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A factorial field experiment was designed to test the effects of small mammals and above- and below-ground invertebrates on plant species richness and composition in native tallgrass prairie at Konza Prairie Research Natural Area, northeast Kansas. Over a 4-year period, Microtus ochrogaster densities were maintained by live-trapping in fenced plots, and invertebrate levels were reduced using the pesticides carbaryl for above-ground invertebrates and an organophosphate (isofenphos) for belowground invertebrates. ANOVA according to a split-plot design of plant species biomass data harvested in 1984 and 1986 revealed few significant effects of either small mammal densities or pesticide application. Of 54 species harvested from both sample dates, only 10 were significantly affected by either treatment. Analysis of species richness according to 8 life-form classes provided a clearer pattern of response than did biomass either by species or life-form class. For example, numbers of C4 grasses were reduced by increasing small mammal densities, whereas numbers of C4 annual forbs were lowest when above-ground herbivory was reduced. While consumers have been shown to have strong effects on successional communities, the few significant results observed in this study suggests that the manipulated levels of small mammals and insects had few effects on a mature tallgrass prairie.

Native unploughed tallgrass prairie from Konza Prairie, Kansas, USA is described with respect to plant species compositional changes over a five year period in response to fire and topography. The principal gradient of variation in the vegetation is related to time since burning. Species show an individualistic response in terms of relative abundance to this gradient. Both the percentage of and cover of C4 species and all grasses decrease as the prairie remains unburnt. Forb and woody plant species numbers and abundance increase along this gradient. A secondary gradient of variation reflects topography (i.e. upland versus lowland soils). Upland soils support a higher species richness and diversity. Upland and lowland plant assemblages are distinct except on annually burnt prairie. The interaction between burning regime, topography and year-to-year climatic variation affects the relative abundance of the plant species differentially. The most dominant species overall, Andropogon gerardii, was affected only by year-to-year variation (i.e. climate). Its position at the top of the species abundance hierarchy was unaffected by burning regime or soil type. The other dominant species showed a suite of varying responses to these factors.

Eleven experimental treatments were applied to 2 x 2 m plots over 2 yr at Konza Prairie Research Natural Area, Riley County, Kansas, to ascertain why burning tallgrass prairie causes increased production and flowering. Warming of the soil in unburned plots resulted in an increase in both total production and flower stalk production of dom- inant tall grasses, primarily big bluestem (Andropogon gerardii) and Indian grass (Sor- ghastrum nutans), but the increase was small (34% increase in biomass; 78% increase in number of flower stalks) compared with that in burned plots (151 /% increase in biomass; 435% increase in flower stalks). Increased surface light intensity also appears to be a factor affecting changes in productivity following burning as suggested by the combined responses of increased productivity with removal of standing dead, whether by clipping or burning, and decreased productivity with shading. Further, the addition of ammonium nitrate in- creased yield 41 % and flowering 168% for the dominant grasses, suggesting that any factor increasing nitrogen availability would affect these vegetative parameters. Neither ash left from burning nor heating of the soil surface during burning produced detectable effects on subsequent vegetative growth. Different results for some parameters between years and between species suggest that many complex interactions operate to affect the grassland's response to burning, but surface light, soil surface temperature, and nitrogen appear to be particularly important factors.

response of height to fire was variable. In contrast, density and production of flower stalks were usually greater on the annually burned sites, whereas soil effects were inconsistent. Production of flower stalks for all three species combined ranged from 0 to 670 g/m2 during the 4-year period with maximum production occurring in a mesic year which followed a drought year. Various estimates of net primary production (aboveground biomass) have been used as ecological descriptors of grassland ecosystems throughout the world. Variations in aboveground productivity among grasslands in North America may range from 0 to 1000 g/m2/yr but within grassland types

As part of a long-term study of greater prairie chicken (Typanuchus cupido pinnatus) ecology in northeastern Kansas (Slade et al. 1965; Robe& 1966; Watt, 1969), an attempt was made to correlate movements and locations of prairie chickens with habitat types. In order to accomplish this, the various habitat types on a 2,500-hectare grassland study area had to be described. Species composition alone could not provide all the information necessary to evaluate the habitat potential of a grassland for prairie chickens. Emlen (1956) indicated that vegetation screening efficiency and density were as important as species present in describing avian habitats. Specifically, Hamerstrom et al. (1957) stated that height and density of grass were “clearly more important to the prairie chickens than species composition.” Various optical means have been used to measure the height and density of vegetation (Wight, 1938; Webb, 1942; Mossman, 1955).