Soil Health on Rangelands: Biotic State Back »

In the last iGrow article about soil health on rangelands, I wrote about energy flow. In this article in the Rangeland Soil Health Article Series, I want to focus on the biotic state. But first a short history lesson.

Range Management: Origins & history

Early on in the range management profession (late 1800s and early 1900s), scientists and practitioners saw the need to better understand rangeland management because the Western rangelands of the USA were showing signs of widespread degradation. In 1916, Fredrick Clements published his seminal book, “Plant Succession”. Clements is credited as the “father” of plant ecology and the range management profession built their theories of range science on his important work.

In 1949, E.J. Dyksterhuis published his landmark paper in the newly formed Society for Range Management’s Journal of Range Management on the “Condition and Management of Range Land Based on Quantitative Ecology”. Dyksterhuis, a Soil Conservation Service employee, built on Clements’ ideas of plant succession and laid out the concept of quantifying range condition or what we call today the similarity index. This paper gave us a way to calculate a range condition score (1-100%) and classify the vegetation as either “poor” (1-25%), “fair” (26-50%), “good” (51-75%), or “excellent” (76-100%) condition in relation to what the expected climax plant community should look like. He grouped plants into three categories on how they responded to heavy grazing (Decreasers, Increasers, and Invaders) and expected percentages of these three categories in the climax stage. Over time, the range profession cataloged and studied rangeland plants as to how they responded to grazing, drought, and fire.

Early SDSU Range Studies

In the early 1940s, universities across the Great Plains started stocking rate studies to understand what happened to rangeland plants and livestock production at different grazing intensities. In 1942, South Dakota State University (South Dakota State College back then), began a long-term stocking rate study at the Cottonwood Range and Livestock Research Station in Western South Dakota. This study, managed later by James K. “Tex” Lewis in the early 1950s and continued by Patricia Johnson, became a hallmark of South Dakota’s important contribution to our understanding of range management. Along with my colleagues, I used the information from Cottonwood to publish several important papers on grazing efficiency, livestock economics, and drought.

Contemporary Range Studies

In my range science classes at SDSU, I emphasize to students that we are really “plant detectives”, like Sherlock Holmes of range science, reading the vegetation on the landscape and interpreting how our range management practices work. This starts at an early age with kids that attend Rangeland Days and in high school with FFA and 4-H programs in South Dakota. Okay, back to the biotic state (Figure 1).

Figure 1. Color coded monitoring indicators of nutrient cycling, water cycling, the biotic state, and energy flow that are involved in ecosystem processes (modified after Pyke et al. 2002; Pellant et al. 2005; Orchard 2013).

Identifying Decreasers, Increasers, and Invaders

You probably have guessed from the previous discussion that being able to identify plants and how they respond to grazing, drought, fire, etc. is key to monitoring the health of your rangeland vegetation and ultimately your soils.

  • Decreaser species (desirable) are those that livestock find palatable and regrow fairly rapid if adequate residual leaf area is left. If decreasers are grazed too hard (not leaving enough residual leaf area) and too frequent (not having long enough rest period), they will begin to decrease in plant vigor (biomass, cover, density, and height) and can eventually be replaced by other species. Familiar decreaser species are western wheatgrass, big bluestem, sideoats grama, purple coneflower, and leadplant.
  • Increasers (undesirable) are those that respond positively to heavy grazing. They are usually less palatable and thus don’t get grazed to the same extent that decreaser species do under heavy grazing. Increasers usually don’t regrow as fast as decreaser species to survive in a grazing environment, because they tend to put more energy into grazing deterrents. Increaser species are blue grama, buffalo grass, red threeawn, cudweed sagewort, scarlet globemallow, western snowberry, and pricklypear cactus.
  • Invaders are those that need a disturbance to create a niche for them to establish. Invaders are usually annuals or biennials. These plants are poor competitors and when pastures are grazed properly, invaders tend to disappear. Some familiar plants classified as invaders are foxtail barley (perennial), cheatgrass, curlycup gumweed (biennial), common sunflower, and snow-on-the-mountain.

Monitoring Plant Communities

Each range site (or ecological site in today’s terminology) has a particular set of plants that make up the climax plant community. Soils, slope and aspect play an important role in dictating what the expected climax plant community should look like. Not all soils and landscape positions will produce the same vegetation. Grasslands typically have about 80% of their biomass as grass, 15% as forbs, and 5% as shrubs. These percentages vary quite a bit depending on your region and ecological site. The Natural Resources Conservation Service (NRCS) has a great website called the web soil survey where you can map out the ecological sites of your pastureland. Through this website you can view the percentages of each plant type (grasses, forbs, and shrubs) that comprise the plant community.

You use these percentages to determine how similar your plant community is to the climax plant community or any other community as defined by the plant community model (Figure 2). The beauty of these models is that you can determine what actions need to be taken to jump from one plant community to another.

Figure 2. Plant communities and transitional pathways for a Clayey ecological site in Western South Dakota. Provided by NRCS.

The Bottom Line

Our ability to interpret the plant community using this framework enables the range manager to make informed decisions with confidence regarding their grazing practices to improve rangeland health. If you don’t know what you are looking at how do you know if something is wrong or needs improvement?

Plants are an indicator of your management. Monitoring the biotic state will help you make informed decisions regarding overall rangeland and soil health.

Rangeland Soil Health Article Series

Visit the links below to view other articles in the Rangeland Soil Health series:

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