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Winter Hardiness and Phenology of the 8pecies .. 189 EcoLOGICAL STUDIES OF Bronws tectorum E<'ological Monographs VoL 25, No. 2 LEWISTON WATER PLANT (e!ev. 226m) Prt at Study Depth of Area Month Highest Lowest Mean Normal Actual snow, (elev. temr t•mp temp ppt ppt sleet & 350m), OF OF OF in. in. hail. in.

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 dominant tall grasses, primarily big bluestem (Andropogon gerardii) and Indian grass (Sorgastrum 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 increased 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.

Two— by two—meter plots of undisturbed, nearly pure Andropogon gerardi prairie were subjected to four treatments: burning, clipping and removal of the litter, burning the clipped litter and returning the ash, and the control (natural litter). Treatments were started in early April before growth began. Differences in results among the denuded plots were small and nonsignificant, but highly significant differences were found between denuded and control plots. Tiller number was increased 1.5 to 2.7 times by removal of litter. Growth began earlier in denuded than control plots. On May 31 yields were twice as great in denuded as in control plots. On September 1 ovendry yields were about 340 g/m2 in denuded and 180 in control plots. Soil temperatures were 1°/5°C higher in denuded than control plots the entire growing season, the differences lessening as the season progressed. Soil moisture was appreciably higher in control plots the entire season. The short—term effects of spring burning in undisturbed bluestem prairie with clay—loam soils are apparently related primarily to litter removal rather than to nutrient changes.

Highlight:Postsettlement invasion of trees and shrubs on the bluestem prairie of Geary County in the Kansas Flint Hills was assessed using aerial photos, General Land Office survey data, and field observations. Tree cover increased 8% from 1856 to 1969 throughout the county, although on regularly burned sites combined tree and shrub cover was effectively maintained at presettlement amounts. On unburned sites, aerial photographs showed that combined tree and shrub cover increased 34% from 1937 to 1969; section-line data showed that tree cover alone increased 24% from 1856 to 1969. Data from two sites suggested that herbicide spraying only slowed the invasion rate. Woody plants increased only slightly on shallow, droughty clay loam soils located on level uplands, ridgetops, and upper slopes. On deeper and more permeable middle-and lower-slope soils, woody plants increased more than 40% from 193740% from to 196940% from . In 1937by 1950 they had increased to 89%; change was slight thereafter. The increase in coverage of the lowland soils from 1856 to 1937 suggests that these soils are rapidly invaded. We conclude that on the Flint Hills bluestem prairie rangeland, (1) burning has been effective in restricting woody plants to natural, presettlemen t amounts and (2)-soil type and topography affect the rate of woody-plant invasion.