Progress report for LNC15-372
Project Information
Sericea lespedeza is an invasive, non-native legume threatening native and restored tallgrass prairie by reducing grassland productivity and biodiversity through prolific seed production and competition with native species. Current control methods strive to reduce seed production and are only marginally successful. We propose to evaluate if altering fuel load, burn season and fire frequency can effectively reduce sericea lespedeza densities both independently and in conjunction with other commonly used management strategies (i.e. herbicide use and mowing). We hypothesize that by changing timing of fire and amount of fuel in areas where sericea lespedeza is problematic, the beneficial impacts of fire are maintained while at the same time reducing the success of sericea lespedeza. The first part of this project is designed to evaluate the impact of fuel load, fire season, and fire frequency on sericea lespedeza productivity, plant density, and seed production. The second part of this study is designed to evaluate grazing influences on fire temperature and duration in pasture-scale prescribed burns. We will measure fire temperature and duration with pyrometers and airborne infrared cameras during both parts of the study. Through this project, we hope to provide land managers with additional management tools to control sericea lespedeza while at the same time increasing the quality of life of producers through reduced herbicide exposure and improved profitability because of reduced herbicide expenditures and increased rangeland productivity. This method may also be adapted to target other invasive species in fire-adapted systems by targeting vulnerable life-stages.
Objective 1: Evaluate total standing biomass, grass standing biomass, and sericea lespedeza standing biomass in response to burn season coupled with herbicide, mowing, and fuel load addition treatments.
Objective 2: Evaluate sericea lespedeza growth and reproductive output in response to burn season coupled with herbicide, mowing, and fuel load addition treatments.
Objective 3: Build a fire model based on fire conditions and common management practices to predict burn conditions necessary to produce fire temperatures lethal to sericea lespedeza seed.
Objective 4: Determine the economic cost of managing sericea lespedeza infestations with fire and other supplemental treatments compared to herbicide application alone.
Cooperators
Research
Hypothesis 1a: At the end of the growing season, we expect total standing biomass to remain the same between fall and spring prescribed fire treatments, and decrease when mowed in combination with fire.
Hypothesis 1b: At the end of the growing season, we expect grass standing biomass to remain the same between fall and spring prescribed fire treatments, and increase with herbicide applications in combination with fire.
Hypothesis 1c: At the end of the growing season, we expect sericea lespedeza standing biomass to decrease with fall prescribed fire treatments and increase with spring prescribed fire treatments. We also expect sericea lespedeza standing biomass to decrease under mowing and herbicide treatments in combination with fire treatments.
Hypothesis 2a: We expect sericea lespedeza growth to be slowed by fall prescribed fire treatments in relation to spring fire, and mowing and herbicide treatments will further reduce sericea lespedeza growth in combination with fire treatments.
Hypothesis 2b: We expect that fall fire treatments will eliminate that year's seed production during the burn, and will also reduce seed production in the following growing season because resources are removed by fire before the plant can translocate the resources belowground when entering dormancy.
Hypothesis 3: We predict that fuel load and fuel moisture will be the primary predictor variables influencing fire temperature in tallgrass prairie. As such, we therefore expect to find higher fire temperatures in patch-burn grazed prairies than in annual-burn grazed prairies because of greater fuel loads in patch-burned grazed pastures. We also expect highest fire temperatures to occur within 1 m of the ground surface due to the distribution of fuels.
Hypothesis 4: We expect that the economic cost of managing sericea lespedeza infestations with fire will be less than the cost of repeated herbicide applications.
Overarching hypothesis: We predict that by changing timing of fire and amount of fuel in areas where sericea lespedeza is problematic, sericea lespedeza vigor will be reduce while maintaining the beneficial impacts of fire.
