Pawnee National Grassland Research Articles

Soil Organic Matter Recovery in Semiarid Grasslands: Implications for the Conservation Reserve Program

Although the effects of cultivation on soil organic matter and nutrient supply capacity are well understood, relatively little work has been done on the long‐term recovery of soils from cultivation. We sampled soils from 12 locations within the Pawnee National Grasslands of northeastern Colorado, each having native fields and fields that were historically cultivated but abandoned 50 yr ago. We also sampled fields that had been cultivated for at least 50 yr at 5 of these locations. Our results demonstrated that soil organic matter, silt content, microbial biomass, potentially mineralizable N, and potentially respirable C were significantly lower on cultivated fields than on native fields. Both cultivated and abandoned fields also had significantly lower soil organic matter and silt contents than native fields. Abandoned fields, however, were not significantly different from native fields with respect to microbial biomass, potentially mineralizable N, or respirable C. In addition, we found that the characteristic small‐scale heterogeneity of the shortgrass steppe associated with individuals of the dominant plant, Bouteloua gracilis, had recovered on abandoned fields. Soil beneath plant canopies had an average of 200 g/m2 more C than between‐plant locations. We suggest that 50 yr is an adequate time for recovery of active soil organic matter and nutrient availability, but recovery of total soil organic matter pools is a much slower process. Plant population dynamics may play an important role in the recovery of shortgrass steppe ecosystems from disturbance, such that establishment of perennial grasses determines the rate of organic matter recovery.

Charadrius montanus: Montane, Grassland, or Bare-Ground Plover?

The Mountain Plover (Charadrius montanus) is an aridland member of the Charadriidae. This plover is generally considered an associate of the North American shortgrass prairie, which is dominated by blue grama (Bouteloua gracilis) and buffalo grass (Buchloe dactyloides; Graul 1975). The species breeds at many locations across the western Great Plains plus at isolated locales in western Colorado, Wyoming, and New Mexico (Leachman and Osmundson 1990) and recently in eastern Utah (K. S. Day pers. comm.). Continental populations of the Mountain Plover declined 63% from 1966 to 1991 (Knopf 1994), with the historic and current breeding stronghold being the Pawnee National Grassland in Weld County, Colorado (Graul and Webster 1976). Currently, a second major breeding population of Mountain Plovers is on the Charles M. Russell National Wildlife Refuge, Phillips County, Montana. Unlike when found on the grassland landscape of Weld County, Mountain Plovers in Phillips County selectively nest in prairie dog (Cynomys spp.) towns (Knowles et al. 1982, Olson and Edge 1985) in vegetative settings that include prickly pear (Opuntia polyacantha), fringed sagewort (Artemisia frigida), big sagebrush (A. tridentata), western wheatgrass (Agropyron smithii), and blue grama. Collectively, Weld and Phillips counties provide nesting habitat for approximately one-half of the continental population of Mountain Plovers. Despite the differences in vegetation associations at the two major nesting locales, both Graul (1975) and Olson and Edge (1985) have described the tendency of plovers to place nests in areas of low herbaceous vegetation, reduced shrub cover, and near prominent objects such as cow-manure piles or similar-sized rocks. However, plover nests on Montana prairie dog towns also occur in areas of approximately 27% bare ground, a descriptor not mentioned by Graul (1975). The bare-ground variable may have some significance in light of recent findings of plovers sometimes nesting on plowed fields (Shackford 1991, pers. comm.) and descriptions of wintering habitats of plovers that mention use of freshly plowed ground in the San Joaquin and Imperial valleys of California (Grinnell and Miller 1944). We used a methodology similar to that employed in the Montana studies to ascertain if nest sites of Mountain Plovers also include a component of bare ground in native habitats on the

Cooing Activity and Nesting of Mourning Doves in Northeastern Colorado

Cooing Activity and Nesting of Mourning Doves in Northeastern Colorado

The soil microfungal community of a South Dakota grassland

The soil microfungi of a western South Dakota grassland were quantitatively surveyed using the dilution plate technique. A 250-membered sample yielded 62 taxonomic entities. Principal forms included Acremonium sp. 4407, Aspergillus fumigatus, A. niveus, A. terreus, Chrysosporium pannorum, Fusarium oxysporum, F. solani, Mammaria echinobotryoides, Mortierella gracilis, Paecilomyces marquandii, Penicillium funiculosum, Penicillium janthinellum, Penicillium lilacinum, and Trichoderma harzianum. Comparison to other grassland surveys has revealed that the South Dakota community is most like that from the Pawnee National Grassland in eastern Colorado with less similarity to mycofloras reported for grasslands in Wisconsin and Oklahoma. Aspergillus terreus, A. fumigatus, A. niveus, Fusarium oxysporum, F. solani, Penicillium janthinellum, P. lilacinum, and Mortierella gracilis are prominent in temperate grassland communities worldwide. A slight seasonal trend was detected at the species level. Aspergillus fumigatus and Paecilomyces marquandii were predominant forms in the spring collection while Penicillium janthinellum and Papulospora sp. were present in greatest numbers in the fall. Relative densities for other species indicated that there may be heightened activity in populations of infrequent taxa in the spring. Twenty-seven and 10% of the colonies developing on dilution plates prepared in the fall and spring, respectively, grew from spores.

Decomposition of Microbial Cell Components in a Semi-Arid Grassland Soil

Cell component fractions (C-labeled) were prepared from bacterial and fungal cultures isolated from the Pawnee National Grassland in northeastern Colorado and tested for seasonal changes in degradability. The decomposition of cell component fractions was monitored from May to December of 1977 and during March of 1978, using soil samples taken at 2- to 3-week intervals. The release of CO(2) from bacterial and fungal cell walls was inversely related (P < 0.01) to the soil moisture content. Except for cytoplasm isolated from an Aspergillus sp., all other cytoplasmic and polysaccharide fractions did not demonstrate a significant relationship between soil moisture and decomposability. In general, bacterial cell walls and polysaccharides were more susceptible to decomposition than fungal cell walls, although the seasonal changes in decomposability for both fractions were similar. These patterns of cell component utilization indicate that the decomposition of cell wall material may be more closely linked, on an inverse basis, to the availability of soil moisture and release of soluble, low-molecular-weight organics resulting from primary production events.

Summer Biomass of Soil Microarthropods of the Pawnee National Grassland, Colorado

Summer Biomass of Soil Microarthropods of the Pawnee National Grassland, Colorado

Grassland Biome Network: Results of First Year

Tawny grass floating in an indigo sky bowl . . . pungent sage . . . prickly wind rushing the nostrils . . . deserted homestead, covered wagon tracks . . . tepee circles, dinosaur bones.... These are remnants of America gone by. They are also what remain of the American prairies. These, the Pawnee National Grasslands between Nunn, Colo., and Cheyenne, Wyo., serve as headquarters for one of the more ambitious ecological undertakings in the United States today-the grassland biome studies of the International Biological Program