Horses on the Prairie

During November 2013, BRIT became the temporary home of twelve horses who helped our researchers study the impact of grazing herbivores on our restored prairie habitat. Prairies used to be home to bison, elk, deer, and other large herbivores whose hooves would aerate the soil and whose grazing habits (and ability to provide fertilizer) helped with the germination of native plants and grasses. As the horses ate down the grass, sunlight was also able to penetrate further into the foliage, which allowed new seedlings to grow and made for a healthier prairie.

Can't resist new grass

Found a shady spot

View from the terrace

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Focus

Our original objectives for the project were to:

reduce the vegetation / forage cover to about 30% (70% reduction) of the amount measured prior to the arrival of the horses
open the ground cover to allow more sunlight at a lower level
convert much of the biomass into fertilizer that will increase soil carbon and nitrogen levels
pack in the seeds that had recently matured on the majority of prairie grasses and forbs into the pasture

Process

Prior to working on the prairie, we:

conducted an experiment that focused on the outcomes of additional types of soil and fermentation supplements
measured cover and species dominance over three randomly located transects
generated surface and aerial photographs of the prairie (the “before” pictures)
walked the area of the prairie, making note of the patchiness and species diversity

Once the horses arrived, we left them undisturbed for two weeks as they ate, slept, and played in their temporary prairie home.

Results

After the horses left, we observed the following:

Cover foliage had been reduced to about 50% of the original density.
Most of the taller grasses and forbs had been knocked down, and some had been pulled up.
The grasses had been unevenly grazed. For example, patches of buffalo grass were cropped down to 2 inches with some evidence of the plants being pulled up, while other patches of buffalo grass had not been grazed at all. Similar observations were made for most species in the pasture.
The manure appears to have changed to a lighter color than when the horses first arrived, with fairly even-sized, firm plops.
Manure production was good. (If each horse produced 50 lbs per day, 12 horses x 14 days = about 8,400 lbs of fertilizer was deposited on the prairie.) Each day the horses worked for us, they processed about 600 lbs of inert cellulose that would otherwise take months to break down without the benefit of their digestive processes.
Seeds packed into the soil were clearly seen in all areas of the pasture.
There were some exposed areas that appeared to have little vegetation. However, we know that these areas were there prior to the arrival of the horses but were hidden by the growth of other plants.

Would We Do It Again?

Prairies that are not managed do not stay prairies. Perennial bunchgrasses create dense stands and thick layers of old leaf material, crowding out annual grasses and forbs that need to space and sunlight to germinate each year. Woody plants (e.g., mesquite, juniper, pecan, oak) eventually get big enough to create shady areas, changing the soil moisture and chemistry. The horses we brought into our prairie were but one tool for prairie management; in the absence of hosting the horses every year, we can manage the prairie through mowing or burning to achieve similar results.

Epilogue

In January 2021, we finally got our chance and successfully burned our prairie for the first time (read about it here!). Because of the highly urban location of our pocket prairie, we are in a great spot to demonstrate to city dwellers what historical prairies and prairie management techniques look like. We hope to cycle through these three techniques — grazing animals, burning, and mowing — over the years to continue educating our growing community.