A Savanna Life in a Technological World

Serengeti Grazing Lessons Part IV

Serengeti Grazing Lessons Part IV

It is Newton’s laws that have changed history more than the ideas of any other person. At least, that’s what I ‘m going to say this week. I might say something different next week. No one seems to argue with me so maybe next week I will say that it was Jon Bon Jovi’s ideas that changed history most. Anyway, a hundred years after they were published Newton’s ideas created a handful of mechanical innovations that would go on to dramatically change the course of history and influence every moment of our lives. Wouldn’t all you ecological engineers like a similar set of rules? Well, the good news is that such a set of rules exists. The bad news is that no one knows what they are. They are just wondering around on the Serengeti and no one has cared enough to go find them. Until we have a systematic understanding of how grazing ecosystems work, all I can do is try to peek through the keyhole.

But first, there is another rule that I follow obediently (though reluctantly), which is to tell you about what happened here on the ranch this week. We had our first significant rain of the wet season on Friday. We’ve had 3/4 of an inch since the first of May, but we don’t expect rain at all in the summer. That’s just how life goes. No big whoop.

We irrigate, but its flood irrigation and it doesn’t get to the higher spots. There is still plenty of green grass, though due to our cool summers, abundant fog, and deep soil. Our soil goes down about four hundred feet, though no one is sure exactly how deep. I spent Friday in the rain walking around with Hazel-and-Ava-the-pups. We were lazily pushing the cattle off of the Eastside and onto 30 acres on the other side of the road. I have all the fences pulled out, ready to do a big fence project, so they have had the run of the place for… I guess about a month. That is pretty embarrassing as it breaks all the rules I have lived by. But that’s just how life goes. No big whoop.

Though I am not sure that a month-long grazing period is perfect, I am surprised at how good it looks. In contrast, the pasture I moved them onto has been resting for six weeks. Some of it is fantastic, but other places are pretty tall, even if it’s only eight inches high. That is tall enough for it to have developed a stem. I think this is what the smart people call an ‘elevated meristem.’ Smart people, chime in if I am right or wrong. Whatever it’s called, the cattle will not eat the stem and the grass will probably not regrow from that stem. If it does, it will only barely grow and the cattle will not eat that regrowth, the little pom poms on poles. This is one of the more important points of grass biology and I don’t hear it come up when gurus talk about grass. So consider yourself warned; thick stems will cause you to lose grass production, lose animal performance, and lose big chunks of your life. Newton it is not, but it’s a new rule to live by. No big whoop.

Speaking of rules and stems, when the herds out on the Serengeti plain start to run out of grass at the end of the wet season, they move north to the central part of the park. There the ground starts to roll and dip and sprout a few trees. This area has a little higher rainfall and the grasses are mid-height. The quintessential grass of the area, Themeda triandra, looks just like little bluestem from a distance. In the wet season, these areas receive very little grazing pressure, as the animals prefer the more nutritious, drier range out on the plains, as any rancher would guess. So these grasses are pretty mature. Herds hit this mature forage like a wall and it causes all sorts of distortions in herd shape. There is lots of grass to get through and it sits in their guts like a tractor battery. Besides, no wildebeest is anxious to be the first animal to push into this grass, which is lion- colored and approximately lion-height. So they play an elaborate game of, “You go first. No, you go first.” This game causes the wildebeest to form bands, shoulder-to-shoulder. It’s like when you keep the poly wire in a break fence but just move all the posts three feet forward. The cattle all line up on the new grass like they are eating from a bunk. Except these lines stretch for many miles, every wildebeest or zebra taking a step in rigid formation, eating what it can reach from that position, before taking the next step. In this way, they literally eat their way through these mid-grass regions.  

This is mob grazing before mob grazing was cool and it is hardcore mob grazing. When I saw this on the Serengeti, it looked like this was the highest animal density possible for a couple of minutes. The ground behind the herds was practically free of grazers, in fact, it was free of most everything with all that stomping and trampling. This created an easy avenue of escape when the herds faced an attack and provided a stress release valve that most of our mob grazing herds lack.

So there is plenty of evidence for an analog to mob grazing in the Serengeti. And the way people are, those who want to mob graze will take this post as evidence that they are right and have been all along, just like people who want to continuous graze will take next weeks blog post as evidence of the same. And that’s the beauty of ranching; the only one you have to fool is yourself. Indeed, in these regions of the park, this is practically the only form of grazing that occurs. However, over most of the park, this sort of density never happens. I repeat my plea for a Serengeti study that gives us managers practical information about density and recovery time over all of the ecosystem. But since the whole year’s grazing happens over the course of a few minutes in this part of the ecosystem, here it is easy to be sure; they’re pretty darn dense.

