Trusting the Resilience of Prairies

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.

Restored sand prairie at The Nature Conservancy's Platte River Prairies, Nebraska. This prairie
Restored sand prairie at The Nature Conservancy’s Platte River Prairies, Nebraska. This prairie was seeded in 2002 and has been managed with sporadic intensive grazing and fire.

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.

This is a brief summary
This brief summary was part of the 1944 paper referenced above that documented how prairies reacted to the drought years of the 1930’s.  The paper is worth reading if you’re interested in how prairies might respond to droughts in the future.  You can click on the image to make the print larger.

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.

Ragweed
Western ragweed is visually dominant this summer in this part of my family prairie which is recovering from being grazed hard most of last year.  Big bluestem and other grasses are still present, but are weakened from last year’s grazing.  Stiff sunflower and other perennial forb populations are expanding.

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.

Annual plains sunflowers (Helianthus petiolaris) were super abundant throughout the Nebraska Sandhills in 2013, following the severe 2012 drought. I would love to see this kind of prolific blooming of short-lived plants on portions of our Niobrara Valley Preserve each year.
Plains sunflower (Helianthus petiolaris), an annual, was super abundant throughout the Nebraska Sandhills in 2013, following the severe 2012 drought. I would love to see this kind of prolific blooming of short-lived plants on scattered areas of our Niobrara Valley Preserve each year.  We are trying to create that scenario by intensively grazing selected pastures/patches of prairie each season and then letting them recover while others are hit hard.

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.

This 2013 photo shows a restored Platte River Prairie recovering from severe drought, fire, and intensive grazing from the previous year. Grasses are weak, but opportunistic forbs are prolific, including many that provide excellent resources for pollinators and lots of seeds for insects and wildlife.
This 2013 photo shows a restored Platte River Prairie recovering from severe drought, fire, and intensive grazing from the previous year. Grasses are weak, but opportunistic forbs are prolific, including many that provide excellent resources for pollinators and lots of seeds for insects and wildlife.

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.

This fenceline photo from our family prairie was taken in September 2014. The pasture on the left had been grazed hard all season, while the one on the right had been largely rested for more than a year.
This fenceline photo from our family prairie was taken in September 2014. The pasture on the left had been grazed hard all season (the grass is about 2-3 inches tall), while the one on the right had been mostly rested for more than a year.  Besides helping to increase plant diversity, this kind of grazing also creates a variety of habitat conditions across the prairie.
This is the same fenceline as shown above (just slightly uphill). The grasses on the left have recovered from the long intensive grazing in 2014 and are ready to be hit hard again next season. The ragweed on the right is enjoying a good year after that area was grazed intensively for most of 2015.
This is the same fenceline as shown above (just slightly uphill) as it looked in mid-August of 2016. The grasses on the left have recovered from the long intensive grazing in 2014 and are ready to be hit hard again next season. The ragweed on the right is enjoying a good year while the competing grasses are recovering from being grazed intensively for most of 2015

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.

This is one of our restored prairies at the end of August of this year. The grasses were grazed hard all season, and eventually went dormant during a hot dry spell. Many of the forbs were also grazed, but not all of them. This site will likely be very weedy looking next year.
This is one of our restored Platte River Prairies at the end of August of this year. The grasses were grazed hard all season, and eventually went dormant during a hot dry spell. Many of the forbs were also grazed, but not all of them. This part of the site will likely be very weedy looking next year.
This is the same restored prairie as shown above, but the photo was taken several years ago during a year it wasn't being grazed. It will look like this again in a few years.
This is the same restored prairie as shown above, but the photo was taken several years ago during a year it wasn’t being grazed. It will look like this again in a few years.

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.

So…who’s with me?

Patch-Burn Grazing in Missouri Prairies

If you read this blog frequently, you know I manage many of our prairies with combinations of prescribed fire and grazing.  I like the heterogeneous habitat structure I get from patch-burn grazing, and have documented benefits to plant diversity in our prairies.  (I’ve summarized the experiences I’ve had with multiple variations of patch-burn grazing here.)

Patch-burn grazing with cattle is still viewed with skepticism by many people – especially some in eastern tallgrass prairies.  I can understand why people would be concerned about the potential impacts of cattle grazing on some plant species and prairie communities, and I certainly don’t advocate cattle grazing for all prairies.  However, I also think that many common concerns stem from limited experience with cattle grazing.  If the only cattle grazing I’d ever seen was the kind that annually beat grasslands down to the ground and resulted in soil erosion and a gradual loss of native plant diversity I’d be skeptical too – to say the least! 

