At our Niobrara Valley Preserve (NVP), we’re experimenting with prairie management techniques to see if we can create a wider range of habitat conditions than is found throughout much of the Nebraska Sandhills. On many Sandhills ranches, pastures look fairly similar to each other in terms of vegetation structure. That’s because Sandhills ranchers tend to be careful in their grazing management to avoid wind erosion that can cause “blowouts” of bare sand. As a result, pastures are rarely grazed intensively enough to create wide expanses of bare ground. If intensive grazing does happen, it’s usually on a small scale and/or for short periods of time, which allows for quick recovery of grasses.
Overall, the ecology of the Nebraska Sandhills seems very healthy. It’s a huge and mostly intact grassland landscape, and because of the dry sandy soils, topography and diversity of vegetation, there is quite a bit of habitat heterogeneity that is independent of management. As you walk across most Sandhills pastures, you will move through both short/sparse vegetation and taller/dense vegetation, and occasionally come across other structural components like yucca plants or plum thickets. Wildlife and insect species can often find the habitat structure they need somewhere in that pasture, though it might be in a small patch surrounded by other habitat types. That seems to be true even for many bird species, which have relatively large breeding territories. As an example, in pastures with fairly tall vegetation, we often see and hear horned larks that are (apparently) nesting in a few small and scattered patches of the short vegetation structure they prefer. Those patches of short habitat often occur in gravelly flat areas or in favorite feeding areas for cattle, where grass growth is weak because of frequent grazing.
We’re trying to figure out more about how management with patch-burn grazing or other similar grazing systems affects Sandhills ecology. Patch-burn grazing has part of the management of our bison pastures at NVP since the early 1990’s. Because of that, we know Sandhills vegetation can recover from fires that are followed immediately by season-long intensive grazing. However, we still don’t know much about how many animal species might respond – positively or negatively – to the kind of large patch heterogeneity created by this kind of management. Instead of pastures with interspersed small areas of tall and short vegetation, we’re trying to create large patches (500-1000 acre patches within 10,000-12,000 acre pastures) of each habitat type and then shift the location of those patches between years.
Creating large patches of various habitat types could bring both advantages and disadvantages to different species. As an example, large patches could create an abundance of resources that support larger and more viable populations of some animal species. On the other hand, a vole who likes thatchy habitat could wake up in the middle of a 1000 acre burn, and it would have to make a long dangerous trip to find a more suitable place to live. Trying to evaluate those potential costs and benefits is a big challenge for us.
One possible advantage of the kind of shifting mosaic of habitat approach we’re trying is that it helps avoid risks that come from having the same habitat conditions in the same place year after year. Just as crop rotation can help avoid buildups of pests and pathogens, shifting habitat types from place to place could have important benefits. For example varying the location of habitat types from year to year could limit disease outbreaks and help prevent predators or herbivores from building up large and potentially destabilizing populations.
The most intriguing part of our experimentation for me, though, is the idea that we could create large ‘recovery patches’ where grasses have been weakened by a full season of intensive grazing and the plant community is temporarily dominated by opportunistic, mostly short-lived plant species. That combination of short grasses and tall ‘weedy’ wildflowers can provide excellent brood-rearing habitat for some birds and important structure for reptiles and invertebrates that need to regulate their body temperature by moving quickly from sun to shade as needed. Studies in other landscapes have shown that this kind of recovery patch habitat creates pulses of high insect biomass, which could have numerous impacts – including the provision of an awful lot of food for wildlife. In addition, if an abundance of opportunistic plants include species beneficial to pollinators, that could provide quite a bonanza of resources for bees, butterflies, and other insects.
In most of the Sandhills, patches of ‘weedy’ habitat tend to be in small, static and widely scattered locations such as around windmills or other places where cattle or bison frequently congregate. We’re wondering what might happen if we created big patches of the same habitat type and shifted their location from year to year. In our Platte River Prairies, patch-burn grazing (and similar strategies) has sustained prairie plant diversity over many years, but we haven’t looked closely for similar responses in the Sandhills. In addition, we know a little about how birds respond to patch-burn grazing in the Sandhills, but not much about impacts on other species like lizards, pollinators, small mammals, or invertebrates. Now we’re trying to collect data on the responses from all those different organisms.
