Semi-arid Rangelands Research Articles

Using Postfire Spatial Variability to Improve Restoration Success with Seeded Bitterbrush

Seed-based restoration of wildlife-important shrubs following wildfire is a management priority in many ecosystems. However, postfire restoration success is spatiotemporally variable and establishment from seed frequently fails in arid and semiarid rangelands. There may be opportunities to improve restoration success by taking advantage of small-scale spatial variability in environmental characteristics. Woody plants create distinct postfire microsites, which may influence establishment and growth of seeded species, under their canopies (canopies) compared with between their canopies (interspaces). Immediately after fire, former canopies generally have less vegetation and greater soil nutrient concentrations compared with interspaces. Thus, former canopy compared with interspace microsites may be more favorable for establishment and growth of seeded species, but rapid exotic plant invasion of former canopy microsites may hinder success. We evaluated seeding bitterbrush (Purshia tridentata Pursh DC) after wildfire in former western juniper (Juniperus occidentalis ssp. occidentalis Hook) canopy compared with interspace microsites at six locations for 3 yr post seeding. Bitterbrush abundance was 3.6-fold greater in former canopy compared with interspace microsites after 3 yr. Bitterbrush height was 1.5 to 2.5-fold greater in former canopy compared with interspace microsites. The first year after fire, exotic annual grass cover was 15.6-fold greater in interspace compared with canopy microsites. Abundance and cover of other herbaceous vegetation were generally also greater in the interspace. Exotic annual grass and native bunchgrass abundance increased substantially over time in former canopy microsites, suggesting abundant resource availability. Less herbaceous competition and presumably greater resource availability in former canopies probably resulted in greater success of seeded bitterbrush. These results suggest that capitalizing on spatial variability in environments can be used to increase restoration efficiency. After fire in western juniper−encroached rangelands, former juniper canopy microsites are a favorable environment for establishment and growth of seeded bitterbrush and could be targeted for restoration efforts to improve efficiency.

Mulch more so than compost improves soil health to reestablish vegetation in a semiarid rangeland

Up to half of the world's drylands have degraded, dysfunctional soils that lower success rates of restoration efforts to reestablish lost vegetation. Because soil amendments of organic matter have the potential to improve multiple ecosystem functions and overall soil health, we added a mulch of whole mesquite (Prosopis velutina) branches—both alone and in combination with 3 and 6 cm of compost—to a degraded semiarid rangeland. We then measured effects of these organic amendments on a suite of soil health indicators as well as plant cover and abundance. We found that surface applications of these amendments improved several indicators of soil health after two summer growing seasons. Soil temperature decreased and soil moisture increased in all treatments with organic amendments. However, during drier times of the year and in response to smaller rain events, mulch alone increased soil moisture more so than when combined with compost. As expected, total soil nitrogen was greatest with compost addition. Soil organic carbon, water‐stable aggregate size, and microbial abundance did not respond significantly to any treatment. Mesquite mulch increased native plant cover and abundance when applied without compost and increased plant cover when combined with 3 cm of compost, but it did not increase plant abundance or cover when combined with 6 cm of compost. Collectively, these results suggest that a thin layer of compost—but particularly woody branches used as mulch—can improve success rates of revegetation in dryland ecosystems by moderating the soil microclimate.

Organic and inorganic soil carbon in a semi-arid rangeland is primarily related to abiotic factors and not livestock grazing

