Importance of Fire
Fire is an important driver of many North American ecosystems, particularly grasslands. The influence of fire on the plant community is largely attributed to its removal of dead standing plant material, impact on forage quality, and the impact on grazing animals. Cattle production in undisturbed tallgrass prairie can be low due to the accumulation of dead standing plant material. However, fire can increase production over 75%. Historically, large bison herds followed fire as they were attracted to the lush regrowth that emerged. Today, managers use prescribed burning to capitalize on this change in forage quality for cattle production.
Forage quality is typically expressed as crude protein (CP) which is based on the nitrogen content of forage. This nitrogen content is critical for microorganisms in the rumen. Other measures of forage quality include palatability (typically associated with texture and moisture content) and digestibility (largely based on fiber and lignin). The primary influence of fire on forage quality is the removal of standing, dormant plant material. Forage quality is largely a function of time: as plants age (mature) they decrease in quality. This decrease in quality is due to the increase in fiber and lignin content, resulting in reduced digestibility and animal consumption. Prescribed fire remove dormant plant material, increasing the nutrition and digestibility of post-fire regrowth. While prescribed fires are commonly conducted during the late winter or early spring, growing season (summer) fires have the same effect and can boost forage quality during a period of the year where it is typically decreasing. Furthermore, the interaction of fire and grazing will impact below ground plant growth by increasing nitrogen mineralization and plant nitrogen availability, and improving the root tissue quality.
Benefits of Higher Forage Quality
Forage quality is a critical component of cattle production including reproductive efficiency, rebreeding, calf production, animal growth and milk production. Understanding the importance of fire to native rangeland plants and the potential benefits to cattle can be a useful tool for ranch managers.
Michael D. Porter is a senior wildlife and fisheries consultant with the Samuel Roberts Noble Foundation in Ardmore, Oklahoma. He has worked with the Foundation for 33 years. Through the Foundation, Mike provides wildlife and fisheries management technical assistance to land managers in south-central Oklahoma and north-central Texas. Prior to working with the Noble Foundation, he was self-employed as an independent wildlife management consultant to ranchers in South Texas. His career has been devoted to helping people, especially land managers, better understand and conserve wildlife and fisheries resources.
Mike earned a Bachelor of Science Degree in wildlife and fisheries sciences and a Master of Agriculture Degree in wildlife science from Texas A&M University. Mike is a certified wildlife biologist, a certified professional in range management, a certified Oklahoma hunter education instructor and a certified Oklahoma aquatic resources education instructor.
Mike has considerable experience managing white-tailed deer, northern bobwhite, eastern bluebird, beaver, waterfowl, largemouth bass, channel catfish, bluegill, grass carp, ponds, hunting leases, prescribed fire, woody plantings, aquatic vegetation, soil erosion as well as other natural resource issues.
Japangrass (Microstegium vimineum) is a nonnative, invasive annual grass that is capable of overtaking forest understories in eastern U.S. forests. Fire is one tool that can be used to manage Japangrass. Fire prescriptions to control Japangrass include burning in early spring just after Japangrass germinates, but before overstory trees have leafed out, or burning during August and September before Japangrass has seeded. Burning during mid-summer is difficult because of high litter moisture as a result of overstory forest shading. Japangrass can also be managed using a variety of herbicides, including grass-selective herbicides at relatively low application rates.
Gasoline, diesel, and kerosene are the fuels most often used in drip torches. Recommended mixture ratios depend on personal preference and ambient temperatures. A common mixture is 60% diesel or kerosene and 40% gasoline when temperatures exceed 75ºF. When temperatures are below 75ºF, a 50:50 ratio may be used. Exceeding 50% gasoline is not recommended because of increased volatility. Greater diesel/kerosene mixtures may be useful under high fuel moisture conditions.
