Semi-arid Rangelands Research Articles

The association pattern of structural and biomass traits of capparis spinosa L. with topographic and soil factors

Understanding the plant's functional traits is the first step for recognition of present patterns in plant vegetation, responding to environmental conditions and how they affect the environment. Capparis spinosa is one of the important medicinal, edible and marketable species which sparsely grows in large parts of Marl lands on semi-arid rangelands of East Azerbaijan province, Iran. Therefore, in addition to measuring plant traits (structural and biomass traits), ecological association of these traits with environmental factors were also studied in August 2016. For this purpose, vegetation cover studied through selecting four representative masses having different environmental properties within research grazing exclusion area and establishing sampling network inside the areas. So, for each mass, thirty 3m2 plots (1.5 × 2 m) with 30 m intervals from each other established along with three 300 m-long transect. A composite soil sample up to plant rooting depth was collected from each transect. Slope percent, aspect and elevation were recorded as topographical factors. Also, vegetation traits measured in 5 healthy plant stands in each mass. In order to study the association pattern of structural and biomass traits with environmental factors (soil and topography), according to calculated gradient length, the method of redundancy analysis (RDA) was used. Totally, on the spatial scale, the soil factors had a greater influence on structural and biomass traits than topographic factors. So that the percentage of clay, electrical conductivity, acidity, silt percentage and gypsum content had the greatest impact on biomass traits. Structural traits were also most affected by the percentage of clay, electrical conductivity, soil moisture content and amount of gypsum. By investigating the relationship between plant characteristics and environmental factors, the results of this research are applicable to preservation, rehabilitation and development of this species as a multi-purpose plant in pasture areas. Meanwhile, measured traits are the essential requirements for calculating the diversity of performance.

Growth in three Karoo shrub species under various grazing treatments: the tracking of marked individuals over 25 years

Growth studies of long-lived shrubs are uncommon. In semi-arid rangelands, livestock and wildlife grazing influence growth processes and may interact with changing climate. Tierberg-LTER, excluded from livestock since 1987, and two adjacent ranches allowed for a comparative growth study of three shrub species (Osteospermum sinuatum – palatable, Pteronia empetrifolia – moderately palatable, and P. pallens – unpalatable) across contrasting present ungulate herbivory (none in exclosures, wildlife only, or livestock and wildlife combined) and past livestock herbivory (moderate and overgrazed). Marked individuals were measured at irregular intervals over 25 years. Stem basal diameter (mm), height (m) and two canopy diameters (m) were measured at the onset of the study and in 2014. Mean basal diameter growth (mm y−1) varied between species and treatments. Change in mean attribute values was influenced by interactions with grazing history and treatments. Some historical and grazing treatments had a negative effect on the palatable O. sinuatum and no significant effect on moderately palatable P. empetrifolia or unpalatable P. pallens. The age of the originally marked individuals are unknown but >70% of these individuals survived over the 25-year period. Our results support previous findings that dwarf shrubs in deserts are slow growing and long lived, and that grazing regime affects plant growth.

Using APAR to Predict Aboveground Plant Productivity in Semi-Arid Rangelands: Spatial and Temporal Relationships Differ

Monitoring of aboveground net primary production (ANPP) is critical for effective management of rangeland ecosystems but is problematic due to the vast extent of rangelands globally, and the high costs of ground-based measurements. Remote sensing of absorbed photosynthetically active radiation (APAR) can be used to predict ANPP, potentially offering an alternative means of quantifying ANPP at both high temporal and spatial resolution across broad spatial extents. The relationship between ANPP and APAR has often been quantified based on either spatial variation across a broad region or temporal variation at a location over time, but rarely both. Here we assess: (i) if the relationship between ANPP and APAR is consistent when evaluated across time and space; (ii) potential factors driving differences between temporal versus spatial models, and (iii) the magnitude of potential errors relating to space for time transformations in quantifying productivity. Using two complimentary ANPP datasets and remotely sensed data derived from MODIS and a Landsat/MODIS fusion data product, we find that slopes of spatial models are generally greater than slopes of temporal models. The abundance of plant species with different structural attributes, specifically the abundance of C4 shortgrasses with prostrate canopies versus taller, more productive C3 species with more vertically complex canopies, tended to vary more dramatically in space than over time. This difference in spatial versus temporal variation in these key plant functional groups appears to be the primary driver of differences in slopes among regression models. While the individual models revealed strong relationships between ANPP to APAR, the use of temporal models to predict variation in space (or vice versa) can increase error in remotely sensed predictions of ANPP.