Soil has the ability to sequester carbon (C) and mitigate anthropogenic enrichment of carbon dioxide, however numerous variables influence its C storage potential. Climate, soil properties, plant species composition, and livestock management practices, may all influence C storage in rangeland soils. The purpose of this study was to examine the relative importance of these factors in predicting organic and inorganic soil C in a semi-arid rangeland in northern Arizona USA. Sampling sites at 60 locations within the 40,469 ha Diablo Trust Ranches were selected using a stratified random method to encompass five distinct soil series across a precipitation gradient (230 mm–623 mm mean annual precipitation) with fence-lines that separate actively grazed areas with adjacent areas that have excluded livestock for at least 20 years. A total of 240 soil samples were collected from two depths (0–5 cm and 20–25 cm) in grazed and adjacent ungrazed sides of fences. Soil texture, bulk density, plant community composition, root biomass, soil organic carbon (SOC) and soil inorganic carbon (SIC) were measured. Across the precipitation and soil gradient, SOC was highest (up to 28.6 Mg ha−1) in the surface layer of clay-rich soil derived from basalt and SIC was highest (up to 74.7 Mg ha−1) in subsurface soil derived from limestone. General linear models showed that grazing had no significant impact on total soil C, instead, soil depth and soil texture were the main predictors of SOC and SIC. Precipitation was positively correlated with SOC and negatively correlated with SIC. Soil texture and precipitation were highly autocorrelated, so only soil texture was included in structural equation models (SEMs). Separate SEMs for surface and subsurface soils showed that soil texture (and autocorrelated precipitation) was the strongest predictor of SOC, SIC and plant community composition at both soil depths. The relative abundance of C4 grasses was higher in grazed plots and was positively correlated with root biomass at the soil surface. Also, surface root biomass was weakly positively related to SOC while both surface and subsurface roots were negatively related to SIC. This study shows the importance of interactions among multiple factors in predicting soil C stocks and that SIC can be a substantial C reservoir in dryland soils, especially those derived from sedimentary parent material. We could not detect an influence of livestock grazing on either SOC or SIC in this landscape scale study. This suggests that in this semi-arid rangeland it may be difficult to increase total soil C storage through livestock management.

Short-term responses of herbaceous vegetation to bush clearing in semi-arid rangelands of South Africa

Bush thickening reduces herbaceous species diversity and forage production, leading to a decline in grazing capacity. Hence, altering the micro-climate and woody-grass competition in bush-encroached rangelands using bush clearing is instrumental for the restoration of herbaceous vegetation. The short-term recovery potential of herbaceous species composition, basal cover and biomass production was assessed following bush clearing at Makapaanstad, North West province, South Africa. The mean density was 6908 woody plants ha−1, with Vachellia tenuispina encroaching at 6301 plants ha−1. Paired observations were conducted in bush-cleared sites (where woody plants were cut using saws, with stumps treated with picloram at 1% concentration) and uncleared sites (where the woody cover was left intact). Forty-nine different herbaceous species were recorded, with grasses being more abundant in cleared (62%) than in uncleared sites (50%). Herbaceous species showed interspecific responses, with Brachiaria eruciformis and Panicum coloratum colonising in cleared sites, whereas the frequency of other species remained comparable between cleared and uncleared sites. Graminoids, largely bunch grasses, had a significantly greater basal cover in cleared (496 cm2 m−2) compared to uncleared (301 cm2 m−2) sites. Likewise, total biomass production was significantly (p = 0.05) higher in cleared (760 kg DM ha−1) than in uncleared (636 kg DM ha−1) sites. The principal component analysis (PCA) showed that most herbaceous species were associated with soils having high total nitrogen and nitrite. Seedlings of forbs (r2 = 0.81), grasses (r2 = 0.97) and succulents (r2 = 0.98) were highly associated with nitrate-rich soils. Our results revealed that even at a short term, bush clearing is important for the restoration of herbaceous vegetation.

Impact of Grazing on Diversity of Semi-Arid Rangelands in Crete Island in the Context of Climatic Change.

