Shortgrass Community Research Articles

A gap dynamics simulation model of succession in a semiarid grassland

We applied a gap dynamics conceptualization of succession to a semiarid grassland by focusing on gaps produced in the belowground resource space by death of an individual of the dominant species, the perennial grass blue grama ( Bouteloua gracilis (H.B.K.) Lag. ex Griffiths). We developed a gap dynamics simulation model to examine long-term successional dynamics on gaps, time required for B. gracilis to recolonize gaps, and spatial variability of gap dynamics at the scale of the landscape. The model is similar to gap models used in forest, but is based on belowground resource use and life history characteristics of plants in shortgrass communities, and incorporates effects of small-scale disturbances and stochastic environmental factors. Average time required for B. gracilis to dominate biomass on a simulated plot was 20 years, a more rapid recovery time than has been reported from experimental studies of large-scale disturbances. Our initial simulations assumed the only control on establishment of B. gracilis seedlings was the occurrence of a restrictive set of microenvironmental conditions. A second set of simulations incorporating effects of seed availability resulted in an average recovery time of 65 years. The scale dependence of successional processes important to recruitment of B. gracilis plants is indicated since this is still a faster recovery time than was observed experimentally. Aboveground biomass on the simulated plots was dominated by B. gracilis through time and space. Relative proportion of aboveground biomass and average biomass values for each species were comparable to the composition of shortgrass plant communities at the Central Plains Experimental Range study site in northcentral Colorado. This initial analysis suggests that gap processes are important to shortgrass communities, and that a gap dynamics conceptualization based on the importance of small, frequently occurring disturbances is a promising alternative to the previous conceptual model of shortgrass communities based on effects of large-scale disturbances.

Fort Hays State University Natural Areas

Two natural areas are supervised by the Department of Biological Sciences at Fort Hays State University and are known as the and the Cedar Bluff In 1900 the Federal government granted old Fort Hays to Kansas. The 35 acre (14.2 ha) relict natural area was included in the 4160 acres (1683.5 ha) that became Fort Hays State University. The area is located in the SE 1/4 Sec. 1, T. 14S, R. 19W in Ellis County. The relict area has not been grazed since 1902. Ruts made by wagons coming to and from the Fort remain and can be seen cutting across the relict area. The topography of the relict area is characterized by steep to gentle slopes bordering a central drainage area. The site contains strata of the Niobrara Chalk, particularly the Fort Hays Limestone Member. A cap of Loveland Loess overlies the Fort Hays Limestone on upland areas. Parent materials consist of loess, limestone, alluvium, and shale. Four major communities are found in this area. The upland shortgrass community is dominated by buffalograss (Buchloe dactyloides), blue grama (Bouteloua gracilis) and western wheatgrass (Agropyron smithii), and occurs on deep loessial soils of the Mento series. The hillsides are dominated by big bluestem (Andropogon gerardii), little bluestem (Andropogon scoparius), and side-oats grama (Bouteloua curtipendula). The shallow calcareous Brownell soils underlying the hillside community support diverse forb populations. A homogeneous big bluestem community parallels the major drainage and is developed on alluvial and colluvial Armo soils. A large ravine traverses the relict area and is dominated by big bluestem, kochia (Kochia scoparia), and common sunflower (Helianthus annuus). The weediness of the lowland community is possibly the result of seepage from the farm pond located on the upper end of the drainage. The lowland has alluvial Roxbury soils.

