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UrbanVegetation_Gaoming.indd Page 398 12/26/11 7:00 PM user-f494 /203/BER00002/Enc82404_disk1of1/933782404/Enc82404_pagefiles Urban Vegetation Urban vegetation includes all types of plant life found in city environments, from preexisting native species to those introduced to improve landscapes. It is found in urban forests and parks, along roadsides, around ponds and streams, and even in vacant lots. Properly managed urban vegetation can help reduce air pollution, noise, and dust, and add oxygen and visual appeal to otherwise bland cityscapes. major component of seminatural vegetation in cities is the anthropochory community (comprising companion plants), which relies closely on anthropogenic (human) interference under urban habitats and plays a special role in composing urban vegetation, mainly grasses (Jiang 1989). Introduced plants can be categorized into roadside trees, urban forests, parks, gardens, street greenbelts, and so on. U Function rban vegetation refers to all types of plants that grow in urban environments, such as forests, parks, roadsides, and wasteland areas (Jiang 1993). As a significant part of urban ecosystems, urban vegetation can not only help clean and freshen air quality by reducing dust and environment pollution, but it can also help maintain the ecological balance of urban environments. Urban vegetation also plays an important role in indicating and monitoring environmental pollution. Categories Researchers have different ways of categorizing urban vegetation. Some classify it as urban forest, parks and green spaces, gardens and lawns, wall or roof plants, and wetlands (Guntenspergen 1998); others identify roadside trees, greenbelts in streets, green areas in parks, grasslands, and aquatic green spaces (Huang et al. 1990). More simply, some have divided urban vegetation into three types: relict (or remnant) natural communities retained as they were before urbanization, weed communities occupying new urban habitats, and artificial green spaces (Ohsawa and Da 1988). Another way of looking at urban vegetation is according to its three main types: natural plants, seminatural plants, and introduced plants. Natural plants are those that existed before city construction. The Urban vegetation has multiple functions. The main role, however, is to help maintain the urban environment, which is easily affected by all kinds of pollutants, thereby improving human living conditions. For instance, urban vegetation can adjust microclimatic conditions, clean up air pollutants, reduce dust, dampen noise, and maintain ecological balance. Urban vegetation can also serve aesthetic and educational purposes. Generally, the function of urban vegetation is closely related to the type, for example, forests, grasses, and/or wetlands. Urban forests improve urban environments more dramatically than other types. For instance, the temperature in urban forests can be roughly 6°C–16°C lower than urban open space on sunny summer days. In a case study in the city of Beijing, the air passing through a fruit-bearing forest 80–100 meters wide reduced the concentration of hydrogen fluoride in the atmosphere 22 percent compared to open space of the same width (Wang 1998). A forest belt 40 meters wide also reduced noise about 10–15 decibels (Wang 1998). Development Along with global urbanization, the distribution of urban vegetation is being further specialized. According to the 398 www.berkshirepublishing.com © 2012 Berkshire Publishing Group, all rights reserved. UrbanVegetation_Gaoming.indd Page 399 12/26/11 7:00 PM user-f494 /203/BER00002/Enc82404_disk1of1/933782404/Enc82404_pagefiles URBAN VEGETATION United Nations Educational, Scientific and Cultural Organization (UNESCO), 60 percent of the world’s population will live in cities by 2030 (Wibly and Perry 2006). On one hand, people tend to change urban habitats into areas of development, which exposes them to human disturbance. Adverse effects such as urban pollution become more and more serious, thus putting the urban vegetation into a state of strong instability. A case study conducted in Chiba City, Japan, showed that from 1952 to 1981 forest coverage declined from 51 percent to 8 percent. Meanwhile, land-use patterns had changed dramatically: farmlands and forests had been turned into residential areas and once-natural hills had been covered with buildings (Ohsawa and Da 1998). Exotic Species On the other hand, various types of urban plant communities appear in cities, such as anthropochory communities and introduced plant communities. Besides, human beings bring numerous exotic species to cities, while they destroy and discard a huge variety of native species. Whether those influences or interferences are conscious or unconscious, direct or indirect, they ultimately alter the natural features of urban vegetation, its composition, structure, and function. As a result, much urban vegetation has completely lost its natural traits (Huang et al. 1990). For instance, urban vegetation depends largely on fertilization, pesticides, and irrigation to live, similar characteristics to crops in agricultural systems. People like to bring exotic plants to cities for various purposes, but they often pay no attention to local dominant species. Such