The rangelands of Crete island (Greece) are typical Mediterranean habitats under high risk of degradation due to long-term grazing and harsh climatic conditions. We explored the effect of abiotic (climatic conditions, altitude) and biotic factors (long-term grazing by small ruminants) on the floristic composition and diversity of selected lowland (Pyrathi, Faistos) and highland (Vroulidia, Nida) rangelands. In each rangeland, the ground cover was measured, and the floristic composition was calculated in terms of five functional groups: grasses, legumes, forbs, phrygana, and shrubs. The aridity index, species turnover, species richness, Shannon entropy, and Gini–Simpson index (with the latter two converted to the effective number of species) were calculated. Our results reveal that highlands are characterized by the highest aridity index (wetter conditions). Lowland rangelands, compared to highland, exhibited a higher percentage contribution of grasses, legumes, and forbs, while species turnover decreased along the altitudinal gradient. The Shannon entropy index was correlated (a) positively with Gini–Simpson and mean annual temperature and (b) negatively with mean annual precipitation, aridity index, and altitude. Moreover, the Gini–Simpson index correlated positively with mean annual temperature and negatively with altitude. Our results could help to understand the effects of grazing on rangeland dynamics and sustainability in semi-arid regions in the context of climatic change.

Estimation of aboveground biomass production using an unmanned aerial vehicle (UAV) and VENμS satellite imagery in Mediterranean and semiarid rangelands

Rangeland management requires frequent and accurate estimation of aboveground vegetation biomass (AGB) as a proxy of forage production. However, traditional methods for AGB measurement are time-consuming and only provide a low number of spatiotemporal measurements. Newly developed remote sensing platforms such as UAVs and new generation satellites allow unprecedented large-scale and frequent monitoring of rangeland vegetation that is typically produced in marginal lands characterized by high surface heterogeneity. This study used high-resolution UAV data and the new multi-spectral VENμS satellite to monitor AGB production for two consecutive years in a Mediterranean and semiarid grassland rangeland in Israel. We then studied the effects of grazing intensity and precipitation along the growing season on AGB. Data were collected from two long-term ecological research sites with plots under controlled grazing pressures (i.e., no grazing, moderate, and intensive grazing). We used high-spatial-resolution UAV imagery for land cover classification in order to mask different levels of mixed pixels in the VENμS satellite images along the growing season. A support vector regression model (SVM) for satellite-based AGB estimation was developed using more than 600 ground-truth AGB measurements collected during 2019–2020. The effect of the percentage cover for mixed pixel removal was examined. The results showed an improvement in the prediction model by 35% and reduced the RMSE by half for the support vector machine regression model's best prediction. The best AGB prediction results were achieved by including satellite pixels with over 50% vegetation cover. For the first time in Eastern Mediterranean rangelands, our study illustrates the benefits of high-integrated remote sensing data (i.e., satellite and UAV) for generating more accurate AGB estimations even in highly heterogeneous ecosystems in terms of surface cover. Such an approach can provide crucial and better information for sustainable rangeland management under varying spatiotemporal and climatic conditions.

Importance of timing: Vulnerability of semi-arid rangeland systems to increased variability in temporal distribution of rainfall events as predicted by future climate change

Natural resources of semi-arid rangelands in the (sub-)tropics are major pillars of food security and livelihoods to millions of people. Besides increasing pressure due to human population growth, high spatial and temporal variability in precipitation leading to highly erratic production of primary biomass has high potential to render the exploitation of ephemeral concentrations of these resources unsustainable. While future climate models predict a general decrease in precipitation for many semi-arid rangelands, the increase in variability of rainfall and its dynamics are important aspects in assessments of climate change impact that only recently gained scientific attention. Building on a spatially-explicit, agent-based model of free-ranging livestock herds in semi-arid rangelands (RaMDry) that accounts for the metabolic energy budget of foraging animals, we assessed the vulnerability of rangelands and livestock production systems as a result of the effects of ongoing changes in precipitation and its variation, as well as its temporal distribution. Based on a coupled-reservoir model conceptually relying on a two-stage cascaded linear reservoir, we developed, implemented and validated a refined forage production module in RaMDry to predict primary productivity of semi-arid grassland and its impacts on livestock production from daily rainfall. Our results show a highly significant effect of increased temporal diffusion of precipitation events on the ecosystem and its productivity. The anticipated diminution in total precipitation and increased inter-annual variation indicated no severe aggravation of the general situation for livestock keepers in terms of system productivity. However, alterations in timing of individual precipitation events resulted in substantial temporal reduction of forage resources in terms of their quantity and quality and major negative impact on livestock body weights. Our findings shed light on the profound consequences of inter-seasonal dry spells as one important aspect of climatic changes on livestock production systems in (sub-)tropical, semi-arid rangelands.

