Study On Plant Community Characteristics Of Abandoned Cropland In The Loess Plateau Hilly Region Of Northern Shaanxi

In this study,we choose 70 restoration plant communities as the main objects in three typical watersheds in Yan'an City,Shaanxi Province.Through field vegetation surveys and statistical analysis,species composition,species diversity and its influencing factors,functional diversity and spatial pattern of regularity of herbs in different plant communities were analyzed.Simultaneously,the effects of different management modes on niche of dominant populations in grassland was explored.These work can evaluate the adaptation status of returning farmland to community in order to provide scientific basis for the restoration and reconstruction of degraded vegetation in this area.The main conclusions are as follows:1.Analysis of species composition of returning farmland community in Loess Hilly Region of Northern Shaanxi Province.The study area consisted of 28 families,76 genera and 91 species of plants,Asteraceae,Leguminosae,Poaceae dominated.Plant communities in Loess Hilly Region has experienced Artemisia scoparia ? Lespedeza davurica ? Artemisia sacrorum and Stipa bungeana ? Artemisia sacrorum and Lespedeza davurica ?Bothriochloa flaccidum and Artemisia sacrorum.Robinia pseudoacacia,Armeniaca sibirica,Platycladus orientalis,Caragana intermedia can promote plant community succession in research area.The important value of plant species in different plant communities with different site conditions was difference.2.Study on species diversity of plant communities in Loess Hilly Region of Northern Shaanxi ProvinceWith restoration age rising,the total species number,Margalef richness index,Shannon-Wiener diversity index and Pielou evenness index at grassland presented the trend of increasing firstly,then decreasing.The highest value was observed in 20 a and Simpson diversity index was opposite.The total species number,Margalef richness index,Shannon-Wiener diversity index and Pielou evenness index of plant communities were much bigger under the site conditions of shady slope,downhill,boaom of trench,6~15 degrees of slope and 16~25 degrees of slope.Simpson diversity index was much bigger under the site conditions of sunny slope,mountaintop,36~45 degrees of slope and 0~5 degrees of slope.The value of Total species number,Margalef richness index,Shannon-Wiener diversity index and Pielou evenness index in these communities of Robinia pseudoacacia,Platycladus orientalis,Armeniaca sibirica,Caragana intermedia were greater than other communities.Simpson diversity index was largest in Pinus tabuliformis community.Correlation analysis showed that precipitation,illumination and physical and chemical properties of soil in different regions should be synthetically considered in the process of farmland.3.Study on functional diversity of plant communities in Loess Hilly Region of Northern Shaanxi ProvinceThe community who take the largest function richness index and function evenness index is the plant community regenerated for 20 years,and maximum functional divergence index value appeared in the plant community regenerated for 13 years.The function richness index and function evenness index of plantations in shady slope are significantly higher than these vegetation communities in sunny slope,but functional divergence index is inverse.The function richness index and function evenness index of plantations in bottom of trench and down-slope are significantly higher than these vegetation communities in middle-hill,uphill and mountaintop.The functional divergence index is biggest in mountaintop and minimal in groove.With slope gradient rising,the functional diversity index at communities presented the trend of increasing firstly,then decreasing.The highest value was observed in 15~20 degrees of slope.The functional diversity index of Robinia pseudoacacia,Armeniaca sibirica,Platycladus orientalis,Caragana intermedia and Hippophae rhamnoides were larger than other plant communities.The researche of functional diversity index show that Robinia pseudoacacia,Armeniaca sibirica,Platycladus orientalis,Caragana intermedia and Hippophae rhamnoides should be widely planted in Loess Hilly Region.Large area vegetation restoration can be implemented under the site conditions of shady slope,half-shaded slopes,downhill,bottom of trench,and 15~20 degrees of slope in the study area.In order to restore vegetation,the species appropriate to the environment should be selected in other site conditions.4.Analysis of plant communities spatial pattern in Loess Hilly Region of Northern