Open Gate Rotational Grazing

An alternative approach to facilitating wildlife and plant diversity in grazed prairie.

Based on the last 20 years of experience and data collection, the shifting mosaic approach to habitat management seems to support plant and animal diversity and foster ecological resilience in our prairies.  One of the most important parts of our shifting mosaic management is that each patch of prairie goes through a progression of season-long intensive grazing, followed by a multi-year recovery period.  At any time, only part of a prairie is in each phase of the system (intensive grazing, early recovery, late recovery), so there is always a variety of habitat structure available (short, “weedy” and tall) for wildlife.  In addition, as that grazing/recovery progression occurs, plant species experience a different set of growing conditions each year.  Regardless of its competition ability or strategy, each plant is ensured favorable conditions for its growth and reproduction at least once every few years.  Based on our long-term data sets, our management has sustained plant species richness, and both conservative and opportunistic plant species are persisting in our prairies.

A fenceline contrast at our family prairie shows the kind of habitat heterogeneity found in a shifting mosaic approach to prairie management.

Patch-burn grazing is one way to create a shifting mosaic, but it’s certainly not the only way.  While patch-burn grazing has some attributes that make it easy to implement (no need for cross fences or moving animals during the season), it does require regular application of prescribed fire, which can be difficult for some landowners.  In addition, patch-burn grazing is very different from the kinds of rotational grazing systems many ranchers are comfortable with and have set up their pastures for.  We’ve been experimenting with an approach to creating a shifting mosaic that keeps many of the wildlife and diversity-friendly attributes of patch-burn grazing but might fit better within the comfort zone and logistical framework of many ranchers.

For lack of a better idea, I’m currently calling this approach “Open Gate Rotational Grazing”.  It is not a rigid prescribed grazing system, but rather a general and adaptable way of managing multiple grazing paddocks within a prairie.  It’s similar to a traditional deferred grazing strategy, but with one big difference.  In most rotational grazing systems, cattle are moved from one pasture to the next, closing the gate behind them to allow the previous paddocks to rest.  In the open gate system, when cattle are presented with their next paddock, the gate behind them remains open – allowing the cattle to continue grazing the initial paddock even as they have access to new grass.

In a traditional rotational grazing system, cattle are progressively moved through a series of paddocks, closing the gate behind them.  In a deferred rotational system, at least one paddock is usually rested for the season.
Under an open gate approach, gates are left open when new paddocks are made available, allowing cattle to graze both the new paddock and the one(s) they had been grazing before.

The idea started one year when we weren’t able to get a burn done in a prairie under patch-burn grazing management.  Since we didn’t have a burned patch to focus cattle grazing, we instead used electric fence to concentrate the cattle in the area we’d hoped to burn.  We kept them in the enclosure until they had it grazed pretty short.  Then we removed the electric fence and allowed cattle to access to the whole site.  For the remainder of the season, the cattle continued to focus most of their grazing in that former enclosure, attracted by the tender regrowth.  As a result, the overall grazing pattern was fairly similar to what we’d expect with patch-burn grazing.  Seeing how strongly cattle were drawn back to where they’d grazed earlier provided the seed for the open gate rotational system.

On my family prairie, I’ve been using the open gate approach for the last several years.  I have four paddocks, and I basically think of the gates between those paddocks as relief valves.  We start with the cattle in one paddock, and when they have grazed most of the grass down in that pasture, I open the gate to an adjacent paddock so they have more options.  The cattle can keep grazing the regrowing plants in paddock #1, but they aren’t forced to eat more than they want to in that paddock because they have another whole paddock available to them.  If the cattle graze down most of the plants in the second paddock, I can open a gate to a third paddock and provide them with even more options.  I keep the fourth paddock closed off for the entire season so it can rest.  I choose a different paddock to start with each year.

The result of an open gate approach is that one paddock is grazed all season long, one is rested all season, and the others have intermediate levels of grazing.  This results in heterogeneity of habitat structure as well as a wide range of growing conditions for plants.  Each year, grazing starts in a different place, shifting the disturbance regimes among the various paddocks.

