Assessing Grazing Impact On Plant Functional Group And Plant Ecotypes

Livestock grazing is one of the major human activities that cause a change in plant community structure and composition.Rainfall has been considered as a key factor in controlling productivity and determining suitable grazing intensity in temperate grasslands.management policies for grazing can mediate the productivity of grasslands.Both the duration and intensity of grazing are important,controllable factors affecting the response of plant communities.The current study was conducted to(i)examine the Grazing Impact on Community Characteristics with different plant functional groups(ii)study the response of plant functional groups to grazing intensities(iii)study the change of Plant Species Functional Groups in Grazing Succession(v)study the relationship between Plant Functional Group and Soil Factors(vi)study the effect of grazing intensity on C3 and C4 species and species diversity,in addition to the impact of grazing intensity on species richness and aboveground biomass(AGB)in Hulunber grasslands,Northeastern China.The grazing experiment was designed with four grazing intensities(0.00,0.23,0.46and 0.92Animal Units ha^-1,where 1 Animal Unit[AU]=500 kg of adult cows).Three replicates were used for each stocking rate,with each replicated area covering a 5-ha paddock.The 12 plots were randomly distributed over a total homogeneous area of 60 ha.The grazing intensities were achieved by using 0,2,4 and 8 young cows with body weight ranging from 250 to 300 kg per plot.Constant grazing was held for 120 days,from June to September,during four growing seasons(2014-2017).Our study focused on the impact of different grazing intensities(light,moderate,heavy,and no grazing)on plant functional groups,Which include tall perennial grass(6 species),short perennial grass(6 species),shrubs(3 species),legumes(9species),Liliaceae herb(8 species),Annual/biennial plant(11species),short perennial forbs(16 species)and tall perennial forbs(18 species),to identify the sensitive indicators of long term grazing system.(1)We found that the aboveground biomass,coverage,and species richness decreased with grazing intensity from 213.88,43,and 31 respectively in heavy grazing density to 60.24,22.5,and 25 in control,the high palatable abundant species were in perennial tall grass functional group(6 p/m²),perennial short grass functional group(5 p/m²),and legumes(3p/m²).Most of the species in our experiment,was medium(annual/biennial plant,Liliaceae herb,shrub,and forbs functional groups)represented close to 65.38%of the total plant cover.Tall and short grass functional groups were the main highly palatable species(17.95%)and included the perennial grass Leymus Chinensis.Other dominant species are less palatable(short and tall forbs functional groups)14.10%and Poisonous(legumes)(2.57%).(2)We found that the pattern different species water ecotype was most of the decrease species belong to mesophyte water ecotype,while the most of increase species belong to widespread,the most of compensatory species)and fluctuated stable species and rare species belong to mesoxerophye.(3)Also we found that each plant functional group showed a different response to grazing intensity.Perennial tall grasses dominated by high palatable mesophyte and mesoexerophyte grass showed a significant decrease with grazing intensity.In contrast,the medium palatable xerophyte and widespread grasses were the predominant perennial short increases with grazing intensity.The tall perennial forbs dominated by the mesophyte grass also decreased,but the decrease was non-significant.The influence of grazing density on species is also related to soil factors(soil nutrient,soil moisture,soil temperature,and soil bulk density).Some functional groups,such as tall fescue and Liliaceae herbs,remain stable,which may be related to the soil environment changes caused by grazing activities.(4)The aboveground biomass of perennial tall grass(PTG),perennial short grass(PTF),Liliace herb(LILY),annual/biennial plants(ABP)and shrubs(SHR)differed significantly(P<0.05)among the grazing intensities.The control plot had the highest perennial tall grass(102.0 g/m²)biomass while the least was recorded for Modrate grazing(21.0 g/m²)and Heavy grazing(4.0 g/m²)plots.Similarly,perennial tall forb(47.4)and LILY herbs(14.7)biomasses were higher in the control plot and the lowest was recorded in the Heavy grazing(10.9 and 0.98 g/m²)plot.(5)We found that the relationship between species richness and grazing intensity supported the moderate disturbance hypothesis,the total species richness increased under light and moderate grazing intensity.However,the responses of each PFG to grazing have differed.As grazing intensity increased,so did the richness of short species(short perennial grass,perennial short forb,and legume)in the community.The richness of shrub is unaffected by grazing.With increasing grazing intensity,the aboveground biomass of tall perennial grass and perennial tall forbs decreased significantly,while that of annual/biennial plant functional groups increased.The community diversity and evenness of annual/biennial plants increased significantly with grazing intensity.The dominance of the C3 species decreased obviously while C4 species increased,which may be associated with the environmental change caused by grazing activity.We conclude that heavy grazing harms plant functional group richness and aboveground biomass.This study's findings could provide a standpoint for assessing the current grazing management scenarios and conducting timely adaptive practices to maintain the long-term ability of grassland systems to perform their ecological functions.Also,the finding of this study have practical implications for range management and productivity maintenance in the arid and semiarid grasslands,it is feasible to take some management practices such as ameliorating soil water and proper grazing to improve ecosystem functioning and prevent grassland degradation.