Quail and rain in semiarid rangelands: Does management matter?

AbstractRainfall is a strong driver of quail populations on southwestern rangelands and can account for a large portion (~70–95%) of the variability in regional quail production and abundance. Landowners have attempted to moderate these boom‐and‐bust fluctuations via management; however, presently it is unknown whether management can increase or stabilize quail populations in semiarid environments or whether rainfall remains as influential at small spatial extents. Our objectives were to evaluate the efficacy of management at mitigating the effects of rainfall on northern bobwhite (Colinus virginianus) populations on semiarid rangelands and to quantify the influence of rainfall on bobwhite density at smaller spatial extents. We conducted a study to evaluate these objectives during 2014–2020 in the Rio Grande Plains (n = 11 sites; 1,100‒6,500 ha) and Rolling Plains (n = 4 sites; 1,900‒4,000 ha) of Texas, USA. We estimated bobwhite density during late autumn (Dec‒Jan) on all sites using helicopter surveys within a distance‐sampling framework. We also obtained site‐level seasonal rainfall (Apr‒Aug) and quantified management intensity via landowner surveys and a scoring rubric to categorize sites into 3 classes (low, medium, and high management intensity). Bobwhite populations during this study experienced a boom‐bust cycle in both the Rio Grande Plains and Rolling Plains, with mean bobwhite density fluctuating considerably (0.57‒2.96 bobwhites/ha and 0.02‒2.88 bobwhites/ha, respectively). In the Rio Grande Plains, mean bobwhite density significantly increased from low to high management intensity in 2015 (1.12 ± 0.17 bobwhites/ha vs. 2.87 ± 0.39 bobwhites/ha, respectively), 2016 (1.06 ± 0.20 bobwhites/ha vs. 2.96 ± 0.36 bobwhites/ha, respectively), 2017 (0.73 ± 0.16 bobwhites/ha vs. 1.91 ± 0.32 bobwhites/ha, respectively), and 2019 (0.42 ± 0.14 bobwhites/ha vs. 1.01 ± 0.26 bobwhites/ha, respectively; P < 0.05). In addition, rainfall at the site level accounted for a low amount of the variation in bobwhite density (r2 = 0.09; P < 0.01). Similarly, in the Rolling Plains, mean bobwhite density significantly increased from low to high management intensity in 2015 (1.30 ± 0.27 bobwhites/ha vs. 2.20 ± 0.29 bobwhites/ha, respectively) and 2016 (1.26 ± 0.26 bobwhites/ha vs. 2.88 ± 0.34 bobwhites/ha, respectively; P < 0.05). Rainfall at the site level also accounted for a low amount of the variation in bobwhite density (r2 < 0.02; P = 0.82). Our findings suggest that management can increase bobwhite density beyond that of less‐managed properties but does not completely eliminate inter‐annual fluctuations in semiarid environments. In addition, rainfall appears to exert less of an influence on bobwhite density at a site level (e.g., 2,000 ha) than has been documented at a regional level (e.g., ≥8 million ha).

Borana rangeland of southern Ethiopia: Estimating biomass production and carrying capacity using field and remote sensing data

Assessing rangeland productivity is critical to reduce ecological degradation and promote sustainable livestock management. Here, we estimated biomass productivity and carrying capacity dynamics in the Borana rangeland of southern Ethiopia by using field-based data and remote sensing data (i.e., normalized difference vegetation index (NDVI)). Data was collected from both rainy and dry seasons when biomass production was high and low respectively. Results of linear regression showed that both biomass production (R2adj = 0.672) and NDVI value (R2adj = 0.471) were significantly decreased from 1990 to 2019. Field data and NDVI values for mean annual biomass showed a significant linear relationship. The model accuracy in the annual relationship between the observed and predicted biomass values was strong (R2adj = 0.986) but with high standard error, indicating that the observed biomass production in the rangeland area was not in good condition as compared with the predicted one. This study suggests that, using NDVI data and field-based data in combined way has high potential to estimate rangeland biomass and carrying capacity dynamics at extensively grazed arid and semi-arid rangelands. And to use for estimating stoking rates and predicting future management techniques for decision making.