Assessing ground conditions of small sites by aerial infrared photography

The false-colour infrared photograph of Lightmoor Tip in the Forest of Dean, Gloucestershire (Fig. 1) was taken using a radio controlled camera plane. The tip is associated with past coal extraction from the Carboniferous Limestone. In this example, infrared and natural colour aerial photography were used to determine topographical and subsurface information. Geomorphological and ecological processes have created various microenvironments at the site. The majority of the soil supports vegetation. The aerial infrared photograph shows not only the major plant communities, but also their health and relative densities. Dark red to dark pink areas correspond to healthy, dense growths of vegetation, whilst colour tones of pink and grey depict poor or stressed vegetation. Exposed substrates and routeways appear greenish blue to light grey. Increased amounts of surface moisture result in darkening of ground colours. A short grass community forms the initial colonizer of the tip and dominates the site. Grass health is poor on steep slopes, particularly over rock and scree debris, where vegetation is absent in places. Notably healthy, dense growths of grass are visible in zones where there may be water collection or seepage. A second natural community, consisting of gorse and low shrubs, is present on more sheltered and gentle slopes. The majority of this vegetation is thin and in poor health. Development from the short grass to scrub vegetation has progressed where the slopes are stable. The configurations of these slopes and nature of the vegetation would suggest that they represent older scree debris. Figure 2

Sixty Years of Successional History Behind a Moving Sand Dune Near Olduvai Gorge, Tanzania

Sixty Years of Successional History Behind a Moving Sand Dune Near Olduvai Gorge, Tanzania

Effects of Livestock Grazing on Sediment Production, Edwards Plateau of Texas

The influence of short duration grazing (SDG), moderate continuous grazing (MCG), heavy continuous grazing (HCG), and grazing exclusion on sediment production of midgrass and shortgrass-dominated communities was evaluated over a 20-month period on the Texas Agricultural Research Station located near Sonora in the Edwards Plateau, Texas. A combination of cattle, sheep, and goats was used in each grazing treatment. Sediment production was consistently less from the midgrass (bunchgrass) than from the shortgrass (sodgrass) community. The HCG pasture was severely overgrazed and resulted in excessive soil loss. The midgrasses in this pasture were destroyed after 26 months of overgrazing. Sediment production from the SDG pasture stocked at double the recommended rate increased during the study period. The SDG pasture, by the end of the study, had lost more sediment from both the midgrassand shortgrass-dominated communities than the MCG pasture. Sediment loss from the midgrass community in the MCG pasture was consistently low during the study; however, sediment production from the shortgrass community decreased in the MCG pasture. Sediment production from the midgrass community in the non-grazed pasture remained consistently low throughout the study, but the shortgrass community showed a strong decrease in sediment loss during the study. Historically, grazing has been an integral part of rangelands (Mack and Thompson 1982) and native herbivores have coevolved with grasslands and most shrublands. However, the introduction of domestic livestock increased the potential for adversely impacting rangeland watersheds. Rangelands by their very nature are naturally large contributors of sediment (Branson et al. 1981). Livestock grazing has the potential of altering the amount and kind of vegetation, which in turn potentially alters surface soil hydrologic characteristics (Blackburn et al. 1982). Reductions in the amount of vegetation may increase raindrop impact, decrease soil organic matter and aggregates, increase surface soil crusting, and decrease infiltration rates (Chapman 1933, Branson and Owen 1970, Blackburn 1975, Wood and Blackburn 1981). Altering the kind of vegetation may also increase sediment losses. Sediment production of sagebrush (Artemisia spp.) canopy zones in Nevada was less than that of the adjacent interspace areas (Blackburn 1975). Sediment loss from shortgrass-dominated sites in the Rolling Plains of Texas was greater than from adjacent midgrass or shrub canopy sites. Livestock grazing altered the sediment loss most from the midgrass-dominated areas and had little or no influence on the shrub canopy zones or shortgrass areas (Wood and Blackburn . 1982). Much interest has been generated by specialized grazing systems and their potentials for decreasing erosion and adding economic benefits to the ranching industry. However, little information is available to support many of the claims concerning specialized grazing systems (Gifford and Hawkins 1978, Blackburn et al. 1982). The purpose of this study was to determine: (1) the influence Authors are graduate research assistant, and professor of watershed management, Range Science Department, Texas AM and professor of range science, Texas Agricultural Experiment Station, Sonora 76950. Published with approval of the Director, Texas Agricultural Experiment Station, as TA1 8839. Manuscript received July 25, 1983. of heavy continuous grazing, moderate continuous grazing, short duration grazing, and no grazing on sediment loss, and (2) the variables influencing sediment loss.

