Burning and Climate Interactions Determine Impacts of Grazing on Tallgrass Prairie Systems

Tallgrass prairie may respond differently to prescribed burning and subsequent preferential grazing, termed pyric herbivory, under variable climate conditions. This 6-yr study (2011−2016) compared tallgrass prairie pastures that were subjected to burned and unburned conditions while exposed to grazing under differing climate conditions in the Southern Great Plains of the United States. The study area consisted of six pastures, three burned and three unburned. Each burned pasture was further divided into three patches and subjected to a 3-yr rotational burning cycle. The Enhanced Vegetation Index (EVI) derived from Landsat 7/8 (EVI_LS) and Moderate Resolution Imaging Spectroradiometer (MODIS, EVI_MOD) was used to indicate vegetation production depending on size of pastures. On the basis of EVI_LS, most burned patches (11 of 18) had lesser production (overall difference of 3%) than unburned patches within the same pasture. The differences were larger (13%) in a drought yr (2011) compared with normal (3% in 2013) and wet (<1% in 2015) yrs. The distribution of precipitation controlled EVI_LS for periods during and after grazing. The burned patches tended to have lower EVI_LS during grazing periods than the unburned patches within the same pasture, probably because of selective grazing of newly grown grass in recently burned patches. In contrast, the differences in EVI_LS between during and after grazing periods were mostly (78%) smaller in burned than unburned patches. However, more variations in EVI_LS existed among pasture comparisons due to landscape heterogeneity. Similar results were observed with EVI_MOD. Overall, results demonstrated that pyric herbivory management and climate determine the impacts of grazing on tallgrass prairie systems. The contrasting seasonal forage availabilities in burned and unburned patches, indicated by different seasonality of EVI, also suggests that patch burning might better balance the quantity and quality of the grass available for cattle grazing.     

Plant Community Response Following Removal of Juniperus virginiana from Tallgrass Prairie: Testing for Restoration Limitations

Woody plant encroachment in natural grasslands is a widely documented global phenomenon that alters ecosystem dynamics by altering historic vegetation composition and suppressing herbaceous productivity. Abundant woody plants often suppress native plants sufficiently to establish successional thresholds difficult to reverse without species augmentation. Juniper (Juniperus virginiana L.) is expanding in North American tallgrass prairie, but it is currently unknown if encroachment creates successional restrictions that limit restoration potential. We selected 16 50×50-m sites with juniper canopy cover ranging from zero to approximately 75% in tallgrass prairie near Stillwater, Oklahoma, USA. Juniper trees were removed from 7 of the sites along the gradient of juniper canopy cover. Canopy cover of plant species and herbaceous plant productivity were estimated at each site 1 year before and 1, 2, and 5 years after tree removal. Before trees were removed, plant species richness and productivity declined as juniper canopy cover increased, and plant community composition dissimilarity of reference sites increased as juniper canopy cover increased. These relationships remained consistent on all non-removal sites throughout the study. The first year after juniper removal, species richness increased on all removal sites compared to intact sites and productivity on removal sites increased two years after removal. Plant community dissimilarity between reference sites and juniper removal sites remained relatively high (30–60%) the first two years after tree removal on all removal sites, but dissimilarity was about 22% 5 years after juniper removal. Within 5 years, removal sites were comparable to reference plant communities. Grassland restoration frequently requires species manipulation and additional seeding, particularly when overcoming successional limitations. Juniper encroachment into tallgrass prairie alters plant community species composition and productivity. However, in our study, juniper associated succession limitations were not apparent, and complete autogenic restoration was achieved within 5 years without seeding or species manipulation.     

Blackland Tallgrass Prairie Vegetation Dynamics Following Cessation of Herbicide Application

We studied short-term (1–3 years) responses of plant species and functional group abundances, richness, evenness, diversity, and similarity following cessation of 25 years (1972–1997) of herbicide application in a remnant of Blackland Tallgrass Prairie in central Texas. Substantial increases in plant cover from 1998 to 2000 were observed for annual forbs (359%–900%), primarily attributable to firewheel (Gaillardia pulchella Foug), but C4 perennial grass cover only marginally increased (22%–23%). These disproportionate increases elicited a directional compositional change in the plant community with dominance shifting from C4 perennial grasses to annual forbs. Species richness, evenness, and diversity decreased from 1998 to 2000 for May, but increased for June, sampling date. Conservation efforts pertaining to remnants of Blackland Tallgrass Prairie need to be cognizant that dramatic short-term effects on vegetation dynamics will occur following cessation of annual herbicide applications, and that enhancement of perennial forbs may require seeding or transplanting species.     