activities can destroy native urban vegetation. Although relict communities can reflect the distribution of zonal vegetation, the dominant species will gradually disappear and be replaced by those that adapt to urban habitats. As a result, the dominant species in urban plant communities are often not obvious (Jiang 1993). People often neglect comprehensive assessments before widely adopting exotic plants, leading to the uncontrolled spread of invasive species. Such a phenomenon is more likely to occur during the process of introducing herbaceous plants. Eichhornia crassipes, or common water hyacinth (native to the Amazon www.berkshirepublishing.com • 399 basin), and Eupatorium adenophorum, a flowering shrub native to Mexico (also called snakeroot), have brought great harm to both urban and rural environments in China (Bao 2008). In the beginning, people may bring in the invasive species for economic purposes (e.g., Eichhornia crassipes was supplied as feed for pigs in the 1950s) or simply to beautify the urban environment (e.g., the ornamental tree Rhus typhina), but they later realize the harmful effects when those species become dominant in new spaces such as urban landscapes. Proposals Since numerous plant species are immigrants to urban habitats, urbanites have become increasingly disconnected from indigenous species and natural ecosystems (McKinney 2006). To counter this, ecological principles should be abided in the selection of urban plants. Increasing awareness of the niche that each species occupies would provide indigenous species a better chance for survival. Choosing and making good use of native species for the greening of urban habitats should be fully considered in the future. There are still many deficiencies in urban greening, such as a decrease of native species, scarcity of plant diversity, and a lack of ecological background features (Bao 2008). A comprehensive investigation of native species and a study of the genetic diversity of dominant species should be conducted. In addition, selection of indigenous species, especially trees, should be emphasized because of their large biomass and ability to provide habitats for birds and other urban creatures. Introduction of exotic species should be appropriately considered. Furthermore, city designers need to conduct environment impact assessments to avoid the malignant spread of invasive species before introducing exotic species into urban settings. JIANG Gaoming and BO Wenjing Chinese Academy of Sciences See also Best Management Practices (BMP); Brownfield Redevelopment; Disturbance; Ecological Restoration; © 2012 Berkshire Publishing Group, all rights reserved. UrbanVegetation_Gaoming.indd Page 400 12/26/11 7:00 PM user-f494 /203/BER00002/Enc82404_disk1of1/933782404/Enc82404_pagefiles 400 • THE BERKSHIRE ENCYCLOPEDIA OF SUSTAINABILITY: ECOSYSTEM MANAGEMENT AND SUSTAINABILITY Ecosystem Services; Invasive Species; Landscape Architecture; Light Pollution and Biological Systems; Nitrogen Saturation; Permaculture; Pollution, Nonpoint Source; Pollution, Point Source; Rain Gardens; Road Ecology; Tree Planting; Urban Agriculture; Urban Forestry FURTHER READING Bao, Mingzhen. (2008). On urban bio-diversity and landscape plants planning in China. Chinese Landscape Architecture, 7, 1–3 [in Chinese]. China Environmental Protection Network. (2009). China’s 283 invasive species cause 200 billion CYN economic losses [in Chinese]. Retrieved August 6, 2011, from, http://w w w.sei.gov.cn/ ShowArticle2008.asp?ArticleID=179267 Guntenspergen, Glenn R. (1998). Introduction: Long-term ecological sustainability of wetlands in urban landscape. In Thomas R. Detwyler & Melvin G. Marcus (Eds.), Urbanization and environment: The physical geography of the city (pp. 229–241). Belmont, CA: Duxbury Press. www.berkshirepublishing.com Huang Xiaoyang; Lin, S. H.; Han, R. Z.; & Yao, Yuqi. (1990). Urban vegetation in Beijing and its function. In Langzhou Chen & H. Y. Zheng (Eds.), Ecological, social and economical designing for BeijingTianjin region (pp. 42–60). Beijing: Ocean Press [in Chinese]. Jiang Gaoming. (1989). Anthropochory in cities. Chinese Bulletin of Botany, 6, 116–120 [in Chinese with English summary]. Jiang Gaoming. (1993). Urban vegetation: Its characteristic, type and function. Chinese Bulletin of Botany, 10, 21–27 [in Chinese with English summary]. McKinney, Michael L. (2006). Urbanization as a major cause of biotic homogenization. Biological Conservation, 127, 247–260. Ohsawa, Masahiko, & Da, Liang-Jun. (Eds.). (1988). Integrated studies in urban ecosystems as the basis of urban planning (III). Chiba, Japan: Chiba University. Stanvliet, R.; Jackson, J.; Davis, G.; De Swardt, C.; Mokhoele, J.; Thom, Q.; & Lane, B. D. (2004). The UNESCO biosphere reserve concept as a tool for urban sustainability: The CUBES Cape Town case study. Annals of the NY Academy of Science, 1023, 80–104. Wibly, Robert L., & Perry, George L. W. (2006). Climate change, biodiversity and the urban environment: A critical review based on London, U.K. Progress in Physical Geography, 30, 73–98. Wang, Bosco Shang. (1998). Urban vegetation and its construction technology. Acta Scientiarum Naturalium Universitatis Sunyatseni, 37, 9–12 [in Chinese with English summary]. © 2012 Berkshire Publishing Group, all rights reserved.