Evaluating the variability of ANPP in central Iranian arid and semi-arid rangelands using CASA model and its relationship with climatic factors

Aboveground Net Primary Production (ANPP) plays an important role in regulating ecological processes and carbon cycle in arid and semi-arid rangelands. Hence, this study aimed to investigate the spatio-temporal variability of rangeland ANPP in seven bioclimatic zones in Isfahan Province using the Carnegie-Ames-Stanford Approach (CASA) ecosystem model fitted with MODIS-NDVI and climatic data during 2000–2016. The model evaluation indicated a good agreement between the estimated and observed ANPP (R2 = 0.917). In concomitant with the precipitation gradient, the mean annual ANPP increased from east towards west and southwest of the region from zero to 160 g C m–2 yr–1. The maximum and minimum ANPP values occurred in humid and cold as well as hyper-arid and warm zone, respectively. The annual temporal variability of ANPP was analyzed in response to climatic factors (precipitation and temperature), Temperature Vegetation Dryness Index (TVDI) and Standard Precipitation Index (SPI) drought indices. The drought was found as the most important factor affecting ANPP. The minimum and maximum ANPP values were observed in 2000 (23.23 g C m–2 yr–1) and 2014 (41.73 g C m–2 yr–1). The maximum ANPP occurred in May and June during which temperature, as an important factor in plant growth, reached its optimum and precipitation affected with a time lag. The annual rangeland ANPP was positively associated with precipitation and negatively with temperature.

Improving ground cover and landscape function in a semi-arid rangeland through alternative grazing management

The development and adoption of sustainable grazing strategies is important to improve the functionality and productivity of agricultural landscapes. Alternative grazing systems incorporating periods of planned rest may achieve this compared to continuous grazing systems, but the evidence is conflicting. Using paired paddock contrasts, soil characteristics, ground cover and landscape function (i.e. soil stability, nutrient cycling, infiltration and landscape organisation indices) were compared between alternative grazing management (incorporating periods of rest), traditional (continuous) grazing, and areas managed for conservation (ungrazed by commercial livestock but grazed by native and feral herbivores) on contrasting soil types in semi-arid rangelands. Relationships between the response variables and understorey floristic biodiversity measures were also explored. Total ground cover was greater under conservation management than grazing, and was greater under alternative grazing than traditional grazing management. Indices of landscape function, including stability, nutrient cycling, patch area and landscape organisation were significantly greater, and interpatch length significantly shorter, under conservation compared to traditional grazing management. Alternative grazing management had intermediate values of landscape function which did not differ significantly to traditional grazing or conservation treatments. Ground cover and floristic biodiversity measures were often positively correlated, but there was no clear relationship between most landscape function and plant biodiversity indices. Landscape function may be important in detecting changes in rangelands that remain undetected by floristic diversity measures. Alternative grazing strategies incorporating planned rest have the potential to improve ground cover with the associated benefits of improved productivity and landscape function compared to continuous grazing regimes.

Low‐tech riparian and wet meadow restoration increases vegetation productivity and resilience across semiarid rangelands

Restoration of riparian and wet meadow ecosystems in semiarid rangelands of the western United States is a high priority given their ecological and hydrological importance in the region. However, traditional restoration approaches are often intensive and costly, limiting the extent over which they can be applied. Practitioners are increasingly trying new restoration techniques that are more cost‐effective, less intensive, and can more practically scale up to the scope of degradation. Unfortunately, practitioners typically lack resources to undertake outcome‐based evaluations necessary to judge the efficacy of these techniques. In this study, we use freely available, satellite remote sensing to explore changes in vegetation productivity (normalized difference vegetation index) of three distinct, low‐tech, riparian and wet meadow restoration projects. Case studies are presented that range in geographic location (Colorado, Oregon, and Nevada), restoration practice (Zeedyk structures, beaver dam analogs, and grazing management), and time since implementation. Restoration practices resulted in increased vegetation productivity of up to 25% and increased annual persistence of productive vegetation. Improvements in productivity with time since restoration suggest that elevated resilience may further enhance wildlife habitat and increase forage production. Long‐term, documented outcomes of conservation are rare; we hope our findings empower practitioners to further monitor and explore the use of low‐tech methods for restoration of ecohydrologic processes at meaningful spatial scales.