Nondestructive Estimation of Standing Crop and Fuel Moisture Content in Tallgrass Prairie

Accurate estimation of standing crop and herbaceous fuel moisture content (FMC) are important for grazing management and wildfire preparedness. Destructive sampling techniques have been used to accurately estimate standing crop and FMC, but those techniques are laborious and time consuming. Existing nondestructive methods for estimating standing crop in tallgrass prairie have limitations, and few studies have examined nondestructive estimation techniques for FMC in this environment. Therefore, our objective was to develop robust models for nondestructive estimation of standing crop and FMC in tallgrass prairie. We calibrated and validated stepwise multiple linear regression (SMLR) and artificial neural network (ANN) models for standing crop and FMC using data collected in tallgrass prairies near Stillwater, Oklahoma. Day of year (DOY), canopy height (CH), Normalized Difference Vegetation Index (NDVI), and percent reflectance in five wavelength bands were candidate input variables for the models. The study spanned two growing seasons and nine patches located within three pastures under patch burn management, and the resulting data set with > 3 000 observations was split randomly with 85% for model calibration and 15% withheld for validation. Standing crop ranged from 0 to 852 g m^? 2, and FMC ranged from 0% to 204%. With DOY, CH, and NDVI as predictors, the SMLR model for standing crop produced a root mean squared error (RMSE) of 119 g m^? 2 on the validation data, while the RMSE of the corresponding ANN model was 116 g m^? 2. With the same predictors, the SMLR model for FMC produced an RMSE of 26.7% compared with 23.8% for the corresponding ANN model. Thus, the ANN models provided better prediction accuracy but at the cost of added computational complexity. Given the large variability in the underlying datasets, the models developed here may prove useful for nondestructive estimation of standing crop and FMC in other similar grassland environments.     

Field Test of Digital Photography Biomass Estimation Technique in Tallgrass Prairie

Fuel loading information is important for prescribed fire planning, evaluating wildfire risk, and understanding fire effects in grassland. Yet fuel loads in grasslands often go unmeasured because of the time required to clip plots and process samples, as well as limited access or proximity to a drying oven. We tested the digital photography biomass estimation technique for measuring fuel load in grasslands in two national parks in the eastern Great Plains. The method consists of using percentage image obstruction, as determined by digital photography, to estimate vegetation biomass based on a linear transformation (i.e., regressing dry clipped weights against percent digital obstruction). We used the technique with some modification and measured digital obstruction at two sites at Wilson’s Creek National Battlefield, Missouri (WICR), and three sites at Tallgrass Prairie National Preserve, Kansas (TAPR). The method did not result in strong correlations at either of the two sites at WICR (Site 1: r²=0.02; Site 2: r²=0.32), but performed relatively well at TAPR (Site 1 [<1 yr since burn]: r²=0.82; Site 2 [2 yr since burn]: r²=0.57; Site 3 [1 yr since burn]: r²=0.88). Linear regressions for the three sites at TAPR did not differ in slope (P>0.05). In general, the denser the vegetation, the weaker the relationship between the vegetation biomass of clip plots and the percentage image obstruction of digital images. The digital photography technique may not be useful for estimating fuel loads in grasslands with relatively high biomass (>80 g · 0.1 m^?2) or digital image obstruction >50%. Large amounts of litter may also potentially reduce the accuracy of the technique.     

