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Northern mixed-grass prairie rangelands are threatened by increasing drought severity and invasion by annual grasses. However, it is unclear whether climate change will amplify or dampen this invasion. We tested separate and combined effects of livestock grazing and experimental rainfall manipulation on invasion by annual brome grasses—cheatgrass (Bromus tectorum L.) and field brome (Bromus arvensis L.)—in two mixed-grass prairie sites (Montana and Wyoming, United States). To provide management-relevant results, we manipulated precipitation at five levels representing a gradient of precipitation reduction and implemented grazing strategies selected by stakeholders to represent realistic management choices: destock, stable, and heavy grazing scenarios. We measured soil moisture and three plant properties of invasive annual bromes (aboveground primary production, percent greenness, and percent cover) during two water manipulation yr (2019, 2020) and one recovery yr of natural rainfall (2021).
Imposed precipitation reduction generally decreased absolute annual brome biomass and induced earlier senescence. However, during the recovery year, we observed prolonged time to senescence in the formerly droughted plots. In Wyoming, summer grazing had little appreciable effect on annual bromes, perhaps because annual bromes mature early in the growing season (mid-June) and may therefore be less affected by summer grazing. However, in the first year after ending water treatments during a natural drought in Montana, under heavy grazing, annual brome production marginally increased from 32.4 ± 10.6 kg · ha–1 to 130.8 ± 111.8 kg · ha–1 (mean ± standard error) with prior severe precipitation reduction. The magnitude of responses tended to be site dependent, which may be due to inherent vegetation differences between our sites, as well as site-scale differences in natural precipitation patterns. Together, these results suggest that annual brome abundance may increase in the context of drought combined with heavy grazing, a more likely scenario with continuing climate change.
Using parasiticides, or chemical dewormers, on rangeland livestock is a decision that impacts not only livestock health but also broader ecosystem functions. Although we know that livestock producers in the United States are increasingly using parasiticides, we know little about what sociopsychological factors are driving their decision making processes. Following the theory of planned behavior (TPB), this study investigates producers' intention to stop or reduce their use of parasiticides using logistic regression techniques. Survey data were collected from a random sample of 2 416 farming operations in South Dakota grazing livestock. While controlling for socioeconomic and demographic factors, we find that among the three TPB constructs of attitudes, subjective norms, and perceived behavioral control, negative attitudes about the effects of chemical dewormers are the only factor with a relationship to producers' reduction in parasiticide use. We also find that those with a college degree were significantly more likely to reduce or stop using parasiticides. The adapted model of TPB appears to provide a suitable framework for examining parasiticide use among South Dakota producers and our findings also suggest that future interventions aimed at promoting rangeland sustainability should include an understanding of producers' attitudes in relation to desired behaviors.
Rangelands are often ignored in the discussion of using management to sequester carbon; however, demonstrating that carbon storage could be paid by carbon credit markets would be a significant advancement for rangeland conservation. The additional amount and cost of carbon sequestered was quantified by simulating seeding perennial grass and shrub species in sagebrush shrublands dominated by non-native annual grass and forb species (NNAGF) compared with doing nothing in a 485 623 km2 area of interest (AOI) centered around Nevada, United States. Using Sentinel-2 satellite imagery, NNAGF cover was mapped across the AOI to locate areas dominated by NNAGFs. Spatial state-and-transition simulation models with a carbon stock-and-flow submodel simulated the seeding of perennial species in NNAGF-dominated sagebrush shrublands in the Columbia Plateau ecoregion (IL Ranch, Nevada), north-central Great Basin ecoregion outside the North American Monsoon (TS-Horseshoe Ranch, Nevada), and the southeastern Great Basin ecoregion within the North American monsoon (PVMH landscape, Utah). The net biome productivity (NBP) and cost per unit area of sagebrush shrublands was quantified by simulating restoration of NNAGF to perennial vegetation over a 25-yr period. The unseeded PVMH landscape, IL Ranch, and TS-Horseshoe Ranch were sinks of carbon (i.e., positive NBP) at 84 g, 9 g, and 11 g C·m–2·yr–1, respectively. About 58–90% of NBP was stored in the soil. The IL Ranch required only small levels of seeding and was a small sink of C at 0.71 ± 0.65 g C·m–2·yr–1, whereas the additional NBP for the seeded PVMH landscape was 19.9 ± 10.6 g C·m–2·yr–1. Across the AOI, the most and least carbon stored, respectively, was in Utah (136 132 metric ton·yr–1, cost: $287M) and the central Great Basin (3 196 metric ton·yr–1, cost: $23M). Positive NBP values reported here showed that carbon sequestration in sagebrush shrublands compares favorably with those of more productive systems in the United States and worldwide.
Resource selection is a process in which animals maximize resource acquisition through unequal use of heterogeneous resources on the landscape. Thus, shifts in resource and disturbance gradients should cause animals to shift resource use and distribution. Although there is an increasing body of evidence about the impacts of disturbance risk on wildlife populations, relatively few studies have assessed fine-scale impacts of human disturbance on wildlife. Our objective was to identify differences in day and night resource selection. Elk (Cervus canadensis) may be able to reduce consequences of coal bed natural gas development through expansion of resource use at night, thus ameliorating population impacts. To collect fine-scale temporal data, we used locations from 55 female elk equipped with Global Positioning System collars, as well as habitat and human disturbance variables for a study system in northeastern Wyoming. We used a mixed-effects model framework integrating frequency of individual elk to quantify shifts between day and night elk resource selection within a coal bed natural gas field. Elk exhibited differences in day and night resource selection, whereby they used areas with decreased forested cover and closer to roads at night. However, there was greater variation in resource selection at night compared with daytime. Our results suggest across each day, elk shifted fine-scale resource selection to take advantage of local resource gradients and response to disturbance impacts.
