Recently, my mom was camping and walking a prairie in southeast Nebraska. She came across a plant that is readily visible this time of year. You can easily spot this plant in roadside pastures going 50 miles per hour. To really appreciate it, you need to get up close. This plant is called Snow-on-the-mountain. This plant is highly visible due to the bright white margins on large, showy floral bracts. Cattle will not graze this plant as the leaves contain a milky bitter juice.
Disturbance = Snow-on-the-mountain
Snow-on-the-mountain will only appear in a grassland when some kind of disturbance occurs. The seed is in the soil, waiting for the opportunity when the soil becomes disturbed, and bare ground appears. As you know, we are proponents of appropriate animal impact and disturbance of our pastures. Do you see some bare ground in the photo above? This area was a bale grazing site from a year or two ago. Heavy animal impact and leftover hay set back the prairie grasses leaving some exposed, bare ground. This disturbance gave snow-on-the-mountain, and other “invader plants” or opportunistic plant seeds, an opportunity to do their work.
As noted above, animals will avoid grazing snow-on-the-mountain! Since animals will not disturb the growing snow-on-the-mountain plant, much of the bare soil is being covered which protects the area for other plants to reestablish. I would also venture a guess that as snow-on-the-mountain falls to the ground and decomposes here, it will provide nutrients and minerals needed for the next succession of plants to arrive and do their work to reestablish the prairie in this location.
Disturbance = Edge Effect
Are you familiar with the ecological “Edge Effect“? In the simplest terms I can think of, edges are areas of increased energy flow. There is just more activity at the edges. We are always looking for ways to increase energy flow in our pastures. Ultimately, we want that energy to end up in our cattle and the meat that our customers consume.
Compare the following two photos for edge effect within our pasture.
Another way to compare these two sites for overall energy flow would be to measure the energy captured during the growing season in total pounds per acre of production.
- The disturbed site would have 6,000+ pounds per acre production.
- The undisturbed site would produce 4,000 pounds per acre.
Carbon = Energy
Most of the increased production in the disturbed site will be a result of the significant boost of carbon that this site received, along with an appropriate opportunity to rest. The addition of hay, from the bale grazed, along with cattle manure, gave this site a surge of carbon. By managing our cattle grazing for short duration and long recovery periods, the plants in the disturbed area had the resources and time they needed to generate significant production.
The undisturbed site shown above is ready for animal impact. The plants shown in the undisturbed site must receive grazing and stomping to lay the grasses flat on the ground. Once the plant material is laid on the ground, it can be acted on by soil microbes and turned into soil carbon. If the grass plants are not grazed and stomped to the soil surface, the plant material will oxidize and the carbon will escape into the atmosphere (lost energy!).
Management – Disturbed vs. Undisturbed
The disturbed site will not require much, if any, grazing management to lay the plant material onto the ground. When the herd is moved into this patch, the cattle will seek out this area with a diversity of plants. In short order, all the plants will be consumed or stomped.
The undisturbed site will require more management. We will need to “right size” the paddocks when we come through this area to make sure the animal impact is appropriate to graze and stomp the undisturbed grass stand to the ground. Once on the soil surface, soil macro and microorganisms will do their magic and convert that carbon into soil carbon (energy).