Shaanxi ProvinceResults showed that distributing of plant species in the abandoned farmland followed the power law accurately in Loess Hilly Region of Northern Shaanxi Province.Plant communities in abandoned farmland were stronger aggregated distribution pattern than in the random distribution.With restoration age rising,the spatial heterogeneity index value in the grassland presented the trend of increasing firstly,then decreasing.The highest value was observed in 20 a.The spatial heterogeneity index value of communities in shady slope are significantly higher than these vegetation communities in sunny slope.The spatial heterogeneity index value of communities in bottom of trench and down-slope are significantly higher than these vegetation communities in middle-hill,uphill and mountaintop.With slope gradient rising,the spatial heterogeneity index value in the plant communities presented the trend of increasing firstly,then decreasing.The highest value was observed in 16~25 degrees of slope.The spatial heterogeneity index value of herbaceous layer under Caragana intermedia,Platycladus orientalis,Armeniaca sibirica and Robinia pseudoacacia were greater.This indicated that these species can be widely planted in Loess Hilly Region of Northern Shaanxi Province.The community spatial distribution pattern of abandoned farmland mainly decides by dominant species,sub-dominant species and rare species.5.Niche characteristics of dominant plant populations in grassland of loess hilly region of China with different management stylesThe results showed that,The niche breadths of Lespedeza davurica,Artemisia sacrorum,Leymus secalinus,Artemisia scoparia and Poa sphondylodes which appeared in five treatments of the grasslands were larger than other species at YangQingChuang valley.The number of species which had the niche breadth value greater than four in enclosure,lightly grazing,fertilization,clipping and deratization were seven,six,three,three and three respectively.The order of niche overlap was as follows: enclosure> lightly grazing> fertilization> clipping> deratization.In addition,the results demonstrated that there had no linear relationship between the niche overlap and niche breadth of tested species in the grasslands at four management styles except fertilization.Niche analysis indicated that the enclosure and lightly grazing management styles can facilitate the community succession.On the other hand,fertilization,clipping and deratization management styles had negative effects on vegetation restoration.From the perspective of forages development,enclosure,fertilization and clipping management styles,are advantageous to superior forage grass progress.In summary,The analysis result of species composition,species diversity,functional diversity and spatial pattern indicated that planting Robinia pseudoacacia,Armeniaca sibirica,Platycladus orientalis and Caragana intermedia can facilitate the community succession.Pinus tabuliformis and Malus domestica community made community structure be briefness and single,which had negative effects of vegetation restoration.Robinia pseudoacacia,Artemisia sacrorum,Lespedeza davurica,Artemisia giraldii and other drought-resistant species were suitable growth in sunny slope,Armeniaca sibirica,Platycladus orientalis,Rosa multiflora and Indian strawberry were suitable growth in shady slope.Artemisia scoparia,Artemisia sacrorum and Phragmites australis were suitable growth on the top of hilly.Robinia pseudoacacia,Armeniaca sibirica and Platycladus orientalis were suitable growth on middle slope and upper slope.Caragana intermedia and Hippophae rhamnoides were suitable growth on downhill and the range of 36~45 degrees of slope.Artemisia sacrorum,Artemisia scoparia,Stipa bungeana,Phragmites australis and other herb were suitable growth within the range of 0 ~ 5 degrees of slope.Robinia pseudoacacia,Armeniaca sibirica,Platycladus orientalis and other arbor were suitable growth within the range of 6~15 degrees and 16~25 degrees of slope.Armeniaca sibirica,Caragana intermedia and Hippophae rhamnoides were suitable growth within the range of 26~35 degrees of slope.Large area vegetation restoration can be implemented under the site conditions of shady slope,half-shaded slopes,downhill,bottom of trench,and 15~20 degrees of slope in the study area.In order to restore vegetation,the species appropriate to the environment should be selected in other site conditions.Enclosure,fertilization and clipping management styles are advantageous to the recovery of grassland community,which can be widely used to restore grassland vegetation in this area.