Human interventions and global environmental changes are increasing and threaten ecosystem services (ES) worldwide. Managing ES is a challenging task; it is essential to understand the temporal and spatial distribution of ES and the benefits derived by a human. However, ES variability in time and space has yet to be studied. Therefore, the current study investigates spatiotemporal variations of different ES indicators, individually and in combination, in the Shazand Watershed across three time periods: 1998, 2008, and 2016. Five indicators were selected to assess different dimensions of ES, including plant production, water provision, soil stability, maintenance of habitats and genetic diversity for plant and animal nurseries and reproduction, and recreation potential. We then used multiresolution segmentation to create a spatial composite indicator measuring the integration of the study indicators. SCI was used to describe spatiotemporal variations of ES through time at the subwatershed level. The results indicated that individual ES indicators display spatial variations across space and time. Moreover, comparing the spatial composite indicator across periods showed that all 24 subwatersheds could not supply more ES. However, the areas located in the central and the western part of the watershed appeared to have better ES conditions. According to the results, revising the current management plans and allocating environmental funding would benefit these areas. The results are applicable for future spatial planning of sustainable ecological conservation strategies for the Shazand Watershed and similar regions.
The adoption of silvopastoral systems enables the achievement of sustainable intensification using multiple arrangements and species in the same area. This study aimed to evaluate the forage production of buffel grass and determine soil microbial biomass and enzymatic activity in two arrangements of a silvopastoral system. The study design was a randomized block with four replicates using a 2 x 4 factorial arrangement. The factors were two arrangements of the silvopastoral systems (buffel + Eucalyptus urograndis = SPS1 and buffel + pigeon pea + E. urograndis = SPS2) and four distances from the E. urograndis trees (2, 4, 6, and 8 m). Soil sampling was carried out at 0–5, 5–10, and 10–20 cm depths to evaluate microbial nitrogen (Nmic) and carbon (Cmic), while the activity of β-glucosidase and urease enzymes was evaluated at 0–5 and 5–10 cm. Buffel grass in the SPS1 showed higher canopy height, total dry mass, and root mass values. In SPS1, the highest total dry mass (3290.7 kg·ha–1) was observed at 8 m from the trees. At a 5–10 cm depth, Cmic was higher at 2 m than 8 m from the trees. The highest value of Nmic was found at 5–10 cm, at a distance of 2 m. The SPS2 showed a higher Nmic than the SPS1 at the 10–20 cm depth. The β-glucosidase activity was higher at a distance of 2 m in SPS1 at 0–5 and 5–10 depths. Urease activity was lower at 8 m at both depths. Thus, we observed the highest values of root-and-shoot biomass of buffel grass in SPS1 system at 8 m from the E. urograndis trees. However, the soil microbial response indicated that the intensification using tree, legume and grass in silvopastoral systems increased soil microbial activity.
Understanding spatiotemporal variability of aboveground biomass (AGB) in alpine grassland ecosystems is required to better formulate sustainable grazing strategies, especially in climate-sensitive areas such as the Qinghai-Tibet Plateau. Drawing from recent modeling results, we analyzed spatial variability in grassland AGB over seasonal and annual timescales. Theoretical livestock carrying capacity (LCC) was predicted in relation to projected warming and simulated pika disturbance. We found that elevation and slope were key determinants of the distribution of AGB and its change. Although grasses and shrubs occupied an equivalent area, the latter generated approximately double the amount of total biomass, but the former generated slightly more available biomass. Although pika habitat extended over 45.3% of the study area, the impacts of pika only reduced the total available AGB (AGBV) by < 0.07%. The actual LCC (2.16 SU · ha–1 [sheep unit per hectare]) of the study area was lower than the theoretical LCC (2.77–2.96 SU · ha–1). Under climate warming scenarios of 1.0°C, 1.5°C, and 2.0°C, the actual LCC can be increased by 0.82-1.25, 0.99-1.53, and 0.77–1.23 SU · ha–1, respectively. Although systematic climate warming increased AGB, impacts were especially marked at lower elevations and on north-facing slopes because of higher soil water availability. Results highlight that rather than implementing LCC in a static manner in light of climate warming, deeper understanding of biomass availability and the combined effects of climate change and topographic heterogeneity is required to support better management of grasslands.
Rangelands may offer valuable habitat for invertebrate wildlife, helping conserve ecologically and economically significant organisms, like native bees. In some systems, livestock may affect bees by consuming or trampling blooming plants that bees rely on for food. One potential way to reduce potential negative effects of livestock on bees is to delay grazing on floristically rich parts of the landscape until after peak bloom (i.e., phenologically targeted grazing). To test the outcome of this method, we collected bees using pan traps and counted blooming stems from May to September in grazed and ungrazed sites. Our sites were located in two experimental cattle grazing systems in the Pacific Northwest, United States, in which cattle turnout did not occur until after peak forb bloom. One system was located in bunchgrass prairie, and the other was located in riparian meadows. Our objectives were to 1) quantify seasonal variation in bee and blooming plant communities and 2) measure how or if these communities responded to grazing. In both systems, bee and bloom species richness peaked in June and bloom abundance and diversity were highest in May and June. Bee abundance and diversity were more variable throughout the season. We observed significantly lower abundance, richness, and diversity of blooming species in the riparian system in response to grazing, potentially decreasing floral resource availability for bees, but did not detect a concomitant negative effect on bees. In the bunchgrass system, we observed no significant negative effects of grazing on bees or blooming plants. This suggests that for areas with high-quality bee habitat, site-specific, phenologically targeted grazing may moderate negative effects of livestock on bee and plant communities. Range managers could use alternative grazing locations (e.g., old fields, early senescing sites, more intensively managed pastures), if available, during peak bloom to mitigate potential herbivory effects on bees and blooms.
