Reduction Of Grasses Research Articles

Multiple global change drivers show independent, not interactive effects: a long-term case study in tallgrass prairie.

Ecosystems are faced with an onslaught of co-occurring global change drivers. While frequently studied independently, the effects of multiple global change drivers have the potential to be additive, antagonistic, or synergistic. Global warming, for example, may intensify the effects of more variable precipitation regimes with warmer temperatures increasing evapotranspiration and thereby amplifying the effect of already dry soils. Here, we present the long-term effects (11 years) of altered precipitation patterns (increased intra-annual variability in the growing season) and warming (1°Cyear-round) on plant community composition and aboveground net primary productivity (ANPP), a key measure of ecosystem functioning in mesic tallgrass prairie. Based on past results, we expected that increased precipitation variability and warming would have additive effects on both community composition and ANPP. Increased precipitation variability altered plant community composition and increased richness, with no effect on ANPP. In contrast, warming decreased ANPP via reduction in grass stems and biomass but had no effect on the plant community. Contrary to expectations, across all measured variables, precipitation and warming treatments had no interactive effects. While treatment interactions did not occur, each treatment did individually impact a different component of the ecosystem (i.e., community vs. function). Thus, different aspects of the ecosystem may be sensitive to different global change drivers in mesic grassland ecosystems.

Application of an improved vegetation index based on the visible spectrum in the diagnosis of degraded pastures: Implications for development

AbstractInadequate pasture management causes land degradation through reduction of grass, increased presence of invasive plants or pests, compaction, erosion, and nutrient deficiency. The recognition of pasture degradation is therefore essential. Remote sensing satellite systems allow us to do so at regional‐to global scales. A struggle is in progress nowadays is to improve detection accuracy and implement high‐resolution surveys at farm scales using low‐cost unmanned aerial vehicles (UAVs). The pasture imagery can be translated into maps of degraded pasture using the popular NDVI as diagnostic parameter, but their generation using a UAV requires a high‐cost NIR sensor, while the struggle is to use low‐cost UAVs equipped with RGB cameras. The first step to recognize degraded pastures using RGB cameras is to define a suitable vegetation index. Thus, the purpose of this study was to present the total brightness quotient of red (TBQR), green (TBQG), and blue (TBQB) bands. The test to the index resorted to LANDSAT‐8 satellite images captured over the environmental protection area of Uberaba River basin (Minas Gerais, Brazil) in the 2017–2019 period. The images were not captured by a UAV because the equipment was not then available. The results were promising given the large detection accuracy (88.63%) of the TBQG and the high (0.965) correlation between TBQG and NDVI. Besides, the TBQ‐based areas of degraded pasture (17,486.3–25,180.1 hectares) were larger than the NDVI counterparts (12,066.9 hectares). This is an additional reason to oversight degraded pastures based on the TBQs, as they seek for improved environmental compliance and economic development.

The Impact of Green Space Layouts on Microclimate and Air Quality in Residential Districts of Nanjing, China

This study numerically investigates the influence of different vegetation types and layouts on microclimate and air quality in residential districts based on the morphology and green layout of Nanjing, China. Simulations were performed using Computational Fluid Dynamics and the microclimate model ENVI-met. Four green indices, i.e., the green cover ratio, the grass and shrub cover ratio, the ecological landscaping plot ratio and the landscaping isolation index, were combined to evaluate thermal and wind fields, as well as air quality in district models. Results show that under the same green cover ratio (i.e., the same quantity of all types of vegetation), the reduction of grass and shrub cover ratio (i.e., the quantity of grass and shrubs), replaced by trees, has an impact, even though small, on thermal comfort, wind speed and air pollution, and increases the leisure space for occupants. When trees are present, a low ecological landscaping plot ratio (which expresses the weight of carbon dioxide absorption and is larger in the presence of trees) is preferable due to a lower blocking effect on wind and pollutant dispersion. In conjunction with a low landscaping plot ratio, a high landscaping isolation index (which means a distributed structure of vegetation) enhances the capability of local cooling and the general thermal comfort, decreasing the average temperature up to about 0.5 °C and the average predicted mean vote (PMV) up to about 20% compared with the non-green scenario. This paper shows that the relationship vegetation-microclimate-air quality should be analyzed taking into account not only the total area covered by vegetation but also its layout and degree of aggregation.

