Semi-arid Rangelands Research Articles

Adaptation strategies to environmental and policy change in semi-arid pastoral landscapes: Evidence from Ngamiland, Botswana

Semi-arid rangeland pastoral areas have been affected by diverse pressures; livestock diseases, human-wildlife conflicts, droughts and resource scarcity as a result of fragmented landscapes that constrain pastoral livelihoods. In Botswana, pastoralists' adaptations remain insufficiently documented. Adaptation strategies are responses to livelihood constraints and if mainstreamed into development programmes can counter negative impacts arising from ecosystem deterioration. Using iterative participatory rural appraisal methods, this study examines adaptation strategies that pastoral societies in Ngamiland, Botswana have used to cope with pressures in their pastoral socio-ecological system. Findings show a move towards mixed and spatially varied livelihood strategies. Mixed agro-pastoral farming, intensification of flood recession farming, fishing and a network of self-help groups have developed over the last few decades of significant policy and environmental change. Pastoralists have become more sedentary with increases in petty trade and higher dependency on social welfare programmes. As the ability to adapt has positive attributes for livelihood sustainability and resilience, there is a need for practical initiatives that improve pastoralists' adaptive capacity, such as reforming pastoralists' institutions and expanding infrastructural development in pastoral areas so as to enable access to markets. These also include the need to share insights more widely across the district, nationally and regionally.

Grazing and aridity reduce perennial grass abundance in semi-arid rangelands – Insights from a trait-based dynamic vegetation model

Semi-arid tropical rangelands substantially contribute to livelihoods of subsistence farmers, but are threatened by undesired vegetation shifts due to climate change and overgrazing. Grazing-induced shifts of the grass community composition are often associated with rangeland degradation. To identify sustainable management strategies, a process-based understanding of grass functional diversity and rangeland dynamics is required. We present a new scheme for aDGVM2, a dynamic vegetation model for tropical ecosystems, that distinguishes annual and perennial grasses based on trait trade-offs to improve the representation of rangeland communities. Additionally, the model includes a new scheme that describes selective grazing and grazing effects on grass-layer composition. We tested the new model version for various grazing intensities along a precipitation gradient in South Africa. Mean annual precipitation below 500 mm constrained rangeland productivity and carrying capacity. Increasing grazing intensity reduced rangeland productivity and increased annual grass abundance. Heavy grazing resulted in annual grass dominance. Livestock preferred perennial over annual grasses at low grazing intensities at all except the two driest sites; preference switched to annual grasses at intermediate intensities, and became non-discriminating at high grazing intensities. Rangeland recovery after removal of grazers required 2–15 years. We conclude that management intervention reducing or eliminating grazing pressure during and after stress years is crucial to allow rangeland recovery and avoid permanent degradation.

Which spatial distribution model best predicts the occurrence of dominant species in semi-arid rangeland of northern Iran?

Rangelands with more than 8000 plant species occupy nearly 54.6% of the land area of Iran and thus are accounted for a rich plant genetic storage. Mazandaran province has 378,000 ha of rangelands with high plant species richness and diversity due to its climate conditions but plants distribution is at risk because of non-principle management, land use change and as a result changing environmental factors. Vegetation management strategies can be guided by models that predict plant species distribution based on governing environmental variables. This is especially useful for the dominant species that determine ecosystem processes. In fact, modelling algorithm in each SDM determines its suitability for different ecosystems. Our aim was to compare the predictive power of a number of SDMs and to evaluate the importance of a range of environmental variables as predictors in the context of semi-arid rangeland vegetation. The selected study area, the Sarkhas rangelands (northern Iran, 36°10′ 42˝ N - 51°19′ 11˝ E), covers approximately 4358.9 ha of Mazandaran province. The efficacy of four different modelling techniques as well as Ensemble model was evaluated to predict the distribution of five dominant forage plant species (Vicia villosa, Stachys lavandulifolia, Coronilla balansae, Sanguisorba minor and Alopecurus textilis). The used models included artificial neural network (ANN), boosted regression trees (BRT), classification and regression trees (CART), and random forest (RF). Ensemble, RF and CART had the highest area under curve. The AUC obtained for Vicia villosa, Stachys lavandulifolia, Coronilla balansae, Sanguisorba minor and Alopecurus textilis, were 0.90, 0.72, 0.76, 0.69 and 0.75 respectively. Ensemble model was the model that most consistently demonstrated high predictive power across species in the rangeland context investigated here. BRT exhibited the least predictive power. An importance analysis of variables showed that soil organic C according to the CART model (0.396) and K according to the RF model (0.396) were the most important environmental variables.

