Prairies are grasslands dominated by native grasses associated with a diverse assemblage of flowering herbaceous plants known as forbs. The particular set of grasses and forbs depends on local environmental factors, particularly moisture, topography, and soil depth and richness. The most luxuriant prairies, such as tallgrass prairies or mesic prairies (a type of habitat with a moderate supply of moisture) support a very species-rich community that includes grasses over 8 feet tall. They are delightful communities to visit, with dozens of new species of forbs, or non-woody stemmed plants that are not grasses, coming into flower each week, attracting butterflies and other pollinating insects as well as birds that feed and nest there.
According to early survey records, tallgrass prairies and oak savannas once covered much of southern Wisconsin. Almost all have disappeared because these lands are unmatched for agriculture. Mixed grass and short grass prairies are mainly located west of Wisconsin as moisture levels decrease towards the Rocky Mountains, but rare remnants can be found here on sand barrens and steep rocky hillsides unsuitable for agriculture.
We live in a transition zone between the deciduous broad-leaved forests to the east and the prairie grasslands to the west. While prairie species (even those of mesic prairies) are better adapted to drought than are deciduous trees, ecologists agree that the prevalence of fire was an extremely important factor in determining community type. Before European settlement, fires caused by lightning or deliberately set by Native Americans swept through areas not protected by natural firebreaks every one to a few years.
Prairie species have a large fraction of their biomass (as much as 66%) underground, allowing them quickly to regrow after grazing or fire. Fire sets back invading shrubs and trees (and now many alien weeds), removes litter from the ground allowing it to warm up more quickly in the spring, and returns nutrients to the soil. It seems to stimulate both flowering and vigor of many prairie species. Thus, the forest’s tendency to spread westward into grassland was limited by dry climate and fire and the prairie’s tendency to spread eastward was limited by the inability of its smaller plants to compete successfully with trees for light.
We hope to reestablish both prairie and savanna in the Lakeshore Nature Preserve, but this is going to be a long-term process. Prairies are quite hardy once they have become established (provided they are burned regularly) but hard to get going, particularly on sites that have been plagued by invasive weeds. Prairie plants are perennials and put most of their energy in early years into growing roots. This makes it difficult for them to compete in the short run with pioneer plants (weeds) whose strategy is to grow lots of above ground shoots, leaves, and flowers and to produce lots of seeds.
UW-Madison’s Biocore Program has been carrying out tallgrass prairie restoration in the Preserve since 1997.