While managing a prairie or savanna with controlled burning is much more effective, high-mowing a grassland can also be a useful management tool, especially when and where burning is not possible. Mowing can be used to prevent or control an invasion of woody saplings and shrubs, control non-native cool season grasses while promoting native warm season grasses, and control annual and biennial weeds, particularly for newly planted grasslands. Mowing during the growing season can help promote native species by controlling one or more invasive or undesirable species and can help save time and resources. For instance, manual removal of each flowering stem of European sweet clover in a heavily invaded prairie may take several days or weeks, whereas mowing might take one day. It can also significantly reduce or even eliminate the need for chemical herbicides.
Typically, mowing is necessary when establishing a new prairie or savanna planting. Most of the native species seeded in prairie reconstructions will take a couple of years to fully establish. During the first year in particular, much of the plant growth is occurring in the root system underground. Mowing one or more times during the first year or two provides extra nurturing to the young native seedlings by helping to control the many annual and biennial weeds vying for the same light, water and nutrients. At this time, mowing will have a minimal effect on the short, newly emerging native seedlings. During the new habitat’s formative years it is important to provide extra nurturing so that the native species can fully establish and form sustainable populations for years to come.
As with any management activity, negative effects do occur, and a determination must be made as to whether the benefits outweigh the costs. As an example, tall grassland vegetation is very beneficial to many species of wildlife by providing cover from predators, nesting areas and thermal protection from harsh winter weather. However, it is often necessary to mow grassland restorations during the interim between controlled burns in order to control small tree saplings from growing too large. Otherwise, the area may quickly become a forest, rather than a prairie. As with controlled burns, small refugia (areas not burned or mowed) are left to support wildlife populations. Another undesirable effect, especially if mowing occurs during the growing season, is that native species could also be negatively impacted, maybe failing to produce viable seed or have reduced vigor. Nevertheless, most native prairie and savanna species are well-adapted to periodic disturbances and will likely respond positively following control of invasive species.