This study investigated the influence of rangeland land cover on infiltration rates (IRs), field-saturated hydraulic conductivity (Kfs), and soil water repellency in Patagonia. Four land cover types (shrubs, dwarf heath shrubs, bare soil, and Inter tussock) were examined to assess their effects on hydrological processes. IR was measured using the single-ring method, and soil water repellency was evaluated using the Beerkan method. We hypothesized that land cover type affects IR, Kfs, and soil water repellency. The results showed significant variations in IRs among land covers, with Tsf displaying lower rates than the other covers. Soil water repellency was prevalent in shrub and dwarf heath shrub–covered soils. Lateral flow was observed, indicating limited water infiltration. The obtained Kfs values were higher than the calculated hydraulic conductivity values (Ks). However, further investigation is required to assess the impact of capillarity (i.e., α*) on Kfs determination. This study enhances our understanding of hydrological processes in rangeland ecosystems and provides valuable insight into land management practices. By elucidating the relationships among land cover, IR, Kfs, and soil water repellency, this study contributes to sustainable water resource management in arid and semiarid regions.
Invasive plants are regarded as both drivers and passengers of change in the ecosystems they invade. In both conditions, these plants are reported to cause significant changes in soil biological, physical, and chemical characteristics, which have a long-lasting impact in the invaded soils compared with the surrounding uninvaded soils. One of the mechanisms of such change is the addition of both aboveground and belowground plant organic material. The goal of this study was to explore the plant-soil feedback in a non-native invasive grass, Guinea grass (Megathyrsus maximus) that invades rangelands, agricultural fields, and natural areas in the tropics and warm temperate regions. We hypothesized that the soil under Guinea grass is significantly different from natives. We also hypothesized that high tissue nitrogen leads to a higher litter nutrient status, driving this change. To test these hypotheses, we selected five different sites with significant Guinea grass invasion history and analyzed the soils under Guinea grass and coexisting native grasses. Our results show there was no significant difference between Guinea grass and natives in the amount of organic matter in the soil, but the nitrogen (N) content in both soil and leaf tissue in Guinea grass and natives was significantly different. The higher N content in the leaves was strongly correlated with soil N, moisture, and organic matter salinity, and negatively correlated with soil pH. Therefore, our results show that due to its nitrogen-rich leaf tissues, Guinea grass adds higher-quality litter back into the soil, resulting in a higher nutrient pool in its rhizosphere compared with the native grasses, thereby further aiding in the invasion success of Guinea grass.
In mixed C3/C4 grasslands of the southern Great Plains of North America, honey mesquite (Prosopis glandulosa Torr.) invasion facilitates the dominance of the C3 midgrass Texas wintergrass (Nassella leucotricha [Trin. & Rupr.] Pohl) to the detriment of warm-season grasses. Little is known about the viability of targeted grazing as a treatment method for reducing Texas wintergrass biomass and reproduction, particularly under mesquite canopies. We quantified the effects of targeted grazing treatments (grazed once [G1], grazed twice [G2], and control) and mesquite canopy position (under canopy [UC] and outside of canopy [OC]) on Texas wintergrass basal area, total dry matter (DMY) per basal area, live DMY per basal area, dead DMY per basal area, leaf length, total number of reproductive culms per plant, number of fungus-infected reproductive culms per plant, and rate of reproductive culm development over 2 yr at two study sites. Targeted grazing reduced leaf length and biomass and slowed reproductive development of the wintergrass plants that cattle could more easily access. Environmental factors and differences in mesquite physiognomy at the two study sites likely interacted with grazing treatments, making it challenging to separate the impacts of targeted grazing treatments from other factors. Results suggest mesquite removal is likely necessary to increase cattle access to Texas wintergrass, particularly in stands with multistemmed trees.
Willows are an important component of western riparian zones as their roots stabilize streambanks, their overstory mediates stream temperature, and aquatic biota use their stems and leaves as forage and building material. We evaluated 1894 stream reaches in the Inland Pacific Northwest for the presence of willows and detected one or more willow species at 1 247 (66%) of those reaches. Most stream reaches where willow was present had two or more willow species. We identified 23 unique species, of which 11 were found in 50 or more stream reaches. Across all sites, stream reaches with willow were more likely to be in the southern high-elevation portion of the study area. Distribution models constructed using random forests included a measure of spatial location (latitude, longitude, elevation) as one of the top predictors for 10 of the 11 common species. Only one species included a stream reach-scale attribute (bankfull stream width) as a top predictor, although two species had gradient or percent of the reach forested as a secondary predictor. While spatial location within the study area was a key factor in determining species presence, differences among species resulted in willows being found across the range of landscape and stream reach conditions except where forest cover in the reach was high (> 75%). Given that willows share characteristics such as rapid root growth, rhizomes, flexible stems, and vegetative reproduction, in many situations different species may respond as functional equivalents when it comes to protecting streambanks, providing habitat for fish and wildlife, and promoting stream heterogeneity. Ongoing threats to willows near streams on public lands include grazing, water diversion, mining, and climate change. Each of these threats can be at least partially addressed by identifying stream reaches inhabited by willow and establishing reach-scale management objectives for this taxon.