Our research indicates patch-burn grazing results in significantly higher fire temperatures because increased fuel loads help produce fire temperatures lethal to sericea lespedeza seeds (Bell and Koerner, unpublished data). Most previous studies of fire impacts on sericea lespedeza have been conducted on small 1-5 m2 plots. Fire temperature, duration and behavior in small-scale plots is likely different than in large pastures. This study utilizes large-scale (50 X 50 m) plots and pasture-scale measurements of fire characteristics to ensure the experimental manipulation portion of this study is applicable to the pasture-scale. In the plot-scale study we will evaluate the impact of fuel load, fire season, and fire frequency on sericea lespedeza control with replicated treatments. Control of sericea lespedeza is evaluated by measuring productivity, plant density, and seed production. We will also measure dormant season minimum soil temperatures in different burn treatments to see if critical temperatures that damage the plant crown are reached. In a second pasture-scale study we will evaluate if burn conditions at the plot-scale are achieved at the pasture-scale. We will measure fire temperature and duration with pyrometers and unmanned aerial vehicles, commonly called drones, outfitted with infrared cameras at both the plot-scale location and in pastures.
We are taking both experimental approaches for several reasons. We are not applying treatments or engaging in fall burning at the pasture-scale because their effects on sericea lespedeza are unknown, and the level of infestation is quite variable both within and between pastures. Currently, land managers are excited about the prospect of using fire to control sericea lespedeza, but are resistant to fall burning because of fears of high levels of erosion. In addition, monitoring changes in sericea lespedeza density and/or productivity at the pasture-scale is prohibitive at this time. Use of drones with infrared cameras may allow us to estimate sericea lespedeza abundance at the pasture-scale because it is green much later into the growing season than most native species, but we will not be able to determine if that is the case without access to the drones with infrared cameras and additional exploration. Additionally, we would need the ground-measurements of sericea abundance we are collecting to correlate with the spectral data obtained by the drones. By combining approaches, we hope to find that fall burning, especially with additional fuel loads, is effective at controlling sericea lespedeza with little to no erosional loss or loss in grass productivity.
Site Descriptions and Experimental Design
Plot-scale – This study is located at the Marais des Cygnes National Wildlife Refuge operated by the US Fish and Wildlife Service (US FWS) near Pleasanton, Kansas. The site is a typical prairie restoration planted with native tallgrass species approximately 25 years ago with a widespread sericea lespedeza infestation. The site is divided into 50 m X 50 m burn plots. Burn treatments will be spring annual, spring triennial, fall annual, fall triennial and no burn with four replicate plots of each burn treatment. Spring burns will occur in March/April, and fall burns will occur in September/October. Each burn plot is subdivided into four sections. Each section will receive one additional treatment: fuel load supplementation, herbicide addition, mid-summer mowing, or fire only. Fuel load is supplemented by broadcasting prairie hay harvested from nearby locations at least 2 weeks prior to burning to allow hay to settle before prescribed burns. The amount of hay distributed on each subplot will approximately double the fuel load. Herbicide treatments will involve broadcast spraying with an ATV mid-summer using triclopyr (Dow Remedy® EC) and in fall using metasulfuron methyl (DuPont Escort® XP). Herbicides will be prepared and applied at the manufacturer’s suggested rate. On mowed subplots, clipped biomass will remain after mowing because sericea lespedeza densities are high enough that biomass would not be hayed (or grazed).
Pasture-scale – This study utilizes 6 pastures managed under an annual-burn grazing or patch-burn grazing strategy. Pastures are located within a 50-mile radius of Emporia, KS. Individual patches in patch-burn pastures are typically burned at three year intervals in spring with one patch burned each year whereas annual-burn pastures are burned each spring. All sites are native tallgrass prairie with limited sericea lespedeza infestations. Prescribed burns will occur in the spring burn-season at a time set by collaborators. Fire temperatures, fuel load, burn conditions and fire duration will be measured at these sites as described in following sections.
Sericea Lespedeza and Total Productivity – Plot-scale
Plots were established in June 2014, and baseline data on sericea stem density, productivity and seed production was collected prior to the first burn treatments. We are measuring sericea lespedeza stem density using 1 m2 quadrats with a minimum of 4 quadrats measured in each subplot. Productivity samples are collected near the end of the growing season (late August), and productivity is estimated by clipping all biomass at 4 locations in each subplot using a 0.5 m2 quadrats [1]. Biomass samples are sorted into grass, forb, sericea lespedeza and litter categories, and then dried at 70 C for 48 hours. Each vegetative category is weighed independently. Total productivity is the sum of grass, forb and sericea lespedeza production. We are not designating between forage and non-forage plants because the abundance of non-forage forbs other than sericea lespedeza is minimal at the site. For plots that are not burned in a given year, litter samples are collected in March, before the growing season, and used to estimate the proportion of litter in the biomass samples that was produced in that growing season.