The open gate approach can be used with just about any rotational grazing system, as long as there are adjacent paddocks that can be opened up.  One key component of the open gate approach is that paddocks grazed early in the season continue to receive grazing pressure for the rest of that season without forcing cattle to eat progressively lower quality forage as the season goes on.  Instead, cattle can regulate their diet freely, choosing between previously grazed areas and those they haven’t yet grazed.  Typically, when cattle are given that kind of choice, they eat very little other than grasses.  This works out well for pollinators because it means many wildflowers are allowed to grow and flower amongst grazed grasses.

At our family prairie, the open gate approach seems to be helping with our continuing quest to increase plant diversity in areas formerly dominated by grasses.  New plants are introduced via overseeding (after a season of intensive grazing), and then persist under our grazing management.

In the open gate system, there is great flexibility about when, and how intensively, each paddock is grazed each year, though some of that flexibility depends on how the paddocks are arranged.  Ideally, all the paddocks would be connected through a single hub so the manager can choose to open any gate to any pasture, as needed.  However, my family prairie doesn’t provide that amount of flexibility (the four paddocks are arrayed in a donut-like loop, with no way to connect them through the donut hole) and the approach still works.  Most of the time, the paddock grazed most intensively one year gets complete rest the next.  However, the pattern of grazing each year always depends upon how I think recovery from previous years’ grazing is going.

I think there are great benefits to longer grazing periods and longer rest periods than are typically found in rotational grazing systems.  Certainly, those prolonged grazing and rest periods can provide a greater variety of wildlife habitat conditions, especially on the shorter and taller ends of the vegetation structure spectrum.  In most rotational grazing systems, cattle are moved out of a pasture before grasses are grazed very short, allowing them to recover quickly.  In addition to reducing habitat heterogeneity, that approach can favor strong grass dominance at the expense of wildflowers and plant diversity.

Even when grazing pressure is intense within each paddock of a traditional rotational system, short duration grazing may not foster habitat heterogeneity.  For example, if a paddock is grazed hard in May, it might suppress cool-season grasses, but warm-season grasses won’t be much affected, and once cattle are removed, summer vegetation will fill in quickly, resulting in vegetation structure of moderate to tall height.  The same can happen with summer grazing bouts followed by fall growth of cool-season grasses.  By maintaining grazing pressure for the entire growing season, two things happen.  First, there is sustained short vegetation structure for wildlife that need it.  Second, and perhaps more important, all dominant grasses are weakened by that long term grazing, leading to a fairly long recovery period (1-3 years, depending upon grazing intensity and geographic location), during which wildflowers and other plant species are temporarily released from that grass competition.  That long recovery period creates terrific wildlife habitat and also helps sustain plant diversity.

While prescribed fire isn’t necessary in open gate rotational grazing, it can certainly be incorporated.  The paddock to be grazed all season could be burned before the season starts, for example, which would further add to its attractiveness to livestock (and remove eastern red cedar trees, excess litter, etc.).  At my own prairie, I haven’t been using fire for a variety of reasons, including that I’m so busy burning for work I don’t have time/energy to burn my own place.  So far, I’ve been happy with the way the prairie is responding in the absence of fire, but if I can get myself better organized, I wouldn’t mind doing some burning.  If nothing else, it would mean less time cutting little cedar trees with loppers.

Prescribed fire is not a strategy all ranchers are willing or able to include in their operations.  The open gate approach provides options for creating a shifting habitat mosaic without relying on regular prescribed fire.

I don’t have many years of experience with this open gate approach, or much data to help me understand all the nuances of its impacts on flora and fauna.  However, what I’ve seen from early experiments seems promising.  I’m sharing the idea and our experiences so far, not because I’m endorsing the open gate approach as the next big thing, but because I hope others might find ways to try it and report back.  Because the basic idea is as simple as not closing a gate when opening a new paddock, it can be employed in many different scenarios if people see potential for it.  Also, I’m not trying to claim or patent the idea, and I’d be shocked if there aren’t people reading this that have already tried it in various forms.  If so, I’d love to hear about it.

A Skeptical Look at Mob Grazing

Mob grazing is attracting a lot of attention lately, especially among people who are fans of other intensive rotational grazing systems.  Usually, mob grazing is an extreme form of rotational grazing, in which high numbers of cattle are grazed in very small areas – for very short periods of time.  Often, cattle are given a new area to graze daily (or more frequently) and formerly grazed areas are allowed to rest for several months or more before being grazed again.  The intensity of grazing in individual paddocks varies by the rancher or grazier running the system.  In some cases, that intensity can be very high.  Proponents list off multiple benefits to the land from mob grazing, including increased soil organic matter, weed control, and “grass health”.

