• Ideal Free Distributions of Mobile Pastoralists in Multiple Seasonal Grazing Areas

      Moritz, M.; Hamilton, I. M.; Scholte, P.; Chen, Y. -J. (Society for Range Management, 2014-11)
      The pastoral system in the Far North Region of Cameroon is best described as an open system in which mobile pastoralists have open access to common-pool grazing resources. We hypothesized that there is a self-organizing management system of open access to common-pool grazing resources and predicted that we would find an Ideal Free Distribution (IFD) of mobile pastoralists within seasonal grazing areas. In this paper we used mobility data and remote sensing data from two seasonal grazing areas at the end of the dry season in three consecutive years to evaluate that hypothesis. We found evidence of an IFD in the two seasonal grazing areas of the Logone Floodplain and the Lake Maga area. These findings offer further support for our hypothesis that there is a complex adaptive system in which pastoralists distribute themselves effectively over available grazing resources. © 2014 Society for Range Management
    • Incorporating Plant Mortality and Recruitment Into Rangeland Management and Assessment

      Svejcar, T.; James, J.; Hardegree, S.; Sheley, R. (Society for Range Management, 2014-11)
      Rangeland management is largely focused on managing vegetation change. Objectives may include managing against change if the desired vegetation is in place, or attempting to create a shift in vegetation if the desired plant community is not present. There is a rich body of research documenting influences of disturbance and management on rangeland vegetation. However, in many cases the information is largely observational and does not identify mechanisms driving change. We propose using the regeneration niche concept to more effectively predict when vegetation change is possible and to suggest successional direction. Simply stated, as plants die and leave gaps in the community, recruitment of new individuals will dictate successional direction. Recruitment requires that propagules are present, that the propagules find safe sites in which to establish, and that the seedlings and young plants are able to compete with existing vegetation and survive. In many rangeland communities, perennial bunchgrasses are a key to stability and invasion resistance. Existing literature shows that most rangeland bunchgrasses have average life spans of 10 yr or less, so periodic recruitment is necessary to maintain communities in which they are a major component. Disturbance can influence plant population dynamics, and we suggest classifying disturbances based on how they influence mortality and recruitment. We also suggest that more emphasis be placed on the concept of critical transitions and less on the degree of disturbance per se. In other words, a small disturbance at the wrong point in community composition (low plant density and high gap size for example) can cause a transition, whereas major disturbance in a high condition community may yield little risk of transition. We suggest that a focus on mortality and recruitment will provide a mechanistic approach for predicting vegetation change and making management decisions. We refer to this approach as recruitment-based management. © 2014 Society for Range Management
    • Interactive Effects of Nitrogen Deposition and Grazing on Plant Species Composition in a Serpentine Grassland

      Pasari, J. R.; Hernández, D. L.; Zavaleta, E. S. (Society for Range Management, 2014-11)
      The interaction of resource availability and disturbance can strongly affect plant species richness and the spread of exotic plants. Several ecological theories posit that disturbance mediates the richness-reducing effects of increased competition as resource levels rise. In the low-nutrient serpentine grasslands of the San Francisco Bay Area, the fertilizing effects of atmospheric nitrogen (N) deposition may threaten native species by promoting nitrophilic exotic grasses. Attempts to mitigate these N deposition effects have focused on cattle grazing as a strategy to reduce exotic grass cover. We simulated realistic N deposition increases with low-level fertilization, manipulated grazing with fencing, and monitored grazing intensity using camera traps in a 4 yr factorial experiment to assess the effects of grazing and N deposition on several measures of native and exotic species dynamics in California's largest serpentine grassland. Our results suggest that native species diversity may increase slightly under low-level N deposition with moderate grazing in this system. However, grazing may not be effective at limiting exotic cover as N accumulates in the future. Examination of treatment trajectories using principal response curves indicated that responses to grazing might be determined more by functional group (forb or grass) than origin (native or exotic). Grazing intensity varied dramatically within the single stocking rate used to manage this ecosystem. Given this variation and the contrasting effects of grazing on different functional groups, more targeted management may be required to improve conservation outcomes. © 2014 Society for Range Management
    • Invasion is Contingent on Species Assemblage and Invasive Species Identity in Experimental Rehabilitation Plots