Prescribed fall burning is commonly used worldwide on rangeland sites to enhance vegetation resources and restore disturbed ecosystems, but little is known about how it may alter microbial communities and insect activities. We used two site treatments (low- to moderate-burn severity plots and unburned control plots) at a high-elevation (2 100 m above sea level) shrub-steppe rangeland site. Four yr after the prescribed burn, captured insects primarily consisted of Coleoptera (beetles), Hymenoptera (ants, bees, and wasps), and Orthoptera (grasshoppers and crickets) species with similar or greater numbers captured on burned plots as compared with unburned plots. We used wood stakes to assess microbial population changes. Aspen (Populus tremuloides Michx.) and pine (Pinus taeda L.) wood stakes were placed horizontally on the soil surface and vertically into the mineral to determine microbially altered wood decay rates. In mineral soil, mass loss (wood decay) of both aspen and pine increased significantly in the burned plots after 5 yr. Surface aspen also had increased decay in the burned plots, but pine surface stakes were unaffected. Surprisingly, at this high-elevation site we also found subterranean termites (Reticulitermes tibialis Banks) feeding on both stake species, with greater numbers on aspen stakes in burned plots leading to greater wood mass loss and organic matter turnover rates. Our results suggest that that fall prescribed burning can enhance insect numbers and microbial decay in sagebrush-steppe ecosystems. Understanding these changes can help land managers predict the influence of fall prescribed burning operations on soil biological properties and insect communities.
William J. Price, April Hulet, K. Scott Jensen, Eva K. Strand, Chad S. Boyd, Kirk W. Davies, Dustin D. Johnson, Barry L. Perryman, Yanming Di, Sergio A. Arispe
The invasive annual grass, medusahead, infests rangelands throughout the West, from the Columbia Plateau to the California Annual Grasslands and the Great Basin. Dominating secondary succession in the sagebrush steppe, medusahead can degrade the habitat of threatened species such as the greater sage-grouse. This research explores the potential of dormant season grazing as an applied management strategy to reduce the negative impacts of medusahead while promoting recovery of perennial vegetation at the landscape scale. In particular, it assessed grazing with four treatments from 2018 to 2020: traditional grazing (May–October), dormant season grazing (October–February), traditional + dormant season grazing (May–February), and no grazing. After 2 yr of grazing treatments, biomass, density, cover, and fuel continuity did not differ between treatments (P > 0.05). However, biomass measurements were significantly different between years, which is likely due to greater than normal precipitation in 2019 and 2020. Between 2018 and 2019, annual grass biomass increased by 81% (666–1 212 kg ha–1) and perennial grass biomass increased by 165% (118–313 kg ha–1). Litter biomass decreased by approximately 15% in every year since 2018 (2 374, 2 012, and 1 678 kg ha–1 in 2018–2020). There were not significant differences in cover or density of annual and perennial grasses between treatments and years. Our results indicate that 2 yr may not be adequate time for dormant season grazing treatments to be effective in reducing the abundance of medusahead and that after 2 yr of treatments, dormant season grazing does not have a detrimental effect on perennial vegetation.
Mixed-species herbivory, along with prescribed fire, is one of the most effective ways of controlling woody plant encroachment in the southern Great Plains and comes with the added benefits of maintaining grazing efficiency and rangeland productivity. Despite its experimental stage success, most landowners in the southern Great Plains have not fully adopted mixed-species herbivory as a range management tool. This study aimed to understand the barriers to the adoption of mixed-species herbivory by soliciting information from rangeland owners in the southern Great Plain states of Texas, Oklahoma, Kansas, and Nebraska. We found that more than 40% of landowners in the southern Great Plains are not aware of mixed-species herbivory and < 10% of them have adopted the practice. Landowners who were previously aware of mixed-species herbivory were less likely to think that it provides lower returns compared with traditional grazing. Many landowners, however, reported a lack of sufficient infrastructure, labor, or equipment as barriers to adoption. We suggest that extension efforts and outreach campaigns focused on the needs and concerns of landowners can change perceptions around the effectiveness of mixed-species herbivory as a land management tool to enhance the resiliency of rangeland ecosystems in the southern Great Plains.
Jacy S. Bernath-Plaisted, Maureen D. Correll, Scott G. Somershoe, Angela M. Dwyer, Andy Bankert, Adam Beh, Humberto Berlanga, W. Alice Boyle, J. Lizardo Cruz-Romo, T. Luke George, James Herkert, Nicola Koper, Alberto Macías-Duarte, Arvind O. Panjabi, Oscar M. Ramírez-Flores, Barry Robinson, Irene Ruvalcaba-Ortega, Julie Sibbing, Erin H. Strasser, Mieke Titulaer, William E. Van Pelt, Tammy VerCauteren
North America's grassland birds remain in crisis despite decades of conservation efforts. This review provides an overview of factors contributing to these declines, as well as strategies and resources available to a diversity of stakeholders to help conserve grassland bird communities with an emphasis on the Great Plains—a grassland region of global ecological significance and a habitat stronghold for grassland birds. Grassland bird declines are driven by historical and continuing threats across the full annual cycle including grassland habitat loss, agriculture intensification, woody encroachment, and disruption of fire and grazing regimes. More recently, energy development activities, the use of neonicotinoid pesticides, and anthropogenic climate change have emerged as additional threats. While threats to grassland birds are numerous and often synergistic, possibilities for conservation are also diverse and multifaceted. Land set-aside programs, incentives and voluntary practices for producers, improved environmental management by energy and utility companies, and policy and regulation can all contribute to the conservation of these unique species. We suggest that future grassland bird research should focus on poorly studied aspects of the annual cycle, such as overwinter survival and habitat use, and the migratory period, which remains completely unexplored for many species. Filling these knowledge gaps may facilitate more sophisticated population modeling that can identify limiting factors and more effectively guide investment in conservation.
