• Hurricane Sourgrass: Scourge or Blessing!

      Judd, B. Ira (Society for Range Management, 1965-11-01)
      A plea is made for research on hurricane sourgrass in the tropics. In spite of its reputation as a troublesome weed under many conditions, it produces feed in time of drought when more palatable species remain dormant.
    • Hydrologic and Biotic Effects of Grazing vs. Non-grazing Near Grand Junction, Colorado

      Lusby, G. C. (Society for Range Management, 1970-07-01)
      The effect of grazing on the hydrology of salt-desert type rangeland has been studied near Grand Junction, Colorado for the past 14 years. Measurements of precipitation, runoff, erosion, and vegetation have been made in four pairs of watersheds. One of each pair has been grazed by cattle and sheep as is normal in the region, and the other has not been used since the beginning of the study. Measurements made 10 years apart show that all four grazed watersheds have had a slight increase in the amount of bare soil and rock and a decrease in ground cover; cover on ungrazed watersheds has remained essentially unchanged. Runoff in the ungrazed watersheds has been about 30 percent less than in the grazed watersheds and sediment yield has been about 45 percent less. The greatest change in each of the relationships occurred about 3 years after livestock were excluded from one watershed of each of the pairs. Preliminary studies indicate that within areas of similar physiography, runoff is directly related to the percentage of bare soil present on a watershed.
    • Hydrologic and Erosion Responses of Sagebrush Steppe Following Juniper Encroachment, Wildfire, and Tree Cutting

      Pierson, Frederick B.; Williams, C. Jason; Hardegree, Stuart P.; Clark, Patrick E.; Kormos, Patrick R.; Al-Hamdan, Osama Z. (Society for Range Management, 2013-05-01)
      Extensive woodland expansion in the Great Basin has generated concern regarding ecological impacts of tree encroachment on sagebrush rangelands and strategies for restoring sagebrush steppe. This study used rainfall (0.5 m2 and 13 m2 scales) and concentrated flow simulations and measures of vegetation, ground cover, and soils to investigate hydrologic and erosion impacts of western juniper (Juniperus occidentalis Hook.) encroachment into sagebrush steppe and to evaluate short-term effects of burning and tree cutting on runoff and erosion responses. The overall effects of tree encroachment were a reduction in understory vegetation and formation of highly erodible, bare intercanopy between trees. Runoff and erosion from high-intensity rainfall (102 mm h-1, 13 m2 plots) were generally low from unburned areas underneath tree canopies (13 mm and 48 g m2) and were higher from the unburned intercanopy (43 mm and 272 g m-2). Intercanopy erosion increased linearly with runoff and exponentially where bare ground exceeded 60%. Erosion from simulated concentrated flow was 15- to 25-fold greater from the unburned intercanopy than unburned tree canopy areas. Severe burning amplified erosion from tree canopy plots by a factor of 20 but had a favorable effect on concentrated flow erosion from the intercanopy. Two years postfire, erosion remained 20-fold greater on burned than unburned tree plots, but concentrated flow erosion from the intercanopy (76% of study area) was reduced by herbaceous recruitment. The results indicate burning may amplify runoff and erosion immediately postfire. However, we infer burning that sustains residual understory cover and stimulates vegetation productivity may provide long-term reduction of soil loss relative to woodland persistence. Simply placing cut-downed trees into the unburned intercanopy had minimal immediate impact on infiltration and soil loss. Results suggest cut-tree treatments should focus on establishing tree debris contact with the soil surface if treatments are expected to reduce short-term soil loss during the postcut understory recruitment period.
    • Hydrologic and sediment responses to vegetation and soil disturbances

