Analysis Of Threshold And Evaluation Of Vegetation Natural Restoration On Steep Slopes Of Loess Area In West Shanxi Province

Vegetation restoration in arid slope in the Loess Plateau has been received extensive attention,vegetation restoration in erosion gully slope above 55 degree is urgently needed to capture by Forestry Ecological Engineering.To fully understand the status and characteristics of vegetation in this type of site,it will be used to guide the development of vegetation restoration strategies.With the application of RS and GIS tools,100 sample plots with different aspects on steep slopes of Caijiachuan in Ji Xian of Shanxi Province were selected as research objects through field investigation.On the basis of division of site types,vegetation community was investigated,species composition and diversity in different habitats of steep slope was analyzed and compared.Using an approach of spatial sequence instead of temporal sequence,establishing natural communities secondary series,combinating site quality evaluation and difficulty degree of vegetion natural restoration of 30 samples,vegetation natural restoration on steep slope was evaluated.And with an average age of the dominant species of wood to build time series,the threshold of vegetation cover,the threshold of trees living stable with shrub and grass,the threshold of tree density were analyzed.Conclusion are as following(1)Steep slope will be divided into 3 groups of site types according to different slopes,the steep slope group(35??45°),dangerously steep slope group(45°?55°)and similarly vertical slope group(>55°).Steep slope group is the biggest share with 76.07 percent,the others were 20.23 percent and 3.70 percent(2)Vegetation coverage and diversity overall decreases with the increase of slope on steep slope above 55 degree,species composition presents some differences.Vegetation cover and diversity of steep slope group and dangerously steep slope group has obvious difference with similarly vertical slope group(p<0.05).Trees and shrubs were balanced on steep slope group and dangerously steep slope group,trees and shrubs in the community has certain advantages,like Populus davidiana,Quercus wutaishansea,Cotinus coggygria,Cotoneaster multiflorus.The proportion of tree species decreased with the increase of slope,drought resistance and light-demanding or low water consumption species became to dominant on similarly vertical slope group,like Ulmus macrocarpa,Rosa xanthina,Wikstroemia chamaedaphne and Artemisia Sp.(3)Comprehensive analysing site factors,difficulty degrees of vegetation natural restoration on steep slope were classified into easy,normal,difficult and extremely difficult degree by analytical hierarchy.Soil Moisture,the content of organic matter and slope were the key factor affecting vegetation restoration in difficult site in the steep slope.The sampling plots with easy and normal degree of natural restoration could be restored by natural restoration,while those with relatively higher difficulty degree should apply the releavant artificial recovery measures to improve vegetation restoration.(4)According to the degree of community restoration degree(RD)and succession of vegetation,recovery process was divided into three stages,they were respectively the early stage,the mid-stage and the late stage.Natural restoration of degraded community was a process in which lower community was replaced by higher one successivel,There were higher restoration speed(RS)but lowest restoration degree CRD)in the early stage;the moderate RD and RS in the mid-stage;the slowest RS and the highest RD in the late stage.The vegetation focused on the regeneration in eraly stage,the community structure adjustment in the mid-stage,and the function coordination or improvement in late stage.The RD above 0.8 could be presented after more then 35 years,but it would take a long time to restore total eommunity function of forest.(5)The natural restoration strategy was different for the three site types,the vegetation community RD was the higuest in the early stage for the steep slope group and dangerously steep slope group,while the vegetation community RD was the higuest in late stage for the similarly vertical slope group.The best community RD has reached 0.8 for the steep slope group and dangerously steep slope group,however,for the similarly vertical slope group,the maximum community RD is ouly 0.5,and the effect of natural vegetation restoration is not obvious(6)Vegetation maximum coverage could reached 95.26 percent on shady slopes and semi-shady slopes for the steep slope below 55 degree,but only 89.74 percent on sunny slopes and semi-sunny slope.The threshold of vegetation cover was 55.35 percent on shady slopes and semi-shady slopes for the similarly vertical slope group,39.04 percent on sunny slopes and semi-sunny slope.45 percent arbor cover was the ecological threshold of trees living most stable with shrub and grass on the steep slope below 55 degrees,the fitness threshold of arbor cover to shrub and grass was 13.05 percent to 81.97 percent on shady slopes and semi-shady slopes,and was 18.22 percent to 73.52 percent on sunny slopes and semi-sunny slope.(7)For the steep slope group and dangerously steep slope group,threshold of tree density was 1343 trees per hectare on shady slopes and semi-shady slopes,that was 810 trees per hectare on sunny slopes and semi-sunny slope.For the similarly vertical slope group,threshold of tree density was 557 trees per hectare on shady slopes and semi-shady slopes,that was 413 trees per hectare on sunny slopes and semi-sunny slope.