      Leffler, A. J.; Leonard, E. D.; James, J. J.; Monaco, T. A. (Society for Range Management, 2014-11)
      Ecological studies often suggest that diverse communities are most resistant to invasion by exotic plants, but relatively few local species may be available to a rehabilitation practitioner. We examine the ability of monocultures and diverse assemblages to resist invasion by an exotic annual grass (cheatgrass) and an exotic biennial forb (dyer's woad) in experimental rehabilitation plots. We constructed seven assemblages that included three monocultures of grass, forb, or shrub; three four-species mixtures of grasses, forbs, or shrubs; and a three-species mixture of one species from each growth form in an experimental field setting to test resistance to invasion. Assemblages were seeded with cheatgrass and dyer's woad for two consecutive years and quantified as biomass and density of individuals from each exotic species. Soil NO3- and leaf-area index were examined as predictors of invasive plant abundance. Cheatgrass invasion was greatest in forb and shrub assemblages, and least in mixed grass or grass monoculture; dyer's woad invasion was greatest into mixed grass or grass monoculture, but least into monoculture or mixed-species assemblages composed of forbs or shrubs. The community composed of grasses, forbs, and shrubs suppressed invasion by both species. Consequently, assemblages were most resistant to invasion by species of the same growth form. Moreover, these monocultures and mixtures were generally similar in conferring resistance to invasion, but a monoculture of big sagebrush was more resistant than a mixture of shrubs. Soil NO3- was correlated with invasion by cheatgrass, whereas LAI was correlated with invasion by dyer's woad, suggesting these species were more limited by belowground and aboveground resources, respectively. Overall, increasing diversity with limited species did not necessarily enhance resistance to invasion. © 2014 Society for Range Management
    • Season and Intensity of Burning on Two Grass Species of the Chihuahuan Desert

      Luna, M.; Britton, C. M.; Rideout-Hanzak, S.; Villalobos, C.; Sosebeex, R. E.; Wester, D. B. (Society for Range Management, 2014-11)
      We investigated effects of three burning seasons under two simulated fuel loads on plant mortality and basal area of small and large blue grama (Bouteloua gracilis [H.B.K.] Lag) and broomgrass muhly (Muhlenbergia rigida [H.B.K.] Lag) plants in the southern Chihuahuan Desert of Mexico. We simulated prescribed fire with a portable propane burner calibrated to match time and temperature curves reached at 1 700 kg · ha-1 and 2 800 kg · ha-1 fine fuel loads. Large (initial basal area > 10 cm2) and small (initial basal area ≤ 10 cm2) plants were used. For each species, we randomly treated 50 plants in each size class each season at each fuel load; 50 control plants of each species and size received no fire treatment. We estimated basal area change from measurements recorded photographically. Blue grama mortality was affected by season of burning, simulated fuel load, and plant size. Small blue grama plants had higher mortality than large plants. Burning at the high fuel load in winter increased basal area of large blue grama plants; in contrast, basal area was not affected by summer burning, and was reduced by spring burning with high fuel load. Basal area of broomgrass muhly plants was reduced by summer and winter burning and these responses were independent of fuel load and plant size. Our results suggest that winter is the most suitable season for prescription burning to improve southern Chihuahuan Desert grasslands: prescribed fire during this time reduced basal area of broomgrass muhly plants, had the highest mortality on broomgrass muhly, had a positive effect on basal area of small blue grama plants, and had no effect on basal area of large blue grama plants. © 2014 Society for Range Management
    • Targeted Grazing of White Locoweed: Short-Term Effects of Herbivory Regime on Vegetation and Sheep

      Goodman, L. E.; Cibils, A. F.; Lopez, S. C.; Steiner, R. L.; Graham, J. D.; McDaniel, K. C.; Abbott, L. B.; Stegelmeier, B. L.; Hallford, D. M. (Society for Range Management, 2014-11)
      White locoweed (Oxytropis sericea Nuttall) and nontarget vegetation response to 2 yr of targeted grazing by sheep, one treatment of picloram plus 2, 4-D (HER) or no treatment (CON) were compared. Serum of sheep that grazed locoweed intermittently (IGZ, 5 d on locoweed followed by 3 d off locoweed) vs. counterparts that grazed locoweed continuously for 24 d (CGZ) was also examined. Alkaloid toxicity was inferred by serum levels of thyroxine (T4), triiodothyronine (T3), alkaline phosphatase (ALKP), aspartate aminotransferase (AST), and swainsonine, as well as behavior and body weight gains. Three sites were used in a randomized complete block design. IGZ, CGZ, and HER treatments reduced locoweed density (P < 0.01), canopy cover (P < 0.01), number of flower stalks (IGZ: P = 0.02, CGZ and HER: P = 0.01), and plant size (P < 0.01). White locoweed seed density in the soil seed bank was not reduced with grazing, and nontarget vegetation was mostly unaffected by treatments. Grass canopy cover increased in grazed and herbicide plots throughout the study (IGZ: P = 0.03, CGZ and HER: P < 0.01). Percentage bare ground was unchanged (IGZ: P = 0.46, CGZ: P = 0.44) in grazed plots but decreased (P = 0.03) in HER plots. After 24 d, ewes in the IGZ treatment had lower levels of serum ALKP (P < 0.01) and AST (P = 0.02) and marginally lower swainsonine levels (P < 0.07) than CGZ ewes that tended to exhibit lower serum T3 (P < 0.07) and similar serum T4 (P = 0.25) levels. Time spent feeding on locoweed tended to differ (P = 0.06) between treatments. Body weight gain was the same (P = 0.19) regardless of treatment. IGZ of locoweed-infested rangeland with sheep may be a viable short-term means of reducing locoweed density without detrimentally affecting animal health. © 2014 Society for Range Management
    • Testing for Thresholds in a Semiarid Grassland: The Influence of Prairie Dogs and Plague