      Giordanengo, J. H.; Frasier, G. W.; Trlica, Frasier (Society for Range Management, 2003-03-01)
      Soil erosion has been linked to stream sedimentation, ecosystem degradation, and loss of rangeland productivity. However, knowledge of soil loss, as it affects rangeland productivity or ecosystem sustainability is lacking. We evaluated the effects of 3 levels of vegetation cover reduction (0, 27%, and 43%) and soil removal (0, 12, and 24 tonnes ha-1) on soil surface runoff and sediment yield in a sagebrush [Artemisia tridentata var. vasseyana (Rydb.) Beetle] steppe under simulated rainfall. Time to runoff initiation was affected by the vegetation cover reduction treat- ments, but not by the soil removal treatments. The 43% vegeta- tion canopy reduction treatment resulted in a shorter time to runoff initiation than did the 27% and 0% canopy reduction treatments (p = 0.002). Results from analysis of covariance indicated that vegetation reduction and soil removal did not significantly affect sediment yield or runoff quantities in the first year following treatments. Multiple regression analysis revealed total sediment yield was related to forb cover, sand in the upper soil profile (0-5 cm), and the amount of bare ground. Time to runoff initiation was positively correlated with slope. Despite the lack of significant treatment differences, we do not conclude that these soil removal and vegetation reduction treatments had no affect on soil surface hydrology and sediment yield. There are numerous studies that show a strong relationship between vegetation reduction and soil erosion. Future research at this site may reveal long-term treatment effects that were not apparent in first year results.
    • Hydrologic characteristics immediately after seasonal burning on introduced and native grasslands

      Emmerich, W. E.; Cox, J. R. (Society for Range Management, 1992-09-01)
      Fire on rangelands used as a management tool or as an unwanted wildfire removes vegetation cover. Vegetation cover is thought to be a dominate factor controlling surface runoff and erosion. Vegetation removal by a burn should have an immediate effect on runoff and erosion. Surface runoff and sediment production were evaluated immediately after fall and spring season burns at 2 locations with different soil and vegetation types for 2 years in southeastern Arizona. The evaluations were conducted with a rainfall simulator at 2 precipitation intensities. Immediately after a burn there was not a significant change in runoff and erosion, therefore, vegetation cover by itself was concluded not to be a dominate factor controlling surface runoff and erosion. The increase found in surface runoff and sediment production from the burn plots was not significantly greater than the natural variability for the locations or seasons. Significantly higher surface runoff and sediment production was measured in the fall season compared to the spring at 1 location.
    • Hydrologic Characteristics of Vegetation Types as Affected by Livestock Grazing Systems, Edwards Plateau, Texas

      Thurow, T. L.; Blackburn, W. H.; Taylor, C. A. (Society for Range Management, 1986-11-01)
      Infiltration rate and sediment production were assessed in oak, bunchgrass and sodgrass vegetation types in moderate continuous (MCG), heavy continuous (HCG), and intensive rotation (short-duration, SDG) grazing systems and in a livestock exclosure (LEX). Infiltration rate was related to the total organic cover and bulk density characteristics of the site (R2 = .86). The amount of cover was more important than type, indicating that protection of soil structure from direct raindrop impact was the primary function of cover on infiltration. The SDG and HCG pastures had lower total organic cover with correspondingly lower infiltration rates compared to the MCG and LEX pastures. Bulk density, an indicator of soil structure, was significantly lower in oak mottes than in the grass interspace, but there was no significant difference between pastures. Sediment production was related to the total aboveground biomass and the bunchgrass cover of the site (R2 = .79). Obstruction to overland sediment transport and protection from the disaggregating effect of direct raindrop impact were the primary functions of the total aboveground biomass and bunch-grass cover. Total aboveground biomass was greatest in the oak motte and least in the sodgrass interspace, consequently the sod-grass interspace had the greatest amount of sediment production and the oak mottes had the least sediment production. Midgrass cover and total aboveground biomass in the MCG and LEX pastures was significantly greater than in the SDG and HCG pastures; thus sediment production from the MCG and LEX pastures was significantly lower than from the SDG and HCG pastures.
    • Hydrologic characteristics of vegetation types as affected by prescribed burning

