Forbs and shrubs key to healthy prairie
July 30, 2010
As I approach my “senior years,” (mind you, I said approach – I’m unwilling to admit arrival), an associated characteristic is being memory challenged. My loss of recall seems to vary between brief and immediate. Nonetheless, I am confident that I don’t remember a summer during which the display of prairie wildflowers has been more spectacular or prolonged. Ample moisture and favorable temperatures have stimulated many plants to partition resources to reproductive growth, which for broadleaved plants includes showy flowers.
In Northern Great Plains grasslands, forbs and shrubs are typically a minor component of the vegetation. When asked about rangeland management objectives, many ranchers will respond with their desire to “grow more grass.” The importance of palatable perennial grasses to the feed supply for livestock, particularly cattle, justifies this emphasis. A related sentiment is reflected in a question I often get regarding one or another species of broadleaf plant – “what good is that?”
While the importance of grass plants is obvious, broadleaved plants support a number of ecological functions that are essential to the integrity of rangelands. Many of these functions relate to the habitat provided for other organisms. Grouse chicks, along with other prairie birds, depend on insect larvae and adults for a substantial portion of their food supply. Many of these insects, in turn, depend on forbs as their principal habitat, requiring specific plants for food and/or reproduction.
Pollinators and their essential role in agricultural production have received increasing attention recently as dramatic declines in numbers of these organisms have been recognized. Whether bees, butterflies or birds, many of these animals depend on broadleaved plants, and their showy flowers, as sources of nectar and other food components. An entomologist pointed out to me just recently how important a wide diversity of flowering plants was for pollinator habitat. A healthy prairie has something blooming for most of the growing season, from early spring through fall. Loss of this important diversity creates gaps in habitat for pollinators and other species.
In addition to above ground habitat, forbs and shrubs also contribute to healthy soils. Grass plant roots are fine and fibrous. Some forbs have broad tap roots that can penetrate restrictive soil layers and improve moisture infiltration and facilitate cycling of nutrients. One large class of rangeland plants, legumes, is essential to the nitrogen cycle. While rangeland production is most often limited by moisture, nitrogen supply can be limiting during periods of ample precipitation. Without the inputs of nitrogen fixation provided by bacteria “hosted” by roots of legume plants, vegetation production would be compromised.
So… forbs are good for birds and bees, but what about livestock? Dietary studies demonstrate clearly that cattle consume primarily grasses because of their abundance on most rangelands and their preference. However, that contribution of broadleaved plants to livestock nutrition is critical. Of primary importance is a role in mineral nutrient supply. Appropriate and “balanced” intake of calcium and phosphorus are necessary for livestock health and function. Grasses tend to accumulate calcium in higher concentrations, while phosphorus concentrations are higher in forbs. By consuming forbs in addition to grasses, livestock are more likely to maintain nutrient balance of these important minerals. As grasses mature, concentrations of energy and protein decline. While similar patterns are true of most forbs and shrubs, a number of species are peculiar because they cure well and provide higher nutrient levels late in the growing season or even during winter. Winterfat is a clear example. As its name implies, stockmen value its contribution of digestible energy and protein during the dormant season.
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Enjoy the glorious beauty of this year’s wildflower display. And if the question “what good are they?” comes up, appreciate their contributions to the scenery. But in addition, remember how your “bottom line” is improved through nitrogen and nutrient supply as well as habitat provision for wildlife and pollinators that may be essential to you, or your neighbor’s, cultivated crops.