Woody shrubs increase soil microbial functions and multifunctionality in a tropical semi-arid grazing ecosystem

Woody encroachment is of global concern in arid and semiarid regions around the world. Due to reduction in grass (forage), woody encroachment is viewed as ecosystem disservice and degradation, even though this may not reduce ecosystem functions. Often, management perceptions of degradation remain inadequately informed by knowledge of ecosystem processes. We compared 11 biotic variables related to soil and microbial functions under shrubs against paired-adjacent grassland:- carbon, nitrogen, C:N ratio, organic matter, plant-available N, N-mineralization rate, microbial biomass C and N, basal respiration, and metabolic-quotient. We summarized these as a multifunction-index. We also measured five soil physico-chemical covariates:- pH, conductivity, bulk density, texture and water holding capacity. These 11 biotic variables were 15–48% higher under shrubs than under grass; multifunction-index was also higher (by 366%). After accounting for spatial autocorrelation and background differences in physico-chemical covariates (redundancy analysis), altered ecosystem functions were attributable to shrubs. Overall, shrubs can enhance ecosystem functions, and maintain important ecological processes through concomitant changes in soil physico-chemical properties. While shrubs should not be equated to ecological degradation, they present a challenging triage of ecosystem service, disservice, and function for grasslands. Management strategies could benefit from targeting patterns of nutrient re-distribution under shrubs.

Bison grazing increases arthropod abundance and diversity in a tallgrass prairie.

How grazing-induced ecosystem changes by ungulates indirectly affect other consumers is a question of great interest. I investigated the effect of grazing by American Bison (Bos bison L.) on an arthropod community in tallgrass prairie. Grazing increased the abundance of arthropods, an increase that was present in both herbivorous and carnivorous assemblages, but not in detritivores. The increase in herbivores and reduction in plant biomass from grazing resulted in an arthropod herbivore load almost three times higher in grazed plots compared with controls. Among herbivores, the sap-feeding insect guild was dramatically more abundant, while chewing herbivores were not affected. Herbivorous and carnivorous arthropod richness was higher in grazed plots, although the response was strongest among herbivores. Arthropod abundance on individual grasses and forbs was significantly higher in grazed areas, while plant type had no effect on abundance, indicating that the change was ecosystem-wide and not simply in response to a reduction in grass biomass from grazing. The response of arthropods to grazing was strongest in the early part of the growing season. Published research shows that ungulate grazing, although decreasing available biomass to other consumers, enhances plant quality by increasing nitrogen level in plants. The arthropod results of this study suggest higher plant quality outweighs the potential negative competitive effects of plant biomass removal, although other activities of bison could not be ruled out as the causative mechanism. Because arthropods are extremely abundant organisms in grasslands and a food source for other consumers, bison may represent valuable management tools for maintaining biodiversity.

Evaluation of Bulk Density and Vegetation as Affected by Military Vehicle Traffic at Fort Riley, Kansas