      Hester, J. W.; Thurow, T. L.; Taylor, C. A. (Society for Range Management, 1997-03-01)
      The objective of this study was to determine how rangeland hydrology of oak, juniper, bunchgrass and shortgrass vegetation types is altered by fire. The research was conducted at the Sonora Agricultural Experiment Station on the Edwards Plateau, Texas. Infiltration rate and interrill erosion were measured using a drip-type rainfall simulator. Terminal infiltration rates of unburned areas were significantly greater on sites dominated by oak (Quercus virginiana Mill.) (200 mm hour-1) or juniper (Juniperus ashei Buchh.) (183 mm hour-1) than on sites dominated by bunch-grass (146 mm hour-1) or shortgrass (105 mm hour-1). Terminal infiltration rates on burned areas were significantly reduced on sites dominated by bunchgrass (110 mm hour-1), shortgrass (76 mm hour-1), and on oak sites that were cut and burned (129 mm hour-1). Soil organic matter content (r = .61), total organic cover (r = .59), and aggregate stability (r = .53) were the variables most strongly correlated with infiltration rate. Measured soil structure properties were not altered by fire, therefore, differences in infiltration rate between unburned and burned treatments were attributable to variations in the amount of cover. The terminal infiltration rate of cut and burned juniper sites (162 mm hour-1) was not changed significantly after the fire because the associated good soil structure properties allowed rapid infiltration even after cover was removed. Good soil structure properties were also present on the oak sites, but the infiltration rate significantly decreased as a result of the temporary hydrophobic nature of the soil on this site after burning. Prior to burning, interrill erosion was much lower under the tree sites (oak = 2 kg ha-1; juniper = 34 kg ha-1) than on bunchgrass (300 kg ha-1) or shortgrass (1,299 kg ha-1) sites. After burning, interrill erosion significantly increased for all vegetation types (shortgrass = 5,766 kg ha-1; bunchgrass = 4,463 kg ha-1; oak = 4,500 kg ha-1; juniper = 1,926 kg ha-1). Total organic cover (r = -.74) and bulk density at 0-30 mm (r = .46) were most strongly correlated with interrill erosion.
    • Hydrologic Impacts of Mechanical Seeding Treatments on Sagebrush Rangelands

      Pierson, Frederick B.; Blackburn, Wilbert H.; Van Vactor, Steven S. (Society for Range Management, 2007-11-01)
      In and around the Great Basin, United States, restoration of shrub steppe vegetation is needed where rangelands are transitioning to annual grasslands. Mechanical seedbed preparation can aid native species recovery by reducing annual grass competition. This study was designed to investigate the nature and persistence of hydrologic and erosion impacts caused by different mechanical rangeland seeding treatments and to identify interactions between such impacts and related soil and vegetation properties. A cheatgrass (Bromus tectorum L.)-dominated site was burned and seeded with native grasses and shrubs in the fall of the year. An Amazon-drill and a disk-chain seeder were used to provide varying levels of surface soil disturbance. An undisturbed broadcast seeding was used as a control. Simulated rainfall was applied to 6 large (32.5-m2) plots per treatment over 3 growing seasons at a rate of 63.5 mm h-1. Rainfall was applied for 60 minutes under dry antecedent moisture conditions and for 30 minutes, 24 hours later under wet antecedent moisture conditions. The disk-chain created the largest reduction in infiltration and increase in sediment yield, which lasted for 3 growing seasons posttreatment. The Amazon-drill had a lesser impact, which was insignificant after the second growing season posttreatment. Surface soil properties showed little correlation with treatment-induced hydrologic and erosion impacts. Hydrologic recovery was strongly correlated with litter dynamics. The seeding treatments were unsuccessful at establishing seeded plant species, and the site once again became dominated by cheatgrass. A continuous upward trend in biomass production and surface litter cover was observed for all treatments between the beginning and end of the study because of cheatgrass invasion. Although the initial goal of using mechanical seeding treatments to enhance recovery of native grass species failed, cheatgrass production provided sufficient biomass to rapidly replenish surface litter cover necessary for rapid hydrologic stability of the site. 
    • Hydrologic impacts of sheep grazing on steep slopes semiarid rangelands

