Monday, September 9, 2013

Plant Story: the amazing drought-tolerant buffalo grass, Buchloë dactyloides

buffalo grass, Buchloë dactyloides
buffalo grass, Buchloë dactyloides
growing in a path
   Last post (link) I talked about how buffalo grass, Buchloë dactyloides (grass family, Poaceae) spread because it was eaten and planted by bison (the American buffalo, Bison bison), and how it provides all-year nutrition for bison (and cattle). One result of this mutually beneficial relationship was that bison spread buffalo grass all over central North America.

    However, just being carried by bison isn't enough to explain the wide natural distribution of buffalo grass. The plants had to to survive in the places bison took them. And they did, very well indeed. Buffalo grass is characteristic of the North American high plains--in fact it is one of the three most abundant grasses. It is highly successful in a region of frequent droughts, long and short, mild and severe.

buffalo grass flower stalks, dime for scale
buffalo grass flower stalks,
dime for scale
male left, female right
    Buffalo grass is well-adapted to drought. First, it is not very big. It is basic--but true anyway--that bigger plants need more water. Buffalo grass covers the ground effectively, but doesn't get very tall (10"maximum).

    In dry regions more of each plant is underground, as roots, than in wetter areas. Approximately 3/4 of the buffalo grass plant is below ground. Where the plant goes up 8" (20 cm), it goes down 16-24." Furthermore, its roots fill the space below ground very thoroughly. Buffalo grass can prevent plants with deeper roots from competing with it because its roots are so efficient that they capture 100% of the rain from light or moderate rains. If no water gets past the buffalo grass, plants with deeper roots die of thirst.

buffalo grass, Buchlöe dactyloides
buffalo grass, Buchlöe dactyloides
expanding out onto the path

    It is a tribute to the dense roots of this little plant that early settlers used it to build sod houses. Buffalo grass roots are so densely packed that buffalo grass sod can be cut into blocks and built into walls. That is what the first settlers on the North American plains did, since there was no wood. (See description of building a Sod house). Across the high plains, buffalo grass sod was the preferred sod to cut for building.

      The plant is also exceptionally drought-tolerant. If the water runs out, buffalo grass goes dormant. The plant lies there, brown and dead-looking (but full of edible goodies for bison, of course). After a rain, within a couple hours, plants that looked dead become green and begin growing again. Most other prairie plants take much longer to respond after it rains.
buffalo grass, male flowers
buffalo grass with male flowers

     Finally, buffalo grass flowers opportunistically. That is, it will flower any time during the growing season. Most prairie grasses have a particular time of year in which they flower and develop fruit. If conditions are poor at that time, they have to wait until next year. Not buffalo grass. If it gets enough water and the temperatures are halfway decent, it can flower from April to August. So, whenever bison eat it, there are likely to be seeds to carry away.

   Carried by and feeding bison, well-adapted to drought, Buchloë dactyloides is, with reason, one of dominant plants of North American high plains grasslands.

      These days the prairie is gone, but buffalo grass is widely planted as a turfgrass, for lawns, golf courses, parks because it is short, tough and drought-tolerant. People are probably spreading it even better than the bison did.
buffalo grass, Buchloë dactyloides stolons
buffalo grass, Buchloë dactyloides, spreading 

Comments and corrections welcome. 

Note on names: Experts disagree whether buffalo grass should be called Buchloë dactyloides or Bouteloua dactyloides. While experts disagree, you can take your pick. I'll talk about that in a future post. 

Kathy Keeler, A Wandering Botanist
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