.)
I also have a number of lingering questions about how best to apply intensive grazing and recovery periods to prairies. For example, I strongly suspect that the best results come from intensive grazing bouts that last between a couple months and a full growing season. Grazing for only days or weeks doesn’t seem to stress the grasses as much as longer periods of repeated grazing on those plants. In addition, different grass species grow strongly at different times of year. Because of that, grazing for a short time can just shift dominance from the grasses growing strongly during the grazing bout to species that peak in their growth after grazers leave. Since my objective is to really weaken the entire grass community, I don’t think short grazing periods will do the job – but I’d like to test that more.
I’d also love to see more data on the responses of various vertebrate and invertebrate populations to intensive grazing, recovery periods, and the overall mix of habitat provided by the kind of management I think is important. There is strong research showing benefits to small mammal and bird communities, and some information on invertebrates, but only some of them. Learning more about the response of reptiles and a wider selection of invertebrates to this kind of grazing management would be really helpful.
In the meantime, however, I’m going to keep beating up my prairies. Not only do I think they can take it, I think the prairie communities I work with thrive best under that kind of management. (I will keep an eye on what happens, however, constantly vigilant for signs that I’ve gone a little too far.) I’ll also keep trying to convince others to stop babying their prairies so much. I’m hoping I can find a few ranchers willing to push pastures a little harder than they usually do – allowing longer rest periods to compensate, of course. That shouldn’t require changing stocking rates, but might provide some really nice benefits for pollinators and wildlife species. I know I’m going to continue to face skepticism from many corners, but I really think this concept needs to be explored further. Prairies have shown their resilience over thousands of years. I think we can trust that kind of track record.
This is one of my favorite times of year. It’s not the cool temperatures, the fall colors, or even the fall migrations of birds and insects coming through. Instead, I like this time of year because it’s time to figure out how this year’s prairie management worked and start planning for next year. Closing that adaptive management loop (gleaning lessons from one field season and applying them to the next) is really fulfilling for me. I get to learn something and then put it right to use. The only downside is waiting another year to see how things turn out again!
Earlier this week, I walked through our family prairie and tried to capture the results of 2015. I wasn’t collecting data. Instead, I took a few photos, wrote a few notes, and looked back at some photos and notes from earlier in the season. I mainly tried to measure what I saw against the basic habitat objectives we have for our prairie.
Helzer Prairie Habitat Objectives
1) HABITAT HETEROGENEITY. Provide patches of habitat that cover the spectrum from short/sparse to tall/dense vegetation, with areas of mixed-height structure in between.
2) PLANT DIVERSITY. Increase plant diversity over time by allowing all plant species a chance to bloom and reproduce every few years, and periodically suppressing grass dominance to allow wildflowers a chance to maintain or expand their “territories”.
In general, I was pretty happy with what I saw this week. There was definitely a wide range of habitat structure across the prairie. We began the season by grazing most of the prairie pretty hard to knock back the vigor of smooth brome. After that, we put the cattle into about 1/4 of the prairie for the month of June and then gradually gave them access to more of the prairie as the season progressed until they were grazing about 3/4 of the site by September.
The grasses in the 1/4 of the prairie we grazed in June stayed short all season, and many of the wildflowers were also cropped off. However, some of those wildflowers had a chance to grow back as we spread the cattle out across a larger area and they became more selective about what they ate. Other plants went ungrazed, or only lightly grazed, all season. As a result, the habitat structure was a mixture of short grasses and medium to tall forbs. In July, I found a family of upland sandpipers feeding in that part of the prairie – their still-flightless chick searched for insects in the short grass while staying near the protective cover of the taller forbs.
Elsewhere in the prairie, the height and density of the vegetation varied by how much grazing pressure it received. Areas that were rested much of the year were dominated by tall warm-season grasses, while areas grazed from July through September had much shorter vegetation. Despite the fact that we’re still trying to boost plant diversity across the site (which consists of small prairie remnants surrounded by former cropland planted to grasses by my grandfather in the early 1960’s) there were good numbers of wildflowers blooming through the whole season. In the more intensively-grazed portions, only a few species such as hoary vervain (Verbena stricta), ironweed (Vernonia baldwinii), goldenrods (Solidago sp.), native thistles (Cirsium sp.), and other species panned by cattle were flowering. However, there were many other wildflowers blooming across the rest of the site, including purple prairie clover (Dalea purpurea), leadplant (Amorpha canescens), stiff sunflower (Helianthus pauciflorus), several milkweed species (Asclepias sp.), and many others. The most abundant wildflowers were found in the portions of the prairie the cattle had grazed intensively in 2014 – grass vigor was still suppressed in those areas, allowing both “weedy” and “non-weedy” forbs to flourish.