In addition to productivity estimates, we are also monitoring individual sericea lespedeza plants. A minimum of 5 mature plants in each subplot are tagged and monitored year-to-year. Characteristics evaluated for each of these plants includes number of stems per crown, shoot height, biomass, and seeds production. The same individuals are measured year-to-year unless mortality occurs, in which case, mortality will be noted, and the next closest individual will be measured.
Minimum Soil Temperature – Plot-scale
Wintertime soil temperature at a 5 cm depth will be measured using Hobo External Temperature Data loggers (Onset, Bourne MA). This depth was chosen because this is the approximate depth of the crown of sericea lespedeza. We will install the data loggers in the annual spring burn, annual fall burn and control (unburned) plots after the fall burns are completed, and we will remove them prior to the spring burns. The loggers will be installed each year of the study.
Fire Temperature and Fuel Load
In both the plot-scale and pasture-scale studies we will measure fire temperature using pyrometers and drones with infrared cameras. The description of how drones will obtain fire temperature information follows in the next section, Fire Duration. Pyrometers will be constructed using temperature sensitive paints (79 to 593 C at 28 C intervals) applied to aluminum tiles [2,3]. At each sampling location, pyrometers placed at 0.5 m intervals from the ground surface up to 3 m above the ground surface
Fuel load and moisture content of fuel is measured within 1 m of the location where pyrometers are placed. We determine fuel load by clipping biomass in a 0.1 m2 quadrat on the day of the burn. Biomass is placed in a water-tight container, weighed and dried at 70 C for 48 hours then reweighed. Minimum and maximum litter layer depth and standing dead height are also measured prior to clipping. We will analyze litter layer depth and standing dead height against fuel load biomass to determine if litter layer depth can be used by land managers to obtain a quick estimate of fuel load. Soil temperature, soil moisture, humidity level and air temperature will be recorded just prior to the start of each prescribed burn.
Plot-scale – Fire temperature using pyrometers, fuel load, and moisture content of fuel will be measured at 4 locations in each subplot. Each sampling location is adjacent to where sericea lespedeza stem density measurements are made.
Pasture-scale – In each pasture, we will measure fire temperature with pyrometers and fuel load at a minimum of 30 points in a transect parallel to the most frequent direction of the fires.
Fire Duration
Pyrometers allow us to measure the maximum temperature and the height at which the maximum temperature occurs, but they do not provide any indication of the duration of critical fire temperatures that can effectively be lethal to mature sericea lespedeza seeds. At the time of our fall burns, most seeds are likely to be retained on mature plants, and any seeds released will likely not have an opportunity to move into the soil seed bank through freeze-thaw action. Whether fire reaches temperatures that are lethal to seeds is dependent on the duration of the fire – the shorter the duration of fire, the higher temperatures need to be to kill seeds. We will use a pair drones to monitor the movement of the fire with an attached video camera (GOPRO HERO3+ Black Edition) and the temperature profile over time with an attached infrared camera (FLIR Tau 2 LWIR Thermal Imaging Camera).
In each plot and along each transect in pastures, reference markers will be placed just above ground level so they will be visible in imagery from both cameras. The locations of each reference marker will be geo-referenced using an Archer Hemisphere GPS unit (theoretical accuracy ± 10 cm). The markers are necessary to georeference imagery obtained with drone cameras using geographic information systems software (ArcGIS 10.2.1). Georeferencing will allow us to overlay multiple image types and times to model rates of fire movement and spatial variability in fire temperature. It will also allow us to spatially compare the size of the areas with sericea lespedeza infestations over time with fire temperature, fire duration, pre-fire load, moisture measurements, soil temperature measurements and pyrometer data.