Association patterns reveal dispersal-aggregation dynamics among cattle in a South Texas Rangeland, USA

IntroductionThe spatial association dynamics of free-ranging cattle herds are not fully understood; however, they can have a direct influence on the spatial patterns of resource utilization. The aim of our study was to examine new analytical methods of identifying the spatio-temporal patterns of behavioral dynamics that determine cattle herd dispersal in the semi-arid rangelands of South Texas. We fitted 10 free-ranging cows with global positioning system collars and obtained positions every 5 min for each animal for 21-day trials, twice during the summer and winter period. We used an association pattern recognition software (ASSOC1) and the herd center of gravity to identify the spatial and temporal thresholds that defined dispersion-aggregation patterns and individual position to determine their relation to social dominance.ResultsThe association pattern defining herd membership was that animals spent 70% of their time within 200 m of each other. Dominance ranking did not appear to influence association membership or position within the herd. The cattle showed a more dispersed distribution during summer, but in winter, herd members behaved in a more aggregated pattern. This distribution is contrary to patterns described in more northerly and mountainous regions.ConclusionsThe spatial thresholds of the cattle herd and the overall distance of all members to the center of the herd were smaller during winter and larger during summer, indicating that this study herd congregated during the winter and dispersed during the summer. Although this study uses a herd of 10 individuals in a 100 ha pasture to evaluate spatio-temporal dynamics, our results provide evidence of the ability of current tracking and spatial association tools to detect and quantify seasonal changes in cattle herd dispersion-aggregation patterns. The use of these data collection and analysis methods could prove useful in larger cattle herds, increase our understanding of herd spatio-temporal behavior, and subsequently help in the development of improved management practices.

RESPONSE OF HERBACEOUS VEGETATION TO WOODY PLANT SPECIES IN THE RANGELANDS OF EASTERN ETHIOPIA

<p class="Default">In the lowlands of arid and semiarid rangelands woody plants<em> </em>plays an important role in soil fertility maintenance, providing food, medicine, cosmetics, fodder, fuel wood and pesticides. A better understanding of the interaction of woody plants on their immediate environment is needed to guide optimum management of native vegetation in the production landscapes. However, the response of herbaceous vegetation to woody plant species remains poorly understood. This study evaluates the impact of two dominant woody plant species (<em>Acacia senegal </em>and<em> Balanite aegyptica</em>) on<em> </em>herbaceous<em> </em>vegetation in rangelands of eastern Ethiopia. Eighteen trees of relatively the same diameter at breast height were selected to study the effect of the tree on herbaceous<em> </em>vegetation. Vegetation sample data were collected from under canopy and open areas, and analysed for herbaceous vegetation parameters using two ways ANOVA. The herbaceous<em> </em>vegetation parameters under both woody plant species was significantly higher especially with regard to dry matter (101.3±0.97g/m<sup>2</sup>), basal cover (65.02±0.7%) and species richness (6.9±0.1211 no. species/m<sup>2</sup>) than the open grassland with dry matter (74.2±0.72g/m<sup>2</sup>), basal cover (50.53±0.67%) and species richness (5.3±0.11 no. species/m<sup>2</sup>). The species composition of herbaceous species also showed significant improvements under woody plant canopy with regard to percentage composition of perennial grasses (0.40%) than the open grassland with percentage composition of perennial grasses (0.27%). The positive effect woody plant presence can be also ascribed to some understory species such as <em>Cenchrus ciliaris</em>, <em>Panicum maximum </em>and <em>Eragrostis papposa </em>which have a good pastoral value, grow better under woody plants. Presence of woody plants facilitates the establishment of more palatable herbaceous vegetation under unfavorable climatic conditions that characterize these environments. Therefore, this tree has a significant effect on herbaceous vegetation improvement in resource poor rangelands and as a result, it is important to retain scattered <em>A. senegal</em> and <em>B. aegyptica</em> plants in the rangelands of eastern Ethiopia.</p>

