The southern Great Plains includes portions of Kansas, Oklahoma, Texas, New Mexico, and Colorado. This area is semi-arid grassland that is characterized by a highly variable climate. Within portions of this grassland, resprouting shrubs dominate on certain soil types. This is particularly true for sand sagebrush and shinnery oak which occur on deep sands. Other subdominant shrubs in this region include various species of plum and sumac. These shrubs provide various ecological services. Many species of wildlife rely on them for protective cover, thermal cover, and nesting cover, as well as for food resources. Northern bobwhite, Bell’s vireo, lesser prairie-chicken, and Cassin’s sparrow in particular are associated with shrubs in this region. Additionally, these shrub species are deep rooted and help stabilize soils from wind erosion from fires, as well as during the frequent droughts that characterize the variable climate of the Great Plains.
Direct Impacts to Shrubs
Often, managers wish to know how prescribed fire will affect shrubs. As with all grasslands, the southern Great Plains ecosystem evolved with fire. Thus, it is not surprising that the vast majority of shrub species within this region resprout from the root following a disturbance such as fire. Thus, fire will rarely result in mortality to the plant. However, fire does result in a temporary change in plant composition and structure. Following fire, many shrubs will be top killed. In other words, the above ground portion of the plant is consumed by the fire. The degree to which this occurs will depend on the fuel load, relative humidity, and other factors. Depending on rainfall following the fire, annual forbs (broad leaved herbaceous plants) and grasses tend to increase for the first 2 to 3 years following fire. In shrub dominated areas (sand sagebrush and shinnery oak), this impact is short-lived as the shrubs rapidly resprout and again dominate the site. Over time, the shrub stems will gain height and within 3 to 4 years sand sagebrush and shinnery oak will return to pre-burn conditions. Species such as sand plum will also resprout, but grow slower. This clonal shrub species grows in dense “mottes” where many stems are part of the same individual plant. The edge of the motte is often top killed by fire; while the interior remains unscathed (This will vary with fuel and conditions during the burn). Research has shown that sand plum mottes will increase in area over 330 square feet per year. Thus, depending on the original size of the motte, it may take several years following fire for this shrub to return to pre-burn conditions.
Associated Impacts
The change in plant composition and structure has dramatic impacts to wildlife species and also to livestock production. Wildlife species that require shrubs may be temporarily displaced until the shrubs dominate the site once again. Alternatively, other species which require higher amounts of grass and forb cover will increase on these burned areas for the first few years following a fire. The increase in grass production and crude protein of grass associated with prescribed fire will be attractive for livestock for 2 to 3 years following the fire. Thus, periodic burning in these shrub communities can be a valuable tool to increase livestock performance. However, due to the variable climate patterns, burning only a portion of a pasture in any one year is a good hedge against droughts. Some producers wish to use herbicides to eliminate shrubs in favor of grass to increase livestock performance. First there is no economic benefit to this or should increase in livestock production. It is also a risky practice in an area known for highly erodible soils. Thus, to maintain adequate root biomass for soil stability, and to ensure shrub obligate wildlife has adequate habitat, the use of periodic prescribed fire over portions of a pasture can be used by livestock producers.
Sand plum is a clonal shrub, where many individual stems are part of the same plant. This plant grows in dense “mottes” as seen in this photo. Fire often top-kills some of the stems along the periphery of the motte. However, large mottes generally are not completely top-killed but rather reduced in size by fire. Over time, this motte will expand by vigorous root sprouting stems.
This sand sagebrush plant community was burned 5 months prior to this photo. Notice the sand sagebrush resprouts across the pasture.
Shinnery oak is another clonal shrub that can have thousands of stems per acre. This photo depicts a recent prescribed fire (right portion of photo) and an unburned area (left portion of photo). Notice that the recently burned area is grass dominated. This is a temporary condition as shinnery will return to pre-burn conditions within 3 to 4 years post fire.