Hubbard Fellowship Blog – Anne’s Trip to Colorado

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.

CPER: Another major difference- look at the ground cleared by a small prairie dog colony!

CPER: Another major difference- look at the ground cleared by a small prairie dog colony!  Photo by Anne Stine.

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.

View of CPER HQ from top of bluff.  Photo by Anne Stine.

View of CPER HQ from top of bluff. Photo by Anne Stine.

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.

Home.

Home.  Photo by Anne Stine

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Lessons From a Project to Improve Prairie Quality – Part 1: Patch-Burn Grazing, Plant Diversity, and Butterflies

We recently completed a large multi-year restoration and management project at our Platte River Prairies.  Our specific objectives were to improve habitat quality for various at-risk prairie species and evaluate the impacts of our management on at-risk butterflies – particularly regal fritillaries.  The project was supported by the Nebraska Game and Parks Commission, who funded our work with two State Wildlife Grants (U.S. Fish and Wildlife Service money).  Over five years, we conducted fire/grazing management in our prairies and enhanced plant diversity through overseeding and seedling plugs.  We measured the results of that work by measuring changes in prairie plant communities and by looking at the use of our prairies by regal fritillaries and other butterflies.

Plant diversity and buttterfly habitat were the objectives of our 5-year project.

We’ve worked hard to get plant diversity in our restored prairies, including this one.  We wanted to know whether or not our management was maintaining that diversity, and also how it was affecting butterflies.  The prairie shown here was being grazed at the time of the photo – July 2009.  The Nature Conservancy’s Platte River Prairies, Nebraska.

The following is a brief summary of the major lessons we’ve gleaned from the fire/grazing component of the project, including implications for future management and restoration work.  I will summarize the overseeding/seedling work in a separate upcoming post.  If you want more details, you can see our entire final report to the funding agencies here.  As a warning, the report is 14 pages long, with an additional 21 pages of Appendices, full of tables and graphs.

What We Did
Between 2008 and 2012, we treated over 1,500 acres of prairie with varying applications of patch-burn grazing management.  During that time, we altered the timing of burning and the intensity of grazing from year to year, and included years of complete rest from grazing in some prairies.  For the purposes of this project, we evaluated the results of our work in two main ways:

–          We measured changes in plant diversity and mean floristic quality.

–          We conducted three years of butterfly surveys to evaluate how regal fritillaries and other butterfly species responded to our restoration and management work.

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