Mob grazing in central Nebraska. Cattle are just being moved from the paddock on the left to the one on the right. These cattle were being moved multiple times per day.

My purpose for this post is not to make any kind of final judgement on mob grazing, but to point out a few things that concern me from a prairie conservation perspective – and perhaps slow down the mob grazing bandwagon just a bit.  Those of you who have followed my blog for any length of time are aware that I’m generally a fan of using grazing as a tool for prairie management.  There is abundant data showing benefits of grazing to wildlife habitat and plant species diversity, both on my own sites and others.  I don’t advocate grazing for all prairies, but I do think prairie managers should look at grazing with an open mind, and consider how it might help them achieve specific objectives.

In the case of mob grazing, however, I’m very concerned about what I’ve seen in my (limited) personal experience, and even more concerned that I’ve been unable to find ANY published research on the topic.  I think there are good reasons to cautious before buying into anything supported only by testimonials, so I’m nervous about how strongly mob grazing is being promoted.  To be clear, I’m approaching this from a prairie conservation perspective, not a graziers perspective, so my thoughts should be taken in that context.

Impacts on Soil Organic Matter

Returning to the purported benefits of mob grazing, let’s look at soil organic matter first.  While there are various explanations of how mob grazing affects organic matter in the soil, the general idea seems to be that mob grazing cattle eat about 60 percent of the standing vegetation and stomp the remaining 40 percent into the soil.  Thus, soil organic matter increases and becomes more productive.  This has never jived with my understanding of soil organic matter (soil carbon) production, so I checked with four prominent scientists around the country who study soil nutrient cycling, including soil carbon.  When I asked them if the claims from mob grazing advocates made sense, their response was unanimous and strikingly blunt.  To quote one of them, “That’s totally bogus”.

In reality, soil organic matter is formed mainly by belowground processes, including root decomposition, root exudates, and mycorrhizal carbon inputs.  In prairies, a substantial percentage of plant roots are abandoned to decompose each year and replaced with new roots.  Those old roots provide organic matter in abundance, and more importantly, that organic matter becomes a stable part of the soil profile – and is added to and enhanced by the other two processes listed above.  My panel of experts said that stomping vegetation into the soil might provide a slight and temporary increase in organic matter near the soil surface, but that it would be unstable and wouldn’t last long.  It’s the stable supply of organic matter deeper in the soil profile that actually drives plant productivity, and that supply comes from plant roots themselves.  In fact, the experts suggested that the kind of vegetation stomping I asked them about was likely to have fairly negative consequences.  They thought that soil compaction and disruption of soil structure as a result from heavy trampling would probably decrease -not increase – plant productivity.  None of this means soil organic matter can’t increase under mob grazing, but any increase would be due to the same belowground processes listed above.

As an aside, I’ve heard some rotational grazing proponents talk about why fire is a bad thing in grasslands because it burns up vegetation that would otherwise be incorporated into the soil – thus, fire decreases organic matter in soil.  This is clearly not the case, and has been thoroughly dismissed by multiple researchers who have shown stable or increasing levels of soil carbon under frequent fire.

Some proponents of mob grazing say that this kind of heavy impact adds organic matter to the soil. Scientists who study soil and organic matter disagree, and suggest it’s likely doing more harm than good.  To be fair, not all mob grazing is this intensive.

Impacts on Weeds

A second purported benefit of mob grazing is weed control.  First, of course, we need to define what a “weed” is.  As has been discussed in this blog before, it’s a very subjective term.  Generally, there are two categories of plants that people consider to be weeds; opportunistic plants that take advantage of weakened dominant plants (e.g. ragweeds, annual grasses, and other short-lived rapidly-reproducing plants), and truly invasive species that are non-native to a particular ecosystem and become dominant to the expense of other species.  Let’s look at each of those two in the context of mob grazing.

