Tallgrass Prairie Site Research Articles

A Technique for Quantifying Fire Behavior in Grassland Fire Ecology Studies

A Technique for Quantifying Fire Behavior in Grassland Fire Ecology Studies

Effects of Late Summer Fire on Tallgrass Prairie Microclimate and Community Composition

Two tallgrass prairie sites with different grazing histories and fuel accumulation were burned to investigate vegetation response to wild fires of differing intensity. Headfires were ignited 5 September 1985 under wildfire weather conditions (37 C air temperature, 36%7o relative humidity and wind gusts to 40 km/h). One of the burned plots had not been grazed for the past 3 years and had 1000 g/m2 fine fuel load; the other had been grazed moderately and had 450 g/m2 fine fuel. Fire intensity at the soil surface on the high fuel-load plot was four times that on the the low fuel burn plot. Microhabitat and vegetation responses were monitored the year following burning. Measured vegetative parameters, including tiller density, basal area and production, indicated that rhizomatous tallgrasses revegetated both burned plots quickly. Bunchgrasses decreased in both basal area and production on the high fuel plot. Community composition and productivity differences persisted 1 yr after the fires and were mainly attributable to bunchgrass mortality and microhabitat improvement for ruderal species. The data suggest that intensity is an important factor to consider when developing disturbance theory for tallgrass prairie. INTRODUCTION The tallgrass prairie ecosystem is often cited as an example of a fire-tolerant system which evolved with as a part of its natural disturbance regime (Adams et al., 1982). Tallgrass prairie is not regarded as a strict fire type but it has been shown that protection results in loss of productivity by the dominant grasses (Weaver and Rowland, 1952; Aikman, 1955; Ehrenreich, 1959; Hulbert, 1969; Anderson et al., 1970) and eventual replacement by woody species (Weaver, 1968; Bragg and Hulbert, 1976). Aboriginal and lightning-set fires are believed to have maintained the northern and eastern borders of this grassland well into climatic regions where forest would be considered climax vegetation (Vogl, 1974; Vankat, 1979; Axelrod, 1985). Most controlled experimental fires in tallgrass prairie have been conducted in the spring for a variety of reasons, including: (1) Researchers have long been interested in the increased productivity and renewed vigor of dominant grasses such as Andropogon gerardii Vit. following a spring burn (Curtis and Partch, 1950; Dix and Butler, 1954; Ehrenreich, 1959; Kucera and Ehrenreich, 1962; Hadley and Kieckhefer, 1963; McMurphy and Anderson, 1965; Old, 1969; Kucera, 1970; Launchbaugh and Owensby, 1978; Knapp, 1984a); (2) spring burns can be conducted in relative safety (Anderson, 1982; Wright and Bailey, 1982); (3) it had been incorrectly perceived that in other seasons, particularly summer, was not possible because of green or insufficient fuel (Bragg, 1982) and low probability of lighting-caused ignition (Hulbert, 1973), and (4) summer is not desirable because it removes forage valued for livestock grazing (Bragg, 1982). Prescribed spring burning does little damage to dominant warm-season grasses (C4) while reducing the vigor of cool-season plants (C3), thus giving the vegetation a boost toward theoretical tallgrass climax. This is a much studied and welldocumented phenomenon (Anderson et al., 1970). Additionally, there is a stimulatory effect on the rhizomatous tallgrasses due to the fire, by the removal of litter and timely microclimate improvement (Old, 1969; Knapp, 1984a). However, the intensity of spring fires may differ from that of fires occurring in summer and autumn. Historical accounts (Higgins, 1986) show that 85% of the 'This is journal article no. 5251 of the Oklahoma Agricultural Experiment Station.

Konza Prairie Research Natural Area of Kansas State University

Konza Prairie Research Natural Area (KPRNA) is an 8616 acre (3487 ha) tract consisting mostly of native tallgrass prairie, and is located in southern Riley county in the Flint Hills of eastern Kansas. Following the leadership of L. C. Hulbert, The Nature Conservancy (TNC), with money provided by Katharine Ordway, set aside KPRNA during the period 1971 to 1979. Under ownership and lease agreements between TNC and Kansas State University, the site is managed for research by the Division of Biology. Research activity has been increasing steadily on KPRNA since 1977 when it was set aside for ecosystem research. The core of the management involves experimental manipulation of watersheds with controlled fire (several replicated intervals between fire from 1 to 10 years plus unburned references) and with native and domestic grazers (planned reintroduction of bison and cattle to different treatment watersheds in November 1987) (Hulbert, 1985). The tallgrass prairie ecosystem once covered about 7% of the U.S., i.e., most of the Midwest (Kiichler, 1964). In most states where the type dominated the presettlement landscape (Illinois, Iowa, Indiana, southern Wisconsin, southern Minnesota, northern Missouri, eastern Nebraska, eastern North Dakota and eastern South Dakota) the soils have been plowed and converted to grain production agriculture, among the most productive agricultural areas in the world. Not much unplowed prairie is left and the opportunity for watershed level work under unplowed conditions does not exist at any other tallgrass prairie site in the United States. The National Science Foundation included KPRNA in its network of sites dedicated to long-term ecological research (LTER). That research has been underway since late 1980. Kings Creek, a central tract of 2619 acres (1060 ha) on KPRNA, was added to the U.S. Geological Survey's network of benchmark watersheds in 1979 (Biesecker and Leifeste, 1975) and the drainage area has been identified as a fixed station in the Survey's pilot research program termed National Water Quality Assessment (NAWQA) (Stamer, pers. comm.).