Diversity and functional traits of spontaneous plant species in Algerian rangelands rehabilitated with prickly pear ( Opuntia ficus - indica L.) plantations

The prickly pear (Opuntia ficus-indica L. Miller) is a xerophytic cactus species widely cultivated in arid and semiarid regions worldwide and used in rehabilitation programs of rangelands in Algeria since 1990. This study analyzed the diversity and functional traits of plant species established in prickly pear plantations growing under arid and semiarid climates. A 3-year plant assessment (2008-2010) was carried out using ecological descriptors (abundance, species richness, diversity indices, disturbance index, and Jaccard index) and plant functional traits (life forms, chorological types, dispersal types, Grime's, Noy-Meir's strategies, and morphological types). The results revealed 36 and 31 species in arid and semiarid rangelands, respectively, with remarkable dominance of therophytic (43.2%) and hemicryptophytic plants (41.1%) growing in the semiarid climatic zone. The Shannon and diversity index showed low values (0.93-1.84 in surveyed rangelands) with a maximum of 2.74 in 2009. The disturbance index ranged between 51% and 55% and the dispersion scheme of diaspores was dominated by anemochorous plants. The chorological analysis indicated that the study plants were oriented towards a Mediterranean pattern in the broad sense. The predominant adaptive strategies of Grime were ruderal-stresstolerant (RS), competitive-stress-tolerant (CS) and competitive-ruderals (CR), which were attached to the two strategies of Noy-Meir (aridopassives and aridoactives).

Grain size affects the relationship between species richness and above-ground biomass in semi-arid rangelands

ABSTRACTBackground: Discrepancies in the shape of the productivity–diversity relationship may arise from differences in spatial scale. We hypothesised that there is a grain size effect on the productivity–diversity relationship.Aims: To determine the effect of three sampling grain sizes on the productivity–diversity relationship.Methods: We applied generalised linear mixed effect models on community data from 735 vegetation plots in the Taleghan rangelands, Iran, sampled at three grain sizes (0.25, 1 and 2 m2) to ascertain plant productivity-diversity patterns, while accounting for the effects of site, plant community type, disturbance, and life form.Results: Overall, relationships between biomass and plant species richness were unimodal at grain sizes of 0.25 and 1 m2, and asymptotical at 2 m2. The spurious occurrence of a single large shrub may overwhelm a small-sized sampling unit, resulting in a high estimate of the sample’s biomass relative to species richness. However, the relationship between biomass and species richness at larger grain sizes is more likely to reach an asymptote.Conclusions: Shrubs are partly responsible for driving the relationship between plant biomass and species richness. Given that the frequency of shrubs is highly variable between small plots but not so in large plots, their presence may result in unimodal productivity–diversity relationships at small but not at large grain sizes.

Hydrological dynamics in a small catchment with silvopastoral land use in SW Spain