If opportunistic plants are the weeds of concern, it seems unlikely that mob grazing would help suppress them.  Mob grazing proponents say that the high grazing intensity makes cattle eat – or stomp – all plants in the paddock, thus removing the weeds that cattle wouldn’t normally eat.  Unfortunately, while that might be true in the short-term, it’s the recovery from that grazing that’s more important.  Opportunistic plants are successful because they can recover from intense disturbances faster than others.  Big strong grasses are the biggest competitors to those “weeds”, and those grasses are greatly weakened by severe defoliation.  Until those grasses and other major perennials recover their dominance of the plant community again, opportunistic plants run rampant.  If the time until the next grazing bout allows those grasses to fully recover their vigor, those opportunistic plants will eventually fade – but only until the next grazing bout.  In other words pulses of intensive grazing will result in flushes in opportunistic plant abundance as well.  I would argue that most opportunistic plant species are non-threatening in any regard, but if suppressing them is an objective, the smart strategy is to strengthen the surrounding plant community.

In this pasture, mob grazing was being used as a tool for controlling musk thistle. The heavy grazing intensity did get the cattle to eat some (but not all) of the thistles. (Continued on next photo)

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Although heavy grazing intensity can get cattle to eat at least some musk thistles, areas like this one that are a couple weeks into the recovery from that grazing tell the real story. The severe weakening of dominant grasses opened up space for opportunistic plants (like these numerous musk thistle rosettes) – and the grazing led to the exact opposite of the desired impact.  Fields of blooming thistles can be seen in the background of this photo where they’ve had sufficient time since grazing to reach maturity.

It is possible to reduce the abundance of opportunistic plants in pasture through periodic moderate grazing.  Mob grazing that moves animals through paddocks quickly enough that the lower leaves of grasses are left ungrazed, could actually stimulate the matrix of grass to thicken, due to increased growth of rhizomes and tillers (stems).  Higher density of grass that chokes out other plants might be seen as beneficial from a grazing standpoint if grass is the only thing the grazier wants – especially in tame grass pastures.  However, from a plant diversity and wildlife habitat standpoint in native praireis (the perspective I’m coming from) it’s certainly not a good thing.

In the case of truly invasive plant species, the story is a little more complicated because every invasive species has its own unique strategy for becoming dominant.  In most cases, the invasive plant has been released from pests and pathogens that suppressed it in its native habitat, and the plant species in the community being invaded have not had time to develop strategies to combat it.  In some cases, concentrating cattle grazing into a relatively small area can lead to the defoliation of an invasive species that would otherwise avoid being grazed.  If that ability to remain ungrazed while surrounding plants are weakened by grazing is the primary way that invasive plant gains dominance, that defoliation could reduce its spread.  However, in most cases, the story is much more complicated, and invasive plants use a more diverse mixture of advantages and strategies to force their way into plant communities.  Weakening the surrounding plant community through something like mob grazing is likely to increase the spread of invasive plants rather than decrease it.  I would use extreme caution when testing mob grazing as a tool for controlling invasive plants.

 

Impacts on “Grass Health”

When I first heard the claim that mob grazing increases grass health, my initial response was, “I didn’t know the grass was sick!”  It’s hard to glean from the various claims what the specific benefits to grass health are, or how that health is defined.  I also have a hard time understanding why mob grazing would provide any benefits to grass plants that other kinds of grazing systems don’t – as long as those other grazing systems include a mixture of grazing and rest periods.  As with all other plants, I think its important that grasses are allowed to flower and produce seed periodically, and mob grazing may do that (depending upon the length of the recovery period) – but many other grazing systems do the same, without some of the potential risks I see from mob grazing.  In some cases, I think grass health refers mostly to soil organic matter, which I addressed earlier.  Until I hear more specifics about how mob grazing affects grass health, I can’t really respond more.

Other Benefits – Livestock and Wildlife

I’m not sure how this system can be good for livestock performance – especially when paddocks are grazed very intensively.  Forcing a cow to eat plants it wouldn’t normally eat seems to override the cow’s effective inherent ability to optimize its own diet.  Why would it benefit a cow to eat plants – or plant parts – that are not the best available choices within a larger pasture?  I have the same concern with some other rotational systems, but this takes it to an extreme.  In order to gain weight, cattle test and refine their forage intake on a daily basis, constantly adjusting what they eat based on the phenology of the plants.  Under extreme mob grazing, cattle have to eat the least palatable plant species and plant parts along with the good stuff.  I don’t understand the logic of that strategy, and, in fact, even some proponents of mob grazing admit some “inconsistency” in livestock weight gains.  The only research project I know of that has started looking at weight gains and other aspects of mob grazing has found very poor livestock performance during its first season (2011).  Again, I’m not saying that cattle can’t gain weight in mob grazing systems, only that I think people should be cautious about accepting that claim.

