On Applying Garden Plants To Replace Weeds In City

Alien weeds have became an important element of Chinese weed lfora, and havecaused a serious harm to ecological and economic environments in China. The urbanenvironment is an important area of weed invasion. Shanghai is the largest coastaldevelopmental city in China, with a rich exotic weed flora. There are several usefulmethods to prevent weeds rfom spreading, which include physical control，chemicalprevention, biological control and replacement control. In consideration of thecharacteristics of the social and ecological environment, the replacement control ofalien weeds by using indigenous garden plants can make up the defects of othermethods. Additionally, applying indigenous garden plants to control alien weeds canalso increase species diversity, enhance sense beauty, ecology beauty and culturebeauty of the city.The present paper conducted a research in relation to population and communityecology，invasion biology, plant morphology, plant taxonomy and other aspects. Inorder to provide a replacement control strategy by using indigenous plants to preventweeds rfom city garden landscape，the paper investigated the spring and autumnweeds in campuses and gardens in Shanghai, Based on the data of weed ecologicalimportant values and damage values, the relationships of weeds with theirenvironments were quantitatively analyzed by using Detrended CanonicalCorrespondence Analysis. The demonstration area was built to show to apply gardenplants to control alien invasive weeds in the suburb of Shanghai. The main results areas follows:(1) A total of207random sites on different ecological conditions rfom eightdistricts of Shanghai (including Jing-an，Lu-wan，Huang-pu, Pu-dong，Bao-shan,Xu-hui, Qing-pu and Song-jiang district) were surveyed for flora and ecological study of weeds in spring and autumn, respectively. The results showed:①94weed species belonging to77genera and44families were identified from108random spring sites. While95weed species belonging to77genera and35families were found from99random autumn sites.②Among the125weed species,22weed species belong to two families, Gramineae and Compositae, accounting for35.20%of the total weed species.③58.40%weed species are annual and biennial herbs.(2) A total of37alien weed species were recorded from207sites, which account for29.60%weed species. Most of the alien weed species originated from America (20species), the others from Europe (11species), Asia (5species), Africa (1species).24alien species were introduced accidentally. Others were introduced as grass, vegetables, or ornamental plants deliberately.(3) There are several species of higher frequency, which are Poa annua, Digitaria sanguinalis, Stellaria media, Erigeron philadelphicus, Oxalis pes-caprae, Oxalis corymbosa, Alternanthera philoxeroides, Hydrocotyle sibthorpioides, Youngia japonica, Galium spurium, Veronica persica, Cerastium arvense subsp. strictum, Dichondra micrantha.(4) According to their average risk values from high to low, the main spring weed species were ranked as Oxalis corymbosa(2.44), Alternanthera philoxeroides(1,98), Poa annua(1.70), Youngia japonica(1.41), Digitaria sanguinalis(1.30), Galium spurium(1.26), Convolvulus arvensis(1.15), Cynodon dactylon(0.88), Erigeron philadelphicus(0.71), Cyperus rotundus(0.76), Stellaria media(0.69) and Setaria viridis(0.68); while the autumn weeds ranked as Digitaria sanguinalis(1.95), Cayratia japonica(1.42), Alternanthera philoxeroides(1.38), Oxalis corymbosa(0.84). Zoysia tenuifolia(0.80), Youngia japonica(0.70), Convolvulus arvensis(0.70), Acalypha australis(0.53), Amaranthus blitum(0.45), Calystegia hederacea(0.42).(5) Based on weed ecological important values we obtained, the weed communities of gardens were classified by a cluster analysis and an ordination analysis. Among spring weed communities, six major weed communities could be classified, their dominant weed species being Poa annua, Youngia japonica, Galium spurium， Erigeron philadelphicus, Cardamine leucantha, Oxalis corymbosa’respectively. Seven major autumn weed communities were also identified，theirdominant species being Digitaria sanguinalis, Oxalis corymbosa, Oxalis pes-caprae、Alternanthera philoxeroides, Hydrocotyle sibthorpioides, Cayratia japonica,respectively.(6)Based on the ecological importance values of weeds, the environmentalfactors that affect the distribution of weeds were analyzed by using the method ofCCA (Canonical Correspondence Analysis) and the sotfware of Canoco and PC-ORD.The results showed that the distribution of spring weeds depends mainly on the soilmoisture content, traffic, and managerial lever. Whereas there are ifve factorsinlfuencing the distribution of autumn weeds, which are the coverage of the shrublayer, herb layer, and tree layer, the quantity of illumination，and the managerial levelMost of spring weeds and autumn weeds were found in some similar areas. Theseareas were extensively managed, high rfequent traffic, with little soil moisture content,and few seldom plowing. That is to say, gardens with these environmentalcharacteristics are easily invaded by exotic weeds.(7)Our investigation ori the garden weeds showed:①There are few weeds underthe high density shrub communities, such as Buxus megistophylla, Buxus sinica,Photirtia x fraseri, Pyracantha fortuneana, Rhododendron simsii, Piitosporum tobira,Ligustrum vicaryi.②Our comparison of the weed communities in the sites withhorticultural plants of different life forms showed that fewer weeds invaded incommunities composed by ground cover horticultural plants, like Ophiopogonjaponicus, Vinca major, Euonymus for tune i，Trifolium repens，Tmche lospermumjasmmoides. Most weeds in such environments belong to liana plants.③Severalgarden plant species were recommended in the replacement control strategy，whichare Buxus megistophylla, Buxus sinica, Pittosporum tobira, Ligiistrum vicaryi，Mahonia fortune i, Trifolium repens, Ophiopogon japonicus, Vinca major.(8)Peperomia pellucida was found a newly-recorded alien weed for Shanghai.The potential invasive risk of the alien weed species was predicted by using MaxEntand ArcGis based on12biocliinatic variables and its649occurrence records in the world. We found that Peperomia pellucida has a wide range of potential distributionregions including Taiwan, Hong Kong, Guangdong, Guangxi and Hainan. The actualdistribution of P. pellucida is far narrower than its potential range. The species maycontinue to spread. The country was divided into four regions including high risk area(Taiwan, Hongkong, Guangdong, Guangxi and Hainan), moderate risk area (Shanghai,Fujian and Yunnan)，low risk area (Zhejiang，Hubei, Jiangsu, Anhui, Jiangxi, Tibet,Hunan and Guizhou) and non-suitable area (Inner Mongolia, Beijing, Jilin, Tianjin，Ningxia, Shandong, Shanxi，Xinjiang, Hebei, Henan, Gansu，Liaoning，Chongqing,Shanxi and Qinghai).(9) Atfer a comprehensive comparison of weed replacement control indemonstration area, we found:①Trifoliim repens community was able to effectivelycontrol exotic weeds.②The cost by using Trifolium repens as a replacement plant tocontrol alien weed was significantly lower than other garden plants,③Trfioliumrepens, Buxus megistophylla, Ophiopogon japonicus, and Vinca major wererecommended as replacement plants to control alien weeds in Shanghai.