New Investigation and Challenge for Spatiotemporal Drought Monitoring Using Bottom-Up Precipitation Dataset (SM2RAIN-ASCAT) and NDVI in Moroccan Arid and Semi-Arid Rangelands

Abstract Remotely sensed soil moisture products showed sensitivity to vegetation cover density and soil typology at regional dryland level. In these regions, drought monitoring is significantly performed using soil moisture index and rainfall data. Recently, rainfall and soil moisture observations have increasingly become available. This has hampered scientific progress as regards characterization of land surface processes not just in meteorology. The purpose of this study was to investigate the relationship between a newly developed precipitation dataset, SM2RAIN (Advanced SCATterometer (SM2RAIN-ASCAT), and NDVI (eMODIS-TERRA) in monitoring drought events over diverse rangeland regions of Morocco. Results indicated that the highest polynomial correlation coefficient and the lowest root mean square error (RMSE) between SM2RAIN-ASCAT and NDVI were found in a 10-year period from 2007 to 2017 in all rangelands (R = 0.81; RMSE = 0.05). This relationship was strong for degraded rangeland, where there were strong positive correlation coefficients for NDVI and SM2RAIN (R = 0.99). High correlations were found for sparse and moderate correlations for shrub rangeland (R = 0.82 and 0.61, respectively). The anomalies maps showed a very good similarity between SM2RAIN and Normalized Difference Vegetation Index (NDVI) data. The results revealed that the SM2RAIN-ASCAT and NDVI product could accurately predict drought events in arid and semi-arid rangelands.

Precipitation is the key determinant of topsoil δ15N values in southern Patagonia's semiarid rangelands

AbstractNitrogen (N) cycling in rangeland soils could potentially be controlled by water supply, stocking rates, or a range of other variables, such as ecosystem N stocks. To gauge the relative importance and elucidate possible interactions among these factors, we measured many abiotic variables to identify first‐order controls of δ15N for Patagonia's rangeland soils under contrasting historical grazing intensities. The results showed that δ15N values declined as water availability increased. The effects of precipitation and stocking rate on soil δ15N values were additive, and the effect of precipitation far outweighed the effects of grazing pressure. The soil N stock was a weak predictive variable for modeling variation in δ15N of the soil. Earlier assumptions about an inflection point for N cycling and δ15N values related to aridity were not confirmed. We conclude that variation in water availability drives variation in δ15N values irrespective of grazing intensity. We also conclude that meaningful interpretation of δ15N in soil will require a better mechanistic understanding of the interactions between water and N in the vadose zone than we currently possess.

Monitoring standing herbaceous biomass and thresholds in semiarid rangelands from harmonized Landsat 8 and Sentinel-2 imagery to support within-season adaptive management