The Complementary Relationship of Bison Grazing and Arthropod Herbivory in Structuring a Tallgrass Prairie Community

Large mammal grazing is considered an important biological process that structures many grassland plant communities. While herbivorous arthropods are also important consumers in terrestrial systems, their interaction with large mammal grazing is poorly studied. We performed a field experiment in a tallgrass prairie manipulating arthropod abundance in both bison-grazed and ungrazed areas following a prescribed burn and monitored the plant community for 15 mo. Total plant biomass was unchanged by the end of the experiment, but individual biomass of forbs and grasses was altered by our manipulations. Forb biomass in the bison-grazed/arthropod-reduced plots was two to three times higher than other treatments, while grass biomass was higher in bison-grazed plots where arthropods were unmanipulated. Grass and forb richness showed smaller responses, with a significant difference only in ungrazed areas. Our results suggest that bison grazing and arthropod herbivory work in a complementary way; bison reduce grass biomass, allowing forbs to increase, while herbivorous arthropods reduce forb biomass, allowing grasses to increase. Our study showed that removing herbivorous arthropods may have lengthened the transition from forb to grass dominance, therefore delaying the return of conditions conducive to future disturbance by fire. Therefore, we argue that arthropod herbivory, interacting with large mammal grazing, is an additional important process affecting the plant community composition and disturbance patterns in tallgrass prairies and should be investigated further in additional grassland systems.     

Performance and Economic Returns of Stocker Cattle on Tallgrass Prairie Under Different Grazing Management Strategies

A 4-yr study was conducted to determine performance of stocker calves on tallgrass prairie under three grazing management strategies. Pastures were assigned to one of three grazing treatments. Grazing was initiated in June, and pastures were grazed only during the summer months for 57 to 104 d (79.5 ± 20.7 d). Two of the pastures were grazed season-long. Calves in one of the season-long treatments were fed a protein supplement during the second half of the grazing season; calves in the other season-long treatment were not supplemented (control group). The third pasture, an intensive early stocking (IES) treatment, was grazed at twice the stocking rate used in the season-long pastures for the first half of the grazing season (40 ± 11 d) and rested for the second half (39.5 ± 10 d). Individual stocker performance during the first half of the summer was similar among grazing treatments. Providing supplemental protein during the second half of the grazing season increased BW gain by 30 kg/ha during the last 40 d of the 80-d grazing season and increased BW gain by 12 kg/ha for the entire summer. Over the summer, IES stocker calves produced 24% more gain/ha than season-long stocked calves. Nonetheless, IES management was not more profitable than season-long grazing with or without protein supplementation. Under short-term ownership of calves in the IES system, fixed costs represented a large portion of the total cost.     

Influence of Abrams M1A1 Main Battle Tank Disturbance on Tallgrass Prairie Plant Community Structure

The Department of Defense's Range and Training Land Assessment program provides information and recommendations to range managers regarding the condition of training lands. This information is used to assist in scheduling training areas and in monitoring the effectiveness of rehabilitation projects. Fort Riley Military Installation is a major training reservation located in the Flint Hills of northeastern Kansas, within the tallgrass prairie ecosystem. A randomized complete block design composed of three treatments (M1A1 Abrams tank traffic during wet and dry soil conditions, and a nontrafficked control) with three replications was established in each of two soil types, a silty clay loam and a silt loam soil, on Fort Riley in 2003. Disturbance was created by driving the tank for five circuits in a figure-eight pattern during either during wet or dry soil conditions. Two additional experimental treatments were added during the study: five additional tank passes on one-half of each figure eight in 2004 and burning in 2006. Two areas, a curve and straightaway, within each traffic intensity (and later, burn treatment) subplot were designated for sampling. Aboveground biomass, species composition, and ground cover were measured during each growing season. Recovery of grass and total aboveground biomass in silty clay loam soil was delayed for curve areas and following disturbance in wet soil conditions, respectively. Species composition and ground cover continued to exhibit significant disturbance effects in 2007, with greatest damage observed for repeated traffic under wet soil conditions. Fire effects on vegetation were variable and generally greater for undisturbed control plots than for disturbed areas. The tallgrass prairie typically is considered to be among the most resilient of military training lands, but our research suggests that resiliency is dependent upon soil type and training conditions, and may require longer periods of recovery than previously thought.     

