Assessment of standing crop on grasslands using a visual obstruction technique provides valuable information to help plan livestock grazing management and indicate the status of wildlife habitat. The objectives of this study were to: (1) develop a simple regression model using easily measured visual obstruction to estimate standing crop on sandy lowland range sites in the Nebraska Sandhills, (2) provide sampling and monitoring suggestions in the use of visual obstruction on this grassland type, and (3) compare the visual obstruction technique to the standard clip and weigh procedure. Visual obstruction precisely predicted average standing crop dry weights for the sandy lowland range sites (r 2 = 0.88). A prediction accuracy of ± 295 kg ha-1 was found using a test data set. Two sampling options (A and B) were evaluated using a 2-stage sampling protocol. Option A (1 transect/quarter section) provided more precise estimates applicable to extensive grasslands than option B. However, option A was not applicable to a section (259 ha) or a few sections. Option B (3 transects/section) provided estimates applicable to each section and to the entire area, but it required more intensive sampling than option A to attain the same precision. The visual obstruction technique provided more precise estimates of standing crop than the standard clip and weigh technique when clipping and weighing up to 6 plots per transect. When 7 or more clipped and weighed plots per transect were sampled, standing crop estimates were more precise than using visual obstruction readings. However, since 20 visual obstruction readings/transect (25 minutes) can be sampled in about half the time spent clipping and weighing 6 plots/transect (45 minutes), visual obstruction in combination with a previously estimated regression model provides a simple, reliable, and cost effective alternative to the clip and weigh technique. Regression models should be developed for other grassland types following the methodology described in this paper.

Pre-and post-treatment aerial photography was successfully used to assess the effectiveness of a black-tailed prairie dog management program in the Conata Basin of western South Dakota where zinc phosphide bait was used to control a large and rapidly expanding prairie dog population. Five untreated colonies increased 61 percent in area over a 5-year period while seven treated colonies remained within one percent of their original size during the same time period. A comparison of preand post-treatment aerial photography also showed that mound densities within treated colonies decreased over the 5-year period while mound densities in untreated colonies increased. Reductions in mound densities resulted from mound revegetation due to reduced or a lack of prairie dog activity following rodenticide treatments. An inventory of prairie dog colonies in the Conata Basin was conducted using the posttreatment aerial photography, and a total of 224 colonies covering 23,914 acres was mapped. When compared to the cost of conventional ground methods, the use of aerial photography was cost effective at fust over six cents per acre.

These proceedings are the result of a symposium, "Conserving biodiversity on native rangelands" held on August 17, 1995 in Fort Robinson State Park, NE. The purpose of this symposium was to provide a forum to discuss how elements of rangeland biodiversity are being conserved today. We asked, "How resilient and sustainable are rangeland systems to the increasing demands of a growing human population and to extended periods of drought?" Key programs and issues, identified by a program committee, were addressed by researchers and managers. Their papers provide research results, management findings, and describe management programs currently used to conserve rangeland biodiversity.Keywords: biodiversity, rangeland, sustainability, drought, conservation You may order additional copies of this publication by sending your mailing information in label form through one of the following media. Please send the publication title and number. Telephone

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These proceedings are the result of a symposium, "Conserving biodiversity on native rangelands" held on August 17, 1995 in Fort Robinson State Park, NE. The purpose of this symposium was to provide a forum to discuss how elements of rangeland biodiversity are being conserved today. We asked, "How resilient and sustainable are rangeland systems to the increasing demands of a growing human population and to extended periods of drought?" Key programs and issues, identified by a program committee, were addressed by researchers and managers. Their papers provide research results, management findings, and describe management programs currently used to conserve rangeland biodiversity.