During 2015, just about any animal species should have been able to find what they needed in our 100 acre prairie. Regal fritillaries had violets for their caterpillars and monarch butterflies had milkweed for theirs – and both found abundant nectar plants, including in the most intensively-grazed areas. The varied vegetation structure supported a wide range of grassland nesting birds, including grasshopper sparrows, upland sandpipers, western meadowlarks, northern bobwhites, dickcissels, sedge wrens, and others. Small mammal trails were abundant, as were burrows of the badgers and coyotes that hunt those mice, voles, and ground squirrels. Best of all, there were myriad bees, grasshoppers, katydids, prairie cicadas, spiders, and countless other invertebrates doing their jobs to support and nourish the plant and wildlife communities.
I haven’t yet worked out all the details of next year’s management plans, but I know a few things. The portions of the prairie that were grazed hardest this year will be rested for most or all of next season. We’ll likely bump the cattle stocking rate up a little because of this year’s abundant rainfall and strong grass growth. I’ll try to make sure cattle have early summer access to the areas where I saw lots of first-year sweet clover plants this year – grazing those areas will greatly reduce flowering and seed production. Finally, I’m thinking about letting the cattle stomp around for a week or two in one of the wet areas they’re normally excluded from because the vegetation is getting excessively thick there.
I’ll meet with my grazing lessee (the guy who owns the cattle) in late fall or early winter. Between now and then, I’ll likely change my mind several times about some of my plans and come up with some new ones. Next season we’ll make adjustments on the fly as we see what happens with rainfall, grazing behavior, invasive species, and all the other factors that influence management decisions. Then, about this time next year, I’ll be walking around the prairie, trying to interpret the results of all those ideas and adjustments.
One difference between using cattle grazing and other grassland management options like fire or mowing is that cattle have brains. They can decide where they want to go (within our fences) and what they want to eat, and their behavior isn’t always completely predictable. For example, while we know that cattle will spend more time grazing in the burned patch of a prairie than in unburned areas, it’s always interesting to see what plants they decide to graze on or avoid, and how that changes day to day and season to season. Overall, their unpredictability is a positive for our management because we build it into our plans.
Another interesting facet of cattle behavior is their interaction with us when we’re out in the field. Cattle are often curious and come to investigate what we’re up to – probably because they’re hoping we have something fun to eat with us. I did some plant community monitoring this week and the cattle in that prairie tagged along for a while.
They ignored me all morning, but when I stopped to eat my peanut butter sandwich, the cattle happened to be coming to get water nearby, so they checked up on me. When I finished my lunch and started walking transects again, they followed along just to make sure I wasn’t doing anything that concerned them. (I wasn’t.)
Eventually, they apparently got bored (or hungry) and wandered off, leaving me to work alone. By myself.
I got the chance to spend a couple days in Iowa last week, talking about conservation grazing with staff of the Iowa Department of Natural Resources. They invited me to join a two day workshop discussing various ways to use grazing for conservation objectives. My main role was to kick off the meeting by providing various examples of objectives that can be addressed through grazing. Beyond that, I was asked to participate in the remainder of the workshop and contribute thoughts and ideas as appropriate. I am grateful to have had the opportunity to participate, and came away with a better appreciation for the challenges faced by Iowa prairie managers.
I thought I’d share some of what I covered in my presentation. Essentially, I focused on two broad categories of prairie management objectives that can be addressed through cattle grazing. Those are:
Reducing grass dominance to increase plant diversity
Increasing heterogeneity of habitat
Reducing Grass Dominance
Dominant grass species can sometimes suppress prairie plant diversity by monopolizing soil and light resources. Two categories of prairies seem particularly vulnerable to this: 1) prairies that have been degraded by chronic overgrazing or broadcast herbicide use, and 2) restored (reconstructed) prairies. In Nebraska and Iowa, dominant grasses can include non-native invasive species such as smooth brome (Bromus inermis), Kentucky bluegrass (Poapratensis), tall fescue (Schedonorusarundinaceus), and reed canarygrass (Phalarisarundinacea), as well as native species such as big bluestem (Andropogon gerardii).
When attempting to reduce the dominance of these grasses, it’s important to be clear about what you’re trying to accomplish. If the ultimate goal is to increase plant diversity, it’s not enough to just suppress the vigor of grasses. In order to be successful, a variety of other plant species have to colonize territory abandoned by that weakened grass. A late-spring prescribed fire can temporarily suppress the growth and vigor of smooth brome or Kentucky bluegrass, but often results in robust growth of big bluestem later that season. Trading a dominant invasive grass for an aggressive native grass may not be success if wildflower diversity remains low.
Grazing can play an important role in increasing plant diversity by repeatedly defoliating major grass species that limit plant diversity. The timing, stocking rate, and frequency of grazing can all be adjusted based on the grass species and objectives at a particular site. As an example, we sometimes combine an early spring prescribed fire with intensive grazing (through about June 1) to suppress cool-season invasive grasses such as smooth brome and Kentucky bluegrass. If big bluestem is abundant in the same place, we’ll leave cattle in for much of the summer as well, but at a lower stocking rate. The strategy is to suppress both the invasive cool-season grasses and the native warm-season big bluestem while allowing other plants to thrive and expand their footprint.