Light Interception and Leaf Area Estimates from Measurements of Grass Canopy Reflectance

Grassland is a major component of the Earth's available land. The vast area and remoteness of this ecosystem makes it difficult to assess its condition and monitor productivity by traditional niethods. Remote sensing potentially offers a rapid nondestructive approach for monitoring such ecosystems. A study was carried out in a tallgrass prairie site near Manhattan, Kansas, during the 1983 and 1984 seasons to investigate the feasibility of estimating light interception and green leaf area index (LAI) from measurements of canopy multispectral reflectance. Greenness (G, i) index was found to be strongly correlated with intercepted photosynthetically active radiation ( PAR). Two methods, a direct regression (RGR) and an indirect approach (IND), were used to estimate LAI from Goi index. The LAI values estimated by RGR method were consistently lower than the measured ones; however, good agreement was obtained between the LAI values estimated by IND method and the measured LAI. This suggests that Goi transformation of canopy spectral reflectance is more closely related to the fraction of intercepted PAR by green foliage than the quantity of green LAI.

The use of stable carbon isotope analysis in rooting studies.

Stable carbon isotope analysis was evaluated as a means of predicting the relative proportions of C3 and C4 root phytomass in species mixtures. The following mixtures of C3 and C4 species were used: 1) big bluestem (Andropogon gerardii)/cheatgrass (Bromus tectorum), 2) little bluestem (Schizachyrium scoparium)/cheatgrass, and 3) sorghum (Sorghum bicolor)/sunflower (Helianthus annuus). There was a significant correlation (P<0.01) between % C4 phytomass and stable carbon isotope values for each of the three combinations (r 2>0.98). Root length per mass varied among the five species studied (10.1-94.3 m/g), which resulted in different conclusions depending on whether root values are expressed as length or mass. For example, field samples from a tallgrass prairie site were estimated to contain about 20% cheatgrass on a mass basis, whereas the figure was 68% when expressed in terms of length. The combination of stable carbon isotope analysis with length-for-mass measurements promises to be a useful means of studying root competition between C3 and C4 plants.

Impact of management practices on the tallgrass prairie

The ELM ecosystem-level grassland model simulates the flow of water, heat, nitrogen, and phosphorus through the ecosystem and the biomass dynamics of plants, consumers, and the decomposers. This model was adapted to a tallgrass prairie site in northeastern Oklahoma, USA, the Osage Site of the U.S. International Biological Program Grassland Biome. Several range management manipulations were simulated by the model and the results compared to field data and literature information: (1) altering the grazing intensity, grazing system, and grazing time period; (2) adding nitrogen and phosphorus to the grassland; (3) adding water during the growing season; and (4) spring burning of the prairie.The model showed that cattle weight gain per head, above-ground and belowground plant production, transpiration water loss, standing dead biomass, and the net nitrogen balance decrease with increasing grazing intensity, while soil water content and bare soil water loss increase. A moderately stocked year-round cow-calf grazing system is more beneficial to the grassland than a more highly stocked seasonal steer grazing system because the former increases the aboveground and belowground primary production and the plant nutrient uptake rates. Range manipulations, such as fire, which stimulate uniform grazing of a pasture, increase primary production, cattle weight gains, and nutrient uptake of plants and animals. Model results indicated that adding fertilizer was the best strategy for increasing cattle weight gains per head, while adding water would produce the greatest increase in primary production. Simulation of yearly and triennial spring burns suggests that these treatments increase primary production, plant nutrient uptake, and cattle weight gain per head. Burning increases the nitrogen losses from the systems; however, these losses are greater with annual burns. The model results also suggest the spatial grazing pattern of cattle must be considered to correctly represent the impact of grazing on the prairie.The model is used to describe the behavior of the tallgrass prairie ecosystem, evaluate alternative management strategies, and identify future scientific research and management studies.