<abstract> Abstract. Studies were conducted using military vehicles to determine the influence of repeated traffic on soil compaction and vegetative losses. The resultant data will eventually be incorporated into models such as the Wind Erosion Prediction System (WEPS). A replicated field experiment was conducted in the fall of 2010 on two soils that dominate the military training grounds at Fort Riley, Kansas. Treatments consisted of two vehicle types and three levels of vehicle passes. We used an Abrams M1A1 tank and a High-Mobility Multipurpose Wheeled Vehicle (i.e., Humvee), representing tracked and wheeled military vehicles, respectively. Bulk density, aboveground standing biomass, and plant cover were measured before and after vehicular traffic in the fall of 2010 as well as in the spring and summer of 2011. Samples were taken from curved, straight, and cross-over sections of the vehicle tracks. A mixed-model analysis of variance of these data indicated that the overall mean bulk density under the M1A1 was significantly greater than under the Humvee (p ≤ 0.05). In general, as the number of passes increased, the bulk density under the M1A1 increased significantly (p ≤ 0.05), but the increases under the Humvee were not significant (p ≤ 0.05). Bulk densities were significantly greater in the curved part of the tracks than the straight part of the tracks. Reduction in standing biomass and vegetation cover was more severe on average under the M1A1 than under the Humvee (although not significant at p ≤ 0.05). For both vehicles, biomass and cover were affected more at the curved sections of the track than the straight sections (significant at p ≤ 0.05). Comparison of spring and fall bulk density data showed significant differences at the 0-5 cm and 5-10 cm depths, indicating that the winter freeze and thaw cycles loosened the top soil layers. Subsequent growth showed severe reduction in grass biomass growth in the curved sections of the tracked vehicle paths. Growth in forb species was not significantly affected.

Interactions of the Hemiparasitic Species Rhinanthus minor with its Host Plant Community at Two Nutrient Levels

For root hemiparasites, host plants are both the source of water and nutrients below-ground, but competitors for light above-ground. Hemiparasites can reduce host biomass, and in this way considerably affect the whole plant community. To investigate these effects, we carried out two experiments in an oligotrophic meadow with a native population of Rhinanthus minor. In the first experiment, removal of R. minor was combined with fertilization in a factorial design, and in the second one, we manipulated R. minor density by thinning. The presence of R. minor decreased the biomass of its host community, mostly by suppressing grasses. In this way, the species was able to counterbalance the effect of fertilization, which increased community biomass and in particular that of grasses. Neither the presence of R. minor nor fertilization affected the total number of species or the Shannon-Wiener diversity index (H’) of the host community. However, H’ of grasses was higher and H’ of forbs (non-leguminous dicots) was lower in the presence of R. minor. Reduction of grasses by R. minor favored mainly the dominant forb Plantago lanceolata, which partly acquired the role of a competitive dominant. Effects of R. minor on community diversity seem to be highly dependent on the relative sensitivities of dominant and subordinate species. Fertilization increased the mortality of seedlings, resulting in a lower number of flowering plants. However, surviving individuals on average produced more flowers. Thinning resulted in lower mortality of R. minor plants. This indicates that intraspecific competition in R. minor populations results in negative density dependence.

Testing soil phytolith analysis as a tool to understand vegetation change in the sagebrush steppe and pinyon-juniper woodlands of the Great Basin Desert, USA

Better biological proxy methods are needed to understand changes in arid ecosystems over the recent past. Our objective in this study was to examine the utility of soil phytolith analysis to reflect vegetation changes over the past 200 years, from the end of the ‘Little Ice Age’ to present. The sensitivity of phytoliths to record vegetation changes for this time period was tested by sampling in locations where vegetation changes were known to have occurred based on human records. We used extraction weights to test for the trend in reduction of grasses and increase in woody vegetation over time. We used the relative abundance of soil phytolith morphotypes from native versus introduced grasses to look for the increase in non-native grasses. Then, we examined the phytolith assemblages from soils in a continuous core sampling method with 1 cm increments. Extraction weights decreased by half from the surface to ‘Little Ice Age’ layers and may reflect increasing pinyon-juniper woodland cover. The relative abundance of common introduced grass phytoliths increased by nearly half between the older segments and the surface, which could be a reflection of growing dominance of invasive grasses. The phytolith assemblages varied over time and with depth in continuous core sampling. The patterns of change in both detailed cores appeared to reflect known vegetation changes since the end of the ‘Little Ice Age’. Soil phytolith analysis has the potential to provide much needed biological proxy data for this time period in the Great Basin Desert.