At low stocking rates, cattle tend to keep big bluestem closely cropped, but don’t target most wildflower species. We usually see an abundance of new plants growing in and amongst the weakened brome, bluegrass, and bluestem during the year of grazing and the following year. Those new plants include both short-lived “opportunistic” plants and longer-lived perennial plants. The result is a bump in plant diversity. If we repeat the same kind of treatment every few years, we can often maintain a richer plant community than we can with other management options such as fire or mowing alone.
There are countless ways to employ cattle grazing to weaken dominant plants and stimulate higher plant diversity. I’ve written about other examples previously. You can find a couple of those here and here.
Increasing Habitat Heterogeneity
Cattle grazing can create habitat structure that other management options such as fire and mowing can’t. As they work to meet their nutritional needs, cattle graze some plant species (mostly their favorite grasses) preferentially. Stocking rate, or the intensity of grazing, correlates with grazing selectivity. At low stocking rates, cattle are free to eat only what they really want, resulting in closely cropped patches of grass interspersed with taller clumps of less palatable grasses and wildflowers. When stocking rates are higher, cattle are forced to eat a wider range of plant species, creating a more uniformly short vegetation structure. Both the “lower-stocking-rate-patchy-habitat” and “higher-stocking-rate-uniformly-short-habitat” can be valuable to wildlife and invertebrate species.
The ideal situation is to provide the widest possible range of habitat types within a prairie, or within a series of adjacent or connected prairies. That way, regardless of their habitat needs, most wildlife and invertebrate species will be able to find a place to live. Changing the location of each of those various habitat types from year to year helps keep any species (plant or animal) from becoming so abundant that it impacts other species to the point of reducing diversity.
Because of the unique vegetation structure created by grazing, a wider range of habitat types can be created with grazing than with either fire or mowing. However, it’s also very important to ensure that grazing doesn’t have a detrimental impact on plant diversity in the name of creating wildlife habitat. Significant periods of rest from grazing and careful monitoring of grazing impacts and populations of sensitive plant species are important. If conservation is the primary goal, grazing should be used only when there are specific objectives to meet, not as a default strategy.
I’ve written much more on the topic of creating heterogeneous habitat with grazing in previous posts as well, and you can find a couple examples here and here.
Setting Useful Objectives – And Then Using Them
Regardless of the management tool(s) being employed, the biggest challenge for a prairie manager is to set clear objectives and then follow up on them. Start by defining the outcome you want (different habitat structure, more plant diversity, etc.) and then describe precisely what success looks like. Monitoring doesn’t have to mean spending hours on your knees with a plot frame, it just means measuring the outcome you desired.
For example, if you want more habitat diversity, you could start by listing the types of habitat structure you want (tall/dense, short sparse, patchy forbs with short grass, etc.) and how much of the prairie you’d like to be in each category. Then, you could make a rough map of how the site looks before the treatment and estimate percentages of each habitat type. After your grazing, fire, or mowing treatment, make another map and see if you reached your objective.
If plant diversity is important, decide how you will measure that. This is where a plot frame and repeated sampling across a prairie can be helpful, but there are simpler ways as well. You could pick out 3-5 small areas (less than 10 square meters) that you can find each year and then annually list the plant species you find in each area to see if that number changes over time. You don’t have to identify all the species, just list how many there are. If you are using grazing, it’s also important to figure out which plant species are favorites of the cattle and use that information to ensure that your management allows those plants enough rest from grazing that they can bloom and make seed every few years.
Most importantly, your objectives should drive the adjustments you make to management from day to day and season to season. If you can define what you want, you can see if your management is moving you in the right direction. It’s fine to change objectives as you learn, or as conditions change. In fact, in our Platte River Prairies, while we have some broad objectives (plant and habitat diversity), we set new specific objectives and management strategies each year to respond to what we’re seeing on the ground.
Cattle grazing is just another tool that can be used for the conservation of prairies. It’s not appropriate for all prairies or situations, but can help meet some objectives in ways that other tools (fire, mowing, herbicides) can’t. Conservation grazing differs from ranching in that income doesn’t have to be a major part of the decision-making process each year. On land where conservation is the primary objective, managers can decide when and how to employ grazing (or not) based purely on the conservation challenges they face.
Thanks again to the Iowa Department of Natural Resources for inviting me to their conservation grazing discussion last week. I was impressed by the thoughtfulness and creativity of the staff I met, and I look forward to hearing more about their prairie management and restoration work down the road.
Here are two photos that caught my attention as I was going through timelapse imagery the other day…
In my last post, I showed some timelapse photos from a fenceline at The Nature Conservancy’s Niobrara Valley Preserve in north-central Nebraska. At the time, I promised a good story about the trail that developed on the cattle side (right side) of the fence. As a reminder, the fence in these photos was installed in what had been a cattle pasture, but the left side is now grazed by bison (light stocking rate) and the right side is grazed by cattle (moderate stocking rate). More details on the stocking rates below…
The first photo in which cattle appear in their pasture is this one, taken on June 21 at 6:36 pm.