An additional benefit promoted by mob grazing advocates is that the system increases the carrying capacity of pastures.  This is a tricky claim to evaluate, because it depends upon your definition of carrying capacity.  On the one hand, it’s surely possible to increase the number of cattle in a pasture, and claim that the carrying capacity of the pasture is now higher – though you can do the same with any grazing system.  On the other hand, a more formal range science definition of carrying capacity is “the maximum animal numbers which can graze each year on a given area of grassland for a specific number of days without inducing a downward trend in forage production, forage quality, or soil.”  In other words, carrying capacity isn’t just the number of cows you can put in a pasture, it’s the number of cows that doesn’t degrade that pasture over time.  This latter definition can only be evaluated by long-term data, which doesn’t currently exist for mob grazing systems.

From a wildlife perspective, it’s hard to say what the impacts of mob grazing would be.  Much depends upon the size of the grazing area, the intensity of grazing, and the length of recovery time.  Clearly, very intense grazing that stomps vegetation into the soil will have extremely negative impacts on any nesting birds or invertebrates in that immediate area.  On the other hand, the majority of the site is always in a recovery phase with no active grazing, so there should be a nice diverse mixture of habitat conditions available.  My guess is that mob grazing could be beneficial for many wildlife species – in terms of habitat structure – depending upon how it’s set up.

A bigger issue is that of plant diversity and overall ecological resilience.  While I think that many people overstate the potential negative impact of cattle grazing on “sensitive” prairie plants, including some rare wildflowers, the impacts from mob grazing on those plants could be a legitimate concern.  I think all prairie plants can put up with some degree of defoliation, even when it’s repeated multiple times over a season or two, but I think we would need some careful study of how intensive mob grazing impacts could affect prairie communities before introducing it as a potential management tool.  The potential soil impacts of more extreme versions of mob grazing are particularly concerning.  I’m sure historic prairies were exposed to high concentrations of bison grazing, but I have a very hard time believing that bison stuck around one place and grazed so intensively that they forced themselves to eat substandard forage.  Until I see some well-supported research on the recovery of plant communities, I’m not comfortable exposing native prairies to that kind of severe disturbance.

The Upshot

I’m not against grazing in prairies, and I’m not even against mob grazing per se.  There may be circumstances under which mob grazing, or some variation of it, could be used to achieve certain objectives.  In tame grass pastures, for example, where tilled land has been converted into forage grasses and the sole purpose of the site is to feed cattle, mob grazing might be worth a try.  In those kinds of pastures, the native plant and soil communies have already been severely altered, so out-of-the-box experiments have a relatively low risk of making things worse.  I still don’t buy most of the claims about the purported benefits to livestock, grasses, or soils, but as long as cattle producers test the system with eyes wide open, who am I to say they shouldn’t?

However, in native prairies and rangeland, I think the potential risks of the more extreme versions of mob grazing far outweigh any purported benefits, at least until there is some actual research that says otherwise.  We have abundant evidence that many aspects of native prairie plant and soil communities do not recover well from tillage, and mob grazing impacts can come uncomfortably close to those of tillage, in my opinion.  There are countless other options for using grazing – even intensive grazing – to suppress dominant grasses, control invasive species, create wildlife habitat structure, and achieve other objectives.  I strongly support active experimentation with grazing techniques that could help us with our numerous prairie conservation challenges, but with grazing, as with anything else, it IS possible to have too much of a good thing.

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For those interested, here are two links to relevant research papers on soil carbon (organic matter) and fire/grazing, followed by three non-scientific reports on mob grazing.

Kitchen et al, 2009.  (Effects of fire on mowing on soil carbon and other factors.)

Johnson and Matchett, 2001.  (Effects of fire and grazing on belowground processes)

Glowing review of mob grazing

An even more glowing review of mob grazing

Mixed review of mob grazing