Restoration of plains bison (Bison bison bison) in the northern Great Plains has been controversial for a variety of reasons, including the public concern that bison will supplant cattle on public rangelands. Riparian zones are among the most biologically rich areas within rangelands, but they are highly sensitive to disturbances such as grazing, leading to the public perception that riparian vegetation communities will be negatively impacted by year-round bison grazing compared with the norm of seasonal cattle grazing. Our objective was to evaluate the vegetation community and soil compaction conditions of areas in the northern Great Plains of Montana, where bison have been restored 5–10 yr as year-round grazers, compared with adjacent sites where cattle have been retained as seasonal grazers. Out of the 24 variables we assessed, only 2 significantly differed between the grazer treatments within our study's time frame and stocking rates. Native species diversity was significantly higher in the bison-grazed treatment (F[1,1,5.98] = 8.16, P = 0.03), and woody height heterogeneity was twice as high in the bison-grazed treatment than the cattle-grazed treatment (F[1,5.97] = 5.81, P = 0.05). Although longer-term studies are required, our findings indicate that year-round bison grazing under the current stocking rates did not degrade riparian vegetation communities compared with seasonal cattle grazing and rather benefitted some aspects of the plant community.
The main traditional livelihood in the high Central Andes Plateau, locally known as the Puna, is pastoralism. This system is based on llamas (Lama glama) and sheep (Ovis aries), which graze on natural vegetation (shrub steppe, grasslands, and peatlands). So, the livelihood of Andean communities is strongly influenced by the spatial and temporal dynamics of vegetation. Most of the existing models on herbivory used to estimate sustainable livestock loads require information on the nutritional values and primary production of vegetation, which is lacking for the Argentine Puna. This work aimed to fill the gap by implementing a carrying capacity model using data on annual vegetation growth and herbivore feeding strategies collected in the field in different plant communities. The hypothesis that guided this work was that environmental heterogeneity affects management decisions and should be taken into account to model sustainable animal stocks in Andean pastoralist systems. We estimated carrying capacity based on the MSY logistic model, considering biomass and aboveground primary production of vegetation communities, climatic features, and herbivore selective responses. We compared the estimated carrying capacity with real animal stocks in four production units within the study site in 2013, 2014, and 2017. The results indicate that the carrying capacity presents high spatial and temporal variability. In three of the production units assessed, the livestock—mixed herds of sheep and llamas—were above or near the estimated carrying capacity, even when the stocking rates were reduced during dry periods. The high stocking rates, along with evidence of land degradation, may indicate moderate to severe overgrazing. This work demonstrates the usefulness of estimating the carrying capacity to monitor the pastoral systems at fine space and time scales. These monitoring techniques can facilitate decision making among Puna herders in a biocultural context of knowledge dialog that may foster sustainability in pastoralist livelihoods.
Savanna ecosystems provide resources supporting the livelihoods of millions of people globally. Ongoing exploitation through high livestock densities, among other factors, however, threatens these ecosystems. Shrub encroachment, a consequence of this exploitation, causes severe declines in fodder biomass for cattle. For example, in Namibia, this leads to losses of land productivity of up to 100%. Consequently, we must rethink land-use options to ensure sustainable utilization of savanna resources. In southern Africa, many landowners and custodians have switched to or included wildlife in their management systems, making it an excellent model region to study how changing herbivory affects ecosystems. The diversity of indigenous wildlife species is expected to promote efficient herbaceous layer utilization with browsing herbivores counteracting nondesirable woody plant encroachment. Nevertheless, surprisingly little research has been conducted on the ecological consequences of altering grazer-to-browser ratios.
We developed a large-scale spatially explicit dynamic vegetation model including key hydrological and ecological processes, fire, and an herbivore algorithm that accounts for aggregated animal herds in a heterogeneous savanna landscape. We find that different ratios of wild herbivore feeding types greatly influence vegetation composition and dynamics. By dynamically computing plant biomass as a resource, our model estimates the occurrence of fodder biomass shortages, providing a valuable tool for land users. The model also reports the number of patches with low to medium tree functional cover (10–25%), indicating structural diversity with its implications for species richness, and is thus essential for nature conservation. We find that a herbivore species composition of approximately 40% browsers and 60% grazers is beneficial for plant structural and species diversity. Theoretically, therefore, the browse-graze ratio achieved through wildlife-based land-use can lead to more sustainability and resilience. The interplay between diverse herbivory, vegetation, rain, and fire complicates but also stabilizes the savanna rangeland ecosystem and may contribute to its long-term persistence.
Expansion of exotic annual grass (EAG), such as cheatgrass (Bromus tectorum L.) and medusahead (Taeniatherum caput-medusae [L.] Nevski), could cause irreversible changes to arid and semiarid rangeland ecosystems in the western United States. The distribution and abundance of EAG species are highly affected by weather variables such as temperature and precipitation. The study's goal is to understand how different precipitation scenarios affect EAG abundance estimates and dynamics, and we develop a machine learning modeling approach to predict how changes in annual and immediate past precipitation patterns could affect the abundance of EAG. The machine learning predictive model used seed source from previous years, weather variables, and soil profiles to drive its predictions. We achieved excellent training accuracy (r = 0.95 and median absolute error [MdAE] = 2.36% cover) and strong test accuracy (r = 0.79 and MdAE = 4.54% cover). We developed five versions of EAG abundance maps for 2022 with different precipitation scenarios: 9 yr of average precipitation, half of the average, three-fourths of the average, one and one-half times the average, and two times the average. The approach presented can be replicated to new study domains and easily modified for use with other precipitation scenarios. Developing multiple versions of a year's EAG spatially explicit abundance dataset predictions from multiple weather-based scenarios can provide important information to land managers as they prepare for variable EAG dynamics each year. Informed annual predictions based on weather scenario–driven models have the potential to improve fire preparation decisions.