I’ve really enjoyed digging into all the questions we have about our attempts to create more habitat heterogeneity in the Sandhills. We haven’t had time to answer many questions yet, but we feel like we’re at least creating something different than what exists throughout most of the Sandhills landscape. A few years from now, we might conclude that the heterogeneity we created didn’t really result in any significant positive or negative impacts compared to what exists elsewhere. If that’s the conclusion, we’ll move forward with that in mind. On the other hand, we might find that there are some important positive (and/or negative) impacts of the shifting mosaic approach we’re testing. In the meantime, it’s exciting to have the opportunity to try something different and watch what happens. Stay tuned…
Interesting. I appreciate your work and your posts.
Looking at your pictures I don’t detect any cheatgrass. Do you not have it on your prairies. At Crescent Lake National Wildlife Refuge it is becoming abundant. I visit there once or twice a year since 2011, my daughter lives there, and I see it increase every year, it is sad.
I would like your insight
Hi Angela, we certainly have cheatgrass, yes. It can be pretty abundant at times, but doesn’t seem to persist and outcompete native plants as long as we don’t keep managing the same way each year. We get a little more moisture than Crescent Lake NWR and points to the west, which makes cheatgrass a little less competitive. Also, in many years, a spring burn knocks cheatgrass out for the year because it’s actively growing at the time of the burn. Intensive grazing immediately after the burn can also keep any cheatgrass from being able to establish. If we were going to get abundant cheat, I’d expect it most during the couple of years after the burn/grazing. I don’t have enough experience watching the area closely to know yet how that’s going to work out, but when I see sites that have had a couple years or more to recover, I don’t see much cheatgrass now. I’ll know more in a couple years!
I presume that you work with a variety of ‘experts and researchers’ eg at universities and ? even some private companies to educate yourselves and also give them perhaps a research opportunity. My father back in the 50s to the 70s on a large cotton and wheat farm in the southern Arizona desert valley talked about getting university of arizona ag researchers to try different ‘plots’ and ideas on the farm. Even trained illiterate farm workers to do bug counts by sweeps in the fields to help measure the bug population changes and then when to use insecticide spraying etc.
I thought that was quite smart and a potential ‘win win’ with researchers / experts looking for land agriculture opportunities. Learn from each other.
I think the thing I appreciate is the diversity of grasslands and the range of species that inhabit different types of grasslands. One question I have is how prairie dogs affect the grassland structure. They closely crop the grasses and most forbs in their towns, so wouldn’t prairie dogs reasonably replace an intensive grazing regimen if allowed to thrive, or do the colonies not change locations often enough to let the grass recover? I personally would like to see more prairie dogs on the prairie given how many other species use their burrows, but ranchers don’t particularly like them. Do you have any estimates for how many prairie dogs and colonies are on NVP?
Patrick, you basically described it the way I would. They definitely help create and maintain very short structure (which is how they compete for forage with livestock) but they don’t change location very often. That doesn’t make them ecologically bad, of course, but their habitat patches are different from the shifting mosaic patches we’re trying to create. We have a few small colonies on NVP but we’re pretty limited on the kind of low, flat and dry areas they’re looking for, so the towns are pretty topographically contained.
Thank you for the work you do and for sharing it with people on your blog.
It will be difficult for reptiles, like the lesser earless lizard, to thermoregulate in such large patches that have been intensively grazed. Reptiles like to move between open areas and shade to moderate body temperature.
Blowouts often form in extremely dry microclimates. For example, cold wind coming off of Lake Michigan is heated when reaching land which causes a drastic drop in dew point. This extremely dry air creates a zone that is dessert like supporting cactus and lizards in proximity to eastern deciduous forest slightly further inland.
Honestly, sometimes the things you do to TNC preserves scares me.
Chris this is super exciting!!!!!!!!!! I love what you are doing.
There have been so many hard times in recent weeks in the sandhills. The especially valuable significance of the region is its expanse. Any one weather event might be localized so other places have a situation where birds continue to thrive, based upon my personal opinion.
Perhaps you might write about the value of landscape level conservation of natural features and how this requires widespread cooperation.