A Guest Post from Anne Stine, one of our Hubbard Fellows:
First impressions: Patch-burn Grazing in Short Grass Steppe vs. Mixed Grass Prairie
Our Platte River Prairies here in south central Nebraska are lovely, flowery pastures, but I needed to travel to get a more complete concept of how patch-burn grazing works across different landscapes and precipitation regimes. It was this drive that brought me to the Central Plains Experimental Range (CPER) in the short grass steppe of Pawnee National Grassland in eastern Colorado.
My two guides, David Augustine and Justin Derner, were kind enough to spend a morning showing me around their site. First impressions- the obvious: CPER is much drier. They average 13 inches of rain annually to our 25. We don’t have much in the way of species overlap between our sites. Blue grama with small patches of buffalo grass, wheatgrass, and prickly pear seemed to be the dominant community at the CPER pastures we visited. In comparison, we see big blue stem/switch grass/dozens of forbs/etc etc as the major species in our mixed grass system.
A major management impact of this different precipitation regime is that their sites cannot carry fire year round. There simply isn’t enough fuel. Their estimated fire return interval (the average ‘natural’ length of time between burns on a site) is much longer than ours. The estimate they gave me was 10-40 years. By comparison, much of the tallgrass ecosystem is believed to have a return interval of approximately 3 years. Luckily for them, the harsher conditions are keeping woody encroachment at bay, so they don’t need to burn frequently.
I spent much of my visit puzzling out the major value of fire to the short grass steppe. The benefits in the mixed grass prairie are dramatic. However, most of the positive impacts of fire that we see here in Nebraska (preventing woody encroachment, changing the balance of power within a plant community to favor forbs) just aren’t evident in eastern Colorado. As mentioned previously, trees are not a problem in their drier climate, and forbs were largely absent even on burned areas.
Justin and David explained that burns are critical for habitat heterogeneity, particularly for clearing ground to produce ideal habitat for birds like the mountain plover. They also see a decrease in the amount of prickly pear at a burned site. Burns remove the spines, and pronghorn come in to forage on them over the winter. Forage quality of the native grasses also improves after a burn, similar to at our sites, but this is a smaller and more transient effect as distribution of precipitation over time and the landscape takes over as the most important ecological factor.
I left Colorado with the impression that the mixed grass prairie ‘leans east’, if you will. It is more similar to the tallgrass prairie than the shortgrass steppe. It’s as if some precipitation threshold is crossed once you move west of the mixed grass system, and an entirely new set of challenges replaces what we have east of that line. Here in the mixed grass, periodic, varied disturbance seems to be the key to biodiversity. In the west, perhaps the periodic, varied change in conditions is embedded within the precipitation regime itself. As I travel, I will continue to explore the question of how grassland management for biodiversity changes in different regions.
Glad you got to Colorado — wished we would have known! But you went with some of the best experts in the area. The role and significance of fire in this landscape, historically and today, is always an interesting question. You saw the shortgrass in a pretty dry year (although it was much drier down south in Colorado). But there are some years (and I suspect decades) that are much more moist. I have seen the shortgrass with blue grama between 12-18″ tall along with the other forbs and grasses that are usually taller. Standing biomass can be, depending on grazing pattern, pretty significant in those years. Perhaps the range of 10-40 for a return interval is about right given the variation in moisture and its pattern. What will it be with the changes we are going to face? Come by sometime and we’ll take you to other parts of Colorado’s grasslands. Chris Pague
You should also take a visit farther north to the Short Grass Steppes of western Nebraska to the west of Alliance where Thread Leaf Sedge is a very, very large component of the Steppe say at the Scottsbluff National Monument where prescribed burning is being used. From what I have seen, especially as my father ranched in southern Sioux County many years ago, much of this western Nebraska Steppe has a competition between Blue Gramma and Thread Leaf Sedge for dominance. From what I have observed (no scientific study just personal observation) Thread Leaf Sedge needs fire to regenerate and knock back the highly competitive Blue Gramma from time to time. I could be all washed up though. I have an above ground half barrel in my backyard containing Blue Gramma and Thread Leaf Sedge I dug up as sod in Western Nebraska to which I added some western Colorado sod containing Indian Rice Grass and Galleta Grass (Hilaria jamesii). The Blue Grama seriously outcompetes the other three species and would dominate the whole barrel if I did not pull it out by the rootstems to give the other three some space to live. Just an observation.
Thank your for the interesting comparison. I moved from an area with 30+ inch precip tallgrass prairie to 5+ inch precip sagebrush steppe. Since that time the transition of patch-burn grazing from the east to the west has perplexed me. I observe all the positive impacts of patch-burning (minus the grazing) in my very dry environment if done with historic burn cycles in mind, particularly for restoring the competitive balance betweens fire tolerant and intolerant species. That includes a brief explosion of forbs (or sub-shrubs), at least in my area. Habitat heterogeneity is also restored at different scales if well planned. However, when burns are combined with growing season grazing, it seems to result in a reduction in the plant community as a whole and increase of bare ground in burned areas that might be 1/40th of the landscape or less.
I wonder if there is a point where grazing selectivity and the presence of large grazers at all is influenced more by the varied climate across the landscape caused by large changes in elevation? When wild and domestic grazers are free roaming in these dry areas they seem to move long distances to follow new green vegetation into higher elevations and mesic montane prairies as snows recede. They then return to graze dormant plant matter in the dry prairies when pushed to lower elevations by winter weather.
Could the season of grazing be the overriding issue when examining certain benefits of patch-burn grazing in rain-shadow plant communities such as that found on CPER?
My residence in the shortgrass prairies of western Kansas in 1976-77 was brief but I readily saw the need for fire to cycle the grasses and control prickly pear, red cedar and the exotic siberian elm, among other . The challenge was how to implement it when with risking fire-simulated drought and when ranchers needed every acre of range they owned. I surmised that a grazing rotation could be worked out in which the burned tract would have the option of early rest if conditions became too dry. The problem would be convincing ranchers that the need was worth risk and trouble. (Oddly, the problem is similar in the high rainfall region of Missouri where eastern red cedar is epidemic in cool-season pastures and producers use 110% of it.) The answer may well lie in patch-burn grazing, instead of fenced paddocks, and is significantly more biologically friendly. I continue to be amazed how pbg continues to show us “what we thought we knew isn’t necessarily so”.