Vegetation restoration is an effective measure for increasing the soil organic carbon (SOC) stock and mitigating the impacts of global warming. Grouping soil C according to aggregate particle size can help with more thoroughly understanding the dynamics of soil C during vegetation restoration. However, the dynamics of soil-aggregate-associated C after the restoration of different vegetation types remain unclear. As such, in this study, soil samples from the 0- to 10- and 10- to 20-cm soil layers in natural grasslands and plantations, which are the two most commonly used vegetation restoration types, were used to explore the dynamics of soil-aggregate-associated C for these different vegetation types. These grasslands and forestlands were converted from cropland since 1999. The results showed that soil and aggregate-associated C content were significantly affected by vegetation restoration types and soil depth. Vegetation restoration significantly increased the proportion of macroaggregates (> 0.25 mm) and soil C stocks; however, the improvements in soil aggregates and soil C stocks were similar for the two vegetation types. Vegetation restoration significantly increased the C content of aggregates of different particle sizes but only significantly increased the C stocks of soil macroaggregates, which had the highest C content among all the considered particle sizes. In addition, the contribution of macroaggregate C in the 0- to 10- and 10- to 20-cm soil layers to the soil C in the bulk soil also increased after vegetation restoration, reaching 57–64%. The results of random forest regression showed that the macroaggregate C content was the primary factor affecting the soil C stocks. This study demonstrated that natural succession and plantations have similar abilities to improve soil aggregates and soil C content in the central Loess Plateau and that the dynamics of macroaggregate C content dominate the dynamics of soil C stocks.
Controlling invasive annual grasses is one of the top conservation priorities in the American West. Brome (Bromus spp.) has more recently invaded areas of White Dome Nature Preserve, a conservancy for endemic and endangered or threatened plants in Washington County, Utah, United States, where the use of herbicides could be effective in managing invasion. Ideal habitat for these plants is on gypsiferous soils that are largely associated with biological soil crusts. Intact biological soil crusts are important in a biological communities' ability to resist invasion by annual grasses and are critical for nutrient cycling. However, there is a lack of research on how herbicides affect biological soil crusts and specific rare plant species that are of high conservation priority. We found that indaziflam (Rejuvra, Bayer CropScience, Monheim am Rhein, Germany), applied as a preemergent, was effective at reducing brome density the first growing season after application. Indaziflam also did not initially injure the biological soil crusts. Indaziflam is reported to have multiyear effects of reducing annual grasses, which makes indaziflam a promising herbicide for conservation purposes in areas where the invasive species seed bank needs to be depleted with as little disturbance to biocrusts as possible.
Effective wildfire management requires accurate information about the spatial distribution of fuels. While static maps work well for coarse forest fuels with slow turnover, fine fuels—the driver of rangeland fires—often vary dramatically from year to year. Our goal was to develop a fine fuel forecast to help managers optimally allocate fire suppression resources and funding before the start of the fire season and to identify critical gaps in understanding or data that limit forecast skill. We compiled a historical record of fine fuel loads collected in the Great Basin and combined it with remotely sensed data on herbaceous productivity. Using a Bayesian State-Space approach to account for both process and observation error, we built a “Fuels Model” in which the predicted fuel load at a location depends on the fuel load in the previous year and productivity of the current year. Next, we built a “productivity model” to predict current year production based on remotely sensed data available in early spring. Finally, we combined these two models to generate early spring forecasts for summer fuel loads from 1987 to 2020 and quantified the associated uncertainty. We found that current year productivity contributed twice as much as the previous year's fuel load to the current fuel load. Our productivity predictions reduced mean absolute predictive error by 11% compared with a strong null model without early-season weather covariates. However, when we fed the productivity predictions into our fuel model, the resulting fuel load forecasts had too much uncertainty to inform management decisions, with most uncertainty coming from the process error of the Fuels Model. Reducing this uncertainty will require higher-quality observations of fuel loads. Until those are available, our results suggest that managers could rely on productivity forecasts as a reasonable proxy for fuel load forecasts.
Large herbivores are often considered keystone species, driving the structure composition and dynamics within ecosystems, particularly for rangelands, which are often defined in terms of their productive capacity for livestock and game products. Grazing and foraging ecological research have been instrumental in developing a theoretical and empirical understanding of the role these herbivores play in natural and agricultural systems. We used a variety of text analysis techniques (e.g., topic modelling, geoparsing, taxonomic entity extraction) to assess key questions in the academic literature on grazing and foraging ecology research. These relate to understanding of the spatial and temporal trends and the main topics encapsulated within this research. We identified clear and distinguishable topics of research activity that spanned across methodological and analytical fields and subject matter. The subject matter topics related to specific areas of research (e.g., seed germination and dispersal), systems and modeling (e.g., modeling grazing systems), and management (e.g., rangeland management). Our analyses showed how the prevalence of these topics in the literature changed over time. Rangelands were the most common biome for research, with deer (Cervus and Odocoileus) as the most mentioned genera. The United States produced the most research, but China's output has grown over time. The research demonstrates that grazing and foraging ecology of ungulates (livestock and wildlife) is increasing; is highly dynamic in topic, space, and time; and that rangelands are, and have been, important in the development of research in the fields. Trends suggest that rangelands and rangeland management will continue to be important areas of research with modeling and greenhouse gas emissions growing in prevalence, particularly as China increases its contribution to the corpus.