When managing fields or openings for wildlife that use herbaceous openings, burn frequently enough to prevent plant succession and not allow woody species to dominate the area. This may be every 1-3 years. However, many wildlife species use woody or brushy cover. When managing for these species, the fire-return interval will be longer to maintain desirable woody plant composition and structure. Burning every 4-7 years in the eastern US with low to moderate fire intensity will usually maintain a woodland mosaic with scattered trees, shrubs, brambles, and a herbaceous understory. These intervals are recommended if annual precipitation is greater than 30 inches. In more arid regions, the interval will be longer. For more general information, see “How often should I conduct a prescribed fire?”
This is a common question regarding burning in hardwood forests in the eastern U.S. The short answer is yes, fire can kill hardwoods, but fire can also kill pine trees or any other type of tree. The key to hardwood tree mortality is fire intensity and duration. Low-intensity fire with flame lengths of 6-12 inches typically will not harm upland hardwood species unless woody debris has accumulated at the base of the tree. Use a conservative prescription, on the first burn in particular, to limit fire intensity and duration. Before burning your forest or woodland for the first time, walk through the area you intend to burn and remove any slash or accumulated woody debris from around the trunks of high-value trees, whether for wildlife or timber. Accumulated woody debris, when ignited, may retain heat long enough to damage the cambium (inner bark layer) and injure or stress the tree. Unless there has been a recent windstorm, ice storm, or other such event, most trees will be clear of debris and clearing can be done fairly quickly.
The primary weather conditions to consider when planning and conducting a prescribed fire are relative humidity, wind speed and direction, temperature, and mixing height. Most prescribed fires are conducted with relative humidity between 30–50%. Burning with relative humidity below 25% can be tricky as spotfires are likely and suppression becomes challenging. Burning with relative humidity above 50% is often ineffective because of high fine fuel moisture content. Forecast wind speed is for winds 20 feet above surrounding obstructions. The actual wind speed at ground level is usually less. Wind speeds of 2-15 miles per hour are common for most prescriptions. Winds greater than 15 miles per hour can create containment challenges in the event of an escape or spotfire. Mixing height is the distance aboveground where smoke is mixed with the atmosphere. The mixing height and transport wind speeds at that elevation influence smoke dispersal. A mixing height of at least 1,700 feet is recommended for most prescriptions.
The Fire Learning Network (FLN), is a cooperative program of the US Forest Service, Bureau of Indian Affairs, Bureau of Land Management, US Fish and Wildlife Service, and National Park Service, along with The Nature Conservancy. This network supports public-private partnerships in landscapes that are engaged in collaborative fire planning and implementation, providing a means for sharing and vetting tools and innovations to help expand the use of fire for natural community restoration. FLN communities have been established nationwide and an e-newsletter is regularly publshed.
Three Focal Landscapes of the Great Plains Regional FLN
Among the 47 FLN landscapes now working to accelerate restoration at local, regional and national scales are the three focal landscapes of the Great Plains regional FLN: the Loess Hills (Iowa), Lower Loup River (Nebraska) and Refugio-Goliad Prairie (Texas). These landscapes provide leadership, share lessons learned, and maintain a link to the national FLN for other Great Plains landscapes, including the Prairie Coteau (South Dakota), Niobrara-Sandhills (Nebraska), and Southern Iowa.
Working Hard to Make a Difference in the Landscape
The FLN is working hard to advance lessons learned from mangers and private landowners and to apply them at a scale that will make a difference in the landscape. Strategies include supporting landowner burn associations, helping volunteer fire departments offer prescribed fire to their community members, creating mobile burn crews and offering prescribed fire training exchanges (TREX). As a result of these efforts, 56,000 acres have been treated with prescribed fire during TREX events since 2008. TREX events are a great way to learn from experienced fire professionals as well as to share your skills with others. Look for the annual calls for participants.
To learn more about the FLN and these fire training exchanges visit: http://www.conservationgateway.org/topic/fire-learning-network.
Pre-burn briefings set the stage for successful burns. Maps, whether computer generated or hand drawn, can improve communication. Folks from state, federal, county, The Nature Conservancy, and a volunteer fire department discussed plans for the day’s burn. Photo by Susanne Hickey.