Reduction in grass eating behaviours in the domestic dog, Canis familiaris, in response to a mild gastrointestinal disturbance

Grass eating behaviour in the domestic dog may be related to gastrointestinal distress. To explore this theory, the current study observed grass eating behaviours in dogs fed a standard diet with and without supplementation of a fructo-oligosaccharide (FOS). The FOS diet temporarily induced loose, watery stools to simulate a mild gastrointestinal disturbance. During both FOS Diet and Standard Diet periods, dogs were presented with couch ( Cynodon dactylon) and kikuyu ( Pennisetum clandestinum) grasses, and the time spent eating grass and the number of grass eating and vomiting events was recorded. Our study found that dogs spent significantly more time eating grass when fed the standard diet and producing normal stools than when they were fed the FOS diet and producing loose stools, suggesting that dogs do not use grass to self-medicate a diarrhoeal gastrointestinal disturbance. However, this does not preclude that other forms of gastrointestinal disturbance may be self-medicated by grass eating behaviours. Importantly, dogs did not use grass as an emetic, as there were only two vomiting events and 374 grass eating events observed. Alternatively, the reduction in grass eating may be attributable to a feeling of satiety caused by the fermentation of FOS. For further clarity, future research should examine the effect of other gastrointestinal disturbances, such as constipation (hard, dry stools) or nausea, on grass eating behaviour in the domestic dog.

Genome comparisons reveal a dominant mechanism of chromosome number reduction in grasses and accelerated genome evolution in Triticeae

Single-nucleotide polymorphism was used in the construction of an expressed sequence tag map of Aegilops tauschii, the diploid source of the wheat D genome. Comparisons of the map with the rice and sorghum genome sequences revealed 50 inversions and translocations; 2, 8, and 40 were assigned respectively to the rice, sorghum, and Ae. tauschii lineages, showing greatly accelerated genome evolution in the large Triticeae genomes. The reduction of the basic chromosome number from 12 to 7 in the Triticeae has taken place by a process during which an entire chromosome is inserted by its telomeres into a break in the centromeric region of another chromosome. The original centromere-telomere polarity of the chromosome arms is maintained in the new chromosome. An intrachromosomal telomere-telomere fusion resulting in a pericentric translocation of a chromosome segment or an entire arm accompanied or preceded the chromosome insertion in some instances. Insertional dysploidy has been recorded in three grass subfamilies and appears to be the dominant mechanism of basic chromosome number reduction in grasses. A total of 64% and 66% of Ae. tauschii genes were syntenic with sorghum and rice genes, respectively. Synteny was reduced in the vicinity of the termini of modern Ae. tauschii chromosomes but not in the vicinity of the ancient termini embedded in the Ae. tauschii chromosomes, suggesting that the dependence of synteny erosion on gene location along the centromere-telomere axis either evolved recently in the Triticeae phylogenetic lineage or its evolution was recently accelerated.

Impact of hemiparasitic Rhinanthus angustifolius and R. minor on nitrogen availability in grasslands

Root hemiparasites like Rhinanthus angustifolius C.C. Gmel and R. minor L. have a potential to accelerate the restoration of semi-natural grasslands because they may decrease above-ground biomass of the vegetation. This, in turn, may be beneficial for species diversity. It is known that hemiparasites often accumulate high nutrient concentrations in their above-ground parts, resulting in high quality litter. Because of the short life cycle of many parasitic plants, litter is released early in the season and the main part is not removed from the grassland by hay-making. This has been shown to yield an increased nutrient availability locally. We performed an introduction experiment with R. angustifolius and R. minor in three semi-natural grasslands in Flanders (Belgium). In the second year after sowing, the above-ground nitrogen (N) content of the grasses and of the potential host vegetation (excluding the hemiparasite), was increased in the parasitized plots. The reduction of grass (and legume) above-ground biomass in parasitized plots resulted in a decrease in the total above-ground N uptake of grasses, host and total vegetation (ex- and including the parasite, respectively) of the parasitized plots compared to the control. Furthermore, with a tracer experiment (15N), we demonstrated that the N from the added tracer was relatively less available in parasitized plots, suggesting larger soil N pools in these treatments. This is probably the consequence of increased mineralization, resulting from the high-quality, parasitic litter. Further experiments should be conducted to investigate the impact of hemiparasitic Rhinanthus spp., e.g. on the availability of other nutrients such as phosphorus.