Maternal provisioning to seeds is critical to later plant success, and identifying seed traits that predict successful plant establishment and resilience may facilitate improved plant material selection for rangeland restoration. Although size-standardized measurements are typically recorded for leaf traits, this is not the case for seed traits. In this study, we investigated whether an area-standardized metric, seed-specific mass (SSM), was better associated with seedling performance relative to simple seed mass. We germinated seeds of bluebunch wheatgrass (Pseudoroegneria spicata [Pursh.] A. Löve), crested wheatgrass (Agropyron cristatum L. var. Hycrest II), and Sandberg bluegrass (Poa secunda Presl.) on sterile agar and tracked seed mass, SSM, and subsequent seedling growth and mortality to investigate relationships between seed traits and seedling performance. SSM showed clear variation among species despite similarities in seed mass, and species-specific patterns of mortality most closely tracked variation in SSM. Crested wheatgrass seedlings that survived to 52 wk had significantly greater SSM than those that perished during the study, and surviving seedlings also had significantly longer roots at wk 4 than those that died. Seed mass and SSM each explained variation in seedling traits to some extent. Simple seed mass best predicted variation in early leaf area within species, while root length was best predicted by SSM across species. Our study is indicative that SSM warrants consideration in future studies investigating maternal energetic provisioning and seedling performance.
Quantifying the relationship of different grass functional groups to increasing woody plant cover is necessary to better understand the effects of woody plant encroachment on grasslands. This study explored biomass production responses of three perennial grass groups based on photosynthetic pathway and potential canopy height (C4 short-grasses, C3 midgrasses, and C4 midgrasses) to different percent canopy covers of the surrounding deciduous woody legume, honey mesquite (Prosopis glandulosa). Two methods were used to determine mesquite canopy cover, line-intercept and geospatial analysis of aerial images, and both were used to predict production of the three grass groups. Five years of grass production data were included in the mesquite cover/grass production regressions. Two yr had extreme grass production responses, one due to drought and the other to high rainfall. Of the 3 remaining yr, best-fit curves were negative linear for C4 short-grasses and C3 midgrasses and negative sigmoidal for C4 midgrasses using both cover determination methods, although slopes of the curves differed between cover determination methods. C4 midgrasses were more sensitive than the other grass groups to increasing mesquite cover. Loss of production potential when mesquite cover increased from 0% to 35% was 75.5%, 28.7%, and 23.2% for C4 midgrasses, C3 midgrasses, and C4 short-grasses, respectively. Moreover, production potential of C4 midgrasses under no mesquite cover was 3 and 6 times greater than C3 midgrasses or C4 short-grasses, respectively. Spatial settings of the different grass groups in relation to mesquite tree size and size of intercanopy areas provided indirect evidence that the process of mesquite encroachment in the past 50–100 yr may have negatively impacted C4 midgrasses more than the other grass groups. Results suggest that gains in grass production following mesquite treatment would be limited if the system has degraded to where only C3 midgrasses and C4 short-grasses dominate.
Japanese brome (Bromus japonicus Thunb.) is an invasive annual grass that is common in the Great Plains. Grazing or clipping in the spring has been shown to decrease Japanese brome biomass, but the effect on seed viability is not as clearly understood. We tested two clipping height and two clipping frequency combinations against nonclipped controls to determine effects on productivity and seeds of Japanese brome in greenhouse conditions. Pots containing two Japanese brome plants each were the experimental unit, with six per treatment, and the experiment was repeated a second yr. Plants were clipped to a 75-mm or 150-mm stubble height on a 7-d or 14-d interval starting at the boot stage, or no clipping occurred. Brome biomass was reduced 35% by clipping to 150 mm and 54% with clipping to 75 mm. No biomass differences were detected between clipping frequencies at either clipping height. Cumulative seed production was reduced at least 54% by clipping and reductions increased with shorter clipping and greater clipping frequency. At the end of the experiment, clipped plants had 7–310 seeds per pot, compared with a mean of 2 585 seeds per pot for nonclipped. Mean seed weight for all clipped treatments was 73% less than that of nonclipped plants. Only 15 seeds germinated from the 150-mm treatment clipped every 14 d. Plants clipped at 75 mm, regardless of frequency, and plants clipped to 150 mm weekly did not produce any viable seeds. Defoliation, across clipped heights and frequencies, drastically reduced the number and viability of Japanese brome seed. Targeted defoliation by mowing or grazing can contribute to Japanese brome control through seed limitation.
Tall forb–mixed upland–herb communities are exemplified by high plant diversity and a profusion of luxuriant wildflowers throughout subalpine mountain parklands of the interior western United States. These unique and ecologically important communities remain largely unclassified in terms of their biological and physical attributes and ecological responses to management and disturbances. Land managers need respective classifications to evaluate and guide conservation planning and management for tall forb communities where they occur. In this study, 23 sites from four subalpine areas representing reference tall forb plant communities on the Bridger-Teton National Forest were identified and selected for analysis after a sustained cessation of grazing activities. The purpose of the study was to quantitatively examine tall forb community stands and provide a basis for developing a classification system for identifying future ecological sites, which are essential in conservation planning, implementation and management, and monitoring. Seven tall forb cluster groups were identified with unique plant composition and specific environmental gradients (i.e., plant species richness, diversity indices, elevation, average annual precipitation, surficial geology, three-dimensional geomorphic descriptions, soil clay content diversity dynamics, and foliar, ground, and surface cover). Among the seven cluster groups, we identified 31 families, 112 genera, and 158 plant species on the sample sites (61 species representing native indicator reference species, 86 native secondary indicator species, and 10 introduced non-native species). Beta diversity and plant species turnover ranged from 6.7% to 41.9% among the seven cluster groups, indicating discrete differences in plant species assemblages, plant associations, and site dynamics. The seven tall forb clusters are characteristic of specific and unique plant species composition, species diversity, and environmental factors. Therefore, a specialized site approach with respective guidelines is recommended for assessing and conserving discrete tall forb ecological sites and maintaining key dominant native indicator reference species, rangeland health and proper functioning condition, and defined monitoring protocols.