Notice the absence of a cattle trail in this first photo. Then look at the photo below, which was taken ONE HOUR LATER.
Seriously? A trail formed the very first time cattle walked along the fenceline??
I’m not surprised or bothered by the development of the trail, but I’m relatively shocked that it only took one pass by cattle to make it! I would have expected the gradual development of a path over a few weeks. On the other hand there were 110 cows and 110 calves in the pasture. Rich Walters, Niobrara Valley Preserve manager, pointed out that if all those cattle followed the fence line in single file formation, that was 880 hooves stepping on those relatively loose sandy soils. I suppose that would have an immediate impact.
Here’s one more surprise. The cattle were brought into this pasture on June 2. Why did it take until June 21 for them to (apparently) make their way to the north edge to graze and then create a trail? I can’t say for sure that they hadn’t explored this part of the pasture prior to the 21st, but there isn’t any indication of grazing impact in the timelapse photos taken between June 2 and June 21. It may be that the cattle had enough forage further south (and closer to their water tank) that they just never wandered very far, but I would have expected them to have made an exploratory pass around the pasture within the first few days – just to see what they had to work with…
Before I go further, I’m sure some people are already mentally condemning cattle for their trail-making and other faults, but that’s not the point I’m making here. As I wrote in a recent post, I think cattle are very useful as prairie management tools, and are comparable to bison in most respects – though the formation of these narrow trails is certainly one difference between the two animals. Sure, cattle trails can cause problems, especially in chronically overgrazed sites with steep slopes and erodible soils, but the vegetation beneath cattle trails can also recover pretty quickly if given the chance. In the meantime, trails can provide valuable habitat for reptiles and invertebrates looking for a place to warm up in the morning sun, and are used as transportation corridors by many other animals besides cattle.
Oh, and in case you doubted me, the photo below proves that there truly were bison on the left side of the fence in 2013, though their numbers and the relative size of their pasture to the cattle pasture on the right created a very different grazing environment.
The two sides of the fence looked pretty different from each other by the time cattle were removed, in terms of vegetation height and density. After my last post, several of you asked about the stocking rates on each side. There were approximately 225 bison (cows, calves, and bulls) in the 10,000 acre bison pasture to the left of this fence in 2013. They were grazing year round, but had plenty of room to roam since the Preserve staff had cut back their numbers pretty drastically following the big wildfire in 2012. At that stocking rate, bison didn’t graze very intensively in most parts of the pasture, including the area shown in this photo. On the cattle side of the fence, the 110 cow/calf pairs were restricted to only 640 acres of pasture. Even though they were only in the pasture for about 5 weeks (June 2 – July 12), that’s still a much higher effective stocking rate than that in the bison pasture. The difference in the height of vegetation between the left and right sides of the fence, then, is due to stocking rate, not grazer species.
I’m already learning an awful lot from looking at the first year of timelapse imagery at the Niobrara Valley Preserve, and much of what I’m learning has been unexpected. The rapid formation of a cattle trail is a great example. I’ll be sharing another example within the next week or two, though it’s more of a mystery than a lesson at this point. For now, I’ll just tease that post by saying it has to do with a stick that moves by itself… You can have fun thinking about that for a while!
Among some prairie enthusiasts, there seems to be a perception that plains bison are magical creatures that live in complete harmony with the prairie. They eat grasses but not wildflowers, they float just above the ground to avoid stepping on plants or compacting the soil, and they create tidy little wallows that fill with rainwater for tadpoles and wading birds. Cattle, on the other hand, are evil creatures that seek and destroy wildflowers, removing them from prairies forever. They also stomp all over prairies, trampling plants and birds to death and causing cascades of soil erosion and water pollution.
Let me be clear: I’m a big fan of bison. I feel very fortunate to spend time at The Nature Conservancy’s Niobrara Valley Preserve and other big prairies where I can observe and photograph bison up close. Bison are distinctive, attractive animals that evoke a sense of history and grandeur… but they are also big stompy animals that go wherever they want, poop all over the place, rub on trees, trample plants (and animals), and can cause erosion issues. None of that is good or bad; it just is.
I’m a fan of cattle too. They have big beautiful eyes, individual personalities, and can be more playful than their typically stoic faces might hint at. I enjoy spending time around cattle at our Platte River Prairies and in my own family prairie. In both places, they are a major part of our prairie management strategy, which is aimed at creating and maintaining diverse plant communities and high quality wildlife habitat. (And yes, cattle are also big stompy animals that go wherever they want, poop all over, rub on trees, trample plants and animals, and cause erosion issues.)