Rotational grazing management achieves similar plant diversity outcomes to areas managed for conservation in a semi-arid rangeland

Despite the increasing extent of protected areas throughout the world, biodiversity decline continues. Grazing management that promotes both biodiversity and production outcomes has the potential to improve broad-scale conservation and complement the protected area network. In this study we explored the potential to integrate commercial livestock grazing and conservation in a semi-arid rangeland in south-eastern Australia. Understorey floristic composition and diversity were compared at different spatial scales across three grazing management treatments: (1) continuous commercial grazing management where paddocks were grazed for the majority of the year (≥8 months per annum); (2) rotational commercial grazing management where livestock are frequently rotated and paddocks rested for >4 months per annum; and (3) protected areas managed for conservation with domestic livestock excluded and grazed only by native and feral herbivores. The season of sampling, rainfall, soil characteristics and the spatial location of sites were the dominant drivers of variability in understorey plant species composition; the effect of grazing treatment on understorey plant species composition was relatively minor. However, areas managed for conservation and under rotational forms of commercial grazing management generally had greater floristic richness and diversity than continuously grazed areas, the results varying with season (spring/autumn) and soil type (clay/sandy-loam), particularly at fine scale (1-m2 quadrats). These findings indicate that rotational grazing management on commercial properties has the potential to improve biodiversity conservation outside the reserve system compared to conventional grazing management.

Determination of best sediment estimation model in semi-arid rangelands by using small reservoirs dams sedimentation(case study: daremorid watershed in kerman province)

Determination of best sediment estimation model in semi-arid rangelands by using small reservoirs dams sedimentation(case study: daremorid watershed in kerman province)

Plant litter decomposition in a semiarid rangeland of Argentina: species and defoliation effects

Plant litter decomposition is critical for terrestrial ecosystem productivity. Poa ligularis Nees ex Steud and Nassella tenuis (Phil.) Barkworth are native, desirable perennial grasses in central Argentina’s rangelands. Amelichloa ambigua (Speg.) Arriaga & Barkworth is only consumed when a better forage is unavailable. Litter traps were used to collect aboveground litter during two years. In March 2012, six bags, each one containing either leaf blade (three bags, one per species) or root litter (three bags, one per species) of the three species were located below the canopy of each replicate plant of the studied species (hereafter referred to as ‘location’). Blade litter bags were located on the soil surface, and root litter bags buried at 10cm soil depth. This allowed evaluation of the effects of defoliation, the different species canopies and the microbial community activity around their roots on decomposition of above- and belowground litter. For each species, twenty plants were either defoliated twice (5cm stubble height) or remained undefoliated during the growing season. Litter bags were collected after 2, 7, 13 and 24 months incubation. The study was repeated in 2013, with additional bags were placed for N content determination on leaf blade and root litters. Aboveground litter production was highest in P. ligularis; however, no differences were observed among species when the effect of plant size was eliminated. Aboveground litter of desirable species had higher N content and decomposed faster than that of A. ambigua. The opposite was recorded for root litter. Defoliation had no effect on litter decomposition, but location effects were detected after one year of incubation. Desirable perennial grasses promoted organic matter loss from litter, a key factor in increasing soil fertility in this semiarid ecosystem.

Changes in Soil Organic Carbon Stock Under Different Land Use Types in Semiarid Borana Rangelands: Implications for CO2 Emission Mitigation in the Rangelands

Understanding the impact of land use change on soil organic carbon stock following the conversion of a semiarid rangeland into different land use types is essential to devise an appropriate and sustainable rangeland management strategy. However, there is a knowledge gap as to the impact of currently ongoing land use changes on soil organic carbon stock, which is an important rangeland ecosystem service, particularly in the face of climate change. Thus, this study was conducted to assess the effect of land use change on soil organic carbon stock in three land use types, namely, enclosures, communal grazing and cultivated lands in Borana rangeland. The result indicated that there were significant interactions between land use types and depths for soil organic carbon stock (p<0.0001) and bulk density (p=0.0055) with mean losses of 60% and 69% in soil organic carbon stock from the surface layer (0-10 cm) of communal and cultivated lands, respectively, as compared to enclosure land use type. The results indicated that communal grazing and crop cultivation in the Borana rangeland resulted in significantly decreased soil organic carbon stock. Hence, the current trend must be curbed to put back the system on its right track of resilience and sustainability for its long-term benefit and to mitigate the unprecedented increase in CO2. Therefore, the results of this study would be useful for the improvement of land use management in the future.