Exploring the use of sequential sampling for monitoring organic matter stocks in a grazed and non-grazed Scots pine stand

The possible reduction of soil organic matter stocks under a grazing regime was studied by sequential, intensive sampling over a seven-year period. The measured soil organic matter stocks were highly variable, and overall no significant changes in soil organic matter stocks could be observed. The variation was partly due to methodological errors, but particularly to high spatial variability, which obscures small changes over time. This means that, even in this relatively homogeneous ecosystem with the same parent material and vegetation, quantifying temporal changes in stocks of soil organic matter is very difficult. In order to examine whether significant changes in organic matter stocks could be expected at all, a sensitivity analyses was done using a balance model. We used a simple balance model because we did not want to predict changes in decomposition rates or litter input, but only analyse the potential changes in soil organic matter stock under realistic and more extreme scenarios. The model calculates the development of organic matter stocks under various litter inputs (measured values reduced with 0–70%) and decomposition rates (measured k-values decreased and increased with 50%). In this way, the potential impact of grazing on soil organic matter was explored. The numerical exercise confirmed the results of the observational study and showed that meaningful differences can hardly be expected. Significant differences between control and grazed situations could only be expected under unrealistic conditions or excessively large sample sizes. Because litter input and decomposition are small compared to the stocks of soil organic matter, the latter appeared a very robust parameter, which is hardly reduced by grazing in spite of the obvious reduction in grass standing biomass. It can be concluded that in this kind of field experiments or in monitoring programmes focused on carbon sequestration, sequential sampling will not reveal changes in organic matter stocks, probably not even when measurements are continued for many years. A sensitivity analyses, based on litter input data and different estimated decomposition rates can improve the design of a sampling strategy.

Modelling the trade-off between fire and grazing in a tropical savanna landscape, northern Australia

As savannas are widespread across northern Australia and provide northern rangelands, the sustainable use of this landscape is crucial. Both fire and grazing are known to influence the tree–grass character of tropical savannas. Frequent fires open up the tree layer and change the ground layer from perennials to that dominated by annuals. Annual species in turn produce copious quantities of highly flammable fuel that perpetuates frequent, hot fires. Grazing reduces fuel loads because livestock consumes fuel–forage. This trade-off between fire and grazing was modelled using a spatially explicit, process-orientated model (SAVANNA) and field data from fire experiments performed in the Victoria River District of northern Australia. Results of simulating fire (over 40 years) with minimal or no grazing pressure revealed a reduction in the shrub and woody plants, a reduction in grasses, and no influence on the tree structure given mild fires. While mature trees were resistant to fire, immature trees, which are more likely associated with the shrub layer, were removed by fire. The overall tree density may be reduced with continual burning over longer time periods because of increasing susceptibility of old trees to fire and the lack of recruitment. Increases in stocking rates created additional forage demands until the majority of the fuel load was consumed, thus effectively suppressing fire and reverting to the grazing and suppressed fire scenario where trees and shrubs established.