Effects of Livestock Grazing on Infiltration Rates, Edwards Plateau of Texas

The influence of short duration grazing (SDG), moderate continuous grazing (MCG), heavy continuous grazing (HCG), and gmzingexcusionon iralonntesof -ig--and s asdominated communities was evaluated over a 20-month period on the Texas Agricultural Research Station, located near Sonora in the Edwards Plateau, Texas. A combination of cattle, sheep, and goats were used in each grazing treatment. Infiltration rates were consistently less in the midgrass (bunchgrass) than in the shortgrass (sodgrass) community. The HCG pasture was severely overgrazed and infiltration rates were reduced to about one-half those in the MCG pasture. The midgrasses in this pasture were destroyed after 26 months of overgrazing. Infiltration rates in the SDG pasture, stocked at double the recommended rate, decreased during the study period. Infiltration rates in the SDG pasture shortgrass community, near the end of the study, approached those in the HCG pasture. The greatest infiltration rates for both communities were maintained in the MCG pasture. Infiltration rates for the midgrass community remained relatively stable during the study when the general trend in the SDG and HCG pastures was toward reduced infiltration rates. The nongrazed pasture subsequent to the 1980 drought had a general increase in infiltration rates. Infiltration rates vary naturally in time and space because of normal variations in climate, vegetation, and intensity and duration of livestock use. Few studies have attempted to account for these natural variations. The literature is filled with examples of the adverse impact of heavy or abusive grazing on infiltration rates. Few research projects have studied seasonal or long-term impacts of grazing systems or proper grazing management on infiltration rates (Blackburn et al. 1982). Much interest has been generated by specialized grazing systems and their potentials. Short duration grazing and its potential economic benefits to the ranching industry have become extremely popular (Savory 1978). Little information is available, however, to support many of the claims concerning specialized grazing systems. Gifford and Hawkins (1978) found no published evidence to show that any single grazing system consistently or significantly increased plant and litter cover on watersheds. Other reviews (Van Pollen and Lacey 1979, Beck 1980) of the impacts of grazing support Gifford and Hawkins' conclusions. Most of the information on the impact of specialized grazing systems on infiltration rates come from studies conducted in the Rolling Plains and Edwards Plateau of Texas. The results of these studies indicate that infiltration rates of pastures grazed under a deferred-rotation system (4-3:12:4 mo)1 were similar to those of livestock exclosures and greater than high intensity, low frequency pastures (8-1:17:119 days) or moderate or heavy continuously grazed pastures (McGinty Authors are graduate research assistant and professor of watershed management, Range Science Department, Texas AM and professor of Range Science, Texas Agricultural Experiment Station, Sonora 76950. Published with approval of the Director, Texas Agricultural Experiment Station, as TA-I 8727. Manuscript received May 31, 1983. 'Nomenclature follows Kothmann 1974. et al. 1978, Wood and Blackburn 1981). Infiltration rates of pastures grazed under a high intensity, low frequency system were similar to moderate continuously grazed pastures (Wood and Blackburn 1981, Blackburn et al. 1982). Livestock grazing can alter infiltration rates of rangeland soils by removing protective plant cover and by trampling. Vegetation and mulch cover serve to protect the soil surface from raindrop impact and influence soil surface properties such as bulk density, organic matter content, and aggregation (Osborn 1954, Copeland 1963, Blackburn 1975, Meeuwig and Packer 1976, Blackburn et al. 1982). Reduced infiltration rates as a result of livestock grazing have been attributed to: ( loss of vegetation cover, (2) decreased mulch cover, (3) decreased amounts of vegetation standing crop and mulch, (4) increased bare ground, and (5) increased bulk density as a result of trampling (Alderfer and Robinson 1947, Knoll and Hopkins 1959, Reed and Peterson 1961, Branson et al. 1962, Copeland 1963, Dee et al. 1966, Rauzi and Hanson 1966, Smith 1967, Blackburn et al. 1982). Type of vegetation is important in determining infiltration rates (Blackburn 1975). Infiltration rates are consistently higher in bunchgrass-dominated areas than in sodgrass-dominated areas (Blackburn et al. 1980, Wood and Blackburn 1981). Livestock grazing has the greatest potential impact on bunchgrasses. Not only are bunchgrasses usually the better forage species but they are usually more sensitive to heavy grazing pressure than low-growing sodgrasses (Wood and Blackburn 1981). Objectives of this study were to determine: (1) infiltration rates of pasture soils under short duration grazing; moderate continuous grazing; and heavy continuous grazing; and grazing exclusion; and (2) the variables influencing infiltration.