Hydrological processes were investigated since the year 2000 in a semiarid rangeland with disperse cover of evergreen holm oaks. In this article results are presented on the spatial variation of rainfall in the catchment using a network of 6 raingauges. Results are also presented on soil water dynamics, which were studied under different vegetation covers and varying soil depths. Furthermore, the temporal variation of runoff generation in the basin outlet is reviewed, taking into account different timescales. The following results can be highlighted: Spatial variation of rainfall in the catchment at annual or monthly scale was low. However, large dispersion exists in the case of individual rainstorms, when the differences between the 6 raingauges varied strongly, both for daily values as well as maximum intensities. Events with high spatial variation are presumably related with small, localized storms, particularly those of high intensity and short duration, and those showing low variation are probably of frontal origin. Soil moisture presented seasonal patterns clearly dependent on factors such as rainfall or evapotranspirative demand. Spatial distribution of soil moisture was mainly affected by physiographic terrain characteristics and vegetation covers. Generally, in dry hydrological years, soil moisture was lower beneath than beyond the tree canopies, while the opposite was observed in wet years. Dry situations increase the intensity and duration of soil water deficits, enhance the evaporative demand and increment water storage capacity by covers. Channel flow in dehesas depends highly on the antecedent moisture conditions and particularly on the water content of the sediment-filled valley bottoms. If these areas become saturated, high amounts of runoff are produced during rainfall events. Under high intensity rainstorms Hortonian overland flow is rapidly generated on hillslopes producing a quick channel response. Interannual runoff variation is very high, the more frequent low rainfall years provoke very low total water flow, contrasting with less frequent years of above average rainfall, which are the ones producing high total runoff. It can be concluded that the hydrological dynamics in Mediterranean rangelands with a disperse tree cover are complex, both regarding soil water and catchment runoff, being highly variable in time. Future changes in land use or climate could affect notably the hydrological dynamics of the catchment, and hence similar upland basins. For example, a notable increase of tree cover would reduce water availability of pasture plants, particularly during dry years. A decrease of annual rainfall amounts and/or increased drought intensities, as a consequence of climate change, would enlarge periods of soil moisture deficit for pasture plants, as well as a reduction of runoff.

Suitability of NDVI and OSAVI as estimators of green biomass and coverage in a semi-arid rangeland

Rangelands are often too large and inaccessible to determine biomass accumulation and vegetation cover by ground surveys alone, particularly in semi-arid regions where productivity per unit area is typically low and highly variable. Thus, the development of remote sensing derived spectral indices have been of particular interest to rangeland managers as a more cost-effective means of measuring the characteristics, biomass, and extent of vegetation. The Normalized Difference Vegetation Index (NDVI) is the most widely used spectral vegetation index (VI) by ecologists and agriculturalists today. However, regions with sparse vegetation or soils that generate high reflectance values (e.g., dry sandy soils) can severely hinder the reliability of the NDVI as an accurate estimator of green biomass, saturate remote sensors or produce biased estimates of green biomass and vegetative cover. The Optimized Soil Adjusted Vegetation Index (OSAVI) is a newly formed alternative that can accommodate greater variability due to high soil background values. We evaluated the suitability of the NDVI and OSAVI as potential estimators of green biomass and vegetative coverage in a semi-arid rangeland in south Texas. We compared coverage estimates of herbaceous, bare-ground, and woody vegetation calculated from classified satellite images stacked with either an NDVI or OSAVI band to those from traditional ground surveys. OSAVI-derived coverage estimates of herbaceous and woody vegetation did not significantly differ from those produced by ground surveys in 2015. However, NDVI-based estimates for woody vegetation, as well as bare ground, did differ significantly from estimates generated from ground surveys (p = 0.012, 0.018). In 2016, the OSAVI-derived estimates for all three land cover classes were not significantly different than those produced by ground surveys. Our results suggest the OSAVI to be the most appropriate VI-based estimator of green biomass and vegetative coverage in the semi-arid regions of southern Texas.

Performance of ratio‐based, soil‐adjusted and atmospherically corrected multispectral vegetation indices in predicting herbaceous aboveground biomass in a Colophospermum mopane tree–shrub savanna

AbstractAccurate and near‐real‐time estimation of herbaceous aboveground biomass (AGB) at farm level is crucial for monitoring pasture production and proactive management of stock in semiarid rangelands. Despite its importance, remote sensing has been rarely used by range ecologists and managers in Zimbabwe. This study aimed at assessing the performance of classical multispectral vegetation indices (MVIs) when either singly regressed with measured herbaceous AGB or combined with other visible spectral bands in predicting herbaceous AGB in a Colophospermum mopane savannah. Field herbaceous AGB and corresponding Landsat 8 Operational Land Imager visible spectral data were collected during the 2016–2017 rainy season. Relationships between measured AGB and classical MVIs and extended models of MVIs combined with other visible bands were analysed using bootstrapped simple and stepwise multiple linear regression functions. When MVIs were singly regressed with measured AGB, ratio‐based indices yielded the highest r2 value of 0.64, followed by soil‐adjusted indices (r2 = 0.61), while atmospherically corrected MVIs showed the lowest r2 of 0.58 (p = 0.00). A significant improvement in herbaceous AGB estimation was obtained using a combination of MVIs and other visible bands. Soil‐adjusted MVIs showed the greatest increase (44–46%) in r2, while atmospherically corrected and ratio‐based MVIs poorly improved (<5%). The findings demonstrate that combining MVIs with Landsat 8 optical bands, especially green band, provides the best models for estimating AGB in C. mopane savanna rangelands. These findings emphasize the importance of testing band‐MVI combinations when developing models for estimating herbaceous AGB.