The Texas Soil Observation Network:A Comprehensive Soil Moisture Dataset for Remote Sensing and Land Surface Model Validation

Core Ideas TxSON is a Core Cal/Val Site for the NASA SMAP, SMOS, and Sentinel programs. TxSON consists of 40 in situ locations nested within a 36‐km EASE2 grid cell. Locations monitor soil moisture, temperature, and precipitation at 5, 10, 20, and 50 cm. Hourly, quality‐controlled data from 2015 to 2018 are available. The spatiotemporal variability of soil water content (SWC) at the remote sensing scale requires dense monitoring for calibration and validation. Here, we present an overview of the Texas Soil Observation Network (TxSON), an intensively monitored area in the semiarid rangelands of the central Texas Hill Country. TxSON is a dense network consisting of 40 in situ locations nested at 36, 9, and 3 km within the Equal‐Area Scalable Earth Grid and serves as a Core Calibration and Validation Site for NASA's Soil Moisture Active Passive mission. The 4‐yr dataset consists of hourly SWC measured at 5, 10, 20, and 50 cm. The SWC data are upscaled using arithmetic, Voronoi, and inverse distance weighting for 36‐, (2) 9‐, and (5) 3‐km grid cells. We present the site selection, environmental characteristics, network design, quality assurance (QA), upscaling algorithms, and data structure. Ancillary data include bulk density, particle size, and carbon content for each site and depth. We also provide automated QA for each location and scripts to use our binary flagging in upscaling methods. To summarize, the 36‐km grid cell has a mean bulk density of 1.34 ± 0.18 g cm−3 and a loam textural class. The in situ SWC has a root mean square error of 0.029 m3 m−3 against gravimetric data from 14 field campaigns. TxSON continues to add new locations with additional dense networks planned in other ecotones of the Edwards Plateau. The time series data along with scripts to import, plot, and upscaled SWC are available at https://doi.org/10.18738/T8/JJ16CF.

Characterizing hydrological processes in a semiarid rangeland watershed: A hydrogeophysical approach

AbstractThe complex ecohydrological processes of rangelands can be studied through the framework of ecological sites (ESs) or hillslope‐scale soil–vegetation complexes. High‐quality hydrologic field investigations are needed to quantitatively link ES characteristics to hydrologic function. Geophysical tools are useful in this context because they provide valuable information about the subsurface at appropriate spatial scales. We conducted 20 field experiments in which we deployed time‐lapse electrical resistivity tomography (ERT), variable intensity rainfall simulation, ground‐penetrating radar (GPR), and seismic refraction, on hillslope plots at five different ESs within the Upper Crow Creek Watershed in south‐east Wyoming. Surface runoff was measured using a precalibrated flume. Infiltration data from the rainfall simulations, coupled with site‐specific resistivity–water content relationships and ERT datasets, were used to spatially and temporally track the progression of the wetting front. First‐order constraints on subsurface structure were made at each ES using the geophysical methods. Sites ranged from infiltrating 100% of applied rainfall to infiltrating less than 60%. Analysis of covariance results indicated significant differences in the rate of wetting front progression, ranging from 0.346 m min−1/2 for sites with a subsurface dominated by saprolitic material to 0.156 m min−1/2 for sites with a well‐developed soil profile. There was broad agreement in subsurface structure between the geophysical methods with GPR typically providing the most detail. Joint interpretation of the geophysics showed that subsurface features such as soil layer thickness and the location of subsurface obstructions such as granite corestones and material boundaries had a large effect on the rate of infiltration and subsurface flow processes. These features identified through the geophysics varied significantly by ES. By linking surface hydrologic information from the rainfall simulations with subsurface information provided by the geophysics, we can characterize the ES‐specific hydrologic response. Both surface and subsurface flow processes differed among sites and are directly linked to measured characteristics.

Nutritional evaluation and productivity of supplemented sheep grazing in semiarid rangeland of northeastern Brazil.