Over-Winter Erosion – Plot-scale
One concern with fall burning is over-winter erosion. In early spring or late winter before grass obscures the ground we will fly drones over the burned sites (both spring and fall) to look for signs of overwinter erosion (rills, pedestals, etc.). If there are indications of sheet or rill erosion visible from the air we will digitize their extent. We will also install erosion pins and sediment traps at a few carefully selected locations in spring and fall burned and adjacent unburned locations in the fall immediately after the burns are completed to compare erosion rates [4].
Economic Analysis
To determine whether any practice will ultimately be employed, the economics of alternatives must be analyzed. Determining productivity differences in each of the treatments and comparing the value of increased productivity to the costs of the treatments will yield useful information and should give an indication of whether the practice will ultimately be adopted by producers. Evaluation of the herbicide treatment will be the most challenging especially with variations in sericea lespedeza density. Regardless, we will evaluate broadcast herbicide application costs against spot spraying, burning only, and burning with litter addition. We will have preliminary information in three years, but potential productivity differences between the treatments in that timeframe may not be evident. Thus, expected costs and benefits over a longer time period (e.g., 10 years) will be projected based on the observed data in the study period. The economic analysis of costs and benefits will account for the timing of when costs are incurred and benefits received.
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Objective 1: Evaluate total standing biomass, grass standing biomass, and sericea lespedeza standing biomass in response to burn season coupled with herbicide, mowing, and fuel load addition treatments.
All of the prescribed burns for the annual and triennial fire treatments have been completed, as well as all sampling from the following growing season. Data from the first year (2015) of annual post-fire treatments have been analyzed, and have shown that shifting prescribed fire from spring to fall has no negative affect on grass or total standing biomass. Shifting fire to fall alone did not reduce sericea lespedeza standing biomass or stem density, but coupling fall fire with mowing significantly reduced sericea lespedeza standing biomass so that it was not statistically different from the herbicide treatments. The only treatment that eliminated sericea lespedeza completely was an herbicide application of triclopyr. These early data suggest that grazing, mowing, and/or hay production combined with switching prescribed burning from spring to fall may be a successful strategy to manage this invasive plant species. We expect similar results for subsequent years. Samples from the 2016 and 2017 growing season were collected and processing has just been completed. There was a delay in the processing of samples from 2016 because of staffing difficulties with student employees. The backlog of sample processing has been eliminated, and all of the processing was just recently completed. Analysis of these samples will likely be completed during the Summer 2018. From visual observations of sericea responses at this site, fire alone cannot keep sericea lespedeza in check when the initial densities are high, but a single herbicide treatment to kill mature plants may be sufficient if followed by fall fire annually. Observations also suggest that a 3-year burn cycle may be too long because it allows new plants to mature sufficiently to survive fire.
Objective 2: Evaluate sericea lespedeza growth and reproductive output in response to burn season coupled with herbicide, mowing, and fuel load addition treatments.
From the first year of post-fire sample collection, we found that fall fire coupled with mowing had the greatest influence on plant growth and reproductive capacity. Seeds on the plant experience over 90% mortality when the plant is burned in fall, which likely reduces the annual contribution of seeds into the seedbank. In addition, plants that were burned the previous fall produce nearly half as many seeds per plant than plants that experience spring fire. Plants experiencing fall fire before the beginning of the dormant season will also have significantly less investment into seed production than plants exposed to fire during the previous spring as shown by the seed mass: aboveground biomass. The seed mass:aboveground biomass was approximately 0.01-0.60 g/g for fall burned plants while it was approximately 0.4-2.5 g/g for spring burned plants. We are still processing the second and third year post burn plants but we expect to find similar results for subsequent years.
To evaluate if fall fire is actually lethal to sericea lespedeza seeds, we collected seeds just prior to a fall fire and then immediately after the fire and evaluated the viability of the seeds pre- and post-fire. Sericea lespedeza seed viability dropped from 80% pre-fire to 15% post-fire, showing that fall prescribed fire significantly reduces viability in sericea lespedeza. This large of reduction can have significant impact on the soil seedbank loading of sericea lespedeza seeds especially since a single plant can produce 4000 or more seeds annually. We expect that fall fire can potentially eliminate 100% of the seeds produced in a single year since we obtained these result during less than ideal burn conditions.
