Converting Introduced Grasses to Rangeland
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Table of Contents
Introduced (not native) grasses have been widely planted throughout the Southern Great Plains for livestock forage and soil erosion control. Pastures planted to introduced grasses (hereafter IG) are typically dense with little plant diversity, offering limited value to many wildlife species. Additionally, IG grasses can invade rangelands and outcompete native plants. Rangelands are grasslands/shrublands dominated by native plants that are not managed with supplemental fertility or irrigation. Rangeland includes sites that were never converted to IG and sites that are converted from IG back to native dominated plant communities. This results in lower structural and species diversity, affecting wildlife and livestock grazing potential. Land managers who have multi-use goals may want to reduce or eliminate IG, as they can be detrimental to management goals.
The purpose of this document is to provide guidance for eliminating common IG in Oklahoma, such as bermudagrass (Cynodon dactylon), tall fescue (Festuca arundinacea), and Old-World bluestem (hereafter OWB) species such as yellow bluestem (AKA plains bluestem, King Ranch bluestem, KR bluestem, Bothriochloa ischaemum) and Caucasian bluestem (AKA WW-BDahl bluestem, B. bladhii). Once converted, areas formerly dominated with IG can be managed to promote a diversity of native grasses and forbs (non-woody, broadleaf plants). While the recommendations in this guide are focused on Oklahoma, most of the information contained here is broadly applicable in other areas where these IG species occur.
Benefits of Native Species
Restoring rangelands can provide numerous benefits to land managers. A diversity of native grasses and forbs can offer high-quality livestock forage, an extended grazing period, enhanced aesthetics, and wildlife habitat (including pollinating insects). Moreover, native rangelands are less expensive to maintain since they do not require the inputs (e.g. fertilizers) necessary to maintain IG pastures.
One of the primary reasons that native grass species are preferred by wildlife over IG is that many grow in bunches, which creates a more open structure for ground-dwelling wildlife to move through the vegetation and allows more room for forbs to grow. Big bluestem (Andropogon gerardii), little bluestem (Schizachyrium scoparium), switchgrass (Panicum virgatum) and Indiangrass (Sorghastrum nutans) are common bunchgrasses in Oklahoma.
It is important to note that rangeland historically had many species of forbs and shrubs, in addition to grasses. A variety of native grasses, forbs and shrubs provides food and cover for birds such as northern bobwhite (Colinus virginianus), wild turkey (Meleagris gallopavo), and many species of songbirds. Additionally, white-tailed deer (Odocoileus virginianus) primarily feed on forbs and woody plants (vines and shrubs). The presence of diverse species of forbs and shrubs also increases the abundance and diversity of many insect species, including the monarch butterfly (Danaus plexippus) and various native bee species, which have seen population declines in recent years.
Is Replanting Necessary?
Often, land managers assume they will have to replant a pasture after eliminating IG, and they spend time and money doing so without evaluating the natural plant response or without considering what plants they want/need to meet their land management goals. Because native seeds and rhizomes (roots) can remain viable in the soil for decades and some seeds are readily dispersed from adjacent sites by wind, flooding, and animals, rangeland can often be reestablished without planting following removal of IG.
Many forbs, particularly annual forbs, will germinate from the seed bank within the first year and early pioneering grasses, such as broomsedge bluestem (A. virginicus), will typically show up within the first 2-3 years. For some land managers, especially those with predominantly wildlife goals, allowing natural plant succession to occur without replanting may be sufficient to meet goals. Make no mistake, sites that have been dominated by IG for decades have been under cultivation for crops, or have had repeated herbicide applications are degraded. These sites may never return to historic vegetation within your lifetime. Some perennial plants, including many grass and forb species and some shrubs, may take many years (if ever) to colonize the site depending on past management. This does not mean that the plant community response (plant succession) will be unsatisfactory to your specific goals.
While you may only get 60-70% of the historic plant community to return to a site, this will work fine for many species of wildlife. However, subject to goals, personal patience and the plant response observed on a site, replanting or overseeding may be desired in some cases. This is particularly true if the goal requires specific perennial forbs or shrubs or if the land manager desires highly palatable native forage grasses.
