Seasonal Emission Factors from Rangeland Prescribed Burns in the Kansas Flint Hills Grasslands.

Operational-sized prescribed grassland burns at three mid-West U.S. locations and ten 1-ha-sized prescribed grassland burns were conducted in the Flint Hills of Kansas to determine emission factors and their potential seasonal effects. Ground-, aerostat-, and unmanned aircraft system-based platforms were used to sample plume emissions for a range of gaseous and particulate pollutants. The ten co-located, 1-ha-sized plots allowed for testing five plots in the spring and five in the late summer, allowing for control of vegetation type, biomass loading, climate history, and land use. The operational-sized burns provided a range of conditions under which to determine emission factors relevant to the Flint Hills grasslands. The 1-ha plots showed that emission factors for pollutants such as PM2.5 and BTEX (benzene, toluene, ethylbenzene, and xylene) were higher during the late summer than during the traditional spring burn season. This is likely due to increased biomass density and fuel moisture in the growing season biomass resulting in reduced combustion efficiency.

Restoring fire to grasslands is critical for migrating shorebird populations.

Fire is a disturbance process that maintains the structure and function of grassland ecosystems while sustaining grassland biodiversity. Conversion of grasslands to other land uses coupled with altered disturbance regimes has greatly diminished the habitat available to many grassland-dependent species. These changes have been linked to declines in breeding bird populations, but may also be critical for migrating bird populations such as those shorebird species that depend on mesic grasslands during migration. We examined migratory shorebird use of burned grasslands in the southern Great Plains of North America using DISTANCE sampling to estimate and compare bird densities across recently burned and not recently burned landscapes (1-5 yr post fire). We conducted two surveys per week for 8-10 weeks along a 54-km route starting at the end of March and concluding in mid-May during 2014-2015. We encountered 2,509 total shorebirds in recently burned areas compared to 130 individuals in areas that were unburned. Fire was a major attractant for our three focal species with American Golden-plover (Pluvialis dominica), Upland Sandpiper (Bartramia longicauda), and Killdeer (Charadrius vociferus) densities of 20.48, 11.09, and 26.09 birds/km2 in burned areas compared with 0.00, 1.27, and 0.92 birds/km2 in unburned areas, respectively. This research illustrates the importance of burned grassland for migrating shorebirds, a phenomenon that has largely gone unreported previously. Generally, these findings add to a body of knowledge that demonstrates the value of managing grasslands with historic disturbances that vary over space and time. The application of these findings should improve decision-making for shorebird conservation and provides evidence that prescribed fire planning should include consideration for breeding, transient, and non-breeding populations that vary in their temporal use of the landscape.

Examining the assumptions of heterogeneity-based management for promoting plant diversity in a disturbance-prone ecosystem.

BACKGROUND: Patch-burn management approaches attempt to increase overall landscape biodiversity by creating a mosaic of habitats using a patchy application of fire and grazing. We tested two assumptions of the patch-burn approach, namely that: (1) fire and grazing drive spatial patch differentiation in community structure and (2) species composition of patches change through time in response to disturbance. METHODS: We analyzed species cover data on 100 m2 square quadrats from 128 sites located on a 1 × 1 km UTM grid in the grassland habitats of the Tallgrass Prairie Preserve. A total of 20 of these sites were annually sampled for 12 years. We examined how strongly changes in species richness and species composition correlated with changes in management variables relative to independent spatial and temporal drivers using multiple regression and direct ordination, respectively. RESULTS: Site effects, probably due to edaphic differences, explained the majority of variation in richness and composition. Interannual variation in fire and grazing management was relatively unimportant relative to inherent site and year drivers with respect to both richness and composition; however, the effects of fire and grazing variables were statistically significant and interpretable, and bison management was positively correlated with plant richness. CONCLUSIONS: There was some support for the two assumptions of patch-burn management we examined; however, in situ spatial and temporal environmental heterogeneity played a much larger role than management in shaping both plant richness and composition. Our results suggest that fine-tuning the application of fire and grazing may not be critical for maintaining landscape scale plant diversity in disturbance-prone ecosystems.

Characterizing grassland fire activity in the Flint Hills region and air quality using satellite and routine surface monitor data.

Prescribed grassland fires in the Flint Hills region of central Kansas and northern Oklahoma are a common tool for land management. Local to regional scale impacts on air quality from grassland fires in this region are not well understood, which is important as these types of prescribed fires may increase in the future to preserve broader areas of native grasses in the central U.S. Routine air quality and deposition measurements from sites in and near the Flint Hills were examined for coincident increases during periods of increased prescribed grassland fires. Prescribed fire activity in this region was quantified using satellite detections and multiple publicly available data products of area burned information. March and April comprise over half (41 to 93%) of all annual fire detections in the Flint Hills region seen from satellites between 2007 and 2018 excluding drought years. Annual total fire detections in this region range between 1 and 12 thousand and account for approximately 3% of all fire detections in the contiguous U.S. Annual acres burned ranged from 0.2 to 2 million acres based on U.S. EPA's National Emission Inventory, which accounts for 4 to 38% of grasslands in the area. A comparison of weekly standardized anomalies suggests a relationship between periods of increased grassland fire activity and elevated levels of PM2.5 organic carbon, elemental carbon, and potassium. Daily 1-hr maximum ozone (O3), ammonia (NH3), sulfur dioxide (SO2), and oxidized nitrogen gases measured at Konza Prairie also had increased levels when prescribed grassland fire activity was highest. This detailed characterization of prescribed fire activity in the Flint Hills and associated air quality impacts will benefit future efforts to understand changes in atmospheric composition due to changing land management practices.

Volatile Organic Compound Emissions from Prescribed Burning in Tallgrass Prairie Ecosystems.

Prescribed pasture burning plays a critical role in ecosystem maintenance in tallgrass prairie ecosystems and may contribute to agricultural productivity but can also have negative impacts on air quality. Volatile organic compound (VOC) concentrations were measured immediately downwind of prescribed tallgrass prairie fires in the Flint Hills region of Kansas, United States. The VOC mixture is dominated by alkenes and oxygenated VOCs, which are highly reactive and can drive photochemical production of ozone downwind of the fires. The computed emission factors are comparable to those previous measured from pasture maintenance fires in Brazil. In addition to the emission of large amounts of particulate matter, hazardous air pollutants such as benzene and acrolein are emitted in significant amounts and could contribute to adverse health effects in exposed populations.