• A comparison of satellite-derived vegetation indices for approximating gross primary productivity of grasslands

      Zhou, Y.; Zhang, L.; Xiao, J.; Chen, S.; Kato, T.; Zhou, G. (Society for Range Management, 2014-01)
      Gross primary productivity (GPP) is a key component of ecosystem carbon fluxes and the carbon balance between the biosphere and the atmosphere. Accurate estimation of GPP is essential for quantifying plant production and carbon balance for grasslands. Satellite-derived vegetation indices (VIs) are often used to approximate GPP. The widely used VIs include atmospherically resistant vegetation index, enhanced vegetation index (EVI), normalized difference greenness index, normalized difference vegetation index, reduced simple ratio, ratio vegetation index, and soil-adjusted vegetation index (SAVI). The evaluation of the performance of these VIs for approximating GPP, however, has been limited to one or two VIs and/or using GPP observations from one or two sites. In this study, we examined the relationships between the nine VIs derived from the moderate resolution imaging spectroradiometer (MODIS) and tower-based GPP at five eddy covariance flux sites over the grasslands of northern China. Our results showed that the nine VIs were generally good predictors of GPP for grasslands of northern China. Overall, EVI was the best predictor. The correlation between EVI and GPP also declined from the south to the north, indicating that EVI and GPP exhibited closer relationships in more southerly sites with higher vegetation cover. We also examined the seasonal influence on the correlation between VIs and GPP. SAVI exhibited the best correlation with GPP in spring when the grassland canopy was sparse, while EVI exhibited the best correlation with GPP in summer when the grassland cover was dense. Our results also showed that VIs could capture variations in observed GPP better in drought period than in nondrought period for an alpine meadow site because of the suppression of vegetation growth by drought. © 2014 The Society for Range Management.
    • Detecting the influence of best management practices on vegetation near ephemeral streams with landsat data

      Rigge, M.; Smart, A.; Wylie, B.; Kamp, K. V. (Society for Range Management, 2014-01)
      Various best management practices (BMPs) have been implemented on rangelands with the goals of controlling nonpoint source pollution, reducing the impact of livestock in ecologically important riparian areas, and improving grazing distribution. Providing off-stream water sources to livestock in pastures, cross-fencing, and rotational grazing are common rangeland BMPs that have demonstrated success in drawing livestock grazing pressure away from streams. We evaluated the effects of rangeland BMP implementation with six commercial-scale pastures in the northern mixed-grass prairie. Four pastures received a BMP suite consisting of off-stream water, cross-fencing, and deferred-rotation grazing, and two pastures did not receive BMPs. We hypothesized that the BMPs increased the quantity of riparian vegetation cover relative to the conditions in these pastures during the pre-BMP period and to the two pastures that did not receive BMPs. We used a series of 30-m Landsat normalized difference vegetation index (NDVI) images to track the spatial and temporal changes (1984-2010, n = 24) in vegetation cover, to which NDVI has been well correlated. Validation indicated that the remotely sensed signal from in-channel vegetation was representative of ground conditions. The BMP suite was associated with a 15% increase in the in-channel NDVI (0-30 m from stream centerline) and 18% increase in the riparian NDVI (30-180 m from stream center line). Conversely, the in-channel and riparian NDVI of non-BMP pastures declined 30% and 18% over the study period. The majority of change occurred within 2 yr of BMP implementation. The patterns of in-channel NDVI among pastures suggested that BMP implementation likely altered grazing distribution by decreasing the preferential use of riparian and in-channel areas. We demonstrated that satellite imagery time series are useful in retrospectively evaluating the efficacy of conservation practices, providing critical information to guide adaptive management and decision makers. © 2014 The Society for Range Management.
    • Different root and shoot responses to mowing and fertility in native and invaded grassland

