Structural Characteristics And Restoration Technologies Of Typical Forest Communities In A Suburban Area In Nanjing City

In this paper, the author has investigated species composition and structurecharacteristics of present typical forest communities both in Qixia and Mufu ScenicAreas of Nanjing city. Meanwhile, the resistance of Cinnamomum, Ligustrumlucidum Air., Pittosporum tobria to Al³⁺ stress and the resistance of Cinnamomumlongepaniculatum, Michelia platypetala, Manglietia chingii, Michelia foveolata toheavy metals, such as Pb and Cd have also been studied by means of experimentalmethodology. Some suggestions were given about the selection of appropriate treespecies for the purpose of vegetation restoration and about ways and techniquesfittable for forest restoration in these two areas. Main research results andconclusions were described as follows:(1)Forest communities could be classified into four types, including coniferforest, deciduous broadleaved forest, conifer and broadleaved mixed forest andshrub forest. There exist two main types of conifer forest such as Chinese-fir andforest and Masson pine forest. Deciduous and broadleaved forest include Tiliahenryana forest,Water wax gourd forest, Quercus veriabilis forest, Firmiana simplexforest and Liquidamber formosana forest;the typical conifer and broadleaved forestwas Masson pine+ Pistasia chinensis+L.formosana forest, there were two main kindsof shrub forest like Phyllostachys nidularia forest and Brachystachyum densiflorumforest.(2)According to the composition, disturbance grade and restoration objectivesfof different types of plant communities in Qixia Mount Scenic Area, the authorsuggested three ways for the vegetation restoration, including natural regeneration,artificially-promoting regeneration and tree-planting respectively.(3)The results indicated that the secondary forests in Mufu mount scenic areawas composed of less tree species with small DBH and lower regeneration process.In vertical structure, the number of trees of main species like Broussonetiapapyrifera and Robinia pseudoacacia increased definitely from lower canopy layerto higher layer. This presented nice succession abilities of such plant communities.Human disturbance and environmental pollution could cause the increase of thedominance Broussonetia papyrifera and decrease of species diversity and theninfluenced the ecological function of forest stands.(4)The mortality rates of three species like Cinnamomum, Ligustrum lucidum Ait.,Pittosporum tobria all increased with the increase of Al concentration. Among them,P. tobria presented the lowest resistance ability to Al stress. The root biomass of Pittosporum tobria decreased definitely when the concentration of Al≥2mmol/L,but there existed no significant variation of stem biomass among various Alconcentrations. The leaf biomass significantly decreased when the concentration ofAl was≥4mmol/L compared with lower Al concentration and CK. Both root andleaf biomass of Ligustrum lucidum Ait. decreased rapidly when Al concentration was≥2mmol/L while the stem biomass significantly decreased when the concentrationof Al was≥8mmol/L compared with those of lower concentration and CK.(5)Both the root and stem biomass of Cinnamomum decreased denfintely whenthe concentration of Al was≥1mmol/L while the leaf biomass significantlydecreased when the concentration of Al was≥8mmol/L compared with lowerconcentration and CK.The root/stem ratio and leaf biomass of the three tree speciessignificantly decreased when the concentration of Al was≥4mmol/L comparedwith lower concentration and CK. It was suggested that the stress of Al³⁺ to belowground was greater than aboveground when the concentration of Al³⁺ was≥4mmol/L.(6)The concentrations of Al³⁺ in all Al³⁺ treatments were greater than that of CKin terms of root, stem and leaf at different periods; The concentration of alltreatments of three species increased with the time extended. The concentrations ofAl³⁺ in the root and leaf of Ligustrum lucidum were higher than that of theCinnamomum and Pittosporum tobria and the stem concentration were higher thanthat of the Cinnamomum. It was concluded that the ability of resistance of Al³⁺ ofLigustrum lucidum Ait. was greater than those of Cinnamomum and Pittosporumtobria.The concentrations of Al³⁺ in root, stem and leaf increased with the increasingof the Al³⁺ stress, the concentrations could be ranked as root＞stem＞leaf. Theconcentration of the three species could be ranked as: Cinnamomum＞Ligustrumlucidum Air.＞Pittosporum tobria after 9 months treatment. There was existedexponential relationship between the concentration of root and stem in Pittosporumtobria was while that of the Cinnamomum and Ligustrum lucidum and significantlypositive linear relationship. The Al concentrations in roots and leaves of all threespecies showed significantly positive linear relationship.The values of Ca/Al andMg/Al in root, stem and leaf increased with the increase of Al concentrations.(7)The contents of chlorophyll in Ligustrum lucidum Ait. and Pittosporum tobriawere lower than those of the CK value under the stress of Al except for the0.5mmol/L treatment while the contents of chlorophyll in Cinnamomum was lowerthan those of the CK. The susceptivity of the chlorophyll to Al could be ranked asCinnamomum＞Pittosporum tobria＞Ligustrum lucidum Ait.. The contents of thechlorophyll in three species presented significant linear relationship with theconcentrations of Al in leaves, Ca/Al and Mg/Al ratios under the stress of Al.The cell membrane permeability of the three species increased with the increasing of theAl concentrations and showed significant linear relationship with the concentrationof Al in leaves.The cell membrane permeabilities of Cinnamomum and Pittosporumtobria were more frangible than those of Ligustrum lucidum Ait..(8)Based on the integrated assessment of electric conductivity and chlorophyllcontent and so forth, the resistance capacity of of four tree species to Pb stress couldbe in order: Cinnamomum longepaniculatum＞Michelia platypetala＞Manglietiachingii＞Michelia foveolata;Meanwhile, the resistance capacity of four tree speciesto Cd stress could be in order:Cinnamomum longepaniculatum＞Micheliaplatypetala＞Michelia foveolata＞Manglietia chingii.(9)Among various types of vegetation restoration in the Mufu mount scenic area,Alnus eremastogyne+Pittosporum tobira plantation presented better ecologicalresults than other plantations.