Achieving optimum livestock production on rangelands many times can conflict with wildlife conservation strategies that require lower stocking rates to maintain suitable habitat. Traditionally, livestock producers try to maximize gain per-acre by uniformly managing vegetation in pastures. Often this is achieved either by heavily grazing, burning the entire pasture, or both. This management strategy can create suitable habitat for some wildlife species, but poor quality habitat for others.
Combining the spatial and temporal interaction of fire and grazing (patch-burning) a conservation-based approach to land management can be achieved. This practice can increase rangeland biodiversity by creating heterogeneous vegetation structure and composition that is beneficial to multiple wildlife species. However, for conservation strategies to be successfully implemented, they need to be both effective and economically sustainable. In both mixed-grass prairie and tallgrass prairie, cattle weight gain was compared in pastures with traditional fire and grazing management (continuous grazing, with periodic fire on tallgrass prairie and seasonal grazing without fire on mixed-grass prairie) and conservation based management (pyric-herbivory applied through patch burning), both at a moderate stocking rate. Stocker cattle weight gain, calf weight gain, and cow body condition score were comparable between the traditional and conservation based management at the tallgrass prairie site for the duration of the eight-year study, indicating that conservation management doesn’t decrease livestock production or profitability.
In the mixed-grass prairie pastures, stocker cattle gain was not different between traditional and conservation management for the first four years. However, stocker cattle in conservation based management out gained cattle in traditional management beginning in year five and remained 27% greater for the next six years of the study. Moreover, cattle weight gain under conservation management varied less year to year making profitability more consistent. Traditional management in mixed-grass prairie did not include fire, the process that improved range conditions and likely was associated with increased stocker cattle performance under conservation management. In conclusion, pyric-herbivory is a conservation-based rangeland management strategy that returns fire to the landscape without reduced stocking rate, deferment, or rest.
Figure 1. Cattle weight gain on traditionally managed and patch-burn managed tallgrass prairie.
Figure 2. Cattle weight gain on traditionally managed and patch-burn managed mixed-grass prairie. An * indicates years when patch-burned managed cattle gained more than traditionally managed cattle.
When land managers start a prescribed burning program they often wonder whether fire will kill their grass, particularly during the growing season. To answer this question, the history of grasslands/shrublands needs to be considered. Fire is common through much of North America as a natural disturbance and a land management tool. Native Americans used fire as a part of their everyday existence from cooking meals to preparing camp sites and even hunting and warfare. With so much fire being used, historically, landscapes burned throughout the year. However, the intentional use of growing-season fire as a management tool remains controversial due to potential damage to fire sensitive herbaceous plant species that may be of benefit to both livestock and wildlife.
Growing-season grazing is a common practice that, if done at appropriate stocking rates, can benefit pastures as a whole. The common practice of growing-season grazing and growing-season fire were compared to see if there was a difference in plant growth and survival. For 10 years, plant communities burned in the dormant season and during the growing season and were monitored. The study found that the particular time of year that the fire occurred did not affect the plant community. The amount of rainfall was the dominant driving factor affecting grass production.
Figure 1. The relative abundance of little bluestem in pastures burned in the dormant season or the growing season. The solid line represents the rainfall received on the pastures the previous growing season.
Individual little bluestem plants were burned at multiple developmental stages to see how growing-season fire affected survival and growth. Plant age was the primary factor affecting plant survival with nearly all seedlings dying when burned. However, once plants reached 18 weeks old, survival was nearly 100%. Plant survival was similar for plants that were burned or clipped to simulate grazing suggesting that growing-season burning doesn’t have any greater effect on plants that grazing. One advantage that growing-season burning had was that both aboveground production and belowground biomass were both increased after burning, while growing-season clipping reduced production.
Figure 2. Above-ground grass production on plants either burned and clipped or clipped alone.The letters represent groups that had similar production.
Figure 3. Below-ground root production on plants either burned and clipped or clipped alone.The letters represent groups that had similar production.
Grasses in the Great Plains are well adapted to both grazing and burning during the growing season and can be included in a successful land management strategy.