Sheep production systems in Brazilian caatinga rangelands require supplementation adapted to changes in floristic and chemical composition as dry seasons progress. Meeting sheep nutritional needs in extensive semiarid systems is challenging because of sheep dietary preferences and habits. The objective of this trial was to evaluate the substitutive effect of concentrate supplementation on grazing sheep in the Brazilian caatinga rangeland and its consequences on performance in different seasons. The trial was conducted from March to August 2013 at Embrapa Goat and Sheep in Sobral, Ceará State, Brazil. Thirty-two Brazilian Somali multiparous ewes were submitted to estrus synchronization and controlled breeding. At the start of the trial, ewes averaged 30.45 + 2.60kg body weight (BW). Ewes were divided into four groups and individually offered 0, 200, 350, or 500g supplement head-1 day-1. Intake prediction and digestibility trials were evaluated at three periods: rainy season (April), transition rainy-dry (June), and dry season (August). Sheep weights were taken every 14days to measure their performance from late gestation until weaning. Ewe BW and body condition score changes were determined too. Lamb BW changes were also measured every 14days from birth through weaning. A completely randomized design with split plot arrangement using eight replications was used for intake and digestibility measurements. The differences between supplement offered (0, 200, 350, and 500g sheep-1) and season (rainy, transition rainy-dry, and dry) were submitted to analyses of variance and multiple means were separated, where differences were detected, using the Tukey's test. During lactation up through weaning, ewes supplemented at 500gday-1 had greater BW than ewes without supplement. Ewes supplemented with 200g concentrate head-1 day-1 had 9.1% greater (P ≤ 0.05) BW at weaning and their lambs had 19.7% greater birth and 16.6% heavier wean BW despite lower dry matter intake compared to unsupplemented animals. Supplementation with 200g concentrate increased carrying capacity by 28.8% during the dry season and by 20.5% during the rainy season. This study confirmed that in the dry season, when quality of rangeland forages decreases, supplementation contributes to greater DMI, improves postpartum and lactation BW recovery of ewes, and contributes to greater lamb birth and wean weights. Moreover, supplementation leads to feed substitution effects that may increase rangeland resilience by mitigating overgrazing. Supplementation with 200g concentrate can also prevent negative energy balance for grazing animals, improving longer postnatal recovery, longer intervals between parturitions, fewer double and is necessary to ensure a better BW at birth to lambs.

Mycorrhiza inoculation effects on seedling establishment, survival and morphological properties of Ziziphora clinopodioides Lam.

In this paper, the establishment and growth of medicinal species Ziziphora clinopodioides Lam. were studied through inoculation with two mycorrhizal fungi species, Glomus mosseae and Glomus intraradices, in arid/semi-arid Bahar-Kish rangelands, Iran in 2012 and 2013. The root colonization percentage of Ziziphora, as well as their establishment and growth were enhanced in 2013 using G. mosseae. In this year, less rainfall and higher temperature decreased the survival, growth and morphological traits of the studied plants. Growth and establishment of the inoculated plants using G. intraradices improved in 2013, while inoculation with G. mosseae showed more beneficial effects in 2012. In both years, the strain, the growth and establishment percentage of seedlings in inoculated treatments with mycorrhizal species were significantly improved. According to the results, G. intraradices mycorrhizal fungi is recommended as a biological fertilizer in increasing the forage production and the initial establishment of Ziziphora in arid and semi-arid rangelands.

Assessing the potential of fungi isolated from dieback-affected trees as biological control agents for prickly acacia (Vachellia nilotica subsp. indica)

Prickly acacia (Vachellia nilotica subsp. indica, Family: Fabaceae) is an invasive woody weed in coastal and semi-arid rangelands of Australia. A prominent dieback event was observed on this species in 2010 in north-western Queensland. A Botryosphaeriaceae fungus, Cophinforma sp., was consistently isolated from symptomatic stem tissues. In preliminary studies, Cophinforma sp. and an isolate of Lasiodiplodia pseudotheobromae sourced from dieback-affected Parkinsonia aculeata (Family: Fabaceae) were found to be pathogenic to prickly acacia seedlings and juveniles. In this study, we investigated whether typical dieback symptoms could be replicated under glasshouse conditions and in the field following stem inoculations of these two fungi (either singly or in combination). In the glasshouse trial, stem lesions and leaf mortality were observed following stem inoculation by both of the test fungi although it was greatest in the presence of L. pseudotheobromae. However, no effects on plant growth or mortality were observed. In the field trials (located in central and north-western Queensland) both test fungi caused infection, but significant lesions were only induced by L. pseudotheobromae in central Queensland, and no treatment effects on plant growth or survival were observed at either site over the next two years. Prominent decline in plant vigour was observed in north-western Queensland two years after inoculation, but was presumed to be naturally occurring as it affected controls and neighbouring untreated plants equally. The test fungi were reisolated from lesions in both field and glasshouse trials, but were never found in adjacent tissue, suggesting that infection was successfully contained by the plant’s wound response. We found no potential for the tested fungal isolates to be effective biocontrol agents, although future studies should aim to initiate systemic infections.