      Wilcox, B. P.; Wood, M. K. (Society for Range Management, 1988-07-01)
      Infiltration, sediment concentration of runoff, and sediment production from lightly grazed and ungrazed semiarid slopes were compared using a hand-portable rainfall simulator. The study slope was located in the Guadalupe Mountains of southeastern New Mexico. Average slope steepness was 50%. The objective of this study was to determine the impacts of light grazing by sheep (10 ha/ AU) on steep slope infiltrability and sediment production. Infiltrability on the grazed slopes was 12-17% lower than on the ungrazed slopes. These results are comparable to what has been reported from moderate slope gradients. Sediment concentration of runoff from the lightly grazed slopes was significantly higher than from the ungrazed slopes only at the end of the dry run (45 min). Sediment production was significantly greater from the grazed slopes for the dry run, but not the wet run. Percentage difference of sediment production between the grazed and ungrazed slopes was well within the range published for moderate slope conditions. These data give no indication that steep slopes (30-70%) in semiarid regions are any more hydrologically sensitive to light grazing than are moderate slopes (<10%).
    • Hydrologic modeling of a treated rangeland watershed

      Osborn, H. B.; Simanton, J. R. (Society for Range Management, 1990-11-01)
      The measured runoff from a contour-ripped rangeland watershed is compared with hypothetical runoff based on KINEROS model simulations assuming that the watershed had not been treated. The results indicate that such models as KINEROS can provide a valuable additional tool for evaluation of range treatments and could possibly be used “before the fact” to determine probable water-yield impacts of a rangeland treatment.
    • Hydrologic Response of a Central Nevada Pinyon-Juniper Woodland to Prescribed Fire

      Rau, Benjamin M.; Chambers, Jeanne C.; Blank, Robert R.; Miller, Wally W. (Society for Range Management, 2005-11-01)
      This study was conducted to determine the effect of prescribed fire on surface hydrology in Great Basin pinyon-juniper (Pinus monophylla Torr. & Frém.—Juniperus osteosperma Torr.) woodlands. Infiltration rates were measured using a single ring infiltrometer over an elevation gradient (2 103, 2 225, and 2 347 m) at 3 microsites (tree canopy, shrub canopy, and interspace) and 2 tree cover types (intermediate and high) in August 2001, before a spring prescribed burn conducted in May 2002, and then following the prescribed burn in August 2002. Infiltration experiments were used to calculate saturated hydraulic conductivity (K[ϴs]) rates, and water drop penetration times were determined to evaluate the development of water-repellent soils. Infiltration rates before the burn were greater at the low elevation than at the mid and high-elevation study sites because of differences in measured soil texture. Before burning, the infiltration and saturated hydraulic conductivity (K[ϴs]) rates measured on interspace and shrub canopy microsites were less than on tree canopy microsites at the midelevation study site (2 225 m). Following burning, the intermediate tree cover tree canopy microsites had greater infiltration rates than interspace microsites; all other microsites were similar to each other. No significant differences in K(hs) rates existed among the microsites after burning. However, on the higher elevation study site before the burn, the interspace microsites had final infiltration rates less than the tree canopy microsites, and burning caused no deviation from this trend. Saturated hydraulic conductivity rates at the high elevation did not differ by microsite before the burn, but after burning interspace microsites had K(ϴs) rates less than tree canopy microsites. Burning increased water repellency of surface soils (0-3 cm) for all cover types. Spring burning in Pinyon-juniper woodlands may produce a hydrologic response depending on surface soil texture and vegetation cover. 
    • Hydrologic response of diverse western rangelands