There is also, of course, the little detail that this ‘management’ creates the lowest production over the whole ecosystem. All of the plot’s that showed no positive impact from grazing occurred with this sort of grazing. When you think about it, this should not be that surprising. Remember, the average grazed plot in McNaughton’s study was twice as productive as the average ungrazed plot. McNaughton’s exclosures were one-year exclosures. If the herds don’t graze the mid-grass sections of the ecosystem until after the growing season, they are, for all practical purposes, exclosed. Why would production be any different?

Maybe there is a strand inside of the eco-grazing community and within us eco-grazers that is suspicious of grazing. I suspect that a big part of the impetus behind the sort of ‘mob grazing’ that you are hearing more and more about is a simple idea. If we minimize the effect of grazing, if we let the grass look more like the nature preserve next door than we will create a more natural kind of grazing. That’s a good idea, but it has a flawed assumption at its heart. We are assuming that because the nature preserve next door has the word ‘nature’ in its name, it is natural. If you think about it, in order for this sort of mob grazing to pan out, McNaughton would have had to find that his exclosures produced way more grass than the grazed plots. He would have had to have found that grazing reduced productivity.

The Serengeti shows us that natural grazing is not about reducing the impact of grazing animals on grass. I hate to say it, but this is another way of saying that in a certain way, our neighbors were right.

At this point, McNaughton does an interesting thing. He measures available soil moisture on all the plots. I think many of the people who ‘mob graze’ assume that it conserves water, the logic being since bare ground dries out soil, the more cover there is, the less dry it will be. If the grass were 65 feet high it wouldn’t have to rain for a decade. As you might guess, I am about to burst that bubble.

We should have seen this coming really. If you look at hydrologic tables, four-foot high grass transpires an enormous amount of water, way more than six-inch high grass, due to a vastly expanded surface area. This is the same principal as a chem fallow, where every other year you don’t plant wheat but nuke it with roundup so nothing grows there. This prevents water from transpiring through plants and next year there is enough moisture to grow a crop. This is the sort of example I was talking about last week. Look at what your neighbors do, practices that actually work, and don’t pretend they don’t work. But meld that with the things we are learning about grazing ecosystems. So, on the Serengeti, Grasses that were maintained at a short (but not too short) height during the growing season preserved their water through the wet season and into the dry season far better than tall grass. In fact, by the end of the wet season, the tall grass areas had pretty well reached the hydroscopic minimum, which I am guessing is the point where the plants can’t pry any more water off the soil particles. Smart people? McNaughton ascribes much of the added productivity of grazed plots to this moisture preserving potential.

McNaughton says that it is swards with both the tallest grass and the shortest grass that has the lowest “Rainfall use efficiency,” which is basically like Ranching for Profit’s ADAs/inch of rainfall. McNaughton says that when the grass is very tall it transpires a lot of water and when it is very short, exposing bare ground, it loses a lot to surface evaporation. Funny enough the guy who owns the cattle that I run came up on the fourth of July and made practically the same comment when he looked at our dense pasture and felt how much moisture was still in the soil compared to where he lived. Which Serengeti plots had (by far) the highest rainfall use efficiency according to McNaughton? Grazing lawns.

But! (the ecograzer says) tallgrass has deeper roots. Well, McNaughton looked at that too. He reported that there was no difference in root biomass between tall and short vegetation. This would be interesting but he doesn’t explain his methods in this paper and it seems like a tough one to quantify. However, I will pass on a good anecdotal piece of information that Jeff Wilcox pointed out to me last time this issue came up. He said that above-ground height is probably poorly correlated to root biomass, since for instance, in California grasslands we can have a four-foot tall wild oat (Avena) that has roots that go four inches deep and turns brown on the first hot day. Alternately you have a four inch high Danthonia, which has four foot deep roots and stays green through six months of heat and drought. Sure you can’t chew on that Danthonia every day of the summer and expect for it to thrive, but if we let it suffocate under four feet of Avena, we have failed in the same way, from the opposite direction.

I will try to squeeze in one last finding as my blog posts get taller than the grass I speak out against. McNaughton measured the number of seed heads in grazed plots versus ungrazed plots. He reports that the grazed plots had one-tenth the seedheads as the exclosures. Unfortunately, he doesn’t report the variation in this number. I would think that there would have to be a ton of seed heads in these mid-grass regions of the park, which would mean that the shortgrass regions must have been practically bare of seed heads.

Human lives are short and ecological changes take a long time. Before we spend our lives on moving the ecosystem in a certain direction, it would be good to know if that is the right direction or not. That requires an understanding of the ecological principals in operation. Next week we move on to the far North of the park to continue our myth-busting, this time with ‘continuous grazing.’

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