Long-Term Persistence of Cool-Season Grasses Planted to Suppress Broom Snakeweed, Downy Brome, and Weedy Forbs

Invasive plants are spreading throughout arid and semiarid rangelands of western North America. Long-lived perennial plants that can persist under harsh environmental conditions are needed to compete with invasive species. The objective of this study was to conduct a long-term evaluation of native and introduced grass species planted to suppress and prevent reinvasion of downy brome (Bromus tectorum L.), snakeweed (Gutierrezia sarothrae [Pursh] Britt. & Rusby), and annual forbs. Seeding treatments comprised three introduced grasses: crested wheatgrass (Agropyron cristatum [L.] Gaertner × A. desertorum [Fisch. Ex Link] Schultes), pubescent wheatgrass (Elytrigia intermedia spp. trichophorum [Host] Beauv.), and Russian wildrye (Psathyrostachys junceus [Fisch.] Nevski); a mix of these introduced grass species, three native grasses: bluebunch wheatgrass (Pseudoroegneria spicata [Pursh]), western wheatgrass (Pascopyrum smithii [Rybd.] A. Löve), and squirreltail (Elymus multisetus [J.G. Sm.] Jones); and a mix of these native grass species, or forage kochia (Bassia prostrata [L.] A.J. Scott). The treatments were seeded in October 2003. Frequency and biomass were measured in 2015 and 2017 in Howell, Utah and in 2015 and 2016 in Nephi, Utah. Crested wheatgrass persisted at both locations (> 62% frequency) along with the rhizomatous grass species, pubescent (> 65%) and western wheatgrasses (> 72%). Russian wildrye was still present at Howell (30%) with little remaining at Nephi (7%). Squirreltail frequency was 13% at Howell and 12% at Nephi. Bluebunch wheatgrass was no longer present at either location (< 1%). Forage kochia remained at Nephi (36%) with little remaining at Howell (4%). Downy brome was present at both locations and was suppressed relative to control plots, at Nephi, by crested wheatgrass and the introduced grass mix (< 9%). Downy brome was > 93% in all plots, at Howell, in 2017. In summary, crested, pubescent, and western wheatgrasses were able to persist over 12 yr at both locations.

Exploring management objectives and ecosystem service trade-offs in a semi-arid rangeland basin in southeast Iran

Ecosystem services are increasingly being included as rangeland management objectives along with grazing, restoration, and conservation. These often conflicting objectives can interact and result in tradeoffs where managing for one ecosystem service (ES) can result in the detriment of another. However, there is scarce information for rangeland systems of central Asia. This study aims to assess tradeoffs interactions between different ES in a semi-arid watershed in Iran with centuries of grazing history. We use field data, the Integrated Valuation of Ecosystem Services model, and spatial analyses to explore the interaction and spatial distribution of rangeland health and its effects on: forage production, water yield, carbon stock, soil retention, and soil formation. We summarized ESs into two bundles: 1. forage production and carbon storage and 2. water yield, soil retention and soil formation. Rangeland health across the study area’s three different physiographic regions was determined and ES interaction groups mapped. A classification system of win-win (W-W), win-lose (W-L) and lose-lose (L-L) interactions under current management regimes was also developed using field data and statistical analyses. Findings show a W-L interaction among ESs in the mid-watershed region. Although this region provided the most forage and carbon storage; grazing management practices need to consider the sustainable provision of water yield, soil retention and soil formation. Interaction classes were however W-W in upstream regions where conservation objectives were a priority. Downstream, interaction classes were L-L due to overgrazing and urbanization; thus, restoration and improved management need prioritization. Understanding the spatial distribution of ES interactions can help managers plan for and balance resources with their sustainable supply.