Studying the effects of mycorrhiza and vermicompost fertilizers on the growth and physiological traits of Vetiver Grass (Chrysopogon zizanioides L.)

As an herbaceous, perennial, and evergreen plant, Vetiver Grass (Chrysopogon zizanioides L.) can be used for the improvement and development of arid and semi-arid rangelands. To assess the interaction effect of organic and biological fertilizers on the growth and physiological traits of Vetiver grass, the dry weight of shoots and roots, essential oils, chlorophyll, carotenoids, and proline content were measured. A completely randomized design in factorial layout with three replications was performed in Malayer University’s greenhouse in 2016. The treatments were mycorrhizal fungi on two inoculated (M1) and non-inoculated (M2) levels and vermicompost organic fertilizer in six levelsof (0) (control), 10, 20, 40, 60, and 80% (V1, V2, V3, V4, V5 and V6), which were added to each pot. The results showed that the interaction between different levels of vermicompost and mycorrhiza had a significant (P<0.05) effect on quantitative and qualitative traits of the plants. According to the results, the highest leaf dry weight was seen in VC6M1 treatment and the highest root dry weight wasobserved in VC5M2 and VC6M2 treatments. The highest percentage of essential oil content was observed in VC2M1 and VC5M2 treatments. It was also observed that in the control level of vermicompost and mycorrhizae treatment (VC1M2), the presence of proline index rose to its highest level. The maximum amount of chlorophyll a and carotenoid was seen in VC3M2treatment while the maximum percentage of chlorophyll b was observed in VC2M2 treatment.

Spatial patterns of long‐term vegetation greening and browning are consistent across multiple scales: Implications for monitoring land degradation

AbstractUnderstanding spatial–temporal patterns of terrestrial vegetation response to climate change (long‐term greening/browning) is important for developing strategies to mitigate degradation. Semiarid rangelands are especially susceptible to degradation, which challenges wildlife conservation and human livelihoods that depend on livestock production. In the cold‐arid Trans‐Himalayan ecosystem (northern India), temperature is increasing, and it is also becoming progressively wetter. Yet, counter‐intuitively, there are widespread concerns over degradation. We evaluated whether greening/browning patterns in long‐term satellite‐derived vegetation indices (normalized difference vegetation index [NDVI]) are consistent across different spatial and temporal scales using 6 datasets: MODIS (250 m, 500 m, 1 km, and 5.5 km), SPOT 1 km, and GIMMS 8 km. Results indicate browning in the spring and greening in late summer. Location of hotspots of degradation (browning) was broadly consistent across spatial scales (10−2–102 km2) and were found in regions with warmer temperature and at higher elevations. Broadly, the spatial/temporal pattern of browning does not coincide strongly with location and timing of human land use via livestock grazing. This geographical and seasonal context indicates that vegetation response may be more strongly related to climate than to human land use (overgrazing). Importantly, the dynamic nature of greening/browning, across space and time, is not captured by composite annual metrics (sum‐NDVI, max‐NDVI, and mean‐NDVI). This reiterates the importance of both intraannual and interannual assessments. Location of hotspots indicates that degradation occurs in a spatially contiguous manner, but these are not stationary and instead shift with seasons. Overall, the results show that evaluating the consistency of greening/browning trends across different spatial/temporal scales is critical for understanding and managing vegetation degradation.

