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(2011-06-29 19:56:33)


  The Evolution of Greenway as an Adaptive Landscape Form 适应性景观形态——绿道的演变

  Greenways, sometimes referred to as environmental corridors, landscape linkages, wildlife corridors, or riparian buffers, provide an important way both to protect natural areas and to provide recreation opportunities. The term greenway es form the “green” in green belt and the “way” in parkway, implying a recreational or pedestrian use rather than a typical street corridor, as well as an emphasis on introducing or maintaining vegetation, in a location where such vegetation is otherwise lacking, They also tend to have a mostly contiguous pathway, allowing urban muting via bicycle or foot.


  Little, in his landmark book, Greenways for America, gave a prehensive definition to greenway—a linear open space established along either a natural corridor, such as riverfront, steam valley, or ridgeline, or overland along a railroad right-to-way converted to recreational use, a canal, a scenic road, or other route. He classified greenways into five general types: (1) urban riverside-waterfront greenways; (2) recreational greenways; (3) ecologically significant natural corridors; (4) scenic and historic routes; (5) prehensive greenway systems or works.


  Greenways contribute to many ecological and societal values. They help maintain biological diversity, protect water resources, conserve soils, support recreation, enhance munity and cultural cohesion, and provide species migration routes during climate or seasonal change. Greenways can be used to create interconnected works of open space that may include more traditional non-linear parks and natural areas. They can help to maintain ecological integrity in human-dominated landscapes, especially with regard to sustaining high-quality water reserves and preserving biological diversity. In addition to habitat protection and water quality, greenways are pursuing other objectives, including historic preservation using greenways to highlight area culture and heritage.


  In tracing the evolution of greenways, three distinct stages or “generations” can be identified. These are:


  Generation 1 greenways (pre-1700s-circa 1960). These are the axes, boulevards and parkways that first linked urban spaces—the “ancestral” greenways.


  Generation 2 greenways (circa 1960-circa 1985). These are trail-oriented, primarily recreational, greenways and linear parks that provide access to rivers, streams, ridgelines, railbeds and other corridors within the urban fabric. An important emphasis of most of these greenways is non-motorized travel.


  Generation 3 greenways (circa 1985 onward). These are the emerging “multi-objective” greenways that address needs of wildlife, flood damage reduction, water quality, historic preservation, education and other infrastructure needs in addition to urban beautification and recreation.


  The first generation of greenways were not called “greenways” as such, but they did provide the archetype for special, attractive, corridors weaving their way through the city. These were the landscaped axes and boulevards of Europe and later the parkways of the late nieenth century USA.


  Axes have many important functions and varied themes. As a minimum, axes have three functions: movement, use, and vision-experience. Axes, once introduced, bee a dominant landscape feature. They provide linkage of key features of destination points. The experience of traveling along the axis is as important—if not more important—as the movement and use functions. Modern greenways share these important characteristics as well.


  The first generation of greenways grew out of the axis concept. They evolved from more formal and ceremonial routes of movement into corridors that tried to reintroduce nature into the city.


  In the 1960s, Olmstead, inspired by the European boulevards, proposed linking the College of California at Berkeley to the City of Oakland and the nearby hills with a landscaped “pleasure drive”. The idea included setting aside the Strawberry Creek Valley as a linear park. One important function of his parkways was to prepare visitors approaching a great park-to put them in the mood for the experience to e. Most of the parkway systems planned by Olmstead, however, were also transportation routes—for horse and carriage in Olmstead’s time, and later for automobiles.


  The second generation of greenway is characterized by trail-oriented and non-motorized travel. In the second half of the twentieth century, as the automobile assumed almost total domination of North American cities, bicycles, pedestrians and equestrians sought escape from the noise and fumes. They wanted new non-motorized routes of travel. This was not always easy to achieve, especially in built-up areas where few traffic-free corridors remained.


  In the late 1960s William H. Whyte, reacting to this need to escape automobile, may have been the first person to coin the word “greenway”. In his book, The Last Landscape, he wrote: “There are all sorts of opportunities to link separated spaces together, and while plenty of money is needed to do it, ingenuity can acplish a great deal. Our metropolitan areas are crisscrossed with connective strips. Many are no longer in use…but they are there if we only look”.