Pasture enclosures increase soil carbon dioxide flux rate in Semiarid Rangeland, Kenya

BackgroundPasture enclosures play an important role in rehabilitating the degraded soils and vegetation, and may also influence the emission of key greenhouse gasses (GHGs) from the soil. However, no study in East Africa and in Kenya has conducted direct measurements of GHG fluxes following the restoration of degraded communal grazing lands through the establishment of pasture enclosures. A field experiment was conducted in northwestern Kenya to measure the emission of CO2, CH4 and N2O from soil under two pasture restoration systems; grazing dominated enclosure (GDE) and contractual grazing enclosure (CGE), and in the adjacent open grazing rangeland (OGR) as control. Herbaceous vegetation cover, biomass production, and surface (0–10 cm) soil organic carbon (SOC) were also assessed to determine their relationship with the GHG flux rate.ResultsVegetation cover was higher enclosure systems and ranged from 20.7% in OGR to 40.2% in GDE while aboveground biomass increased from 72.0 kg DM ha−1 in OGR to 483.1 and 560.4 kg DM ha−1 in CGE and GDE respectively. The SOC concentration in GDE and CGE increased by an average of 27% relative to OGR and ranged between 4.4 g kg−1 and 6.6 g kg−1. The mean emission rates across the grazing systems were 18.6 μg N m−2 h−1, 50.1 μg C m−2 h−1 and 199.7 mg C m−2 h−1 for N2O, CH4, and CO2, respectively. Soil CO2 emission was considerably higher in GDE and CGE systems than in OGR (P < 0.001). However, non-significantly higher CH4 and N2O emissions were observed in GDE and CGE compared to OGR (P = 0.33 and 0.53 for CH4 and N2O, respectively). Soil moisture exhibited a significant positive relationship with CO2, CH4, and N2O, implying that it is the key factor influencing the flux rate of GHGs in the area.ConclusionsThe results demonstrated that the establishment of enclosures in tropical rangelands is a valuable intervention for improving pasture production and restoration of surface soil properties. However, a long-term study is required to evaluate the patterns in annual CO2, N2O, CH4 fluxes from soils and determine the ecosystem carbon balance across the pastoral landscape.

One-time application of biosolids to ungrazed semiarid rangelands: 14 yr soil responses

Biosolids have been shown to improve forage production and soil quality on semiarid rangelands in the short term, but less is known about longer-term impacts of one-time biosolids applications. The objective of this study was to determine the effects of a single, surface biosolids application (at 20 dry Mg ha−1) on stability of soil aggregates, bulk density, total carbon (C) and nitrogen (N), permanganate-oxidizable carbon (POXC), polysaccharides, pH, nutrient availability, and soil water content (all at 0–7.5 cm depth) 14 yr following application to ungrazed rangelands in the Central interior of British Columbia. Fourteen years following the biosolids application, aboveground plant biomass was almost two times greater with biosolids application than on control, while exposed mineral soil and microbiotic crust significantly decreased in biosolids plots. Despite differences in aboveground biomass, there was no difference in total soil C and N, POXC, and polysaccharides between biosolids and control plots. Biosolids-amended soil did exhibit significantly greater mean weight diameter of water-stable aggregates, lower pH, increased spring soil water content, and increased availability of Fe3+, Zn2+, Cu2+, and phosphate ions. These findings indicate that the long-term improvements to soil on ungrazed rangeland are possible even from a single biosolids application.

Estimating evapotranspiration in semi-arid rangelands: connecting reference to actual evapotranspiration and the role of soil evaporation

In a context of water scarcity, efforts to increase landscape production should focus on improving water productivity. This requires an appreciation of the various components of evapotranspiration (ET), including soil evaporation (Es) because the latter reflects ‘unproductive’ water loss. Both complex and simple algorithms have been developed to determine ET. In data scarce areas, developing and testing parsimonious algorithms is useful. This study sought to improve a simple single layer ET model by incorporating an Es component. Empirical methods were also explored to predict ET from vegetation indices (VIs), leaf area index (LAI) and reference evapotranspiration (ET0). A large aperture scintillometer and an eddy covariance (EC) system were used to validate the proposed algorithm at three sites over Grasslands and Albany Thicket biomes in the Eastern Cape, South Africa. There was good agreement between the observed and predicted ET with RMSE of 0.30–0.58 mm d−1 when average daily observed ET was 0.43–3.24 mm. The VIs had moderate correlations with the observed data due to the significant role played by Es (65%–84%) across the sites and stomatal conductance at the Albany Thicket site. The simple algorithms developed would make determining ET easier in data scarce regions.