      Balogianni, V. G.; Wilson, S. D.; Vaness, B. M.; Macdougall, A. S.; Pinno, B. D. (Society for Range Management, 2014-01)
      Grassland root responses to mowing and fertility are less well known than shoot responses, even though as much as 90% of productivity in semiarid grasslands occurs belowground. Thus, understanding root responses may aid the management of invasive grassland species such as Agropyron cristatum (L.) Gaerth (crested wheatgrass). We asked whether root responses reflect shoot responses to mowing and fertility in native grassland with and without a major component of crested wheatgrass. We subjected grasslands in northern Montana to 5 yr of mowing at two nitrogen (N) levels and followed root responses with minirhizotrons. Surprisingly, the roots of both native and invaded grasslands were unaffected by mowing and N addition, despite significant changes in shoot mass across both vegetation types. Root length was significantly greater beneath areas heavily occupied by crested wheatgrass (363 m · m-2 image ± 200, mean ± standard deviation [SD]) than areas comprising largely native grassland (168 m · m-2 image ± 128 SD). Also, no interactions occurred between year and any other factor, indicating that there were no changes in belowground responses over the 5 yr examined. In contrast, shoot mass was significantly reduced by mowing (not mowed, 612 g · m-2 ± 235 SD; mowed, 239 g · m-2 ± 81 SD) and was significantly increased by N addition (no added N, 380 g · m-2 ± 215 SD; added N, 488 g · m-2 ± 287 SD). In conclusion, 5 yr of mowing decreased shoot mass, but not root mass. On the other hand, 5 yr of N addition increased shoot mass, but not root mass. Given that most production and competition in grasslands occurs belowground, this suggests that mowing may not be a successful tool for reducing crested wheatgrass root length, regardless of soil fertility. © 2014 The Society for Range Management.
    • Improving restoration of exotic annual grass-invaded rangelands through activated carbon seed enhancement technologies

      Madsen, M. D.; Davies, K. W.; Mummey, D. L.; Svejcar, T. J. (Society for Range Management, 2014-01)
      Cost-efficient strategies for revegetating annual grass-infested rangelands are limited. Restoration efforts typically comprise a combination of pre-emergent herbicide application and seeding to restore desired plant materials. However, practitioners struggle with applying herbicide at rates sufficient to achieve weed control without damaging nontarget species. The objective of this research was to determine if seed enhancement technologies using activated carbon would improve selectivity of the pre-emergent herbicide imazapic. Bluebunch wheatgrass (Pseudoroegneria spicata) seed was either untreated, coated with activated carbon, or incorporated into "herbicide protection pods" (HPPs) made of activated carbon through a newly developed seed extrusion technique. In a grow-room facility, bluebunch wheatgrass seeds were sown in pots that contained seed of the exotic-annual grass downy brome (Bromus tectorum). After planting, pots were sprayed with 70, 105, 140, or 210 g acid equivalent (ae) · ha-1 of imazapic or left unsprayed. Where herbicide was not applied, downy brome biomass dominated the growing space. Imazapic effectively controlled downy brome and untreated bluebunch wheatgrass. Seed coating improved bluebunch wheatgrass tolerance to imazapic at 70 g ae · ha-1. HPPs provided protection from imazapic at all application rates. When untreated seeds and HPPs are compared at the four levels of herbicide application (excluding the no herbicide level), HPPs on average were 4.8-, 3.8-, and 19.0-fold higher than untreated seeds in density, height, and biomass, respectively. These results indicate that HPPs and, to a lesser extent, activated carbon-coated seed have the potential to further enhance a single-entry revegetation program by providing land practitioners with the ability to apply imazapic at rates necessary for weed control while minimizing nontarget plant injury. Additional research is merited for further development and evaluation of these seed enhancement technologies, including field studies, before they can be recommended as restoration treatments. © 2014 The Society for Range Management.
    • Influence of experience on browsing sagebrush by cattle and its impacts on plant community structure

      Petersen, C. A.; Villalba, J. J.; Provenza, F. D. (Society for Range Management, 2014-01)
      Mechanical and chemical methods used historically to rejuvenate sagebrush-steppe landscapes are cost prohibitive. A low-cost alternative is to fashion systems of management in which locally adapted animals use sagebrush as fall and winter forage to reduce feeding costs and to enhance the growth of grasses and forbs during spring and summer. We evaluated the practicality of fall browsing of sagebrush (Artemisia tridentata ssp. tridentata, ssp. wyomingensis) by cattle. To do so, we assessed 1) the foraging behavior and body weights of cattle with varying levels of experience browsing sagebrush, and 2) the ensuing responses of sagebrush, grasses, and forbs to cattle grazing. In spatially and temporally replicated trials from 2007 to 2009, cattle were challenged to eat sagebrush. Pregnant cows with calves (2007 and 2008), bred yearling heifers (2008), and first-calf heifer/calf pairs (2009), supplemented with protein and energy, learned to eat sagebrush as a significant portion of their diet (up to 63% of scans recorded during grazing). Experienced animals consistently ate more sagebrush and lost less weight, or gained more weight, than naive animals in 2008 and 2009 (P < 0.05). Cover, production, and percent composition of grasses and forbs maintained or dropped slightly from 2007 to 2008 but then rebounded sharply in 2009 to much greater levels than in 2007 or 2008 (P < 0.05). A corresponding reduction in shrub cover, production, and percent composition accompanied the increase in forbs and grasses (P < 0.05). Our research suggests grazing by cattle during fall and winter can be effective, biologically and economically, and can lead to habitat renovation and resilience by creating locally adapted systems of management in ways that landscape manipulations with chemical and mechanical treatments or prescribed fire cannot. © 2014 The Society for Range Management.
    • Livestock management strategy affects net ecosystem carbon balance of subhumid pasture

