Yuchun Yan

Impacts of Differing Grazing Rates on Canopy Structure and Species Composition in Hulunber Meadow Steppe

ABSTRACT In this study, the impacts of cattle grazing with differing grazing rates on species composition, canopy structural traits, standing crop of canopy biomass, and plant species diversity were examined in a meadow steppe of the Hulunber grasslands, Northeastern China. Six stocking-rate treatments (0, 0.23, 0.34, 0.46, 0.69, and 0.92 AU.ha-1) with three replicates were established, and observations were conducted from 2009 to 2011. Our findings demonstrate that short-term grazing substantially altered the species composition and relative dominance, standing crop of aboveground biomass, and canopy structural traits, whereas no significant changes in species diversity and evenness occurred in response to different-rated grazing in this meadow steppe, which has a long-term evolutionary grazing history and high-resources availabilities. We found that perennial graminoid significantly decreased, while forbs and annuals increased at the same time, with increasing grazing intensity and duration; canopy height and coverage decreased substantially with increasing stocking rates, whereas significant changes in plant density occurred only at heavy grazing in the second and third years; and significant negative linear relations were found between the standing crop of biomass and grazing intensity in each individual year or for 3 years on average. Significantly highest species richness and canopy dominance occurred only at the intermediate grazing rate in the third year, and intermediate grazing intensity also maintained a highly constant standing crop of canopy biomass in the 3 years, all being in accordance with the intermediate disturbance hypothesis. Our findings imply that monitoring changes in species composition, canopy traits, and standing crop of biomass in grassland communities can provide important references for assessing current grazing management scenarios and conducting timely adaptive practices to maintain the long-term ability of grassland systems to perform their ecological functions.

Current Situation and Prospect of Grassland Management Decision Support Systems in China

China, with wide grassland areas of the second rank throughout the world, is faced with a severe challenge on how to manage its vast and degenerating/degenerated grassland. Computer and network technologies are more and more widely applied in grassland production, research and education, which is just a greatly encouraging field. Tremendous achievements have been made in grassland management decision support system (GMDSS) research in developed countries at present, but there is still a long way to obtain a great development for developing countries, such as China. This paper reviewed the research progress and current situation in the GMDSS research and application in China. Concept models and empirical models are still hugely focused on the corresponding research fields in China, but the integrated GMDSS has not been well developed. Therefore, Chinese scientists must develop the integrated models from the existing models, and accordingly sinicize the GMDSS of models used in the developed countries for availably application. In the other hand, there is a same direction of research and development about the GMDSS not only for developed countries but also for China, which is going to be combined with internet, 3S (GIS, RS and GPS) and virtual technology.

Vegetation patches increase wind-blown litter accumulation in a semi-arid steppe of northern China

Litter decomposition is an important source of soil organic matter and nutrients; however, few studies have explored how vegetation patches affect wind-driven litter mobility and accumulation. In this study, we aimed to test the following hypotheses: (1) vegetation patches can reduce litter removal and facilitate litter accumulation, (2) litter mobility results in the heterogeneous redistribution of carbon and nutrients over the land surface, and (3) litter removal rates differ among different litter types (e.g., leaf and stem). Four vegetation patch types and six litter types were used to investigate the impacts of vegetation patches on litter mobility and accumulation. The results show that compared with almost bare ground patches, patches with vegetation cover had significantly higher litter accumulation, with the shrub patch type having the highest accumulation amount. The rate of litter removal due to wind was highest for the almost bare surface type (P4) and lowest for the shrub patch (P1) and Stipa grandis community (P2) types. There were significant differences in the removal rate among the different litter types. These findings indicate that wind-based litter redistribution among bare, S. grandis-dominated, and shrub-dominated patches is at least partially responsible for increasing the spatial heterogeneity of resources on a landscape scale.

Quantitative monitoring of grazing intensity in the temperate meadow steppe based on remote sensing data

ABSTRACT Grazing intensity (GI) is difficult to measure accurately because of the diversity of grazing livestock, their mobility in the grazing space and the uncertainty of grazing times. Thus, GI monitoring is often only qualitative, while quantitative monitoring is scarce. In this study, models correlating GI, the normalized difference vegetation index (NDVI) and aboveground biomass (AGB) were established based on a controlled GI experiment. The GI derived from NDVI was evaluated using the GI derived from AGB samples, under the principle that AGB is similar for the same GI in the same grassland type. The results showed that the appropriate time to build the model in the study area was from July to August, when there was a negative correlation between GI and NDVI. The simulated GI derived from NDVI was similar to GI derived from AGB, and the R2 (coefficient of determination) values for fresh weight and dry weight were 0.3770 and 0.4292, respectively; the root mean square error (RMSE) were 0.2302 and 0.1953 animal units (AU) ha−1 (1 AU = 500 kg of adult cattle); and the relative error from −20% to 20% accounted for 62.07% and 72.41% of the total samples. Most of the study area was under heavy grazing according to monitoring results from 2010 to 2016, except for a few pastures with rational utilization (0.23 AU ha−1 – 0.46 AU ha−1), and continuous heavy grazing often occurred for many years without rest grazing.

Response of ecosystem CO 2 fluxes to grazing intensities – a five-year experiment in the Hulunber meadow steppe of China

Grazing is the primary land use in the Hulunber meadow steppe. However, the quantitative effects of grazing on ecosystem carbon dioxide (CO2) fluxes in this zone remain unclear. A controlled experiment was conducted from 2010 to 2014 to study the effects of six stocking rates on CO2 flux, and the results showed that there were significant differences in CO2 fluxes by year, treatment, and month. The effects of light and intermediate grazing remained relatively constant with grazing year, whereas the effects of heavy grazing increased substantially with grazing duration. CO2 flux significantly decreased with increasing grazing intensity and duration, and it was significantly positively correlated with rainfall, soil moisture (SM), the carbon to nitrogen ratio (C/N ratio), soil available phosphorus (SAP), soil NH4+-N, soil NO3−N, aboveground biomass (AGB), coverage, height, and litter and negatively correlated with air temperature, total soil N (TN) and microbial biomass N (MBN). A correspondence analysis showed that the main factors influencing changes in CO2 emissions under grazing were AGB, height, coverage, SM, NH4+-N and NO3−N. Increased rainfall and reduced grazing resulted in greater CO2 emissions. Our study provides important information to improve our understanding of the role of livestock grazing in GHG emissions.