TREES AND PONDS
While both bison and cattle can be engaging creatures, there are a few real differences between the way bison and cattle utilize and impact prairies. However, those differences are less stark than you might think. Based on the best available research and expert knowledge, the biggest distinction between bison and cattle behavior in prairies essentially boils down to this: cattle hang around water and trees more than bison do.
That general pattern is reported in many studies comparing the two, but was most reliably demonstrated in a recent study at The Nature Conservancy’s Tallgrass Prairie Preserve in Oklahoma, where GPS collars tracked animal locations through time. That study looked at bison and cattle at similar stocking rates and under the same management regime (patch-burn grazing) – though the bison were grazing year-round in a 23,000 acre pasture while cattle were only present for 7 months/year in pastures of around 1000-2000 acres. The GPS collars showed that cattle were attracted to ponds and trees while bison tended to avoid areas near water and showed no attraction to trees. Importantly, the same study also showed strong similarities between bison and cattle behavior, namely that both were strongly attracted to the most recently burned areas of pastures and tended to avoid steep slopes.
The conclusion that cattle are attracted to water and shade fits with one of the big objections to cattle grazing by some prairie enthusiasts – that cattle tend to “wreck” areas near ponds and tree groves by repeatedly stomping around and defecating in those places. While that can be true, those impacts are highest under high stocking rates, and can be avoided by fencing out ponds and trees or greatly reduced by providing long rest periods between grazing bouts. Those impacts are also less severe in larger pastures, especially when multiple water and shade options are available and cattle are encouraged (or forced) to use each area intermittently. The attraction of cattle to wet and shaded areas can be a real challenge, but it’s not an insurmountable one.
The other beef prairie enthusiasts have with cattle (sorry) has to do with their diet. The perception of many is that bison subsist solely on grass, leaving wildflowers untouched, while cattle eat a high percentage of forbs (broad-leaved plants), often leading to the decline of those species over time. The purported result is that bison-grazed prairies maintain high plant diversity, including an abundance of rare plant species, while cattle-grazed prairies become degraded as numerous forb species are grazed out of existence. While that’s a big overgeneralization, it’s an understandable one because a number of research projects have reached that conclusion.
Unfortunately, those research projects have largely compared bison and cattle under very different circumstances. Diet comparisons are usually made between bison in a single huge pasture (often under patch-burn grazing management) and cattle in a rotational grazing system – often at a higher stocking rate. As a result, it’s not clear whether observed differences between bison and cattle diets are due to biological differences or grazing systems.
Imagine if you were given 30 days’ worth of groceries at the beginning of each month. You’d likely eat many of your favorite foods first and then make do with whatever’s left toward the end of the month. Comparing your diet to that of someone who was allowed to go grocery shopping every day would be completely unfair, wouldn’t it? Unfortunately, that’s essentially the comparison made by many research projects comparing the diets of cattle and bison. Cattle in a rotational grazing system can only choose from the available plants in their particular paddock, and don’t get a new set of choices until they are moved into a new paddock. In contrast, cattle or bison that spend their whole season in a large pasture, especially one in which a portion has been recently burned, can regulate their diet much more freely. They spend most of their time eating their favorite foods (mostly grasses) in the most recently burned patch, but they can also travel elsewhere if the supply in that patch runs low. In addition, by regrazing their favorite plants over and over, livestock can keep them in a state of high nutritional value for much of the season.
We did some research back in 2001 in which we evaluated the forage choices of cattle in a patch-burn grazing system under a moderate stocking rate (Helzer and Steuter 2005). Our data showed that those cattle were very selective toward grasses, and ate very few forbs under those conditions. That research, along with observations other scientists and cattle managers at patch-burn grazed sites, has led to an altered perception of the forage selection differences between cattle and bison – namely, that many of the differences are driven more by grazing system than by biology.
Prairie managers have to make difficult decisions about how to create and maintain diverse plant and animal communities at their sites. One big choice is whether to graze or not to graze a particular prairie. Regardless of whether it is grazed by bison or cattle, a grazed prairie is going to look and act very differently than an ungrazed prairie. Many plants will be stepped on and eaten. Some portions of the prairie will be more heavily visited than others and will get trampled down. Short-lived opportunistic plants will become more abundant, due to the weakening of dominant grasses through repeated grazing. Some managers will see those effects as positive, but others will not – depending upon the management needs of a particular prairie. Regardless, deciding whether or not to graze has far greater consequences than the subsequent decision about whether to graze with bison or cattle.
If the decision to graze has been made, it’s important to recognize the appropriate criteria for deciding between bison and cattle. Bison do act somewhat differently than cattle, especially around water and trees. However, those differences depend heavily on scale. Both cattle and bison create areas of bare soil around drinking water sources, and both create trails as they move from one favorite place to another. In small pastures, those impacts are multiplied because both bison and cattle are forced to visit the same places repeatedly, which can lead to repeated trampling of plants, soil compaction, and other issues. The differences between a small bison-grazed pasture and a small cattle-grazed pasture are pretty minimal.
