The Changing Prairie Ecosystem
Prairie Ecosystem Processes
While prairie is often characterized by its individual components, it is also influenced by natural processes. The prairie is a dynamic landscape modified over time by:
The range of variation of these processes is a critical component of prairie bio-diversity.
FIRE: Prior to western colonization, periodic lightning fires ignited the dry prairie vegetation. Wildfires typically burned surface growth, but usually did not kill off the deep root systems of prairie grasses. Fire also helped impede the colonization of new sites by invader plant species, altered soil structure, and reduced insect populations. When natural fires didn't occur, aboriginal people set fires, to stimulate vegetative growth and bring back animals that depended on early successional vegetation. In the last century prairie grass fires have been routinely suppressed.
GRAZING: Grazing helps keep a prairie in grass. Grass flourishes under the onslaught of ungulate teeth and prairie forbs respond by growing into bushier plants. Grazing prevents trees from overtaking the grasses, because tree seedlings are destroyed when their tips are eaten. Recent evidence using analysis of pollen from prairie lake sediments suggests grazing by bison checked aspen encroachment onto grasslands. The variability of grazing activity created by different animals at different times is a vital part of the ecosystem. While most birds and animals flourish under moderate grazing regimes, species such as ground squirrels and mountain plovers need heavily grazed areas to exist. Meadow voles and Le Conte's sparrows are two species that thrive only in lightly grazed areas.
Drought: The influence of drought on prairie ecosystems can be complex. An 11-year study in Minnesota found that diverse plant communities are more resistant to, and recover more fully from, major drought. Such findings raise concerns about resilience and maintenance of productivity on prairie lands that have been converted to less diverse crop land and tame pasture.
Flooding: Periodic floods deposit seeds and rich silts on river valley floors, and create ideal seedbed conditions for the rejuvenation of riparian cottonwood forests.
WIND: Wind erosion keeps some sand dunes active, providing a home for kangaroo rats and western spiderworts.
1 Alberta Environmental Protection, The Grasslands Natural Region of Alberta, (March 1997), p. 5.
3 Ibid, p. 22
top photo by Carla Koenig | RSS