Effect Of Different Ecological Restoration Measures On The Characteristics Of Typical Grassland Plant Communities In Loess Hilly Region Of Ningxia

The typical grassland in the hilly area of the Loess Plateau is an important ecological barrier and animal husbandry base in Ningxia,which is seriously degraded by natural and human factors.With the implementation of the national ecological restoration project,the area adopts fence enclosure,contour trench and fish-scale pits preparation to promote the rapid restoration of grassland vegetation.Studying the changes of plant community in these ecological restoration is of great significance to the grassland ecological construction in this area.Based on the typical grassland in the loess hilly region of Ningxia,using survey determination combined with quantitative ecological methods,the grassland plant communities under the 0-year(1 year),3 years,6 years,10 years and 15 years were classified in the three ecological restoration measures,studying community succession sequence,species composition,diversity,stability,dominant population distribution pattern and niche,discussing the relationship between plant communities and environmental factors,analyzing the relationship between the main plant species,which provide a basis for the ecological construction of typical grassland in the loess hilly region.The main conclusions are as follows:(1)Two-way indicator species(TWINSPAN)combined with the trend-relational analysis(DCA)divided the study plant community types into eight.Soil available nitrogen,bulk density,organic matter,soil moisture content and total phosphorus are the main soil physical and chemical factors affecting the community distribution in this area.(2)With increasing of recovery time,The vegetation succession sequence of enclosure is Stipa bungeana+Thymus mongolicu communities-Stipabungeana+Stipa grandis communities?Thymus mongolicus+Stipa bungeana communities Stipa bungeana+Stipa grandis communities?Stipa bungeana+Artemisia sacrorum communities;Succession process of contour trench grassland was experiencing Astragalus adsurgens+Pennisetum flaccidum communities Poa annua+Leymus secalinus communites?Sipa bungeana+Thymus mongolicus communities?Thymus mongolicus+Leymus secalinus communities-Stipa bungeana+Stipa grandis communities;Observed succession process of fish-scale pits grassland was Astragalus adsurgens+Pennisetum flaccidum communities-Poa annua+Stipa bungeana communities-Stipa bungeana+Thymus mongolicus communities-Thymus mongolicus+Stipa bungeana communities.As the age of recovery increases,there are nonlinear or spiral changes in dominant species.(3)The number of perennial herbaceous species,proportion of species and important values,and the diversity were the highest at the 10th year under different measures.With the recovery period,the vegetation coverage,height and above ground biomass of the enclosure showed an upward trend,and the coverage of contour trench and fish-scale pits were increased.Vegetation coverage,height and above ground biomass with similar recovery years are the highest in enclosure and lowest in grazing.(4)The richness,diversity and evenness index are lower in enclosure.The communities of each measure are in an unstable succession stage.The similarity between the contour trench and the fish-scale pits was higher.The soil water content was the main factor affecting the plant characteristics in the study area.(5)The pattern of each treatment population is mostly aggregate distribution,followed by random distribution and least distribution.With the increase of the recovery period,the main plant population pattern of the enclosed and horizontal ditch is finally aggregated,however,part of the population pattern of the fish scale pit is finally aggregated.The aggregation intensity of dominant plant populations showed fish-scale pits>enclosure>contour trench measures.(6)Inter-species rejection is more common than attraction under the three measures.The interspecific rejection under the enclosure is stronger than that of the contour trench and fish-scale pits,but the attraction between species is on the contrary.(7)Three restoration measures promoted the widening of the niche of Stipa bungeana and Thymus mongolicus with the recovery years,whereas enclosure and fish-scale pits inhibited the broadening of the niche of Potentilla bifurca.The niche overlap coefficient of Stipa bungeana,Thymus mongolicus and Potentilla bifurca showed fish-scale pits>contour trench>enclosure.Studies revealed that enclosure is more conducive to the increase in perennial herb species,vegetation cover and above-ground biomass while contour trench and the fish-scale pits are more conducive to increased species diversity.Whereas long-term enclosure will reduce species diversity.Therefore,it is necessary to select recovery measures scientifically and reasonably according to local conditions.