2006-07-07 / News

More about flora: Warm season grasses

What are native warmseason grasses and what are their importance?

Native warm-season grasses (nwsg) are grasses historically native to an area that grow during the warm months of the year and are dormant during autumn and winter. They differ from cool-season grasses, which make their active growth during spring and fall. There are many warm-season grasses native to our region; however, seven species are most commonly promoted as cover for wildlife and/or forage for livestock. These are big bluestem, little bluestem, broomsedge bluestem, indiangrass, switchgrass, sideoats gama and eastern gamagrass. Not all of these, however, have the same quality for wildlife habitat or livestock forage. For example, broomsedge offers excellent nesting habitat for bobwhites, but poor forage for livestock.

Using native warm-season grasses for wildlife habitat

Native grasslands are highly endangered ecosystems in New England. Historically, our region contained native grasslands which were maintained by fire. Today, that acreage has been replaced with non-native grasses (e.g. tall fescue, orchardgrass and bermudagrass), agricultural crops, forest cover and suburban development. As a result, several wildlife species dependent upon quality early successional habitat have experienced significant declines in population.

Nswg can be used to enhance early successional cover for species such as bobwhite quail, cottontail rabbit, field sparrow, Henslow's sparrow, grasshopper sparrows, indigo bunting, prairie warbler, dickcissel, Eastern meadowlark, loggerhead shrike, American kestrel, northern harrier and others. Fields of nwsg and associated forbs (broadleaf herbaceous plants) are also used by wild turkeys for nesting and brood rearing and by white-tailed deer for bedding and escape cover. Nwsg are established for wildlife primarily because of the structure of cover provided. Suitable cover is more often a limiting factor for species such as quail, rabbits and grassland songbirds than food, and nswg provide excellent cover as well as food. Importance of open structure

Because most nwsg grow in "bunches," open space at ground level can be provided when bunches are not too dense. An open structure at ground level allows mobility for small wildlife (e.g., quail, rabbits, sparrows and young turkeys) through the field. Dense vegetation and thatch build-up (such as that presented by perennial cool-season grasses) inhibits movement and makes finding food (seed and invertebrates) difficult. When these conditions prevail, the number of animals an area can support is reduced, leading to stagnant or declining populations.

Sparse stands of nwsg with an open structure at ground level are obviously attractive for brood rearing, but they are also used for nesting - one bunch of nwsg represents a potential nesting site - if the field has not been burned or disced in the past year. Birds and rabbits use senescent (dead) leaves of previous years' growth to construct and line nests. An attractive characteristic of nwsg is that senescent leaves and stems remain erect into the following growing season. This reduces thatch build-up, provides protective cover through winter and allows birds, such as field sparrows, dickcissels and indigo buntings, to nest above ground amongst the senescent stems the following spring.

Although moderately dense stands of nwsg may not be as attractive for brooding, they are used for nesting and escape cover. Obviously, these stands may have more potential as nesting sites than sparse stands, but they also offer more protective cover, especially during winter. Extremely dense stands, however, inhibit movement of some small animals and become less attractive. At this point, management is needed to thin the stand. Importance of forbs and shrubs

An open structure at ground level also enables the seedbank (seed in the top few inches of soil) to germinate. Arising from the seedbank are plants such as ragweed, blackberry, partridge pea, beggar's-lice, pokeweed, native lespedezas and annual sunflowers. Forb cover is critical in making a field of nwsg most attractive to wildlife. These plants provide an excellent canopy of brood-rearing cover for quail and wild turkeys; quality forage for deer, rabbits and groundhogs; and later produce seed and soft mast that is an important source of energy through summer and into fall and winter for many wildlife species. Scattered brush and small trees also can make a field of nwsg and associated forbs more attractive to wildlife, particularly bobwhites and several species of songbirds. Bobwhites often use brushy cover as a "covey headquarters" during fall and winter. Indigo buntings, dickcissels, yellow breasted chats, cardinals, prairie warblers, white-eyed vireos, eastern kingbirds and others use scattered clumps of shrubs and small trees for perching and nesting. Many of these shrubs and small trees also offer a valuable food source for many birds and mammals. Examples include American crabapple, wild plum, hawthorn, sumac, wild cherry, persimmon, elderberry, hazelnut, witchhazel, dogwoods, Carolina buckthorn, viburnums and devil's walkingstick.

Winter cover

Nwsg provide quality cover during winter if the grasses are not previously bushhogged or otherwise destroyed. Fields of nwsg are often magnets for rabbits, over-wintering songbirds and deer. This can be especially critical for small wildlife at a time when quality cover is at a premium. Tall nwsg, such as big bluestem, indiangrass and switchgrass, are especially valuable as their stems "lodge" (remain somewhat upright, leaning against each other), continuing to provide cover even after winter rains, snow and wind. Deer seek out nwsg fields on cold, clear days because they can remain hidden in the tall grasses, yet are able to absorb the sun's warm rays. In low-lying bottomlands that periodically flood in winter, fields of switchgrass (especially the Kanlow variety) can attract large numbers of ducks when shallowly flooded.

Courtesy of the University of Tennessee

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