Effects Of Sheep Ingesting And Trampling In Leymus Chinensis Grassland

The herbivore foraging and trampling at the plant-animal interface are the main topics in grazing ecology research. Both the herbivore foraging and trampling are the key factors that affect the animal production, vegetation structure and productivity, and the transformation efficiency of resources in the grassland ecosystems. In this study, we chose large herbivores, sheep, to investigate the impact of sheep foraging and trampling on the grassland based on the view of sustainable developmental economy and environment. We obtained the important results and conclusions as follows.(1) The aboveground biomass and relative density of Leymus chinensis were significantly affected by the grazing intensities, growing season and the interactions of grazing intensity and growing season. Moderate grazing (light and mid) could increase the aboveground biomass of L. chinensis. In contrast, heavy grazing reduced aboveground biomass of L. chinensis and promoted the growth of annual herbs. The aboveground biomass of L. chinensis increased with time under grazed conditions, and decreased with the increasing grazing intensity. While in the control plot (ungrazed), the aboveground biomass of L. chinensis decreased with time and the forbs and legumes increased. The tillering of L. chinensis could benefit from the moderate grazing, but was weakened by the high grazing intensity which thus provided the advantage for invasion of therophyte. The sheep ingesting types were availably influenced by growing season and grazing intensities. For L. chinensis, top-clipping was the main ingesting type of sheep in spring, and defoliating which reflected the higher degree of partial preference was main type in summer and autumn. The stem-drawing rate showed a random ingesting behavior, and it was affected by vegetative biological property.(2) Trampling loss rate is a good indicator to measure a short-term grazing intensity and it is dependent on the grazing intensity and the growing season. The biological property of plants, especially the degree of lignification, is a main factor that largely determines trampling loss rate. Grazing significantly affected the capillary porosity and bulk density of the soils of 0-10 cm and the moisture level in the soils of 0-15 cm underground. As the grazing intensity increased, the soil capillary porosity and moisture declined while bulk density increased.(3) The grazing in rainy day and grazing intensity could affect significantly sheep grazing behavior. The grazing in rainy days by sheep affected ingesting types, and increased the untouched percentage of plants which descended with increasing grazing intensity. It showed that the touched percentage of plants increased with an increase in grazing intensity. However, the sheep's defoliating percentage (indicated the degree of partial preference) had no difference in the rainy days regardless of the grazing intensities, demonstrating that this kind of ingesting type was a random choice under cold and humid weather. When grazed on the rainy days, the sheep would behave differently from the sunny days on choosing its food or discarding. The ingesting loss of gramineous plants did not differ among the different intensities while ingesting loss of forbs, such as Kalimeris intergrifllia, increased with increasing grazing intensities. The trampling loss rate decreased significantly in rainy days. The trampling loss rate had no difference for L. chinensis among the different grazing intensities while increased as the grazing intensities increase for Phragmitis communis. It showed that trampling loss rate of P. communis was still an ideal indicator to measure the grazing intensity even in rainy days. Trampling in rainy days significantly affected the moisture and bulk density of soil that was located less than 5 cm underground and had no visible impact on the deeper soils. Above moderate trampling intensities could accelerate the evaporation from soil and reduces the soil moisture content. On the other hand, moderate trampling intensities could consolidate and increase the soil bulk density.(4) The height and density of standing litter could significantly affect the tillering rate of L. chinensis which increased as the biomass of standing litter declined. The density of standing litter had more impact on the tillering rate of L. chinensis. The aboveground biomass increased with decline of standing litter mass. The most important factor that affects the plant growth is the shading degree. The feed intake of sheep also increased with decreasing litter mass. It was shown that the density of standing litter showed were stronger than the height of standing litter on food choice. The percentage of ingesting types, such as top-cilpping rate, defoliating rate and untouching rate, decreased with the litter mass increasing. The height of standing litter mainly affected the grazing percentage, especially for top-clipping rate, while the density of standing litter could influence the partial preference of sheep appearing as increasing the percentage of defoliating. Both the height and density of standing litter could significantly impact on the trampling loss rate which would be aggravated when standing litter mass decreased.(5) We conducted field experiments with clipping treatments and the application of sheep saliva to the damaged parts of tillers to simulate sheep grazing on the perennial grass L. chinensis during the early growing seasons. The results demonstrated that clipping with saliva application significantly increased tiller numbers eight weeks after treatments in comparison with clipping alone. A key finding is that the effect of sheep saliva on plant growth was short-lived. Clipping with saliva application increased leaf weight in the second week, while clipping alone had no effect. Moreover, clipping with saliva application promoted the elongation of new leaves (not the old ones) in the first week whereas clipping alone was ineffective. The results also showed that there were no differences between clipping with saliva application and clipping alone for relative height growth rate (RHGR) and aboveground biomass. Therefore, we concluded that saliva application to clipping treatment would generate an additional effect compared to clipping alone for the plant and the positive effects are time dependent. The additional effects primarily embodied in the individual level of plant, such as the changes of leaf weight and leaf length. Beyond the level, the effects of saliva only produced many more tiller numbers rather than the accumulation of aboveground biomass.This study was completed mainly by series of field trails and obtained many important conclusions with significant theoretic values and wide potential applications. Firstly, the study innovatively put forward two concepts which abounded the connotation of grazing ecology. The study defined a conception to present ingestive type of sheep at the plant modular level and brought out a new method, the trampling loss rate, to express the trampling density. Secondly, we analyzed the relationship between the trampling loss rate and grazing density, and found that the response to trampling loss rate reflected grazing intensity as well as the damage degree of plant and draw a conclusion that the trampling loss rate was sensitive and stable index. The characters of grazing and trampling were compared and analyzed in rainy days and sunny days. And it would be helpful for managers of grassland to formulate a scientific grazing intensity in rainy days. Moreover the effects of standing litter on plant growth and herbivore grazing behavior was studied by quantitative methods at the first time. And the outcomes from the study would cast a new light on the ecological function of standing litter. Finally, we discovered some mechanisms of the interaction between herbivore and plant and pointed out the effect of saliva was time depended which provided some evidence for coevolution of herbivores and plants.