The Effect of Disturbances in Tall Grass Prairie Sites on an Index of Diversity and Equitability

The Effect of Disturbances in Tall Grass Prairie Sites on an Index of Diversity and Equitability

Small Mammal Energetics in Grassland Ecosystems

Results of quantitative sampling of small mammal populations at different grassland sites for a 3—yr period are compared to evaluate the energy requirements and consumption, according to trophic levels, for total small mammal communities at all seasons in different years. The purpose was to search for patterns of food utilization by these consumers at the different sites. This picture of the bioenergetics of small mammal populations over a wide range of grassland sites was constructed from extensive US/IBP Grassland Biome diet and population data and from physiological information out of the literature. The work represents one step in the process of understanding the role of consumers in the ecosystem. No species occurs at all sites and different trophic strategies predominate among the small mammals at each site: Microtines (herbivores) dominate the tallgrass prairie, sciurids (omnivores) dominate the northern shortgrass prairie, and heteromyids (granivores) dominate the bunchgrass and desert grasslands. Other groups occur at these sites and vary in their importance. At the tallgrass and midgrass sites the small mammal populations are largely dependent on herbage consumption, while at the northern and southern shortgrass prairie sites the rodent fauna is largely dependent on invertebrates. The most uniform distribution of resource utilization by this component of the consumer community occurs at the desert grassland site, where herbage, seeds, and animal matter are all utilized. Relative to the total amount of consumable herbage available (that actually utilized by the small mammal population), this resource is only slightly utilized (from a fraction to a few percent of available). Animal matter, largely invertebrates, is highly utilized at most sites and may in fact be a limiting factor on small mammal populations. The energy consumed by the small mammal population was greatest at the tallgrass prairie site, where the average annual consumption was 172 x 103 kcal/ha (= 720 MJ/ha). However, efficiency of biomass support was greatest at the northern shortgrass prairie site, where consumption of 32 x 103 kcal/ha (= 134 MJ/ha) supported proportionately more biomass (277 g live wt./ha) of animals than at the tallgrass site (935 g/ha). The estimates of population energy requirements presented here compare well with other available estimates. These results emphasize the great between year and site variability, however. Daily population respiration in summer may be as little as 14 and as large as 1,038 kcal°ha—1°day—1. Highest small mammal biomass occurred at the tallgrass (3,075 g live wt./ha) and the desert (2,304 g/ha) sites, and lowest at the midgrass (14 g/ha) site. Within the period of study, small mammal biomass was most stable at the southern shortgrass site and most variable at the tallgrass site. The role of small mammal populations in grassland ecosystem remains incompletely defined. A broader view of the total consumer community in relation to resources is required.

Habitat Heterogeneity and Avian Community Structure in North American Grasslands

In a variety of environments, patchiness of habitat structure appears related to faunal diversity. I examined the relations between vegetational heterogeneity and several attributes of avian communities over a range of North American grassland and shrub steppe situations. Habitat heterogeneity was measured by assessing the variability in vertical density of vegetation within clustered point samples, and an index to express this horizontal patchiness was derived. Heterogeneity was directly related to the areal coverage of bare ground and woody vegetation and to patchiness in litter distribution of sample plots, and inversely related to grass coverage and litter depth. Heterogeneity generally increased with decreasing annual precipitation and primary production, tall grass-prairie sites being the least and western shrub steppe the most heterogeneous. Analysis of breeding bird population censuses from these plots revealed no apparent relationships between habitat heterogeneity and the diversity of breeding avifaunas or the extent of spatial (territorial) overlap between species. The density of breeding bird populations decreased slightly witth increasing vegetation patchiness; the standing crop biomass of the avian community, however, decreased markedly as heterogeneity increased. This pattern appeared to result from a replacement of largesized species by medium-sized species in the transition from tall grass to short grass areas and an increasing dominance of small-sized species in the western Palouse and shrub steppe sites. INTRODUCTION Many workers have recently drawn attention to the relation between habitat structure and faunal diversity. In deciduous forests in eastern North America, for example, the diversity of breeding bird species in a community increases with increasing patchiness or vertical layering of the vegetation (MacArthur and MacArthur, 1961; MacArthur, 1965), and a correlation between increasing habitat complexity and diversity in breeding bird faunas seems most general (e.g., Karr and Roth, 1971; Cody, 1970; Orians, 1969). Diversity in lizard faunas also may be related to habitat complexity (Pianka, 1967; Schoener and Schoener, 1971), and the structure of some small mammal communities may be closely tied to structural heterogeneity of the environment (Rosenzweig and Winakur, 1969). These observations and others have led to the development of a rather extensive body of theory of habitat heterogeneity (e.g., Levins, 1968; MacArthur and Levins, 1964, 1967; MacArthur and Pianka, 1966), although a good deal of this theory remains untested. In forest communities a good share of the increase in bird species diversity with increasing patchiness in the vertical distribution of foliage may be due to an increased vertical layering of the bird species. Spatial overlap between species, as projected on a single horizontal plane, may thus be extensive. In structurally simple habitats such as