Adaptive management requires rangeland managers to respond to changing forage conditions (e.g., standing herbaceous biomass) within the grazing season at the scale of individual pastures. While within-season biomass can be measured or estimated in the field, it is often impractical to make field measurements in extensive rangeland systems with adequate frequency and spatial representation for responsive decision-making by rangeland managers. We sought to develop a single model to accurately predict daily herbaceous biomass across seasonally and annually varying conditions from the Harmonized Landsat-Sentinel satellite time series. We also sought to assess how information about plant community composition derived from a high-spatial resolution map would improve model performance. We used herbaceous biomass data from 1764 ground observations collected over 8 years in North American shortgrass steppe for training in a cross-validated model selection approach to evaluate (1) predictive performance of candidate models both spatially and temporally, (2) relative variable importance of individual spectral bands, vegetation indices, and recently developed broadband spectral angle indices, and (3) the degree to which including plant community composition improved model performance. All 11 candidate models identified in the model selection procedure contained a band angle index and an individual spectral band, and 6 contained one of each input feature type, demonstrating the benefit of combining spectral features for predicting herbaceous biomass across varying conditions. The spatial and temporal cross-validation and selection procedures produced the same top model with similar performance (mean absolute error = 151–182 kg ha−1; R2 = 0.75–0.79), suggesting that a single model performs well over space and time. Including plant community composition in the model reduced mean absolute error by 11–13%. Bootstrapping revealed that –six to seven years of training data were required to achieve consistent model performance across years with varying environmental conditions (e.g., wet, average, dry). The top model could accurately detect (70–87% accuracy) the week that biomass dropped below management-related thresholds as low as 450 kg ha−1 in an independent dataset (n = 950) with modest commission error (10–26%). We discuss how maps showing the probability that herbaceous biomass is below a given threshold can support adaptive management in extensive semiarid rangelands across differing scenarios of risk perception and avoidance. In addition to producing maps to support precision rangeland management strategies, this study demonstrates the importance of combining complementary vegetation indices and acquiring long-term training datasets to achieve reliable predictions of herbaceous standing biomass in highly variable systems.

Monitoring the available forage using Sentinel 2-derived NDVI data for sustainable rangeland management

Management problems could cause rangeland degradation worldwide. Monitoring the seasonal variation of available forage may help to prevent vegetation from deterioration and help to ensure sustainable animal production. Therefore, seasonal variations in the amounts of available forage, and the contents of crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), and digestible dry matter (DDM) were monitored for two years via both ground sampling and Sentinel 2A-derived NDVI data at semi-arid Bozdag Rangelands, Turkey. Available forage significantly varied between 374.4 and 936.4 kg ha−1 through the season and all quality parameters showed significant seasonal variations. Available forage was estimated in strong accuracy only in dry season (r2 = 0.72, P ≤ 0.01), but the seasonal variations of CP, ADF, and DDM contents were estimated in moderate accuracy (r2 = 0.56, 0.40, 0.41 respectively) by the satellite-derived NDVI data. Free Sentinel 2A-derived NDVI values gave promising results for monitoring the forage quality of these semi-arid rangelands, but further research is needed to develop new vegetation indexes for considering woody tissues in vegetation, and higher resolution for greater monitoring accuracy.

Factors influencing migration and settlement of pastoralists in Nairobi City, Kenya

Pastoralism is globally recognized as the backbone of the economy in the vast arid and semi-arid rangelands. Despite its enormous economic contribution, the system is facing a myriad of challenges, among them, land use and land tenure changes, resulting in diminished grazing land. Accompanying such changes is the conversion of traditional grazing lands into other uses such as settlements, with urbanization being one of the key drivers of pastoral system dynamics. Understanding such dynamics in the face of compounding factors such as frequent droughts linked to climate change is key in guiding policy formulation and interventions aimed at achieving a sustainable pastoral production system. This study investigated factors determining migration and settlement of pastoralists in Nairobi City of Kenya. Data was collected through a snowball sampling approach using semi-structured household questionnaires, focus group discussions (FGDs) and key informant interviews (KIIs) in five Sub-counties of Nairobi City County. A total of 144 household interviews, 6 FGDs and 16 KIIs were conducted to elucidate drivers of urban pastoralism, opportunities and challenges encountered by pastoralists in the city. A binary logistic regression model was used to analyse the determinants of their migration. Results show that search for pasture and water resources, and alternative markets especially during droughts, are the main reasons for pastoralists’ migration to the city. In addition, educated herders were found to be more likely to migrate to the city as they pursue wage employment. Whereas these findings revealed that migration to the city exposes pastoralists to diverse livelihood opportunities, they are equally faced by a number of challenges - mainly road accidents involving livestock, frequent land displacements to pave way for development of real estates, and livestock poisoning from sewage and garbage wastes. There is a need for policy and regulatory interventions to recognize pastoralism alongside other forms of urban farming and addressing challenges facing sustainable pastoral production.

