Revegetation For Side Slope Protection Of West Section Of Shanghai-Chengdu Freeway In Hubei Province

Selection of adapted plants set the base of revegetation.Plants' adaptation ability for slope protection,degree and mode of revegetation,community quality and soil erosion correlation during revegetation process were studied,based upon which revegetation techniques were summarized.Main conclusions are as follows:1.Screening of plants for slope protectionNineteen woody plants and eight herbaceous plants were studied for their early competition ability,adverse environmental stress hardness and growth potential,and were classified based upon hierarchical cluster analyze and subordinate function value.The experimental plants can be classified into five categories:Indigofera pseudotinctoria and Solanum deflexicarpum have the best performance;Desmodium sinuatum,Cynodon dactylon,Melia azedarach,Robinia pseudoacacia,Lespedeza cunecta,Vitex negundo, Paspalum notatum rank the second;Festuca arundinacea,Eragrostis curvula,Cudrania tricuspidata,Rhus chinensis,Dodonaea viscosa,Senna obtusifolia,Rhamnus utilis, Ailanthus altissima,Lotus corniculatus rank the third;Pterocarya kunth,Kummerrowia stipulacea,Sapiu sebiferum,Eremochloa ophiuroides,Trifolium repens rank the forth; Pinus massoniana Lamb rank the poorest.2.Revegetation techniques for slope protectionHerbaceous and woody plants competition characteristics and predominance of established species were studied,the results show woody vegetation can be established taking use of the difference of growth habit,and the gap among woody plants set a main factor to affect competition balance.The balance between species with close growth habit are prone to achieved,such as the balance between Solanum deflexicarpum and Vitex negundo, lndigofera pseudotinctorea and Vitex negundo,Lespedeza cunecta and Solanum deflexicarpum, while mixture with wide gaps of growth habit tend to form single predominance species. Mixture of herbaceous and woody species has better performance than that of common herbaceous mixture in 3a.Artificially revegetation has much fewer species,less abundant biodiversity and lower level soil organic matter compared With natural vegetation. Regulation of competition between herb and wood,mixture mode selection,and temporal and spacial alternation growing methods were advised to establish woody plants.Tree types of side slope of highway including hard rocky type,soft rocky type,earth or earth-stony type were identified and corresponding slope protection and revegetation design were carried out,among which vertical landscaping techniques including ladder like hollow brick landscaping,L-shape concave growing for the masonry retaining wall face-landscaping and drilling hole for growth on hard rocky slope were the first practice domestically and lead to early success.3.Effect of revegetation on side slope soil erosion controlRevegetation degree,mode and quality and it's coupling effect with precipitation were studied and results indicated that both revegetation and protection practice of previous vegetation contribute to soil preservation,the degree of revegetation have a positive effect on soil preservation.Well revegetated slope has the least amount of soil loss with 13.8 t/km~2 in rain season.Soil loss amount of early stage of comprehensive slope,poorly and naturally reestablished slope,and simple reestablished slope were individually 75.9%, 27.4%and 23.9%of the rate of bare slope.Soil loss for bare slope can reach 20684.5 t/km~2 in rain season.Soil loss of barren slope and that of simple revegetated slope correlated with precipitation significantly,while well revegetated slope performed insignificantly.Artifial soil slide is the main performance for hard rocky slope and can lead to the failure of revegetation.Different revegetating measures of plants mixture differed in their soil erosion under the precipitation condition of experiment area with an amount of 15406—17926 t/km~2 in rain season.Fast adapted mixture and pioneered mixture of herbaceous and woody plants have the best performance,which including Festuca arundinacea + Festuca rubra + Indigofera pseudotinctorea + Lespedeza cunecta + Alnus cremastogyne Burk + Robinia pseudoacacia,Festuca arundinacea + Festuca rubra + Cajanus cajan + Tephrosia candida +Crotaria assamica,Indigofera pseudotinctorea and Robinia pseudoacacia in the former mixture are idea mode for the area;mixture of Festuca arundinacea + Festuca rubra + Lespedeza cunecta + Indigofera pseudotinctorea + Amorpha fruticosa has the largest soil loss amount than other mixture.Above ground biomass related significantly with soil loss, other than coverage,plants density and other indices.Mixture with fast above ground biomass accumulation should be taken into account for better revegetation.