      Pierson, F. B.; Spaeth, K. E.; Weltz, M. A.; Carlson, D. H. (Society for Range Management, 2002-11-01)
      There are several generalizations or assumptions concerning rangeland hydrology and erosion relationships found in the literature and in the management arena. These generalizations have found their way into rangeland models, where modelers have assumed that diverse rangeland types can be lumped or averaged together in some way to develop one algorithm or equation to describe a process or relationship across the entire spectrum of rangeland types. These assumptions and modeling approaches based on the universal concept may not be appropriate for diverse rangeland types. This paper presents a comprehensive data set of vegetation, soils, hydrology, and erosion relationships of diverse western rangelands, and utilizes the data to assess the validity of the various assumptions/generalizations for rangelands. The data set emphasizes the difficulty in understanding hydrologic responses on semiarid rangelands, where the relationship between plant/soil characteristics and infiltration/erosion is not well established. When all sites were pooled together, infiltration and sediment production were not correlated with any measured vegetation or soil characteristic. A myriad group of factors determine infiltration and erosion, and is dependent on rangeland type and site conditions. The infiltration and erosion responses and correlation/regression analyses presented highlight the risk of using generalized assumptions about rangeland hydrologic response and emphasize the need to change the current modeling approach. Universal algorithms to represent the response of all rangeland types, such as the pooled multiple regression equations presented, will not provide sufficient accuracy for prediction or assessment of management. We need to develop a rationale to organize rangeland types/vegetation states according to similarities in relationships and responses. These functional rangeland units would assist in the development of more accurate predictive equations to enhance model performance and management of rangelands.
    • Hydrologic Response to Mechanical Shredding in a Juniper Woodland

      Cline, Nathan L.; Roundy, Bruce A.; Pierson, Fredrick B.; Kormos, Patrick; Williams, C. Jason (Society for Range Management, 2010-07-01)
      We investigated soil compaction and hydrologic responses from mechanically shredding Utah juniper (Juniperus ostesperma [Torr.] Little) to control fuels in a sagebrush/bunchgrass plant community (Artemisia nova A. Nelson, Artemisia tridentata Nutt. subsp. wyomingensis Beetle Young/Pseudoroegneria spicata [Pursh] A. Löve, Poa secunda J. Presl) on a gravelly loam soil with a 15% slope in the Onaqui Mountains of Utah. Rain simulations were applied on 0.5-m2 runoff plots at 64 mm h-1 (dry run: soil initially dry) and 102 mm h-1 (wet run: soil initially wet). Runoff and sediment were collected from runoff plots placed in five blocks, each containing four microsites (juniper mound, shrub mound, vegetation-free or bare interspace, and grass interspace) with undisturbed or tracked treatments for each microsite type and a residue-covered treatment for grass and bare interspace microsites. Soil penetration resistance was measured at the hill slope scale, and canopy and ground cover were measured at the hill slope and runoff plot scale. Although shredding trees at a density of 453 trees ha-1 reduced perennial foliar cover by 20.5%, shredded tree residue covered 40% of the ground surface and reduced non-foliar-covered bare ground and rock by 17%. Tire tracks from the shredding operation covered 15% of the hill slope and increased penetration resistance. For the wet run, infiltration rates of grass interspaces were significantly decreased (39.8 vs. 66.1 mm h-1) by tire tracks, but infiltration rates on juniper mounds and bare interspaces were unchanged. Bare interspace plots covered with residue had significantly higher infiltration rates (81.9 vs. 26.7 mm h-1) and lower sediment yields (38.6 vs. 313 g m-2) than those without residue. Because hydrologic responses to treatments are site- and scale-dependent, determination of shredding effects on other sites and at hill slope or larger scales will best guide management actions. 
    • Hydrologic responses of a montane riparian ecosystem following cattle use