Simultaneous desires for greater livestock production and reduced purchased feed inputs are further complicated by potential for rangeland degradation and weed invasion. Grazing management that emphasizes greater use of dormant rangeland forages may provide solutions. We tested grazing season (summer or fall) and intensity (moderate or heavy) combination effects on plant community composition and productivity to determine whether rangelands can sustain heavy dormant-season use without reducing native perennials. Treatment combinations were randomly assigned to 20, 60 × 30 m plots that were grazed from 2013 through 2017. Total current-yr biomass was greatest with moderate fall grazing (1 350 ± 41 kg ha–1) and similar among heavy fall, heavy summer, and moderate summer grazing (1 206 ± 41 kg ha–1). Heavy summer grazing had the lightest native species standing crop. Heavy summer grazing reduced perennial C3 grass standing crop 22%, primarily through effects on needle-and-thread (Hesperostipa comata [Trin. & Rupr.] Barkworth) and threadleaf sedge (Carex filifolia Nutt.). Moderate dormant fall grazing increased perennial C3 grass standing crop 15% but also increased the invasive annual, Japanese brome (Bromus japonicus Thunb.). Heavy dormant fall grazing effects did not differ from that of moderate summer grazing for perennial C3 grass or total native species standing crop, but heavy fall grazing reduced cheatgrass (Bromus tectorum L.) 51%. Where B. japonicus and B. tectorum co-occur, moderate growing season grazing combined with heavy dormant fall grazing may be needed to affect both species. Diversity and native species standing crop were similar between heavy fall and moderate summer grazing, but heavy fall grazing caused the least non-native species standing crop. Heavy fall use is recommended as potential treatment to be rotated among pastures over time or focused on pastures that could benefit from effects observed. Effects likely vary with differences in climate or species composition.
The southern Prairie Pothole Region (PPR) of central North America is a highly modified landscape where remnant unplowed prairies could serve as repositories of native plant biodiversity. A previous study paired two historically idle US Fish and Wildlife Service (USFWS) National Wildlife Refuges with nearby privately owned grazing lands in North Dakota and found differences in invasive grass frequency, notably that smooth brome (Bromus inermis Leyss.) was less prevalent on annually grazed lands. A broader assessment, conducted over a wider geographic area, was warranted to investigate whether this relationship held across the southern extent of PPR in North Dakota and South Dakota. To this end, we selected 26 USFWS native prairie sites paired with adjacent/nearby native prairie sites with a history of livestock grazing in the PPR of North Dakota and South Dakota. We estimated plant species' cover in five 10 × 10 m plots at each paired site in June or July of 2021. Plant community composition on USFWS sites was distinct from paired sites under private or state ownership (permutational analysis of variance (P= 0.021, F = 1.935). Additionally, paired t-tests revealed that sites under private or state ownership (with a long-term history of grazing) had higher total species richness (P= 0.006) and floristic quality index (a measure of species richness and disturbance tolerance) values (P= 0.042) than USFWS sites (without a long-term history of grazing). Smooth brome relative cover was lower (P= 0.019) at sites with a long-term history of grazing (13.4% mean relative cover) than paired USFWS sites (23.3% mean relative cover). Given these differences, remnant native prairies with long-term histories of annual grazing may provide unique opportunities for conserving native plant diversity and impeding smooth brome spread in the southern PPR.
Seeding crested wheatgrass (Agropyron desertorum [Fisch.] Schult.) in the sagebrush steppe is a controversial management action. There are concerns that crested wheatgrass may invade new areas and exclude native vegetation because many former crested wheatgrass seedings are near monocultures. However, crested wheatgrass is often seeded to prevent exotic annual grass invasion and stabilize soils after disturbances in areas where native vegetation is unlikely to establish. These areas can be difficult to identify and, consequentially, crested wheatgrass may be seeded in areas it is not needed, such as sagebrush steppe with understories dominated by native perennial grasses and forbs (intact understories). Thus, land managers need to know the potential effects of seeding crested wheatgrass, especially if it can invade and exclude native vegetation in sagebrush steppe with intact understories. We investigated the ability of crested wheatgrass to invade and exclude native vegetation by drill seeding crested wheatgrass into intact sagebrush steppe understories at five sites. To be invasive, crested wheatgrass would need to increase in abundance beyond initial establishment from drill seeding, causing decreases in native vegetation. We measured vegetation cover and density for 7 yr after seeding to evaluate the effects of seeding crested wheatgrass. Crested wheatgrass established with drill seeding but did not increase from its original density. Cover of crested wheatgrass increased with time but was < 2% seven yr after seeding. We found no evidence that seeding crested wheatgrass decreased the cover or abundance of native vegetation. These results suggest that intact sagebrush steppe understories are competitive with crested wheatgrass and, thereby, limit its recruitment and growth. Though crested wheatgrass did not show indications of being invasive in intact sagebrush steppe understories, longer-term evaluations with the inclusion of disturbances that might open safe sites in these communities would be prudent to fully understand its potential effects.
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