We also have conducted a small laboratory experiment to evaluate the necessary soil temperature and time of exposure that sericea lespedeza needs to be exposed to in order to experience over-winter mortality. To connect soil temperature minimums to burn regimes we are also measuring wintertime soil temperatures at a 10 cm depth in a pasture that was burned in fall and one that was burned in spring. The model based on exposures of 5, 0, -5, and -10 C over 6 to 48 hrs showed that soil temperatures of -10 and -5 C can result in probabilities of regrowth from 0 to 20%, respectively. The likelihood of reaching soil temperatures this low is more likely when burning in fall rather than in spring.
Objective 3: Build a fire model based on fire conditions and common management practices to predict burn conditions necessary to produce fire temperatures lethal to sericea lespedeza seed.
We have run into some difficulties with this portion of the project. The infrared camera was not operating correctly during our prescribed burns in spring 2016, and we purchased a different camera. We still have not had success collecting infrared images during a fire, even with the new camera. Part of the difficulties that we are experiencing are due to wind conditions and air turbulence during the fires that impact the safety of flying the drone. We are uncertain if we will be able to obtain any infrared images during our burns. We still have the ground data for all of our prescribed burns from the plot-scale study and and pasture-scale study. That data shows that temperatures are higher under patch-burn grazing management than under annual-burn grazing management, and that head fire heights are significantly taller under patch-burn grazing than under annual-burn grazing management. In addition, we found that the hottest temperatures occur at 0 cm and 50 cm from the ground surface. There is also a significant correlation between litter load, litter moisture and fire temperature. We still hope to be able to determine time duration that fire temperatures exceed critical temperatures that are lethal to sericea lespedeza seeds.
Objective 4: Determine the economic cost of managing sericea lespedeza infestations with fire and other supplemental treatments compared to herbicide application alone.
This objective will not be addressed until summer 2018 of this study.
Educational & Outreach Activities
Participation Summary:
Conference Presentations
Barnes†, A, C Leitch*, BA Koerner. November 2017. Altering fire season to manage an invasive legume, sericea lespedeza. 7th Association for Fire Ecology International Fire Ecology, Orlando, FL. (oral presentation)
Koerner, BA, E Lingenfelter†. January 2017. Fuel Load and Burn Season Effects on Sericea Lespedeza Growth and Reproduction. 70th Annual Society for Range Management Meeting, St. George, UT. (oral presentation)
Koerner, BA, E Lingenfelter†. January 2017. Fuel Load and Burn Season Effects on Sericea Lespedeza Growth and Reproduction. Kansas Natural Resources Conference, Wichita, KS. (oral presentation)
Lingenfelter†, E, BA Koerner. April 2016. Three Minute Thesis: The impact of fuel load and fire season on the control of sericea lespedeza. 32nd Annual Research and Creativity Forum, Emporia State University, Emporia, KS. (1st place recipient of the Three Minute Thesis Competition)
Lingenfelter†, E, BA Koerner. April 2016. The impact of fuel load and fire season on the control of sericea lespedeza. 32nd Annual Research and Creativity Forum, Emporia State University, Emporia, KS. (poster presentation)
Piva†, M., and BA Koerner. April 2016. Fire season and litter load effects on the control of sericea lespedeza. 32nd Annual Research and Creativity Forum, Emporia State University, Emporia, KS. (Oral presentation)
Piva†, M, E Lingenfelter†, and BA Koerner. February 2016. Control of sericea lespedeza: Impacy of fuel load, fire season, and fire frequency on plant density. Kansas Natural Resources Conference, Wichita, KS. (oral presentation)
Lingenfelter†, E, M Piva†, BA Koerner. February 2016. Management implications on the growth and reproductive capacity of an invasive legume, sericea lespedeza. Kansas Natural Resources Conference, Wichita, KS. (poster presentation)
Koerner, BA, M Piva†, and E Lingenfelter†. September 2015. Control of sericea lespedeza: Impact of fuel load and burn season on plant density. America’s Grasslands Conference. Fort Collins, CO. (poster)