Planning for Conversion
Prior to any treatment, land managers interested in conversion should determine their ultimate management goals for the property and why they are interested in removing IG. Livestock production and wildlife habitat can certainly coexist, but livestock production on rangeland will not be the same as on highly fertilized IG pasture. Yet, input costs will be dramatically reduced, so there is a tradeoff. Changes in forage production, input costs, and stocking rates should be carefully considered and discussed with livestock and rangeland professionals. Resources to help with these determinations are included in ‘Additional Information’ at the end of this document.
As previously mentioned, many desirable plants, including forbs, will often respond from the native seedbank and replanting may not be needed. In situations where replanting is required or desired, recognize that native seed mixes can be costly. Technical and financial assistance programs are available to help identify appropriate species to include in mixes and cover the costs of converting an IG pasture to a native mix of grasses and forbs. A land manager interested in wildlife will want a high diversity of forbs in the seed mix—perhaps 30-50% of the mix. This percentage could be even higher in plantings of less than 20 acres (given the higher cost) where monarch butterfly or pollinator habitat is the goal. Forb seeds are typically more expensive than grass seed but are essential for wildlife and often valuable for livestock.
Conversion of IG pastures to rangeland can be successful if the proper steps are followed. Shortcuts generally waste time and money. Many failed conversions are due to inadequate eradication of the IG and rushing the process. Plan on 2-3 years minimum. Before starting a conversion project, it is important to recognize which IG species are present, as this will determine what steps are needed to convert the pasture. Also, the land manager should anticipate what undesireable plants are likely to show up and how to control them. Therefore, you need to become fluent in plant identification and understand which plants are beneficial to your specific goals. Finally, consider the maintenance measures that will be needed to keep the converted pasture in a desired state. Rangelands require maintenance or they may convert back to IG or eventually become a forest (in areas of higher rainfall).
Natural resource managers can help with the preliminary assessment of the property and development of management plans and timelines for the project. Local Cooperative Extension offices, Natural Resources Conservation Service (NRCS) field offices, wildlife department private lands biologists, or wildlife biologists with various conservation groups are good resources for land managers interested in converting IG and promoting a diversity of native plants for target wildlife. Typically, these technical services are provided free to the land manager. See ‘Additional Information’ at the end of this document for further information on how to contact a local biologist.
Control or Eradication Options for Introduced Grasses
Depending upon the dominant species present, different treatments or combinations of practices may be most effective. Below are some common control measures, generally listed from least to most effective.
Site preparation will be necessary on many IG pastures that are dense and have thick litter layers that will intercept the herbicide, making it difficult to kill the target plant. Before applying any herbicide treatments to a field, leaf litter and dead plant matter from previous seasons must be removed to expose the actively growing vegetation to herbicide application. Litter can be removed by haying, grazing, or burning. Regardless of the preparation method used, allow sufficient time for plant regrowth before spraying (usually about 6 inches of growth).
The timing of site preparation will vary depending on the target grass. Prepare the site ahead of the growing season of the target species. In areas where more than one introduced grass is abundant, target the most prevalent grass first.
Soil Erosion Considerations
When converting an IG field to a rangeland, soil erosion is often a concern of land managers. While there is some potential for erosion, it is often much less than expected. The residual litter from the dead, standing grass following herbicide application helps to protect the soil surface from rain impact and runoff and it takes months for this residual litter to decompose. Furthermore, the roots from the dead grasses hold the soil together. Also, except when using a soil-active herbicide, other plants quickly germinate, providing additional soil protection. Pastures that are relatively flat and outside of a floodplain have minimal risk of erosion during the conversion period. Highly erodible sites may not be ideal for long-lasting soil-active herbicides, such as imazapyr.
Natural plant succession is the progression of plants reoccupying the site. Often this results in a desirable composition of native species since a variety of native seeds and rhizomes can remain viable in the soil for many years, or even decades. The native seedbank/rhizome bank is often suppressed by IG that out-compete native plants. With removal of these IG, many pastures will experience a resurgence of native grasses, forbs, and shrubs following treatment. Prescribed burns are a great way to remove residual debris from plants killed by herbicides and stimulate the seedbank for natural plant succession or prepare the seedbed for planting. Treated pastures can be burned a few months after the final herbicide application. If a site was sprayed during the summer, consider waiting till the following spring to burn the area so that the residual dead plant material protects the soil during the winter.