Perceptions of Landowners Concerning Conservation,Grazing, Fire,and Eastern Redcedar Management in Tallgrass Prairie

Successful prairie restoration will depend in part on convincing private landowners with agricultural and recreational use goals to implement appropriate rangeland management practices, such as prescribed burning and cattle grazing, to control invasive species and encroachment of woody plants. However, landowners have been slow to adopt appropriate practices in the US Midwest. The purpose of this study was to explore attitudes and behaviors of private landowners toward prescribed burning and moderate stocking as rangeland management tools. A survey was mailed to 193 landowners (response rate 51%) in the Grand River Grasslands region of southern Iowa and northern Missouri. While 68% of landowners viewed grazing as a legitimate land management tool, only half of landowners thought of fire as a legitimate tool. Over 75% of respondents believed that the increase in eastern redcedar and other trees in grasslands was a problem, with 44% considering it a major problem. Although 84% of landowners said that they had taken action to control eastern redcedar, only 25% had participated in a prescribed burn. Income from agriculture and recreational goals were negatively and significantly correlated (-0.252, P = 0.035). While holding recreational goals constant in the analysis, landowners reporting income from agriculture goals as very or extremely important were negatively and significantly associated with reporting environment and grassland factors as very or extremely important. Adoption of prescribed burning by private landowners might be more widespread if proponents focus on the effectiveness of fire for controlling eastern redcedar, which is viewed as a problem by most landowners in the region. Intervention efforts must include landowners with different goals as part of the promotion and educational process.     

Response of Acacia Sieberiana to Repeated Experimental Burning

We conducted a study on how Acacia sieberiana respond to repeated burning in the Kidepo National Park in northeastern Uganda. The study was conducted to understand effects of common burning regimes (early dry season, late dry season, and no burn [control]) in the area on Acacia sieberiana. The three treatments were applied for three consecutive years to 14 replicate blocks in a randomized block design. All A. sieberiana trees were number tagged and monitored for height and girth (diameter at breast height) growth. All fires were set as head-fires and attained intensity ranging between 422 and 5693 kW · m⁻¹. Both early and late dry season burning increased the number of small (< 49 cm) A. sieberiana trees after 2 yr. Burning did not affect the growth rates. Although the number of trees < 49 cm increased after 2 yr, the mortality in this height class was also increased by the late dry season burning, and after 3 yr of consecutive burning there were no statistical treatment differences in the height class < 49 cm. Late dry season burning also led to high mortality among trees > 250 cm in the third year. Mortality attributed to elephant browsing was important in all treatments but a substantial portion of mortality could not be attributed to any particular cause. In the late burn, fire was the most important mortality factor. Thus, 2 yr of burning may be used as a tool to stimulate recruitment of A. sieberiana, but additional years of late dry season burning will increase the mortality of older trees.     

Tallgrass Prairie Plant Community Dynamics Along a Canopy Cover Gradient of Eastern Redcedar (Juniperus virginiana L.)

North American grasslands make up less than 75% of their historic pre-European settlement area, and they continue to be converted to woodlands by woody plant encroachment. Conversion of grassland to woodland alters nutrient cycling, water use, and light penetration, which drives herbaceous plant community dynamics. Because studies examining this relationship among Juniperus species are limited largely to individual trees, we designed a study to examine the relationship between stand-level canopy cover of eastern redcedar (Juniperus virginiana L.) and the herbaceous plant community. We documented herbaceous plant species composition, abundance, and biomass within a North American tallgrass prairie invaded by eastern redcedar in which canopy cover of eastern redcedar ranged from 0% to 80%. Herbaceous species richness declined as a function of increased canopy cover of eastern redcedar and subsequent loss of open space, but this decrease in species richness closely followed a species–area model. Moreover, composition of C₃ and C₄ grasses and forbs did not change with increasing canopy cover. Herbaceous biomass, which declined with increasing canopy cover, varied most within those plots with intermediate canopy cover. While we found that species richness and biomass declined as canopy cover increased, the decline followed a species–area relationship and was without abrupt change typical of ecological thresholds. We recommend additional research with removal of eastern redcedar trees over a range of canopy cover to assess restoration potential along the encroachment gradient.     