      Augustine, D. J.; Derner, J. D.; Detling, J. K. (Society for Range Management, 2014-11)
      State-and-transition models for semiarid grasslands in the North American Great Plains suggest that the presence of herbivorous black-tailed prairie dogs (Cynomys ludovicianus) on a site 1) creates a vegetation state characterized by increased dominance of annual forbs and unpalatable bunchgrasses and increased bare soil exposure and 2) requires long-term (&gt; 40 yr) prairie dog removal to transition back to a vegetation state dominated by palatable perennial grasses. Here, we examine 1) how the recent history of prairie dog occupancy on a site (1–10 yr) influences the magnitude of prairie dog effects on vegetation composition and 2) how occupancy history affects vegetation dynamics following extirpation of prairie dogs. We used a natural experiment in the shortgrass steppe of northeastern Colorado, USA, where prairie dogs were extirpated from multiple sites during an outbreak of epizootic plague. On sites occupied by prairie dogs for 1–4 yr prior to extirpation, plant cover and composition recovered to conditions similar to unoccupied sites within a single growing season. Larger reductions in perennial C4 grasses occurred on sites occupied for the prior 7–10 yr compared to sites with shorter occupancy histories (&lt; 6 yr). On sites occupied for the prior 7–10 yr, C4 perennial grasses recovered after 5 yr following prairie dog extirpation; in addition, C3 perennial graminoids and forbs remained more abundant (compared to sites with no history of prairie dogs) throughout the 5-yr period. Our findings showcase that prior site occupancy (up to 10 yr) by prairie dogs did not induce irreversible shifts in vegetation state in this semiarid grassland. Rather, vegetation changes induced by prairie dogs represent primarily a phase shift in landscapes where prairie dog populations are regulated by epizootic plague. © 2014 Society for Range Management
    • Vegetation Management Across Colorado Plateau BLM Lands: 1950–2003

      Redmond, M. D.; Golden, E. S.; Cobb, N. S.; Barger, N. N. (Society for Range Management, 2014-11)
      Large tracts of land across the western United States have been managed over the last century in an effort to increase forage production, reduce the risk of wildland fires, and/or restore ecosystem structure and function. Yet documentation of this land-treatment history is lacking. With the use of data collected from Bureau of Land Management (BLM) field offices across the Colorado Plateau, we quantified the number, spatial extent, and implementation cost of tree-reduction and seeding treatments done in piñon (Pinus edulis)–juniper (Juniperus osteosperma, Juniperus monophylla, Juniperus scopulorum) woodlands between 1950 and 2003. Over 247 000 hectares of land were treated, corresponding to 6.6% of the piñon–juniper vegetation type within BLM-owned lands. Tree-reduction treatments involving chaining, bulldozing, or cabling were most prevalent between the 1950s and 1970s, with over 163 000 ha of land treated with these methods. Prescribed burning became increasingly prevalent in the 1980s, with over 43 000 ha burned. In more recent years, hydroaxe treatments have become common (4 400 ha treated), but to a much lesser extent than prescribed burns. Over 60% of these tree-reduction treatments were done in conjunction with revegetation or seeding treatments. Implementation costs of these tree-reduction treatments were over $26.7 million, with the hydroaxe treatment having nearly three times the cost of implementation than all other tree-reduction treatments. The spatial extent of these tree-reduction treatments and associated implementation costs highlight the importance of research examining the efficacy of these treatments and the potential legacy effects. The land-use history reported in this study and the accompanying freely accessible on-line database is a useful tool to guide research and management objectives and methodology. © 2014 Society for Range Management