When you see a prairie like this, it's easy to see how prairie enthusiasts could be nervous about cattle grazing. This Nebraska prairie has never been plowed, but it's missing many prairie plant species - though that is likely due more to past herbicide practices than cattle grazing.

However, chronic overgrazing is one extreme in a broad spectrum of grazing regimes, and cattle can also be used in ways that produce very positive results for plant diversity and wildlife habitat.  The first time I saw a prairie being stomped and chomped by lots of cattle it was pretty unsettling.  However, watching that prairie recover the next year after cattle had been removed gave me a much greater respect for prairies than I’d had before.  Over the last 20 years, I’ve seen that process over and over in many tallgrass and mixed-grass prairies, and the resilience of prairie plants never ceases to amaze me.  Of course, I’ve also seen instances where repeated overgrazing has degraded prairie communities, but that degradation has usually come from not giving plants sufficient opportunity to rest and recover from grazing bouts – not from grazing per se.  (And often because of a history of broadcast herbicide use as well.)

Most of my personal experience with grazing (and patch-burn grazing in particular) has come from mixed-grass and lowland tallgrass prairies in east-central Nebraska.  I’ve also seen a lot of grazing on western tallgrass prairies in Kansas and Oklahoma.  However, my experience with cattle grazing in eastern tallgrass prairies is much more limited – mostly because it is such a rarity.  This summer has given me two chances to observe the impacts of patch-burn grazing on eastern prairies in Indiana and Missouri.  I wrote briefly about the Indiana experience in a previous post, but I want to spend more time on what I saw in Missouri last week.

The Missouri Department of Conservation (MDC) began a research project on the use of patch-burn grazing on public lands prairies back in 2005.  One of their hopes was to increase the habitat quality of those grasslands for prairie chickens and many other grassland species without hurting the diversity or quality of the plant communities.  Many of the prairies they grazed during the project were considered to be some of the higher-quality prairies in Missouri (botanically speaking) so protecting the diversity of those plant communities – and the rare and conservative plant species in them – was extremely important.  Several people, including me, with prior experience using patch-burn grazing provided input to MDC as they designed the project.  During the summer of 2007, I finally got the chance to see some of the grazed prairies during the third year of the research project.  One of those prairies was Taberville Prairie, north of Eldorado Springs.

The burned patch of Taberville Prairie in 2007 (part of the MDC's patch-burn grazing research project). The grazing was pretty intensive in the burned patch, with only a few plant species remaining ungrazed. Even I was a little unsettled by the way the prairie looked. (Sorry about the photo quality, the tour was during the middle of a bright sunny day...)

I remember being a little shocked as I walked around Taberville Prairie back in September 2007, because the cattle had grazed it much harder than I’d expected to see.  The most recently burned patches of the prairie were nearly universally cropped close to the ground, with only a few plant species remaining lightly grazed or ungrazed.  That was pretty different from my own sites, where our relatively light stocking rates lead cattle to graze pretty selectively in burned areas, leaving many forb species ungrazed – even many that are typically considered to be favorites of cattle.  At Taberville, even unburned portions of the prairie showed evidence of moderate grazing, and it was difficult to find conservative plant species such as compass plant, purple coneflower, blazing star, and leadplant.  What I was seeing at Taberville made me wonder whether MDC had pushed the prairie a little further than was prudent.  Of course, the plan was to rest the prairie for several years following the three years of patch-burn grazing, so logic and experience told me this was something the prairie could easily recover from – but even so, I’ll admit it was a little disturbing to see.

This photo shows the patch that was burned in 2006 (the year before the photo was taken). Though grazed less intensively than the 2007 burn patch, there are still few conservative plants visible.

Since my 2007 trip there has been considerable discussion (to put it mildly) among prairie enthusiasts and biologists in Missouri about the impacts of cattle grazing in those prairies where patch-burn grazing was tested, especially on conservative plant species.  I can easily understand why people were concerned – especially after my own experience at Taberville.  I was anxious to see for myself how the prairies had recovered, so I was glad to accept an invitation from MDC to participate in a grassland ecology workshop last week.  The day before the workshop started, I got a tour from Len Gilmore and Matt Hill of MDC, and made my return to Taberville prairie.

MDC's Len Gilmore manages Taberville Prairie. In this photo, he's showing me the kind of vegetation structure favored by nesting prairie chickens. This is a portion of the prairie currently open to cattle - but is not the most recently burned patch.