      Oates, L. G.; Jackson, R. D. (Society for Range Management, 2014-01)
      Temperate grasslands are generally considered carbon (C) sinks, but climate and management likely affect whether they accumulate or lose C on an annual time step. The North Central Region of the United States contains highly productive improved pasture that is used exclusively for livestock grazing and mechanical harvest. The objective of this study was to use a net ecosystem carbon balance (NECB) approach to estimate C accumulation or loss in subhumid pastures under four typical livestock management practices: management-intensive rotational grazing (MIRG), continuous grazing (CONT), haymaking (HARV), and land set aside with no harvests (NONE). MIRG lost significantly less C in 2006 than all other treatments, and in 2007 MIRG was the only treatment that had a positive NECB. For 2006, our model resulted in an average change of-236 ± 15 (CONT),-100 ± 24 (MIRG),-391 ± 11 (HARV), and-276 ± 28 (NONE) g C · m-2 · y-1. For 2007, the change was-234 ± 56 (CONT), 106 ± 69 (MIRG),-200 ± 25 (HARV), and-171 ± 38 (NONE) g C · m-2 · y-1. Increased C fixed as net primary production (NPP) and C imported as hay and grain resulted in the MIRG treatment having the most favorable C balance. Even with imported hay and grain, reduced NPP in the CONT treatment led to a less favorable C balance. In the HARV treatment, high biomass removal drove the negative C balance, while the relationship between reduced NPP and heterotrophic respiration alone drove the negative C balance in the NONE treatment. Climate change mitigation services provided from ecosystem C accumulation relative to cultivation may be warranted for pastures, but when all cross-boundary transfers of C are not considered, significant misconceptions can occur regarding how different management strategies affect the NECB of subhumid pasture. © 2014 The Society for Range Management.
    • Monitoring of livestock grazing effects on bureau of land management land

      Veblen, K. E.; Pyke, D. A.; Aldridge, C. L.; Casazza, M. L.; Assal, T. J.; Farinha, M. A. (Society for Range Management, 2014-01)
      Public land management agencies, such as the Bureau of Land Management (BLM), are charged with managing rangelands throughout the western United States for multiple uses, such as livestock grazing and conservation of sensitive species and their habitats. Monitoring of condition and trends of these rangelands, particularly with respect to effects of livestock grazing, provides critical information for effective management of these multiuse landscapes. We therefore investigated the availability of livestock grazing-related quantitative monitoring data and qualitative region-specific Land Health Standards (LHS) data across BLM grazing allotments in the western United States. We then queried university and federal rangeland science experts about how best to prioritize rangeland monitoring activities. We found that the most commonly available monitoring data were permittee-reported livestock numbers and season-of-use data (71% of allotments) followed by repeat photo points (58%), estimates of forage utilization (52%), and, finally, quantitative vegetation measurements (37%). Of the 57% of allotments in which LHS had been evaluated as of 2007, the BLM indicated 15% had failed to meet LHS due to livestock grazing. A full complement of all types of monitoring data, however, existed for only 27% of those 15%. Our data inspections, as well as conversations with rangeland experts, indicated a need for greater emphasis on collection of grazing-related monitoring data, particularly ground cover. Prioritization of where monitoring activities should be focused, along with creation of regional monitoring teams, may help improve monitoring. Overall, increased emphasis on monitoring of BLM rangelands will require commitment at multiple institutional levels. © 2014 The Society for Range Management.
    • Rangeland health assessment: A useful tool for linking range management and grassland bird conservation?