Environmental Conditions and Grazing Exerted Effects on Arbuscular Mycorrhizal in Plants at Southern Patagonia Rangelands

Arbuscular mycorrhizal (AM) fungi play a major role in maintaining ecosystem functions. AM fungi are found in most ecosystems including rangelands currently under increasing pressures from human activities. Southern Patagonia (Argentina) is a semiarid region influenced by extensive livestock production in rangelands. There is a lack of information about the environmental conditions and functionality of AM fungi in plant species of Patagonia ecosystems associated with livestock grazing. We assessed how soil properties, climatic conditions, and grazing intensities influence the response of AM fungi colonization. We studied most palatable and representative plant species (Poa dusenii, Rytidosperma virescens, Festuca gracillima, Nardophylum bryoides, Mulguraea tridens, and Carex argentina) growing in main ecological areas of Southern Patagonia. Most of the studied plant species (except C. argentina) presented AM symbiosis. AM colonization showed a negative relationship with soil organic carbon and nitrogen and a positive relationship with soil bulk density and pH. Results suggest that plants promoted a higher root AM colonization when soil nutrients and water availability (rainfall) are limiting. Sheep stocking rates had a differential impact depending on the ecological areas and plant life forms. High grazing decreased the AM colonization in the ecological areas with palatable plant dominance, suggesting that the impacts of grazing could lead to further negative effects on the ecosystem. Moderate grazing allows to maintain higher AM colonization, which would probably benefit the aboveground production of palatable plant and, consequently, to herbivores, particularly in degraded rangelands like Patagonian steppes. This study improves the knowledge of AM association in Patagonian semiarid rangelands by increasing our understanding of the impacts of grazing on belowground ecology. This information becomes relevant for grazing sustainable management, which may contribute to food security.

Plant Production in Semiarid Shrubland Communities Amended with Biosolids in Central Mexico

Biosolids application in semiarid rangelands has been proposed as a viable alternative for the rehabilitation of degraded soils. We analyzed the effect of rate, time, and number of applications of biosolids per year on the growth of herbaceous vegetation. Summer and winter single applications and a dual application (summer + winter) of biosolids were tested in two soils (calcareous and igneous) of the southern Chihuahuan desert at four rates (0, 3.5, 7, and 10.5 Mg/ha). A single period of vegetation growth occurs in the summer in this region. No major net changes in biomass were recorded with one application of biosolids in the summer or winter applications on both soil types. Winter biosolids application increased the annual species cover on igneous soil. However, annual species cover decreased in the second year on both soil types with one application (summer) or two applications (summer + winter) of biosolids. The lack of synchrony between the availability of NO3-N and moisture may have been the reason for the highly variable response of vegetation growth on calcareous soil. The igneous soil had better soil moisture retention, probably allowing for increased uptake of nitrate by plants. The largest increases in both biomass and plant cover were obtained for perennials with the dual strategy of biosolids application on igneous soil at higher rates. The patterns of plant biomass and cover responses to biosolids application were different on each functional group and soil type. Biosolids application rate and timing are important for enhancing plant productivity in semiarid areas; overall biosolids should be considered as a viable amendment for rangeland restoration.

Plant Phenology Drives Seasonal Changes in Shear Stress Partitioning in a Semi-Arid Rangeland

Plant Phenology Drives Seasonal Changes in Shear Stress Partitioning in a Semi-Arid Rangeland

Seasonal prevalence of gastrointestinal parasites in desert bighorn sheep (Ovis canadensis) in northern Mexico.