Grazing on rangelands converted from IG should be deferred until plants are well established (2-3 years). A proper stocking rate is essential. Heavy, prolonged grazing pressure over several years can slow regrowth, lower root energy reserves, and increase the susceptibility to unwanted plant invasion. Key grazing management decisions include using a proper stocking rate, limiting repeated heavy use in preferred areas (i.e., near streams, creeks, and water troughs), and providing periodic rest during the growing season through deferment, herding, or patch burn-grazing. Managers should be careful not to stress the developing grass by taking too much forage. Calculating an appropriate stocking rate for each pasture will prevent this from happening. For help calculating an appropriate stocking rate, ask the local NRCS office, refer to fact sheets (https://extension.okstate.edu/fact-sheets/stocking-rate-determination-on-native-rangeland.html), or use online tools like the Rangeland Analysis Platform (https://rangelands.app/production-explorer), which provides estimates of forage production and calculates stocking rates for any areas outlined.
Once the IG have been removed, other problem species may take advantage of the increased availability of resources and space. A weed is simply a plant out of place, or an unwanted plant. There will always be weeds in converted pastures that will require control. Diligent weed control is key to ensuring that new problem species do not encroach on areas following treatment. Undesirable plants can often reproduce quickly and outcompete native plants, enabling them to monopolize resources and limit vegetation diversity. There are multiple plant guides and plant apps that can be helpful in plant identification (see ‘Additional Information’ at the end of this document). Take the time to use these resources to ensure you are controlling problem plants and retaining desirable plants based on your goals. A natural resource professional can help you with this.
Spot spraying reinvading IG should be a top priority for managers to avoid a reinfestation. The eradication of IG will require monitoring for reemergence of treated species. The methods and herbicides recommended above can be used in smaller, more precise applications to efficiently spot-treat any remaining IG grasses.
When assessing weed control options, it is important to remember that most broadleaf plants can be controlled with broadleaf-specific herbicides that do less damage to grasses. Likewise, controlling undesirable grasses with herbicides that target grasses, reduces harm to forbs. It is important to consider management goals and the pasture’s current plant composition before selecting weed treatment options. Below are some common problem species that can be found in converted pastures in Oklahoma and methods that can be used to control them. Note that the herbicide recommendations below are not exhaustive; other herbicide options exist. Always consult the herbicide label for complete information.
Conversion of IG to rangeland has many benefits to land managers. The process of conversion takes time and requires follow-up management, especially in the first few years. The timeline for restoration will vary based on the IG species and what methods were used for control. It is important that land managers carefully plan conversion of IG to rangeland so that time and money is not wasted. Clearly identify and determine management goals and reasons for IG removal prior to any treatments. With patience and diligence, land managers can successfully remove IG that may be detrimental to their management goals.
The benefits of conversion for wildlife and pollinating insects cannot be overstated. The proliferation of IG pastures has eliminated enormous areas formerly usable by various wildlife species. A loss of flowering plants eliminates the use of the area by pollinating insects and birds relying upon insects for their diet. Additionally, converting to rangeland can be beneficial to livestock producers, depending on their grazing strategy.
A variety of control options can be used, but herbicide is often most successful for large-scale conversions. Land managers should carefully consider IG treatments based on the site’s vegetation composition, potential for soil erosion, desired timeline for conversion, and land management goals. Follow-up management should include assessments of plant succession, control of undesirable plants, and periodic disturbance including prescribed fire, grazing, and disking. Grazing can be introduced once plants are well established.
The following summary guidelines can help managers interested in removing IG get started:
- Determine land-use goals
- Identify non-native species that are present
- Plan desired treatment methods
- Prepare site for treatment applications
- Apply treatment as outlined in plan
- Evaluate treatment effectiveness and spot treat undesirable plants
- Reassess vegetation community in relation to goals
- Interseed/reseed, if needed, to meet goals
- Use additional practices to maintain the desired plant composition
For Additional Information
- Assistance (technical and financial) Programs and Contacts
- Benefits of Native Plants
- Plant Identification
- Range Planting, Reseeding, and Overseeding
- Stocking Rates and Forage Production
- Weed or Noxious Species Control