Impact of a White Grub (Phyllophaga crinita) on a Shortgrass Community and Evaluation of Selected Rehabilitation Practices

Impact of a White Grub (Phyllophaga crinita) on a Shortgrass Community and Evaluation of Selected Rehabilitation Practices

Population Density and Biomass of the Desert Termite Gnathamitermes Tubiformans (Isoptera: Termitidae) in a Shortgrass Prairie: Relationship to Temperature and Moisture

Fluctuations in the population density and biomass of Gnathamitermes tubiformans (Buckley) in the upper 30.2 cm of soil were determined over a 2—yr period in a shortgrass community in Garza County, Texas. Linear stepwise multiple regression was used to determine the relationships of termite population densities with environmental factors in this soil increment. Termites were not present in the upper 30.2 cm when the soil temperature at 15 cm was < 9 degrees C. Termite population densities in the upper 30.2 cm of soil varied significantly between years as a function of air and soil temperatures, precipitation and soil moisture. Consideration of data from relatively short time periods alleviated many difficulties in identifying biologically important causal factors. In a year of above—normal precipitation, temperature was the most important factor affecting desert termite population densities, whereas during a year of below—normal precipitation, soil moisture was the most important factor. Biomass of desert termites in the upper 30.2 cm of soil averaged 5.83 g/m2 (live—weight) over the 2—yr period and reached a peak of 23.03 g/m2 during September 1972. The abundance of tunnels and chambers of G. tubiformans decreased with depth in the soil profile. Termites migrated below 124 cm in subterranean galleries to avoid soil temperatures < 10 degrees C.

A POPULATION OF SPIDERS AND THEIR POTENTIAL PREY IN AN OVERGRAZED PASTURE IN EASTERN ONTARIO

The relationships between spiders, their physical environment, and their potential prey are examined. A method of sampling arthropod populations in a short-grass community with a suction sampler and some errors inherent in the method are described. The distribution of individual spiders among the species agreed with Fisher's logarithmic series. The distribution of spiders in space conformed to the negative binomial series, and is ascribed to the distribution of shelters in the community. Though variations in numbers of spiders in parts of the community are ascribed to births and deaths, and to migrations caused by variations of weather, the overall population remained stable. Potential prey species were classified into functional roles and size classes. Size classes of prey conformed to size classes of spiders. Total numbers and biomass of potential prey remained constant over the season, though the constituent elements varied widely with time. No direct relationship between the number of spiders and the number of prey was detected, but a mechanism is suggested whereby the spiders may contribute to stability of prey populations.

Vegation Changes During a 30‐Year Period in Grassland Communities Near Hays, Kansas

Three plant communities near Hays, Kansas, showed considerable change in the composition of their dominant vegetation over the 30—year period from 1932 to 1961. The short grass community was dominated by Buchloe dactyloides and Bouteloua gracilis in 1932 and dominated only by Bouteloua gracilis in 1961. The little bluestem community was dominated by Andropogon scoparius during favorable years but by Bouteloua curtipendula and Bouteloua gracilis during drought years. The dominants of the little bluestem—big bluestem community were Andropogon scoparius and Andropogon gerardi in 1932 but by 1961 Andropogon gerardi was the only dominant. Two droughts periods, 1933—39 and 1952—56, were important in affecting these vegetation changes.