In larger pastures (thousands of acres in size), grazing animals have room to spread out. At that scale, bison-grazed pastures tend to have fewer heavily grazed and trampled areas near trees and standing water than cattle pastures do. While that can certainly be a perk of using bison, it’s also important to remember that even in large cattle-grazed pastures, the proportion of the overall pasture that receives that kind of heavy impact is very small. In addition, there are management options that can be used to minimize the size and severity of those impacts by cattle. Those include fenced exclosures around sensitive areas and tactics that shift the locations where cattle spend most of their time (such as creating new burned patches, turning on/off drinking water facilities, and moving mineral feeders around). The upshot is that there can be some prairie conservation benefits of using bison. However, those benefits accrue most strongly in very large pastures, and even at that scale, there are cattle management strategies that can close that gap considerably. On the flip side, bison come with their own set of complications and costs.
I spend most of my time working at our Platte River Prairies, and I’m often asked why we don’t have bison at those sites. There are several good reasons for that, starting with management flexibility. The cattle that graze our Platte River Prairies belong to our neighbors, and our lease arrangements allow us to dictate how many, where, and for how long cattle graze each year. Between years, or even within years, we can pretty easily change those plans if we get unexpected weather patterns or just don’t like the way things look. That kind of adaptive management is much more difficult with bison, especially because if we had bison, we’d have to own the herd and keep them on our prairies year round.
A second reason we use cattle is financial. It takes a much lower investment in infrastructure and personnel to lease cattle than to own bison. We have to provide a good perimeter fence (usually a four-wire barbed wire fence) to hold cattle in our pasture, and provide water for them to drink. Beyond that, the owner of the cattle trucks them in when we ask for them, and then gathers and trucks them away again when we’re done. If we owned a bison herd, we would need a much stouter, and more expensive fence, and a very expensive corral system to use for an annual roundup, sorting, and inoculation process. In addition, we would be responsible for conducting that roundup, doctoring animals when if needed, and for dealing with buying/selling animals to maintain our desired herd size. All of that takes time and people, and that’s expensive. At our Niobrara Valley Preserve, the 22,000 acres of bison pasture can hold enough bison that income from selling excess animals covers many of those costs. That wouldn’t pencil out in our much smaller prairies down on the Platte River.
The last reason we run cattle instead of bison is that in our relatively small prairies (200-600 acres), the behavior of bison would not be very different than that of cattle. We might see less stomping around in standing water and under trees, but we can already manage those impacts by controlling whether/how often cattle have access to those areas. Most importantly, through our use of patch-burn grazing, electric fence enclosures and exclosures, and our ability to set and change grazing intensity, timing, and frequency, we are getting the prairie management impacts we want by using cattle. We can get cattle to graze very selectively in order to suppress grasses and give wildflowers a chance to flourish, and to create the kind of patchy habitat structure many wildlife and insect species need to thrive. In other cases, we can get them to graze much less selectively in order to create a particular habitat structure or other impact. As a result, we are maintaining resilient and diverse prairies – and that is our ultimate goal.
Plains bison nearly disappeared completely from the grasslands of North America as European settlement spread across the continent. The ongoing recovery of bison is an important indicator of prairie conservation success, and I hope that upward trend continues. At the same time, I worry about the tendency of some to heap accolades upon bison while dismissing cattle as inherently destructive. The differences between them simply don’t warrant that kind of broad categorization. If grassland conservation is our goal, we should be sure we’re open to using whatever strategies (or animals) can help achieve that. In very large prairies, bison may be the best fit – assuming the logistics and costs of owning bison make sense. In other situations, however, deciding whether bison or cattle are most appropriate is not a simple matter. It’s a decision that should be based on facts and management objectives – not on aesthetics or mythology.
Much of what determines the outcome of prairie management treatments is out of our control. Sure, we can decide when to burn a prairie or set the timing and stocking rate for grazing treatments, but cascades of interactions between countless factors such as weather, insect population cycles, and many others can easily overwhelm any decisions we make. Over the holiday season, I found time to analyze some plant community data for one of our Platte River Prairies. The results provide a thought-provoking look at the unpredictable ways prairies respond to management.
The following data are from a prairie that was managed with variant of patch-burn grazing, in which a different portion of the prairie was burned each year (in the spring) and cattle had access to both burned and unburned portions of the prairie during most of the growing season. As typically happens, cattle grazed the most recently burned patch pretty heavily and lightly grazed the remainder of the pasture. Details about the fire and grazing treatments can be found at the end of this post.
If you look at the two graphs below, you can see that there was a significant increase in the average number of plant species (species richness) per square meter between 2012 and 2013 in the portion of prairie that was burned in 2012. There was no significant change in species density in the unburned areas of the prairie – which were also grazed, but much less intensively. Data were collected during June in both years.