Total and structure colonization by arbuscular mycorrhizal fungi in native, perennial grasses of different forage quality exposed to defoliation

Defoliation can compromise the quality and quantity of colonization by arbuscular mycorrhizal fungi (AMF), which contribute to vegetation persistence in semiarid rangelands. The effects of defoliation on total arbuscular mycorrhizal (AM) colonization percentage and on that of its structures (i.e., vesicles, arbuscules) were evaluated on three native, rangeland perennial grass species. These species (i.e., Poa ligularis, Nassella tenuis and Amelichloa ambigua) show different palatability to domestic livestock in Central Argentina. In August 2012, soil + roots (0–10 cm depth) were sampled below the foliage of 12 plants of each species. Half of the plants were then defoliated to 5 cm stubble leaving active meristems intact after defoliation. The other half remained undefoliated. In September, immediately after the differentiation of apical meristems from vegetative to reproductive, soil + roots samples were again obtained and thereafter plants were once again defoliated. The final soil + root sampling was conducted in October (6 plants/species/treatment). The study was repeated on a different plant set during 2013. The percentage of total AM colonization and that its structures were determined. Palatable species did not reach a greater total colonization by AMF in their roots than A. ambigua. Treatments affected the total colonization only at some sampling times (e.g., when it did affect at N. tenuis, the effect of defoliation was not consistent during the study years). At the last date, A. ambigua showed a greater percentage of arbuscules in both defoliation treatments in 2012 and on defoliated plants in 2013. In general, P. ligularis showed a greater vesicle percentage than the other species. Management practices which allow the recuperation of the perennial grasses after a moderate grazing, will not affect considerably their symbiotic relationships.

Quantifying the effects of overgrazing on mountainous watershed vegetation dynamics under a changing climate

Grazing is a major ecosystem disturbance in arid regions that are increasingly threatened by climate change. Understanding the long-term impacts of grazing on rangeland vegetation dynamics in a complex terrain in mountainous regions is important for quantifying dry land ecosystem services for integrated watershed management and climate change adaptation. However, data on the detailed long-term spatial distribution of grazing activities are rare, which prevents trend detection and environmental impact assessments of grazing. This study quantified the impacts of grazing on vegetation dynamics for the period of 1983–2010 in the Upper Heihe River basin, a complex multiple-use watershed in northwestern China. We also examined the relative contributions of grazing and climate to vegetation change using a dynamic grazing pressure method. Spatial grazing patterns and temporal dynamics were mapped at a 1 km × 1 km pixel scale using satellite-derived leaf area index (LAI) data. We found that overgrazing was a dominant driver for LAI reduction in alpine grasslands and shrubs, especially for the periods of 1985–1991 and 1997–2004. Although the recent decade-long active grazing management contributed to the improvement of LAI and partially offset the negative effects of increased livestock, overgrazing has posed significant challenges to shrub-grassland ecosystem recovery in the eastern part of the study basin. We conclude that the positive effects of a warming and wetting climate on vegetation could be underestimated if the negative long-term grazing effects are not considered. Findings from the present case study show that assessing long-term climate change impacts on watersheds must include the influences of human activities. Our study provides important guidance for ecological restoration efforts in locating vulnerable areas and designing effective management practices in the study watershed. Such information is essential for natural resource management that aims at meeting multiple demands of watershed ecosystem services in arid and semiarid rangelands.

Plant Selection and Performance of Two Cattle Types and Camels on Semiarid Rangelands in Kenya

Plant selection pattern and performance of lactating cattle and camels were compared on semiarid savanna rangelands in Kenya in the rainy season (RS) and a transition period (TP) between the RS and the main dry season. It was further evaluated whether supplementation with rumen-degradable protein (RDP) had an effect on these parameters. In both seasons, two cattle types (local ‘Pokot’ cattle and Guernsey × Boran crossbreds) and camels were used, with six females per treatment group (supplemented and nonsupplemented) each (n = 72 animals in total). The experimental periods consisted of 8–10 d of adaptation and 36–40 d of data and sample collection. The diet selected by the cattle types was similar and consisted almost exclusively of grasses. The camel diet consisted mainly of herbs and shrubs with higher contributions of woody plants in the TP than in the RS. Forage from woody plants overall made up a higher proportion of the diet, which was also reflected by a longer browsing time (overall and in the TP) of the supplemented camels compared with the nonsupplemented camels. This result indicates that supplementation of browsers like camels with RDP can be used to increase the intake of forage from woody plants rich in plant secondary compounds, which could be an effective measure for managing rangeland to limit bush encroachment. Overall, no seasonal differences in milk yield were found for the camels and Pokot cattle, but crossbreds had a lower yield in the TP compared with the RS. Overall, the cattle had higher milk fat content than the camels while the camels had slightly higher protein content. Supplementation had no effect on milk yield and composition. The results of diet selection and performance (milk yield) reflect the advantage of camels in arid rangelands.