Paleoclimatic significance of Late Quaternary eolian deposition on the Piedmont and High Plains, Central United States

Presently stabilized dune systems on the piedmont of eastern Colorado and adjacent High Plains have been repeatedly re-activated during the past 20,000 years. Radiocarbon and thermoluminescence age estimates indicate eolian activity late in the last glacial cycle ca. 20,000–12,000 yr B.P. and subsequent episodes of dune reactivation at ca. 6000, 4500 and 1000 yr B.P. Pollen analysis from aggraded buried soil A horizons show a shift from grasses and shrubs to goosefoot, a disturbance indicator. The association of maximum goosefoot levels with the coarsest part of the buried A horizon immediately prior to burial by eolian sand indicates a substantial reduction in grass and dominance of shrubs with onset of eolian activity. The vegetation change and eolian depositional sequence indicates a reduction in plant coverage with regional drought, possibly augmented by bison grazing and surface heating effects. We infer an increase in summer monsoonal precipitation between 13,000 and 9000 yr B.P. reflecting a heightened land-to-sea temperature gradient associated with rising summer solar-insolation values and a meltwater cooled Gulf of Mexico. Dune reactivation in the middle and late Holocene appears to be independent of summer insolation values, but rather reflects a small (< 10°) easterly shift of the Bermuda High and western ridge aloft, difficult parameters to link to a cause and to resolve with climate models.

Effects of Grazing on Cryptogamic Crusts in Pinyon-juniper Woodlands in Grand Canyon National Park

-Previously grazed pinyon-juniper woodlands in Grand Canyon National Park, northern Arizona, were studied to determine the effects of past and present grazing. The occurrence and biomass of cryptogamic crust were compared for five sites in and around the Park along a continuum from never grazed to recently grazed. All sites were similar in soil characteristics, elevation and overstory dominants. Cryptogamic crust was quantified using visible cover estimates and the chlorophyll a content of the crust as an indicator of biomass. Visible crust cover was reduced almost 80% on grazed (5.2%) as compared to ungrazed (23.3%) sites. Crust biomass, as estimated by chlorophyll a content, was reduced on grazed (3.1 ,tg cm-2) compared to ungrazed (9.9 ,tg cm-2) sites. There were no significant differences in species presence and absence data. Significant correlations existed between cryptogamic crust cover and the composition of the respective vascular plant communities, marked by a reduction of grasses and an increase of bare soil.

Maasai herd and flock structures in relation to livestock wealth, climate and development

Information was obtained on the structure of the herds and flocks of a sample of 41 households on the three Maasai Group Ranches in Kenya. The purpose of the survey was to contribute to an intensive study of the livestock production system, and also to assess the amount of information that could be obtained from a herd structure study on its own. Differences in herd structure were related to the livestock wealth of the household, the stage of development of the Group Ranch as well as to the variation in climate, and production alternatives. Data from more than 5100 cattle revealed that Maasai herds contained less steers in 1982 (18%) than in 1968 (22%). The proportion of mature steers had also dropped from 5% (1968) to 2% (1982), with maximum valves of 3·2% on the most developed ranch and 2% for the wealthiest stratum of households. A high percentage of females had been retained (56%) giving a herd structure characteristic of subsistence production with milk as a primary output. This structure also caters for a strong market in immature animals and gives the herd a high potential for recovery after a drought. There appeared to be a trend towards increased use of introduced bulls, notably Sahiwal on the Small East African Zebu, with increased Group Ranch Development. However, this trend was confounded by a decreasing aridity gradient with increased development. On two of the ranches for which 1968 counts were available, cattle numbers were 119% of their previous value whereas small stock were 470%. The reason appears to be that increased sedentarisation without adequate range management has resulted in a severe reduction in grasses, and their replacement by forbs. These plants are more palatable to small stock which are better able to exploit the degraded habitat. Information from more than 2730 sheep and 2300 goats revealed that poor households preferred goats and richer households, sheep. The Small East African Goat was ubiquitous, but the most developed ranch had crossed Dorper onto Maasai sheep whereas the least developed and most arid ranch had introduced Somali Blackhead sheep. The Dorper crossbred catered for a market for mutton whereas the Blackhead was primarily for home consumption of fat. The conclusion is that Group Ranch Development has not projected the Maasai into commercial beef ranching as originally planned, but their production system has not stood still. A study of herd structures was a good way of demonstrating the evolution of the system. The method was simple but was dependent for its success on fairly involved and time-consuming sampling and data collection procedures.