We see this pattern of higher species richness after fire/grazing treatments over and over in our prairies. My explanation of the phenomenon is two-fold, and was covered in more detail in a previous post. First, the burn exposes soil (and seeds) to light, allowing relatively high germination rates of seeds waiting for an opportunity. Second, the concentrated heavy grazing in those burned areas weakens the dominant grasses, prolonging the light exposure of the soil/seeds and also reducing the root masses of those grazed grasses, thereby opening up space belowground for new plants to gain a foothold. Those new plants start both from seed germination and from the rhizomes and buds of existing perennial plants.
The color-coded table below shows some species-level data from the same site that help explain the above graphs. The numbers indicate the frequency of occurrence (the percentage of sample plots each species was found in) each year. Some plant species appear to have responded positively or negatively to the burn and subsequent grazing intensity, while others seem unaffected by those management treatments.
So far, so easy. Fire and grazing are having positive effects on the vigor and occurrence of some species, negative effects on others, and no effect on still others. Cumulatively, the effects add up to an increase in the number of plant species per square meter in the year following the burn. Simple and clean. The next two graphs (below) seem to fit the same pattern, showing similar increases in small-scale species richness in burned patches back in 2007 and 2008, respectively.
Here’s where it gets interesting… The next table (below) shows how individual plant species responded within the three burn patches (2007, 2008, and 2012) between the year of the burn and the subsequent year. Of the 29 most abundant species, only THREE showed the same response to fire/grazing in each of the three years, and another two were consistent in that they didn’t appear to respond at all to management in any of the three years. The remaining 24 species were inconsistent in their responses – some wildly so. Look, for example at indiangrass (Sorghastrum nutans), rough dropseed – aka tall dropseed – (Sporobolus compositus), and blue prairie violet (Viola pratincola, aka Viola sororia). Each of those three species showed a strong increase in frequency of occurrence in the burn patch one year, but a strong decrease in another.
So what are we to make of all this? How can we manage prairies effectively if the impacts of very similar management treatments are so different from year to year?
As far as the first question, it’s clear that other variables – particularly weather – interact strongly with management treatments to influence the response of plant species. Every species has a different optimum range of temperature and moisture conditions, so the timing and intensity of rains and warm/cool spells affects the competitive balance between species differently each season. Many other factors and interactions are also in play. Year-to-year changes in population size of various seed-eating species can influence the seed bank, for example. In addition, the success of a particular plant species in one year catalyzes or suppresses other species (plant, insect, mammal, etc.) in the following year. All of those interactions are signs of healthy prairies, but make it very difficult to predict how those prairies will respond to our management.
As to the question of how we’re supposed to manage prairies in light of all this variability, there are at least two ways to respond. The first is to throw our hands up in disgust because we can’t seem to predict results well enough to make useful decisions. The second option is to relax, embrace the variability, and roll with it.
Our human nature makes us want (need?) control over our environment. In agriculture, landscape architecture, engineering and many other fields, the objective is to manipulate the world to our benefit – often by reducing the variables and controlling the remaining ones. However, when managing ecosystems in order to conserve the diversity of species and their functional roles, that approach simply doesn’t fit. Instead,we need to think differently about both short-term objectives and long-term goals.
To help me deal with unpredictability, I tend to consider prairie management objectives in terms of ecological resilience, rather than in terms of desired responses from particular species. (See this earlier post on ecological resilience for background.) I think of a prairie as a ball in a bowl. The bowl represents a range of conditions, within which the prairie (the ball) maintains its integrity as a prairie – even if it rolls around quite a bit. Some disturbances, such as plowing or broadcast herbicide can quickly push a prairie out of its bowl and into another state, from which it is tremendously difficult to recover. Other disturbances, such as drought, tree encroachment, or intensive grazing may push the ball toward the edge, but as long as those disturbances don’t continue for too many years in a row, the ball doesn’t leave the bowl.
My management objective is not to prevent the metaphorical ball from moving, or to push it toward some optimal part of the bowl. Rather, I have two big objectives:
1.) Make sure the ball can move freely around the bowl in response to disturbances, but nudge it back from the edge when necessary. I celebrate the fact that our Platte River Prairies change in appearance from year to year. That tells me they are rolling around that bowl as they need to do. In order to prevent an exit from the bowl, I make sure that we’re suppressing tree encroachment before a prairie becomes a woodland, and that we’re avoiding the kind of chronic intensive grazing that can push some prairie species to local extinction. During extended droughts, we modify our management to avoid imposing too much additional stress on prairie communities.
2.) Keep the bowl as large as possible by maintaining a high diversity of prairie species, along with the functional roles each contributes. That diversity of function allows the prairie to absorb stress and respond to adversity without leaving the bowl. Maintaining that diversity means manipulating the field of competition between prairie species so that every species can win now and then (by reproducing) and maintain itself within the community. We create an annual patchwork of various fire, grazing and rest treatments and shift the location of those patches from year to year to provide for the needs of as many plant and animal species as possible.
