It’s the fall seed harvest time of the year. Most days, after spending time in the prairie harvesting native plant seeds that we will sow this winter, I emerge covered in a multitude of seeds of various shapes and sizes. And if I am covered in seeds, I’m thinking that perhaps the bison grazing the prairies all day long are also covered in seeds. Indeed, they are!
Bison fur is thick and curly – a perfect magnet for seeds with hooks and hairs whose strategy is to grab on, hold on, and be transported to new locations.
In a 2008 study conducted on 100 bison in Oklahoma1, 2,768 seeds from 76 plant species were found in bison fur. That is a lot of seeds from a lot of different plants—almost an entire prairie ecosystem on each bison!
Building on the idea that bison fur transports seeds, a 2015 study2 in Iowa found that the seeds in bison fur can remain attached for five months. As you can imagine, during that time, those seeds can be transported by the bison a long way from their initial location. Thus, bison are fantastic long-distance seed dispersal vectors for native prairie plant species and are pros at moving genetic material across a landscape for ecosystem health.
Seeds can be moved across the landscape not only by attaching to an animal’s fur or feathers (epizoochory) but also within the body of an animal as the seed passes through the animal’s gut (endozoochory).
In that same 2008 study, dung samples were also surveyed. The study found that an even greater number of seeds were found in dung – 7,418 seeds from at least 70 species. Though many of the seeds in the dung of the bison are damaged in the bison’s gut during rumination and thus do not geminate, several grass species with small seeds pass successfully through the gut and remain viable.
In grade school, I remember learning the concept of a keystone species, a term that stems from the wedge-shaped stone that sits in the top middle of an archway and holds all the other stones of the arch in place. If that keystone is removed, the arch collapses. In the same way, a keystone species – be it an animal, plant, or insect – holds the entire ecosystem in balance. Bison are the keystone species of the prairie, and that is a big deal.
Bison graze, poop, move around and writhe around, and all that changes the habitat around them. Their eating changes the height of the plants, which affects the types of bird species that utilize the prairie, and it influences the speed and intensity of the fires that travel across the prairie. As bison selectively graze, they determine which plants will and which plants won’t produce seeds. Bison dung is fertilizer and is home for many beetles! Bison hooves can crush plants, bury seeds, and churn up the soil, making space for new plants to grow. When bison wallow on the ground, they create low open soil areas that fill with water in the spring for frogs and insects to enjoy and later become spaces where new plants can get started.
When you visit Kankakee Sands this fall, get the bison in your binoculars or snap a photo and zoom in… see seeds? I bet you will! And should you look down and find that you yourself have seeds on your pants and shoes – and I bet you will! – please reflect on the bison as a keystone species. Those big, beautiful animals are moving seeds across a landscape and keeping our prairies thriving, healthy, resilient, spiritual spaces for all of us and future generations.
1 “Seed Dispersal by Bison bison in a Tallgrass Prairie” by Claudia Rosas, David Engle, James Shaw and Michael Palmer
2 Peter Grefory Eyheralde of Iowa State University
The Nature Conservancy’s Kankakee Sands is an 8,400-acre prairie and savanna habitat in Northwest Indiana, open every day of the year for public enjoyment. For more information about Kankakee Sands, visit www.nature.org/KankakeeSands or call the office at 219-285-2184.