      Henderson, A. E.; Davis, S. K. (Society for Range Management, 2014-01)
      Large-scale loss and degradation of North American native prairie coupled with sharp declines in grassland bird populations call for a clear understanding of the effects of livestock production on bird habitat selection. Grassland birds typically select breeding habitat based on a suite of structural and community vegetation features shaped by grazing. Rangeland health indices are a tool for assessing grassland structure and community composition that may offer biologists and range managers common language to achieve grassland bird recovery goals. We used point-count surveys, vegetation measures, and indices of rangeland health to examine bird-habitat relationships on native grassland in southwestern Saskatchewan for 10 grassland bird species. We used an information theoretic approach to compare the support of three hypotheses explaining variation in bird abundance as a function of local vegetation characteristics: bird abundance is best explained by 1) vegetation structure, 2) vegetation structure heterogeneity, or 3) plant community. Vegetation structure variables were present in top-ranking models (i.e., models within four Akaike information criterion units of top model) for eight species and solely comprised top-ranking models for Baird's sparrow (Ammodramus bairdii), chestnut-collared longspur (Calcarius ornatus), horned lark (Eremophila alpestris), McCown's longspur (Rhynchophanes mccownii), and savannah sparrow (Passerculus sandwichensis). Structural heterogeneity variables were present in top-ranked models for grasshopper sparrow (Ammodramus savannarum), horned lark (Eremophila alpestris), and western meadowlark (Sturnella neglecta). Plant composition variables solely comprised top-ranking models for clay-colored sparrow (Spizella pallida) and were present in top-ranked models for grasshopper sparrow and vesper sparrow (Pooecetes gramineus). Our results indicate that vegetation structure variables, namely litter mass, vegetation volume, and bare ground cover, best explain variation in bird abundance. Although the rangeland health index received little support as a predictor of bird abundance, vegetation structure components of the index could be used to communicate grazing management guidelines that maintain grassland bird habitat. © 2014 The Society for Range Management.
    • Semiarid rangeland is resilient to summer fire and postfire grazing utilization

      Vermeire, L. T.; Crowder, J. L.; Wester, D. B. (Society for Range Management, 2014-01)
      Most wildfires occur during summer in the northern hemisphere, the area burned annually is increasing, and fire effects during this season are least understood. Understanding plant response to grazing following summer fire is required to reduce ecological and financial risks associated with wildfire. Forty 0.75-ha plots were assigned to summer fire then 0, 17, 34 or 50% biomass removal by grazing the following growing season, or no fire and no grazing. Root, litter, and aboveground biomass were measured before fire, immediately after grazing, and 1 yr after grazing with the experiment repeated during 2 yr to evaluate weather effects. Fire years were followed by the second driest and fifth wettest springs in 70 yr. Biomass was more responsive to weather than fire and grazing, with a 452% increase from a dry to wet year and 31% reduction from a wet to average spring. Fire reduced litter 53% and had no first-year effect on productivity for any biomass component. Grazing after fire reduced postgrazing grass biomass along the prescribed utilization gradient. Fire and grazing had no effect on total aboveground productivity the year after grazing compared to nonburned, nongrazed sites (1 327 vs. 1 249 ± 65 kg · ha-1). Fire and grazing increased grass productivity 16%, particularly for Pascopyrum smithii. The combined disturbances reduced forbs (51%), annual grasses (49%), and litter (46%). Results indicate grazing with up to 50% biomass removal the first growing season after summer fire was not detrimental to productivity of semiarid rangeland plant communities. Livestock exclusion the year after summer fire did not increase productivity or shift species composition compared to grazed sites. Reduction of previous years' standing dead material was the only indication that fire may temporarily reduce forage availability. The consistent responses among dry, wet, and near-average years suggest plant response is species-specific rather than climatically controlled. © 2014 The Society for Range Management.
    • Short-and long-term influence of brush canopy cover on northern bobwhite demography in southern Texas