Vegetation Response to a One-Time Spent Drilling Mud Application to Semiarid,Mixed-Grass Prairie

Landspraying while drilling (LWD) is an approved disposal method for water-based drilling mud (WBM) systems in western Canada. The mud is applied either on cultivated land, where it is incorporated by cultivation, or on vegetated land where it is not incorporated. This study examined the effects of summer WBM application (0, 15, 20, 40, and 80 m³ · ha^?1) on native vegetation properties. Our results indicated that LWD increased bare ground but decreased lichen cover at the 80 m³ · ha^?1 rate relative to the untreated control. Nitrogen (N), sulfur (S), and magnesium (Mg) concentrations in aboveground plant tissue increased with increasing LWD rate in samples taken 45 d after WBM application, but these differences disappeared 1 yr after treatment. Increase in tissue concentration of phosphorus (P) with LWD rate, however, was only detected 3 yr after LWD. Nonetheless, these changes in tissue chemistry were not associated with significant changes in biomass yield or species composition. Overall, our results suggest that single WBM applications at rates (≤ 20 m³ · ha^?1) commonly used in western Canada, if properly managed, are unlikely to adversely affect native prairie vegetation.     

Coastal Prairie Recovery in Response to Shrub Removal Method and Degree of Shrub Encroachment

Shrub encroachment into grasslands is a worldwide phenomenon with no signs of abating and numerous ecological consequences. In South Texas, honey mesquite (Prosopis glandulosa Torr.) and huisache (Vachellia farnesiana [L.] Wight & Arn.) are two shrubs encroaching into coastal prairies, reducing cover of the dominant native grass, gulf cordgrass (Spartina spartinae [Trin.] Merr. ex Hitchc.), and decreasing habitat for the endangered Aplomado Falcon (Falco femoralis), which requires grasslands or savannas for survival. To determine the best management approach for deterring shrub encroachment and restoring native grasslands, the US Fish and Wildlife Service used several shrub removal techniques within coastal prairies of the Bahía Grande Wetland Complex of the Laguna Atascosa National Wildlife Refuge, a core site for Aplomado Falcon reintroductions. Here, we assess native grass recovery over a 2-yr period in response to these shrub removal methods (mechanical plus prescribed fire and/or herbicide treatments) and degree of shrub encroachment before treatment. In general, areas with high levels of shrub encroachment before treatment had the highest amount of bare ground and lowest grass cover immediately following an initial mechanical treatment; this legacy effect persisted throughout the study irrespective of shrub removal treatment. Regardless of degree of shrub encroachment before treatment, grasses in areas treated with either mechanical or mechanical followed by herbicide methods recovered the slowest, likely due to residual woody material that hindered seed germination. Herbicide treatment following mechanical removal or mechanical removal plus fire effectively hindered shrub regrowth. Overall, mechanical treatment followed by prescribed fire and then herbicide application most effectively promoted grass recovery while hindering shrub regrowth. These findings suggest that grassland recovery following shrub encroachment into South Texas coastal prairies may be promoted through the application of shrub removal methods that combine mechanical, fire, and herbicide treatments.     

Tick Abundance and Levels of Infestation on Cattle in Response to Patch Burning

Patch burning (PB) uses frequent, spatially discrete fires throughout a pasture to create variation in the composition and structure of the plant community. The complex vegetation changes incurred from this type of burning regimen in addition to the focal grazing of cattle induced by PB should reduce tick populations by creating less favorable microhabitats. To determine if a reduction in tick populations occurred on PB pastures, three PB-treated pastures and three control pastures were used. PB pastures were divided into six subplots with one burned rotationally each spring and summer. Control pastures and each PB subplot had a burn interval of 3 yr. Pastures were dragged with 1-m² flannel cloth panels to estimate tick abundance for 4 yr. (2006, 2007, 2009, and 2010). Infestation levels with ticks (i.e., tick burden) and weight for five calves and three cows per pasture were recorded once a month from April to October in 2009, 2010, and 2011. Differences in tick abundance between PB pastures and control pastures were not significant except in 2006 when fewer adult ticks were detected in PB pastures. A total of 13 609 ticks were observed on cattle. Animals on PB pastures had 4 028 (29.6%) ticks whereas 9 581 (70.4%) ticks were on cattle from control pastures. Tick burden was significantly reduced on animals in PB pastures compared to animals in control pastures in 4 out of 6 mo. Significant differences in average daily weight gain of calves in PB and control pastures were not detected. Although differences were not detected in questing tick abundance on pastures, significant reductions of tick burden on cattle in PB-treated pastures indicates that PB can be used to help control ticks in pastures.     