      Flenniken, M.; McEldowney, R. R.; Leininger, W. C.; Frasier, G. W.; Trlica, M. J. (Society for Range Management, 2001-09-01)
      Riparian areas link streams with their terrestrial catchments and decrease water pollution by trapping sediments from upland sources before they reach streams or lakes. Livestock grazing in riparian areas is a controversial practice. If not properly managed, cattle can cause degradation to both the riparian zone and adjacent water body. Vegetative, soil microtopographical, microchannel and hydrograph parameters were measured in a montane riparian community in northern Colorado to quantify the effects of cattle on overland flow and runoff characteristics. Treatments were cattle grazing plus trampling, cattle trampling, mowing, and a control. Water was applied to plots (3 m x 10 m) at a rate of 100 mm hr(-1) using a rainfall simulator. Concurrently, overland flow was introduced at the upper end of the plots at an equivalent rate of 25 mm hr(-1). A high intensity-short duration grazing treatment was used for the cattle-treated plots. Reduction in vegetation stem density and aboveground biomass by cattle decreased microchannel sinuosity and drainage density. Cattle-treated plots had greater flow velocities and depths in microchannels compared with mowed and control plots. Reduced stem density and aboveground biomass by grazing left fewer obstacles to divert flows, which decreased microchannel sinuosity and drainage density. Flows were concentrated into fewer microchannels with deeper flows. Microchannel characteristics were not significant factors affecting total runoff. Stem density and rainfall intensity were the most important factors in predicting runoff characteristics and total runoff. Results from this study have improved our understanding of flow and runoff processes following cattle use of a riparian ecosystem.
    • Hydrologic responses of shortgrass prairie ecosystems

      Weltz, L.; Frasier, G.; Weltz, M. (Society for Range Management, 2000-07-01)
      Runoff hydrographs from 3 separate rainfall simulation runs at 11 different shortgrass prairie sites were evaluated to determine the hydrologic similarity within a single ecosystem at widely separated sites. There were no consistent patterns in the equilibrium runoff among sites and simulator runs. When the sites were stratified by soil type, there were differences in time-to-peak of the runoff event and the regression slope of the rising limb of the runoff ratios. Spearman's rank correlation showed no relation of the rising limb slope regression coefficient to measured vegetative characteristics across all sites. There was minimal correlation between the runoff regression coefficient and the percent cover and bare soil. Differences in the biotic components of the sites were not useful in predicting runoff characteristics. If equilibrium runoff was the measured hydrologic response, the sites were dissimilar. Using the time-to-peak and slope of the rising limb components of the runoff hydrograph, the sites were similar on the same soil type. The technique of comparing components of the runoff hydrograph, other than equilibrium runoff has promise to allow one to quickly compare responses among ecosystems to determine if they have similar hydrological functions. Our study on shortgrass prairie sites indicated that easily estimated factors such as biomass, cover and litter were not good indicators of hydrologic function. Also, it is necessary to identify which portion of the runoff event is most important in the assessment. Future hydrologic and erosion models need to develop nonlinear prediction equations to estimate infiltration rates as a function of cover, biomass, and soil properties and also to stratify soils into functional units to accurately estimate runoff rates.
    • Hydrologic Vulnerability of Sagebrush Steppe Following Pinyon and Juniper Encroachment

      Pierson, Frederick B.; Williams, C. Jason; Kormos, Patrick R.; Hardegree, Stuart P.; Clark, Patrick E.; Rau, Benjamin M. (Society for Range Management, 2010-11-01)
      Woodland encroachment on United States rangelands has altered the structure and function of shrub steppe ecosystems. The potential community structure is one where trees dominate, shrub and herbaceous species decline, and rock cover and bare soil area increase and become more interconnected. Research from the Desert Southwest United States has demonstrated areas under tree canopies effectively store water and soil resources, whereas areas between canopies (intercanopy) generate significantly more runoff and erosion. We investigated these relationships and the impacts of tree encroachment on runoff and erosion processes at two woodland sites in the Intermountain West, USA. Rainfall simulation and concentrated flow methodologies were employed to measure infiltration, runoff, and erosion from intercanopy and canopy areas at small-plot (0.5 m2) and large-plot (13 m2) scales. Soil water repellency and vegetative and ground cover factors that influence runoff and erosion were quantified. Runoff and erosion from rainsplash, sheet flow, and concentrated flow processes were significantly greater from intercanopy than canopy areas across small- and large-plot scales, and site-specific erodibility differences were observed. Runoff and erosion were primarily dictated by the type and quantity of ground cover. Litter offered protection from rainsplash effects, provided rainfall storage, mitigated soil water repellency impacts on infiltration, and contributed to aggregate stability. Runoff and erosion increased exponentially (r2 5 0.75 and 0.64) where bare soil and rock cover exceeded 50%. Sediment yield was strongly correlated (r250.87) with runoff and increased linearly where runoff exceeded 20 mm?h21. Measured runoff and erosion rates suggest tree canopies represent areas of hydrologic stability, whereas intercanopy areas are vulnerable to runoff and erosion. Results indicate the overall hydrologic vulnerability of sagebrush steppe following woodland encroachment depends on the potential influence of tree dominance on bare intercanopy expanse and connectivity and the potential erodibility of intercanopy areas. 
    • Hydrothermal Assessment of Temporal Variability in Seedbed Microclimate