  二十世纪六十年代末,‎威廉H •怀特回应远离机动车的需求,应当是第一http://www.shuizher.cn个使用“绿道”一词的人。在著作《最后的景观》中,他写道:“有很多机会连接分离的空间,这需要大量金钱,巧妙安排可以完成其中很大一部分。http://www.shuizher.cn/blog我们的都市地区交错连接的狭长土地,很多已经不再使用…但是我们仍然可以看到它们的存在”。

  Whereas many urban greenway corridors follow waterways including rivers, streams, shorelines, and canals, another type of corridor came on the sceneabandoned railroads. Like drainage ways and canals, railroad corridors offer pre-established swaths through the landscape. The grades are gentle and, like drainages, the routes often go under or over barriers such as highways, creeks, steep hills or other obstructions. The track corridor provides the “way” and the adjacent undeveloped, vegetated, strips of railroad ownership provide the “green”.


  In the 1960s with modes of travel shifting from track to truck, many lines were abandoned. Thus, the Rails-to-Trails movement began. Inspired by the Illinois Prairie Path and, later, Seattle’s Burke Gilman Trail, there are now thousands of miles of rail trails (Rails to Trails Conservancy, 1990) and dedicated advocates and anizations like the National Rails to Trails Conservancy.


  More recently, greenways are also appeared along gas, water and electrical utility routes. In Florida, three utility panies were contemplated a 515 mile trail system on top of a natural gas pipeline work. A smaller, similar system was built in New Jersey and Delaware connecting nine state parks and wildlife refuges. With thousands of miles of gas pipeline laid each year, as well as equally extensive electric corridors, there could be thousands of new potential trail and greenway corridors.


  In the 1980s two factors tended to change this trail standard somewhat. One was the growing popularity of urban trails, which led to crowing and user conflicts, especially among cyclists, walkers, in-line skaters and equestrians. A wider trail tread of 10 ft to as much as 16 ft was adopted and, in some places, several parallel trail treads were specified with separate lanes for each type of user. The other major factor of change was the advent of the “fat tire” or mountain bike during the 1980s. This type of bike, and related “all-track” (on-street-off-street) bikes, vastly expanded the range of acceptable bike trail systems and greenways were being built unpaved or with more naturalappearing crushed stone su***ces.


  A mon feature of Generation 1 and Generation 2 greenways is that they are primarily amenity oriented. That is, they were developed to address esthetic and recreational needs of city dwellers-beautified axes and corridors as well as non-motorized routes of movement.


  Indeed, they were an adaptive response, a way to offset and mitigate the effects of crowing, automobile fumes, noise, and other ills of urbanization. Although Generation 3 greenways also serve this mitigating function, they have a significantly broader mission. These new greenways pursue multiple objectives such as habitat protection, flood hazard reduction, water quality, historic preservation, education, interpretation, and other purposes.


  Greenways are now seen by many as more than amenities for beautification and recreation. They can also help sustain threatened ecosystems. It should be noted, however, that as these concepts were being formulated, warning flags were going up. Some scientists, including Simberloff and Cox raised concerns that although corridors may offer wildlife benefits, not enough is known about the potential drawbacks such as transmission of disease, fires, and exposure of wildlife to domestic animals and poachers. Others warned that wildlife corridors are not a panacea. Along with greenways that link places, “interior habitat” is still needed, and it is important that the pursuit of greenways not divert attention and resources from saving this kind of habitat as well.


  In addition to habitat protection and water quality, Generation 3greenways are pursuing other objectives, including historic preservation using greenways to highlight area culture and heritage. Rivers, streams, canals, rail lines, and roads often played key roles in the settlement and development of cities, regions, states and nations. In the USA, a number of munities have been working on greenways with historic themes. On the Schuylkill River in Pennsylvania, planners are saving old tunnels, canals, aqueducts and other artifacts as well as working to protect environmental features. They are developing interpretive programs to present the corridor’s heritage in terms its role in industry and transportation, as well as political and social history. The program is striving to have the greenway link together past, present and future as well as geographic points along the corridor.


  Generation 3 greenways also have an educational role. Anne Lusk, champion of the Stowe, VT, trail and a greenway activist, has suggested that greenways and schools make useful partners. She sees greenways as the ideal outdoor classrooms, and suggested that more schools be developed adjacent to greenway corridors and that school children adopt segments of urban greenways that they can care for, learn from, and help, protect. A number of schools have already pursued this kind of policy. In Boulder, CO, a school has nurtured its own wetland and students continually work in this outdoor laboratory and classroom. Numerous similar projects are appearing with multiple benefits.


  Today’s interest in greenways is the current state of a long-term human endeavor—to have an esthetic counter-balance to urbanization. Greenways are here to stay, and the movement draws strength from the fact that greenways reflect an adaptive response to very basic human needs.




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