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.

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Plots in an ungrazed, re—established grassland near Omaha, Nebraska, USA, dominated by little bluestem (Andropogon scoparius), were burned at 3—wk intervals from March through November 1976. The amount of vegetative biomass consumed during burning, a measure of flammability, was high throughout the study period, varying from >99% in April to 84% in mid—June. Areas burned in March were able to carry a second fire in October of the same year. High flammability throughout the growing season, in conjunction with current fire and climatic records, suggests that widespread, late—summer fires were probably common in presettlement, ungrazed, bluestem prairies.

At present, most turtles, all crocodilians, and several lizards are known to have temperaturedependent sex determination (TSD). Due to the dependence of sex determination on incubation temperature, the long-term survival of TSD species may be jeopardized by global climate changes. The current study was designed to assess the degree to which this concern is justified by examining nest-site selection in two species of Pattern I1 TSD geckos (Eublepharis macularius and Hemithecoryx caudicinctus) and comparing these preferences with those of a species with genotypic sex determination (GSD) (Cohoonyx mitratus). Temperature preferences for nest sites were found to be both species-specific and female-specific. While H. caudicinctus females selected a mean nest-site temperature (32.4') very close to the upper pivotal temperature (32OC) for the species, E. mmlarius females selected a mean nest-site temperature (28.7"C) well below this species' lower pivotal temperature (30.5'C). Thus, the resultant sex ratios are expected to differ between these two TSD species. Additionally, nest-site temperatures for the GSD species were significantly more variable (SE= k0.37) than were temperatures for either of the TSD species (E. m l n r i u s SE = 0.10; H. cuudziinctus SE = +_ 0.17), thereby further demonstrating temperature preferences within the TSD species.

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