      Hardegree, Stuart P.; Moffet, Corey A.; Flerchinger, Gerald N.; Cho, Jaepil; Roundy, Bruce A.; Jones, Thomas A.; James, Jeremy J.; Clark, Patrick E.; Pierson, Frederick B. (Society for Range Management, 2013-03-01)
      The microclimatic requirements for successful seedling establishment are much more restrictive than those required for adult plant survival. The purpose of the current study was to use hydrothermal germination models and a soil energy and water flux model to evaluate intra- and interannual variability in seedbed microclimate relative to potential germination response of six perennial grasses and cheatgrass. We used a 44-yr weather record to parameterize a seedbed microclimate model for estimation of hourly temperature and moisture at seeding depth for a sandy loam soil type at the Orchard Field Test Site in southwestern Ada County, Idaho. Hydrothermal germination response was measured in the laboratory for two seed lots of cheatgrass (Bromus tectorum L.), four seed lots of bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] L¨ ove), three seed lots of bottlebrush squirreltail (Elymus elymoides [Raf] Swezey), and one seed lot each of Sandberg bluegrass (Poa secunda J. Presl.), big squirreltail (Elymus multisetus [J.G. Smith] M.E. Jones), thickspike wheatgrass (Elymus lanceolatus [Scribn. And J.G. Smith] Gould) and Idaho fescue (Festuca idahoensis Elmer). Germination response models were developed to estimate potential germination rate for 13 subpopulations of each seed lot for every hour of the 44-yr simulation. Seedbed microclimate was assessed seasonally and for each day, month, and year, and germination rate-sum estimates integrated for a numerical index of relative site favorability for germination for each time period. The rate-sum favorability index showed a consistent pattern among seed lots for different years, and provides a relatively sensitive indicator of annual and seasonal variability in seedbed microclimate. This index could be used with field data to define minimum weather thresholds for successful establishment of alternative plant materials, in conjunction with weather forecast models for making restoration and fire rehabilitation management decisions in the fall season, for evaluation of potential climate-change impacts on plant community trajectories, and in optimization schemes for selecting among alternative restoration/rehabilitation management scenarios.
    • Hyperspectral One-Meter-Resolution Remote Sensing in Yellowstone National Park, Wyoming: I. Forage Nutritional Values