扁穗雀麦种质资源形态和农艺性状变异的初步分析

检测种质资源的多样性对于利用和有效管理种质非常重要。本研究对87份世界来源的扁穗雀麦种质利用常用的9个形态-农艺性状进行了统一田间评价。结果表明,所有采用的性状变异系数均表现出高度的变异,尤其以单株干物质产量、分蘖数和叶宽的变异幅度最大。反映株型大小的各性状之间呈显著相关,茎粗和第一节间长与其余8个性状之间存在显著相关(P<0.01),旗叶宽与倒二叶宽的正相关性最强(r=0.912,P<0.01)。主成分分析(PCA)表明前2个主成分可以解释总变异的74%。反映株型大小的性状以及分蘖数可能是扁穗雀麦种质形态变异的主要来源。基于欧氏距离的UPGMA聚类分析将供试材料分成3个主要的类群,第一类群具有最大的株型表现,茎干粗壮,旗叶和倒二叶宽大,分蘖数中等;第二类群具有中等的株型;第三类群具有较小的株型,叶片短而窄,但分蘖数较多。聚类分析很好地支持了前2个主成分分值的二维散点图的结果。总之,本研究表明扁穗雀麦是一种在西南平原和丘陵地区适应性极强的禾草,其表型多样性对于品种选育和资源收集具有重要的参考价值。     

Frequent Exposure of Mice to Crude Brucella abortus Proteins Down‐regulates Immune Response

Mice repeatedly immunized via the intraperitoneal route with a Brucella abortus antigen lost their ability to develop a strong in vitro lymphoproliferative response. This result correlates with a decreased tendency of the lymphoid population to produce interferon‐γ when stimulated in culture with the immunizing antigen. With respect to the humoral response, as the number of immunizations increased, the animals produced more specific immunoglobulin M and immunoglobulin G1 antibodies. It is postulated that the long‐term exposure of an animal to Brucella antigen changes the nature of the immune response from a T‐cell‐mediated response to a humoral response favouring the establishment of the disease.     

Root Biomass and Distribution Patterns in a Semi-Arid Mesquite Savanna: Responses to Long-Term Rainfall Manipulation

Expansion of woody plants in North American grasslands and savannas is facilitated in part by root system adaptation to climatic extremes. Climatic extremes are predicted to become more common with global climate change and, as such, may accelerate woody expansion and/or infilling rates. We quantified root biomass and distribution patterns of the invasive woody legume, honey mesquite (Prosopis glandulosa), and associated grasses following a long-term rainfall manipulation experiment in a mixed grass savanna in the southern Great Plains (United States). Root systems of mature trees were containerized with vertical barriers installed to a depth of 270 cm, and soil moisture was manipulated with irrigation (Irrigated) or rainout shelters (Rainout). Other treatments included containerized, precipitation-only (Control) and noncontainerized, precipitation-only (Natural) trees. After 4 yr of treatment, soil cores to 270 cm depth were obtained, and mesquite root length density (RLD) and root mass, and grass root mass were quantified. Mesquite in the Rainout treatment increased coarse-root ( &spigt; 2 mm diameter) RLD and root mass at soil depths between 90 cm and 270 cm. In contrast, mesquite in the Irrigated treatment increased fine-root ( &spilt; 2 mm diameter) RLD and root mass between 30 cm and 270 cm depths, but did not increase total root mass (fine + coarse) compared to the Control. Mesquite root-to-shoot mass ratio was 2.8 to 4.6 times greater in Rainout than the other treatments. Leaf water stress was greatest in the Rainout treatment in the first year, but not in subsequent years, possibly the result of increased root growth. Leaf water use efficiency was lowest in the Irrigated treatment. The increase in coarse root growth during extended drought substantially increased mesquite belowground biomass and suggests an important mechanism by which woody plant encroachment into grasslands may alter below ground carbon stocks under climate change scenarios predicted for this region.     

