When comparing how bison and cattle graze and use water, it's apparent that bison are much more adapted to drier rangeland than cattle, and are a bit lighter on the land as well.
Bison have been shown to move from area to area more frequently than cattle, and sometimes considerable distances. Studies done in Canada, North Dakota, Wyoming, and Colorado show that even with a preferred home territory, bison move frequently, seldom staying in the same area for more than 48 hours. Some movements were up to 32 km in a short amount of time.
Bison also spend much less time near water than cattle, usually only heading for water once a day and spending an hour or less at or near the watering hole. In contrast, the ancestors of moden cattle evolved in moister, more tropical woodlands and still retain an affinity for water and wetter areas. Cattle are less efficient water users and have been shown to spend 75% or more of their time within a few hundred yards of water or wetter (riparian) areas when they are available.
What does this mean for the west? Since only about 1% of the area of the prairie is riparian, this means that cattle tend to concentrate around water sources and negatively impact the wetlands much more than the same number of bison would. On the other hand, it's unclear as to whether bison actually consume less water than cattle on the range - I haven't been able to find any definitive studies either way. What IS clear is that feedlot cattle consume about double the water of their rangeland counterparts.
But the most significant water conservation comes not from the introduction of bison, but from the restoration of the prairie itself.
Much of the Great Plains were plowed under and turned to farmland because the native priarie soil was rich and deep. Anyone driving across the Midwest can recount stories about driving across hundreds of miles of cornfields, wheat farms, or soybeans. Agricultural crops grow well here as long as there is enough water - but that's the problem. There often isn't enough rainfall to grow crops so often these miles and miles of fields are irrigated.
The main reason the Great Plains were prairie and not forest is that they are in the rainshadow of the Rocky Mountains. Rain and snow are relatively scarce and unpredictable. Grasses and prairie plants evolved to need less water than trees and shrubs. It's not until we approach the area of the Mississippi River that there is consistent-enough rainfall for crops. Average yearly precipitation in Denver, CO (the western edge of the Great Plains) is less than 18 inches per year (rain and water-equivalent of snow combined)...average precipitation in Chicago is over 35 inches per year at the eastern edge of the Great Plains.
Serveral of the aquifers (groundwater systems) that underlie the Great Plains are in serious decline or locally dry due in large part to crop irrigation. It's becoming clear that we need to deal with this issue now while we have time to plan, rather than waiting for another dustbowl.
Am I suggesting eliminating all of the farmlands on the Great Plains and converting it all to prairie?
No, obviously we need to eat, and the Great Plains is where much of our wheat, corn, and beans are grown. What I will suggest is a three-pronged approach:
- Eat food from as close to your home as possible (covered in another post).
- As a continent, the US and Canada need to develop better dryland farming practices that allow us to farm with little or no irrigation.
- And, as a part of the plan, restore some of the most sensitive or problematic areas of the Great Plains to prairie and raise bison on these restored area to both maintain the prairie and as a source of high-quality, grass-fed meat.