Every few years, the UW-W Grounds Crew engages in a prescribed burn of the prairie areas of the Nature Preserve. This initially seems counterproductive for plants and trees to be burned, but this process invigorates the native plant species. For thousands of years, prairie environments have experienced fire as a way of clearing old debris and rejuvenating the soil. Typically, these fires were set by natural causes (like lightning) or indigenous people trying to get game animals to come out of hiding. Since European settlement of Wisconsin, fires are generally seen as a destructive enemy to structures and other human property, so fire suppression has eliminated this key restorative feature from the landscape.
There are a few concerns when prairies no longer see regular burns. The dead plant material can build up year to year and it makes it more difficult for seeds to germinate and establish new plants. When the reproductive capacity of these plants is limited, there is an increased likelihood of invasive species and other weeds to establish in these open areas and begin to take over the prairie landscape.
Our prairie is still relatively young, with initial efforts for re-establishment beginning in the late 1990s. Before that, it was used for agriculture and later became overrun with woody invasives. Those species were removed and successful seeding efforts have crowded out most of these problem plants, but a few still remain. For example, there has been efforts to eradicate reed canary grass from the low-lying areas of the prairie for many decades with little success, primarily due to their ability to spread by rhizome (underground) as well as by seed.
However, the more noticeable and pervasive invaders are white sweet-clover and yellow sweet-clover. These plants are probably familiar to most people as they are commonly found in roadside environments and other unmanaged areas along agricultural fields. These plants are biennial, which means they only live two years, but they produce a huge number of seeds that can be viable for decades in the soil system. They are also somewhat resistant to fire, but most of them can be culled through prescribed burns. Due to the prevalence of this plant, we plan to burn the prairie three years in a row in totality to attempt to eradicate this problem plant. This does put more stress on the prairie plants to survive, but they are more likely to make it compared to the sweet clovers, which have shallower roots.
It might look pretty desolate now, but prairies respond very favorably to prescribed burns. Keep an eye on our prairie during the spring and summer and you shouldn’t be disappointed with an incredible display of plants with hopefully much less sweet clover! Here are a few photos of the burn from last week.