Plant Community and Soil Environment Response to Summer Fire in the Northern Great Plains

Fire is an important process in many ecosystems, especially grasslands. However, documentation of plant community and soil environment responses to fire is limited for semiarid grasslands relative to that for mesic grasslands. Replicated summer fire research is lacking but necessary because summer is the natural fire season and the period of most wildfires in the western United States. We evaluated summer fire effects on soil temperature, soil moisture, aboveground biomass, root biomass, and functional group composition for 2 yr in semiarid C₃-dominated northern Great Plains. Following pre-treatment measures, four 0.75-ha sites were burned during August for comparison with nonburned sites, and the experiment was repeated the next year on adjacent sites to assess weather effects. Soils were about 0.5°C cooler on burned sites in the first experiment and similar in the second. Burned sites were consistently 1% drier than nonburned sites. Litter was reduced by fire but did not account for changes in soil moisture because differences occurred before the growing season. Current-year aboveground biomass and root biomass were similar between treatments, indicating productivity was resistant to summer fire. Perennial C₃ grasses increased in dominance because of positive biomass responses to fire for all but the bunchgrass, Hesperostipa comata, and a reduction of annual grasses. Perennial C₄ grasses were unaffected by summer fire. H. comata was resilient, with biomass on burned sites equaling nonburned sites the second growing season. Biomass was more responsive to precipitation than fire, and the fire-induced changes in species composition suggest exclusion of fire may be a greater disturbance than summer fire.     

Long-Term Effects of a Summer Fire on Desert Grassland Plant Demographics in New Mexico

Plant demographic responses to an experimental summer fire were monitored for 12 yr on the Sevilleta National Wildlife Refuge, New Mexico, to determine recovery rates of burned plants and evaluate fire effectiveness in preventing shrub invasion of desert grasslands. Fourteen common species of grasses, shrubs, yucca, and cacti were measured for mortality, resprouting, regrowth, herbivory, and reproduction. After the first postfire growing season, black grama (Bouteloua eriopoda [Torr.] Torr.) declined 80% in size, whereas blue grama (Bouteloua gracilis [Willd. ex Kunth] Lag. ex Griffiths) exhibited no decline. Linear regression indicated that B. eriopoda needed 11 yr to recover. Spike dropseed (Sporobolus contractus A.S. Hitchc.) and purple three-awn (Aristida purpurea Nutt.) showed postfire declines in plant sizes, requiring 4- and > 5-yr recovery times, respectively. Sand muhly (Muhlenbergia arenicola Buckl.) exhibited no fire impact. Snakeweed (Gutierrezia sarothrae [Pursh] Britt. & Rusby) sustained 61% fire mortality and reduction in regrowth canopy size. Creosotebush (Larrea tridentata [Sesse & Moc. ex DC.] Coville) had 12% mortality, but survivors recovered over 12 yr. Fourwing saltbush (Atriplex canescens [Pursh] Nutt.) sustained 62% mortality, but recovered plant size in 5–6 yr. Winterfat (Krascheninnikovia lanata [Pursh] A. D. J. Meeuse & Smit) suffered 7% mortality, but required 9+ yr to recover. Pale desert-thorn (Lycium pallidum Miers) survived fire, recovering prefire canopy size in 3 yr. Torrey joint-fir (Ephedra torreyana Watson) exhibited < 1% mortality, and recovered in 2–3 yr. Soapweed yucca (Yucca glauca Nutt.) had < 2% mortality, recovered plant sizes in 2 yr, and increased numbers of rosettes 17%. Chollas (Opuntia imbricata [Haw.] DC. and Opuntia clavata Engelm.) suffered high mortality rates and required > 12 yr recovery times. Results demonstrated that summer fire may counter some shrub and cacti invasion in central New Mexico, but once shrubs mature, fire is less effective in removing woody plants to restore southwestern grasslands.