Greenhouse Gas Emissions from Beef Grazing Systems in Semi-Arid Rangelands of Central Argentina

The livestock sector can be a major contributor to the mitigation of greenhouse gas (GHG) emissions. Within the sector, beef production produces the largest proportion of the livestock sector’s direct emissions. The objective of this study was to assess the on-farm GHG emissions in semi-arid rangelands in Argentina and to identify the relationship between emissions and current farm management practices. A survey recorded detailed information on farm management and characteristics. Assessments of GHG emissions were based on the Intergovernmental Panel on Climate Change (IPCC) Tier 2 protocols. The relationship between farm management and GHG emissions were identified using general linear models. Cluster analysis was used to identify groups of farms that differed from others in emissions and farm characteristics. Emissions per product sold were low on farms that had improved livestock care management, rotational grazing, received technical advice, and had high animal and land productivities. Emissions per hectare of farmland were low on farms that had low stocking rates, a low number of grazing paddocks, little or no land dedicated to improved pastures and forage crops, and low land productivity. Our results suggest that the implementation of realistic, relatively easy-to-adopt farming management practices has considerable potential for mitigating the GHG emissions in the semi-arid rangelands of central Argentina.

Enhancing soil organic carbon, particulate organic carbon and microbial biomass in semi-arid rangeland using pasture enclosures

BackgroundRehabilitation of degraded rangelands through the establishment of enclosures (fencing grazing lands) is believed to improve soil quality and livelihoods, and enhance the sustainability of rangelands. Grazing dominated enclosure (GDE) and contractual grazing enclosure (CGE) are the common enclosure management systems in West Pokot County, Kenya. Under CGE, a farmer owning few animals leases the enclosure to households with relatively more livestock, while GDE is where the livestock utilizing the enclosure are purely owned by the farmer. Livestock management in both systems is via the free-range system. This study evaluated the effect of enclosure management on total soil organic carbon (SOC), particulate organic carbon (POC) and microbial biomass carbon (MBC) and nitrogen (MBN) as key indicators of soil degradation at 0–40 cm depth. The two enclosure systems were selected based on three age classes (3–10, 11–20 and > 20 years since establishment) (n = 3). The adjacent open grazing area (OGR) was used as a reference (n = 9).ResultsRelative to OGR, the pasture enclosures significantly decreased soil bulk density and increased the concentrations of total organic C, POC, MBC and MBN compared to the degraded OGR (P < 0.001). Significantly higher concentrations of POC and MBC was recorded in GDE than CGE (P = 0.01). The POC accounted for 24.5–29.5% of the total SOC. MBC concentrations ranged from 32.05 ± 7.25 to 96.63 ± 5.31 µg C g−1 of soil in all grazing systems, and was positively correlated with total SOC and POC (P < 0.001). The proportional increase in POC and MBC was higher in GDE (56.6 and 30.5% respectively) compared to CGE (39.2 and 13.9% for POC and MBC respectively).ConclusionsThis study demonstrated that controlling livestock grazing through the establishment of pasture enclosures is the key strategy to enhance total SOC, POC, MBC, and MBN in degraded rangelands; a precondition for improving soil quality. Therefore, the establishment of enclosures is an effective restoration approach to restore degraded soils in semi-arid rangelands.

Response of vegetation cover to climate variability in protected and grazed arid rangelands of South Australia

Large-scale drought and wet phases, via ecosystem responses, can significantly influence the global atmospheric carbon budget. Australian landscapes, dominated by arid and semi-arid rangelands, play an important role in this regard. In this study, temporal variation of monthly Normalised Difference Vegetation Index (NDVI) of two rangelands with different grazing intensity were analysed against monthly precipitation and Gravity Recovery and Climate Experiment (GRACE) total water storage (TWS). The results show that regardless grazing regime, over 55% temporal variation of monthly NDVI anomaly can be explained by structured cumulative antecedent precipitation. It appears that the antecedent precipitation forms better predictor variables than GRACE TWS for this study area. The results also show that both grazing and drought reduce vegetation cover, and its response to precipitation. Drought exacerbates the grazing impact on NDVI-precipitation response. These results imply that grazing in arid and semi-arid rangelands can reduce the capacity of ecosystems to assimilate atmospheric CO2 during wet years and episodic wet events. It is important to incorporate temporal structures of intra- and inter-annual antecedent precipitation in investigating vegetation dynamic responses to precipitation. By doing so, it is possible to predict monthly vegetation dynamics to support grazing management.