Prairies are dynamic, and thank goodness for that. Their ability to flex and respond to various stresses is a key characteristic that has allowed them to survive for thousands of years. As prairie managers, we need to facilitate that flexibility instead of becoming frustrated with our inability to predict how prairies will respond to our management. After all, our job is to keep prairies healthy, not turn them into something they’re not just to help ourselves feel more in control.
For those of you who might be interested, here is some additional information about the management treatments applied to the prairie in the above example. The pasture the burns were conducted in is often grazed in conjunction with adjacent prairies, so the total grazed area varies in size from year to year. In each year, the overall management was patch-burn grazing, in which cattle had access to the entire grazing area, but did most of their grazing in the most recently burned patch. The stocking rate shown (AUMs/ac) is calculated for the entire pasture and entire season.
2007 Burn (North 1/2 burned on Apr 16, South 1/2 on May 2)
240 acres grazed overall in 2007. 27 pairs from 4/1 – 10/31 (Approx. 1 AUMs/ac)
2008 Burn (Burned on March 18)
171 acres grazed overall in 2008. 27 pairs from 4/1-5/20, 15 pairs till 9/15 (Approx. 0.7 AUMs/ac)
2012 Burn (Burned on March 30)
300 acres grazed overall in 2012. 75 pairs 4/20-Jun 1, 50 pairs till 10/1 (Approx. 1.3 AUMs/ac)
Guest Post by Eliza Perry, one of our Hubbard Fellows. All photos are by Eliza.
Anne and I have been spending a lot of time with bison over the last four weeks, something neither of us ever thought we’d do. First, we went four hours northwest to TNC’s Niobrara Valley Preserve, our largest property in the state and home to two herds of bison. We were there to help with the roundup of the east bison herd. I didn’t grow up around livestock, so this event was really thrilling for me. Because they are herd animals, bison can get very aggressive just by being separated from the pack, leading to a lot of banging and even some blood. Corrals are designed to safely and efficiently move livestock to minimize their stress. The hope is that the less time they spend inside the corral, the less stressed and agitated they will become and the fewer injuries they will sustain. We didn’t know how to help at first, but soon got the hang of closing the heavy iron gates at just the right moment to allow a manageable number of animals to clamor through the corral system at one time. We must have done okay because we were invited back to a second round up.
Next we drove four hours northeast to visit TNC’s Broken Kettle Grasslands Preserve, Iowa’s largest contiguous prairie, to see how another preserve operates and lend a hand for a few days. Emily Hohman, the preserve’s land steward, showed us around and taught us to winterize fire equipment, which will be important at home after we finish our fall burns. Emily is in charge of stewardship for all of western Iowa, including the management of Broken Kettle’s bison herd. We discussed the challenges of managing large preserves with limited staff in a primarily production-oriented setting, circumstances that we at Platte River Prairies are very familiar with. We also got to whip around in the loess hills on six-wheelers while herding cattle.
On our way back from Iowa we stopped by the Niobrara Valley Preserve again for a board meeting, this time without seeing any bison. But the next week we were back to round up the west herd for a few more days. We got to use the newer corral system, which has several hydraulically controlled gates for an even safer and more efficient sorting process. Because we had already learned the ropes (no pun intended) at the last roundup, Anne and I were able to jump right in.
The evening before the board meeting at the Niobrara Valley Preserve, the staff and trustees met up in the nearby town of Ainsworth for some dinner and socializing, which meant I got to drive through the Nebraska sandhills at sunset. My camera can’t capture how epic this landscape looked at this time of day. It’s nothing like any other place I’ve ever seen.
A guest post by Eliza Perry, one of our Hubbard Fellows. All photos are by Eliza.
Giant black clouds of birds have been erupting from cottonwoods everywhere I go the past few days.
As Anne recently shared, the cows have been taken away from our prairies for the winter and, somewhat surprisingly, their absence has really been felt around here. They were quiet company, but extremely entertaining at times, creeping toward me while I picked seeds until I lurched suddenly just to watch them bolt in the other direction. Before long, they’d crept back even closer to me, and we went on like this for many hours.
I have a quick story to share that I captured driving around on the last afternoon the cows were here, though the story is as much about birds as our dear
cows. I saw a large flock of birds along a fenceline and pulled over to the side of the road to get a better look at them. The cow-bird interaction I witnessed was, or seemed to be, quite playful. And funny.
I know starlings are invasive, outcompeting other species like bluebirds and woodpeckers, and cowbirds have a nesting parasitism habit, but the huge flocks these creatures form are a wondrous sight. I was picking rosinweed one morning when things were going any way but mine (I thought I broke two backpack sprayers in a span of two hours), and a gigantic murmuration passed right over me for about ten minutes, with no end in sight. Just a long, chirping highway. This event, along with my renewed awareness of the quiet, scenic solitude where I work, lifted my spirits and ended my morning funk.
The prairie has a knack for doing that to me – and I imagine it does so for everyone else reading this – so I think I’ll be all right without my cow companions.