We started the tour in a portion of Taberville than had not been included in the grazing back in 2005-2007, but that was currently in year three of a patch-burn grazing rotation.  Len, who manages Taberville Prairie, showed me the kinds of habitat structure they’re trying to create with patch-burn grazing, including nesting habitat for prairie chickens.  We also discussed other aspects of patch-burn grazing MDC is concerned about (and testing) – including potential impacts to headwater streams, most of which are currently fenced out.  The overall look of the prairies under patch-burn grazing this year was similar to those I saw in 2007.  This time, however, I looked harder for conservative plants, and was able to find them in the patches that weren’t the most recently burned.  Most weren’t blooming, but they were certainly alive and well.

This is the most recently-burned patch in the current grazing area at Taberville Prairie. The grazing was obviously very intense (the cattle had been removed the week before my visit).

What I really wanted to see, however, were the portions of the prairie I’d seen in 2007 that had been rested (with one burn) since I’d last seen them.  When we arrived, I think I let out an audible sigh of relief.  The prairie looked great.  Even in what was a very dry summer, the prairie looked like my visual image of Missouri tallgrass prairie.  Lots of showy blazing star flowers and abundant conservative plants, including leadplant, compass plant, purple coneflower, rattlesnake master, and others.  Len took me to several locations where they had built grazing exclosures during the original patch-burn grazing research project.  The exclosures had allowed MDC researchers to compare the ungrazed plant community inside the exclosures to adjacent plots that were exposed to cattle grazing.  Even without seeing the data, being able to walk through and compare those areas that had never been grazed with those that had been exposed to three years of patch-burn grazing (the exclosures had been removed but their locations were still marked) was a powerful testament to prairie resilience.  I looked hard for differences, but the truth is, if Len hadn’t told me which areas had been the grazed areas and which had been the exclosures, I never would have known. 

This is the portion of Taberville prairie shown in my 2007 photo above when there was almost nothing taller than a couple inches. Several years of rest (and a fire) following the three years of patch-burn grazing changed the look of the prairie considerably. Even in a summer during which the prairie had almost no rain in June or July, the plant community looks tall and vibrant.

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The same portion of Taberville Prairie. Compass plant, and many other conservative plant species were abundant.

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Another photo from the same portion of Taberville Prairie (grazed 2005-2007, but rested since then.) Eastern gamagrass (the thick leafy grass with tall stems) was abundant and full of vigor across the prairie. In the burned/grazed patches of Taberville and other MDC prairies gamagrass was being grazed extremely hard - even to the point where I could see rhizomes the cattle had pulled out of the ground. Clearly, gamagrass recovers well from that kind of treatment...

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A final photo from the area grazed 2005-2007 but rested (and burned once) since. This photo shows leadplant in the foreground. Rattlesnake master and purple coneflower (two other conservative plants) were also abundant, but not shown in these photos.

During the next several days at the grassland workshop, I listened to MDC biologists from wildlife and fisheries divisions talk about what they like and don’t like about their experiences so far with patch-burn grazing.  One of the interesting issues they (and I) are wrestling with has to do with the appropriate length of grazing and rest periods.  Figuring out how to mix grazing and rest periods in a way that allows all plant and animal species to “win” periodically is a major challenge.  There was also considerable discussion about how to better evaluate potential impacts to plant communities and streams – as well as exploration of ideas about how to modify current management to better address needs of pollinators, amphibians, and other species.  I think those who are worried about patch-burn grazing in Missouri would have been comforted to hear the thoughtful discussion and see the obvious dedication of MDC staff to the prairies in their charge. 

This bush katydid was one of many insects I saw at Taberville Prairie. I don't think this species is necessarily rare or conservative, but the regal fritillary and Henslow's sparrow I saw nearby are (not that seeing one of each necessarily determines success...)

There are still plenty of important questions about whether, where, and how cattle grazing should be used to manage eastern tallgrass prairies, but the Missouri Department of Conservation is leading the effort to answer some of those.  Early results show improvements in habitat structure for many species of insects and animals, including greater prairie chickens – where they occur.  MDC has asked faculty from two universities to help evaluate impacts on streams, and is fencing out the majority of headwater streams until that evaluation is complete.   The responses of plant species and communities to various fire, grazing, and rest treatments is still being evaluated, and probably will be for some time.  In the meantime, it was good to see confirmation of the ability of plants to bounce back from periodic grazing, even in prairies that are pretty different from the ones I know best.  I think the knowledge that plants (even conservative species) don’t immediately die from being grazed for a season or two gives us a little cushion as we forge ahead with our attempts to find appropriate tools and strategies for maintain the broad array of biological diversity in what remains of tallgrass prairie.  If you live and/or work in the tallgrass prairie region, I hope you’ll be a productive part of that effort.  We need all the help we can get.