Like so many other things, prairies aren’t what they used to be. Back in the nineteenth century and before, they were vast areas of grassland constituting over forty percent of North America’s natural landscape. They were maintained by the action of two main influences: wildfires and plains bison.
Wildfires, sometimes caused by lightning, would sweep across immense tracts of land. They were very frightening for settlers who tried to protect their homes while being prepared to run for the nearest river or creek if necessary. And yet they had enormous benefits.
Tallgrass prairie accumulates a thick thatch of dead material which even bison prefer not to eat. It weakens the grasses making them more vulnerable to invasion by shrubs and trees which in turn cast shade which restricts the sunlight from reaching the native grasses and other plants which need full sun to grow. To this increased shadow, add the effect of insulation provided by the dead leaf litter itself which keeps the ground cold and slows new growth in the spring.
Wildfire is nature’s way of starting over. In one fell swoop it destroys the unwanted biomass and releases nutrients in the form of ash. Prairie grass roots can be as deep as six feet below the soil surface and so are unaffected, unlike other plants. The natural mechanism of self-destruction is reversed: the ground is warm again and grazing animals are able to feed more easily and further stimulate growth.
Nowadays, fires are sometimes started deliberately by ranchers in order to improve cattle forage and generally boost the health of the prairie. But homes are paramount and obviously no-one is willing to take risks over lives and livelihoods, so the health-giving fire doesn’t have free rein like before. Trees get established, the land is given over to other uses, and the whole appearance and functioning of the landscape is changed.
Native Americans also sometimes started fires. Their name for a prairie fire was Red Buffalo, and there is a similarity on more than one level.
Once upon a time, large herds of bison grazed on the grasses and kept them short. They had a symbiotic relationship whereby the extra third of growth produced, beyond what would naturally decompose, was recycled into manure. Also the animals’ hooves stirred the soil around, burying seeds and making hollows in the ground which would trap moisture.
The bison’s habits had a further benefit which isn’t quite so obvious. As prey animals, they evolved to live in herds for mutual protection. They learnt that predators would lie in wait for them close to sources of water and so their natural instinct was to drink quickly, then leave. This meant that they hardly eroded the banks of rivers unlike domesticated species which might lounge around there all day.
Native Americans hunted bison for many uses vital to their livelihood. They drove them into pens, or off the edges of specially chosen cliffs called buffalo jumps, and killed a great many. Once they had horses and guns they were able to kill more. But these numbers were as nothing compared to what was done by the policy of indiscriminate killing practised by European Americans and Canadians who in the course of a century reduced the population of the plains bison from millions to a few hundred – close to extinction, in fact.
Bison and widespread wildfire have largely disappeared. They were of immense importance in creating and sustaining the prairie of the past – an enormous, empty, romantic sea of waving grasses. It’s a sad fact that today tallgrass prairie covers less than one percent of the area it previously covered and is the most endangered large ecosystem in North America.