      Mirik, Mustafa; Norland, Jack E.; Crabtree, Robert L.; Biondini, Mario E. (Society for Range Management, 2005-09-01)
      Hyperspectral 1-m-resolution remote sensing has the potential to reduce the time spent sampling and reduce spatial sampling errors found in traditional forage nutritive analysis over large areas. The objective of this study was to investigate if 1-m-resolution hyperspectral techniques are useful tools to provide reliable estimates of forage nitrogen (N), phosphorus (P) and neutral detergent fiber (NDF) in Yellowstone National Park. The vegetative communities investigated varied in the amount of canopy coverage and species diversity, and ranged from xeric, semiarid environments to mesic, wetland/riparian environments. A large number of simple ratio-type vegetation indices (SRTVI) and normalized difference-type vegetation indices (NDTVI) were developed with the hyperspectral dataset. These indices were regressed against N, P, and NDF values from ground collections. We found that 1) there were strong linear relationships between selected SRTVI and N (R2 = 0.7), P (R2 = 0.65), and NDF (R2 = 0.87) nutritive values on an area basis (g m-2); and 2) there were no strong linear relationships (R2 < 0.3) between a variety of SRTVI and NDTVI and N, P, and NDF on a dry matter basis (g g-1 X 100). The lack of relationship is related to 1) the highly variable relationship between the dry matter biochemical signal and total plant biomass and water content and 2) the weakening of the biochemical signal from exposed soil in low-canopy situations, from nonphotosynthetic vegetation (bark, stems, and litter), and from different plant species.  
    • Hyperspectral One-Meter-Resolution Remote Sensing in Yellowstone National Park, Wyoming: II. Biomass

      Mirik, Mustafa; Norland, Jack E.; Crabtree, Robert L.; Biondini, Mario E. (Society for Range Management, 2005-09-01)
      This study was designed to determine the utility of a 1-m-resolution hyperspectral sensor to estimate total and live biomass along with the individual biomass of litter, grasses, forbs, sedges, sagebrush, and willow from grassland and riparian communities in Yellowstone National Park, Wyoming. A large number of simple ratio-type vegetation indices (SRTVI) and normalized difference- type vegetation indices (NDTVI) were developed from the hyperspectral data and regressed against ground-collected biomass. Results showed the following: 1) Strong relationships were found between SRTVI or NDTVI and total (R2 = 0.87), live (R2 = 0.84), sedge (R2 = 0.77), and willow (R2 = 0.66) biomass. 2) Weak relationships were found between SRTVI or NDTVI and grass (R2 = 0.39), forb (R2 = 0.16), and litter (R2 = 0.51) biomass, possibly caused by the mixture of spectral signatures with grasses, sedges, and willows along with the variable effect of the litter spectral signature. 3) A weak relationship was found between sagebrush biomass and SRTVI or NDTSI (R2 = 0.3) that was related to interference from sagebrush photosynthetic or nonphotosynthetic branch and twig material, and from the indeterminate spectral signature of sagebrush. This study has shown that hyperspectral imagery at 1-m resolution can result in high correlations and low error estimates for a variety of biomass components in rangelands. This methodology can thus become a very useful tool to estimate rangeland biomass over large areas.  
    • Hysteretic Responses to Grazing in a Semiarid Rangeland

      Searle, Kate R.; Gordon, Iain J.; Stokes, Chris J. (Society for Range Management, 2009-03-01)
      Ecological systems comprise a complex array of interacting processes that manifest across multiple scales. Effective management of natural ecosystems has to be underpinned by an understanding of how the scaling of these processes influences system integrity and stability. This is particularly true in semiarid rangelands, which display strong relationships between pattern and process that are fundamental to maintaining ecosystem function. Grazing can disrupt the scaling of these relationships and the mechanistic coupling between pattern and process, undermining the health of grazed semiarid rangelands. This is due to possible hysteretic responses in key system components to increases and decreases in grazing disturbance. We used data from a semiarid rangeland in northern Australia to test for hysteretic responses in system components after the removal of cattle grazing. We found an uncoupling of spatial linkages between vegetation and soil moisture in a severely degraded plot that was not evident in less intensively grazed or recovering plots. Recovering plots protected from grazing for 20 yr showed a scale of spatial linkage between vegetation and soil moisture, and soil organic matter and mineralization flush, of a scale much coarser than that of degrading plots. These findings provide evidence for hysteretic recovery from grazing and demonstrate that comparison of the spatial patterns of vegetation and soil properties is essential for capturing the true state of ecological functionality in this system. This has important implications for assessing ecological function in systems typified by strong natural environmental variation or in which data for pristine conditions are lacking.