This study aimed to describe the shedding pattern of gastrointestinal parasite eggs by a wild population of desert bighorn sheep (DBS; Ovis canadensis) in northern Mexico. Seventy-five fresh faecal samples were collected from the ground in each season within an hour after being expelled by these animals. The generalized linear mixed model showed that eggs per gram of faeces were highest in winter (577 ± 399) and lowest in summer (260 ± 198). Generalized linear models revealed that Strongyloides spp. predominated during most seasons with a peak in summer (85% of faecal samples analysed) and the absence of this helminth in winter. Nematodirus spp. was another helminth present in three seasons, with the presence of this nematode in 35% of the faecal samples in spring and 0% in summer. Other parasites in DBS faeces included Bunostomun spp., Trichostrongylus spp., Cooperia spp., Mecistocirrus digitatus, Haemonchus contortus, Chabertia ovina and Eimeria ovinoidalis. There were differences among seasons in the percentage of these helminths and coccidia in faecal samples for all these parasites. It was concluded that helminths egg output in DBS in a semi-arid rangeland is lowest in summer and spring and highest in autumn and winter. Furthermore, it was shown that DBS in the study site do not suffer from severe parasite burden. Therefore, this nematode parasite burden is compatible with the conservation and well-being of this particular population.

Environmental drivers of above-ground biomass in semi-arid rangelands

Above-ground biomass (AGB), as a key biophysical and functional parameter of rangeland ecosystems, plays an important role in ecosystem carbon (C) stocks. The aim of this study was to explore the important environmental drivers of AGB in an arid rangeland by using structural equation modelling (SEM). Vegetation and soil (physical and chemical properties) were sampled using randomised-systematic methods within sampling plots. The topographic (elevation, slope, aspect, hillshade (i.e. a technique for showing the topographical shape of hills and mountains to indicate relative slopes and mountain ridges)) and climatic (mean temperature (MT), mean precipitation (MP), actual evapo-transpiration (AET) and land-surface temperature (LST)) properties were extrapolated using a raster-based digital elevation-model (DEM) map, and their values extracted at each sampling plot. SEM was then applied to assess the direct and indirect impacts of environmental factors on AGB. The AGB was directly affected by soil (41%, P < 0.05) and climatic properties (34%, P < 0.05). The effect of topographical factors on AGB was non-significant (P > 0.05). However, climatic properties were directly affected by topographical properties, with a path coefficient of 34%. Among soil properties, nitrogen, phosphorus and potassium concentrations, silt content and soil pH were the key factors affecting AGB. Climatic variables (MT, MP) were equally effective in explaining the climate latent variable (with loading factors of −0.97 and 0.99 respectively) and AGB changes. This study highlighted the importance of soil and climatic properties in AGB variation. SEM simplified and revealed the complex relationships among ecosystem components affecting AGB, which could assist proper management of rangelands.

Responses of grass productivity traits to bush clearing in semi-arid rangelands in North-West Province of South Africa

Woody plant encroachment threatens herbaceous plant productivity in many rangelands globally. We evaluated the impact of bush clearing on grass tiller, leaf and biomass production, and tuft sizes in the Kgomo-kgomo and Makapaanstad rangelands in North-West Province, South Africa. In each rangeland, the number of tillers and leaves, tuft sizes and biomass of eight dominant grass species were recorded in bush-cleared and uncleared treatments. The treatment and species interacted significantly (P < 0.001) for tiller and leaf production and tuft sizes. Bush clearing increased tiller production of bunch grasses but not stoloniferous grasses. At Kgomo-kgomo, bunch grasses (Panicum maximum (Jacq.) and Urochloa mosambicensis (Hack.) Dandy] had three to six times more tillers and leaves per plant in the cleared than uncleared treatment. At Makapaanstad, only annual bunch grasses [Brachiaria eruciformis (Sibth. & Sm.) Griseb and Tragus berteronianus (Schult.)] attained twice as many tillers and leaves per plant in the cleared compared to uncleared treatment. Biomass was 1776 ± 159 and 696 ± 159 g m−2 in cleared and uncleared treatments respectively at Kgomo-kgomo and 1358 ± 258 and 1089 ± 258 g m−2 at Makapaanstad. The tufts of bunch grasses were nearly twice as large in the cleared compared with the uncleared treatment at Kgomo-kgomo, whereas only stoloniferous grass tufts increased at Makapaanstad. Overall, bush clearing improved grass productivity and performance, but the responses varied by species.