Spring is the time for early wildflowers, cool rain showers, and northward-migrating birds. It’s also the time during which smooth brome and other invasive cool-season grasses get their annual jump on the competition.
Suppressing invasive grasses and allowing native grasses and forbs to remain competitive in the plant community is one of the most important jobs for prairie managers in our area. In some cases, well-timed herbicide treatments can be successful at knocking back those invasives, but it is usually very difficult to find a window of time when the temperature is warm enough for the herbicide to be effective but when most native plants are safely in dormancy. More commonly, the best option is to suppress the growth of invasive grasses and decrease their competitive ability for that season.
Cow grazing smooth brome in a recently-burned restored prairie. Repeated defoliation throughout the spring season will greatly weaken this brome, allowing other plants to encroach upon its "territory".
We’ve found that grazing is particularly effective at suppressing cool-season grasses, because the grasses are repeatedly defoliated during their growth period, greatly reducing their vigor. The strategy works particularly well for smooth brome because, at this time of the year, brome is by far the favorite food of cattle in our prairies. They’ll eat other invasive grasses too (I watched them working on Kentucky bluegrass this morning, in fact) but if smooth brome is available, they’ll hit that first.
Sometimes we use short-term intensive grazing so that the cattle graze the brome hard, but then are removed from the pasture at about the time warm-season grasses are starting to emerge. That works well to suppress cool-season grasses, but often we end up simply trading dominant cool-season grasses for dominant warm-season grasses – without helping forbs much. This is because the warm-season grasses tend to take advantage of the weakened invasive grasses better than forbs do.
In the case of the above photo, we’re using a variation on patch-burn grazing, in which only a portion of the prairie is burned so that cattle will concentrate their grazing is focused within that patch. In this version of patch-burn grazing, cattle will be present all season, but we will reduce the stocking rate in late May. The idea is to get high grazing pressure on smooth brome during the spring, but also to leave enough cattle in the pasture during the summer so they will selectively graze the warm-season native grasses. With a light summer stocking rate, the cattle eat almost exclusively grasses, leaving wildflowers to grow with less competition from both invasive cool-season grasses and native warm-season grasses. Outside the burned patch, very little grazing takes place at all, especially after the stocking rate is reduced. Next year, a different patch will be burned so we don’t repeatedly stress the same plants each year.
This photo is a good demonstration of the attraction of both recently-burned patches and smooth brome to cattle – even when the brome is only about 2 inches tall! This cow is working over a patch of brome in the restored prairie, even though it also has access to the unburned parts of the same pasture (seen in the far distant background of the photo), which includes some degraded native prairie with lots of smooth brome and other grasses in the 5-8″ height range.
The Prairie Ecologist 
When you talk about heavy and then lower stocking rates, what rates are you talking about?
Jeff – Good question. It’s always hard to talk about stocking rates because they’re tied to soil types and rainfall amounts, etc. I suppose the easiest way to translate them is to talk about NRCS recommendations as a baseline. In our case, our early season stocking rate is a little over what NRCS would recommend for # of animals/acre if we were going all season, and the summer/fall stocking rate is between half and 3/4 of the number of animals they’d recommend for full-season grazing. Does that make any sense? In other words, if we went to NRCS they might recommend that we graze 50 cows for a 6 month season- as a sustainable agricultural rate. In that hypothetical situation, we’d probably use 60 cows for April and May and 30 or so for the rest of the season. Something like that…
And we’re still playing with this idea, so we change what we do from year to year (and prairie to prairie) based on what we saw the previous year. This year we’re using higher stocking rates everywhere because last year was so wet.
Let me know if there’s a better way to explain it.
Chris,
Do you think cows have favorite foods because it tastes different or because they like the texture? From your comments it’s surprising how selective they can be. And I thought my cat was finicky.
Mel,
From what we know, cattle decide what to eat based on experience – they measure their body’s response to different foods and decide what to keep eating based on that. Within a few days of being put into a new pasture, they can usually gravitate to the highest quality forage species – even if they’ve never seen them before. They also learn from each other – especially calves from their mothers.
So the cows’ grazing helps you control the brome? Do you miss the cows in the prairies you don’t have them?
Anna – it helps suppress it enough that other plants can compete better with it. Yes, I can definitely tell a difference between prairies we graze and prairies we don’t.
Patch-burn grazing works against us. We burn portions of our savannas and oak woodlands every spring while the surrounding lands are unmanaged and never burned. The deer intensely seek out these burn areas and hammer the forbs (golden alexanders, columbine, asters, lupine, elm-leaved goldenrod, etc.). Our deer population density goes up by several orders of magnitude in the early spring. Fortunately, the intense grazing relaxes later in the spring as other areas green up, but it is hard to witness it while it is occuring.
David
David – that’s really interesting! I can see where that would be frustrating, of course, but from a scientific point of view it is fascinating. I’ve always wondered how much burned areas would attract deer browsing. I had a study all set up to test it but lost my technician before we could start it.
My thought was that it might be possible to harness the patch-burn area to focus deer browsing into a few areas and release other areas from browsing – and then shift that burn patch around so that every place would get plenty of rest in-between burn/graze events. In your case, you’re locked into the static pattern of annual intense browsing because your neighbors aren’t burning – that’s probably not good. But if you could get your neighbors to burn too, and different areas burned each year, I wonder if that would be helpful to everyone from a moving-window-of-deer-browsing perspective.
I’d love to hear from others that see similar things to what you’re seeing.
Hi Chris,
I suspect your hypothesis is correct based on what we have witnessed. The oldest part of our savanna restoration gets browsed the worst as it has the best herbacious layer. However, other parts are improving (forb layer) and these areas are not browse as heavily so we are getting more plants that escape browsing. Our hope is that through additional restoration efforts we will have so much good herbacious layer that the deer browsing will be insignificant overall. This, of course, assumes the deer population will not expand.
As for surrounding neighboring lands, there are a lot of political and land-use issues to overcome before restoration expands beyond our property borders. Combine this with the severely degraded lands (oak woodlands choked with buckthorn in the understory and overtopping Siberian elms), the task seem unattainable. But then, there was a time when we thought that about our place too.
David
Early accounts (and recent compilations) of the reasons for American Indian burning often mention the result of attracting game (food) for ease of hunting, of which David’s observations would seem to be a graphic demonstration.
Good point James! I often feel that we are simply relearning what earlier inhabitants already new.
David