      Demaso, S. J.; Hernández, F.; Brennan, L. A.; Silvy, N. J.; Grant, W. E.; Ben, Wu, X.; Bryant, F. C. (Society for Range Management, 2014-01)
      Extensive research has been devoted to quantifying the habitat needs and selection of many wildlife species. However, how habitat selection affects the long-term demographic performance of a species largely has been ignored. We used northern bobwhite (Colinus virginianus) and brush canopy coverage-an important habitat component for quail-to evaluate the influence of habitat on short-and long-term demographic performance of this species. We used data from a 5-yr (2001-2005) radiotelemetry study of northern bobwhite in southern Texas to obtain estimates of bobwhite density, survival, and production on three study areas with 5%, 11%, and 32% brush canopy cover. Our objectives were to compare these demographic variables individually among brush canopy cover classes and then simulate their cumulative effect on demographic performance using a simulation model. All demographic parameters were similar among the three brush canopy cover classes. However, simulation modeling indicated that long-term demographic performance was greater on the 11% and 32% brush canopy cover classes. Simulated bobwhite populations were 2-3 times higher in these two cover classes than the 5% brush canopy cover class. In addition, the probability of population persistence was greater in the 11% (0.91) and 32% (1.00) brush canopy cover classes than the 5% cover class (0.54) using a quasi-extinction criterion of ≤ 40 birds (≤ 0.05 birds · ha-1). Our study highlights the shortcoming of considering only short-term effects when comparing habitat given that short-and long-term effects of habitat on demographic performance can differ. © 2014 The Society for Range Management.
    • Spatial and temporal variability in aboveground net primary production of uruguayan grasslands

      Guido, A.; Varela, R. D.; Baldassini, P.; Paruelo, J. (Society for Range Management, 2014-01)
      Aboveground net primary production (ANPP) is a variable that integrates many aspects of ecosystem functioning. Variability in ANPP is a key control for carbon input and accumulation in grasslands systems. In this study, we analyzed the spatial and temporal variability of ANPP of Uruguayan grasslands during 2000-2010. We used enhanced vegetation index (EVI) data provided by the MODIS-Terra sensor to estimate ANPP according to Monteith's (1972) model as the product of total incident photosynthetically active radiation, the fraction of the radiation absorbed by green vegetation, and the radiation use efficiency. Results showed that ANPP varied spatially among geomorphological units, increasing from the north and midwest of Uruguay to the east and southeast. Hence, Cuesta Basáltica grasslands were the least productive (399 g DM · m-2 · yr-1), while grasslands of the Sierras del Este and Colinas y Lomas del Este displayed the highest productivity (463 and 465 g DM · m-2 · yr-1, respectively). This pattern is likely related to differences in soil depth and associated variation in water availability among geomorphological units. Seasonal variability in ANPP indicated peak productivity in the spring in all units, but differences in annual trends over the 10-yr study period suggested that ANPP drivers are operating spatially distinct. Understanding the spatial and temporal variability of ANPP of grasslands are prerequisites for sustainable management of grazing systems. © 2014 The Society for Range Management.
    • Yield response of needle-and-thread and threadleaf sedge to moisture regime and spring and fall defoliation

      Koehler, A. E.; Whisenhunt, W. D.; Volesky, J. D.; Reece, P. E.; Holman, T. L.; Moser, L. E. (Society for Range Management, 2014-01)
      Little information is available to help managers of cool-season dominated semiarid rangelands determine when to begin and end grazing in the spring and fall. Therefore, we evaluated the effects of clipping spring and fall growth on subsequent-year yield of needle-and-thread (Hesperostipa comata [Trin. & Rupr.] Barkworth) and threadleaf sedge (Carex filifolia Nutt.) (USDA-NRCS 2012) using a randomized complete block, split-plot experimental design with fall moisture regimes (ambient or supplemental water) applied to main plots and defoliation treatments applied to subplots. Two combinations of spring defoliation, one for each fall moisture regime, were composed of a factorial array of three spring clipping dates (early May, late May, mid-June) and three levels of defoliation (0%, 40%, 80%). A third combination of treatments was composed of the supplemental water regime and an array of a single spring clipping date (late May), a single fall clipping date (late September, after regrowth), and three levels of defoliation (0%, 40%, 80%) in the same year. Ambient fall moisture was low, leading to continued senescence of needle-and-thread and threadleaf sedge, whereas the application of 10 cm of supplemental water in mid-August stimulated fall growth. The study was replicated with two sets of main plots at four sites in consecutive years, 2002 and 2003. Yield data were collected in mid-June of the year following treatment. Subsequent-year yield of needle-and-thread was not affected by defoliation under average plant-year precipitation conditions (2003) (P > 0.05); however, it was reduced following heavy (80%) late spring (late May or June) defoliation during a drought year (2002) (P > 0.05). Subsequent-year yield of threadleaf sedge was not affected by defoliation in either year (P > 0.05). Because it is difficult to predict when drought will occur, avoiding heavy late-spring grazing in needle-and-thread-dominated pastures in consecutive years would be prudent. © 2014 The Society for Range Management.