Enteric methane output from selected herds of beef cattle raised under extensive arid rangelands

Extensively raised beef cattle contribute to the highest levels of enteric methane (CH4) gas emissions among all livestock. Expensive techniques and logistics hinder monitoring of such gas. Therefore, the objective of this study was to use an inexpensive laser methane detector (LMD) apparatus to determine the enteric CH4 levels from a herd of beef cows raised on semi-arid rangelands. A total of 24 cows were selected from Boran and Nguni cows (n = 12 per breed) from two different farms. The parities of the cows were as follows: parity 1 (n = 6), parity 2 (n = 6), parity 3 (n = 6) and parity 4 (n = 6). An observer used a hand-held LMD to measure enteric CH4 emissions plumes during the late afternoon hours when the animals were resting (either standing or lying down). Point measurements (expressed in ppm/m) were taken for six consecutive days and repeated once after every three months. The ratio of CH4 output per kilogramme DMI was not different in within-breed and between-breed in both seasons. Generally, the dry season recorded the highest CH4 output per kilogramme of live weight of cow. For example, Boran cows in parity 2 produced the highest output of 1.0 ± 0.04 g CH4 per kilogramme live weight of cow while Nguni cows in parities 1, 2 and 4 each produced 0.9 ± 0.04 g CH4 per kilogramme live weight of cow in the dry season. All the animals maintained optimal body condition scores in both seasons (ranging between the lowest of 3.2 ± 0.01 and the highest of 3.4 ± 0.01). Based on the results of the study, it is concluded that cows from both herds produced higher CH4 per kilogramme live weight of cow in the dry season while maintaining optimal body condition scores in both seasons.

Assessing the efficacy of fathead minnows (Pimephales promelas) for mosquito control.

Mosquitoes function as important vectors for many diseases globally and can have substantial negative economic, environmental, and health impacts. Specifically, West Nile virus (WNv) is a significant and increasing threat to wildlife populations and human health throughout North America. Mosquito control is an important means of controlling the spread of WNv, as the virus is primarily spread between avian and mosquito vectors. This is of particular concern for avian host species such as the Greater sage-grouse (Centrocercus urophasianus), in which WNv negatively impacts fitness parameters. Most mosquito control methods focus on the larval stages. In North America, control efforts are largely limited to larvicides, which require repeated application and have potentially negative ecological impacts. There are multiple potential advantages to using indigenous fish species as an alternative for larval control including lowered environmental impact, decreased costs in terms of time and financial inputs, and the potential for the establishment of self-sustaining fish populations. We tested the efficacy of using fathead minnows (Pimephales promelas) as biological control for mosquito populations in livestock reservoirs of semiarid rangelands. We introduced minnows into 10 treatment reservoirs and monitored an additional 6 non-treated reservoirs as controls over 3 years. Adult mosquitoes of species known to transmit WNv (e.g., Culex tarsalis) were captured at each site and mosquito larvae were also present at all sites. Stable isotope analysis confirmed that introduced fathead minnows were feeding at the mosquito larvae trophic level in all but one treatment pond. Treatment ponds demonstrated suppressed levels of mosquito larva over each season compared to controls with a model-predicted 114% decrease in larva density within treatment ponds. Minnows established self-sustaining populations throughout the study in all reservoirs that maintained sufficient water levels. Minnow survival was not influenced by water quality. Though minnows did not completely eradicate mosquito larvae, minnows are a promising alternative to controlling mosquito larvae density within reservoirs. We caution that careful site selection is critical to avoid potential negative impacts, but suggest the introduction of fathead minnows in reservoirs can dramatically reduce mosquito larva abundance and potentially help mitigate vector-borne disease transmission.