Trees History
-Trees are the most visible and tangible form of nature in the city. Their physical size makes them apparent from near and far, their geographical location is not carefully prescribed. They add much to the perceived and physical quality of the urban environment.
- In the 17th century, Baroque gardens of France used them to line road or pathways, which developed to become an influence in 18th century town design. Haussmann used them to line his boulevards in the 19th century, and London employed trees around 1800 in their city squares and parks, which were being laid out as flowing patterns of trees and lawns.
-French Baroque gardens: long, straight, tree-lined roadways or pathways, frequently radial in pattern. They provided owner a clear field of view for hunting while his beaters worked their way through the woods. The design had strong influence on 18th C town design, was pattern for what was envisioned to be the ideal street layout. Hausmann designed wide, tree-lined boulevards to cut through Paris in the 1860s, in order to “disencumber the larger buildings, palaces and barracks in such a way as to make them more pleasing to the eye, afford easier access on days of celebration, and a simplified defence of days of riot”.
-Trees began to appear in London around the 1800 when the city squares and Regents Park were being laid out in flowing patterns of trees and lawns. By the middle of the century, the image of these primarily residential squares was one of trees and grass. The adulation of nature was so strong in England at that time that people felt almost a moral obligation to plant every free area.
-Development in American cities grew out of the French and English examples. The Baroque tree-lined boulevard, which was adopted as the design concept for Washington D.C., was also a primary feature of the numerous urban beautification programs proposed for American cities in the early 20th Century. Paris became the model for Chicago and San Francisco, and for the redesign of Washington D.C., St Louis, Detroit, Los Angeles and Minneapolis amongst others. The main features of these ‘city beautification plans’, in addition to the tree-lined boulevards, were landscape parks, parkways and civic centres. The Baroque primarily influenced city greenery, whilst the Romantic landscape movement was seen in the urban fringe and the urban parks. Suburbs were designed to capture what was the spirit of the natural landscape. Gently curving streets were threaded through wooded, rolling hills. When not wooded, trees were added immediately, and in abundance, to stimulate natural woodland. This ‘natural effect’ was an essential ingredient of the Romantic landscape. The trees tended to ‘visually absorb’ the activities and structures of man. They provided a major element of contrast in the city, which at the time was becoming more and more industrialised in image.
Uses of tree in urban design
-To direct people towards a view of particular significance, or to direct movement. Dense, low-branching trees closely planted can be used to direct pedestrian traffic away from service roads and other traffic areas of potential danger. The use of trees of different heights for street plantings can also be used a visual clues to alert the motorist to changes in the characteristics of streets and related traffic patterns.
-To act as unifying and ordering element. They can serve as a visually consistent element in areas which might otherwise be perceived as chaotic or disorderly because of widely divergent building styles and scales.
-Trees can be used as walls and screens for undesirable views and sounds. To separate incompatible land uses, ie. highways and housing.
-Trees as elements of contrast within architectural or structural environments of steel,brick, wood and concrete.
Environmental values of trees in the city
a)improving soil conditions
trees prevent the erosion of upper horizon of urban soil profiles. Roots form fibrous masses that prevent the soil form washing away. Leaf litter on the surface increase the organic content. Trees help control wind erosion. Trees canopies help retain soil moisture by protecting soil from direct exposure to wind and sun.
b)improving urban hydrology
In heavily urbanized watershed, the process of evaporation and transpiration may be altered. Paving and rooftops lessen the infiltration of water into soil. Vegetation is not as dense, resulting in smaller discharges into the atmosphere through transpiration. Consequently, the amount of water running off across the surface of the land increases. Increased surface flows often result in localized urban flooding. These conditions may be reduced by routing storm water into forested areas of cities to take advantage of the high infiltration capacity of forest soils or by planting trees in undeveloped areas to reduce surface run off. Contemporary society has discovered that encouraging wildlife in the city can produce several benefits.
c)Increasing quantity and diversity of urban wildlife
Certain wildlife species that prey naturally upon insects can be an important component in the biological management of pests. Fluctuations in species population may serve as early warning systems to adverse environmental changes affecting human health. Wildlife need four basic elements to survive: water, food, cover for protection from natural enemies and the elements, and area where they can reproduce and bear their young in safety. Trees can provide three of these basic requirements, and evergreen trees provide year-round cover to escape predators and the elements.
d) Reducing the extreme urban microclimates
Street level urban microclimates can be divided into three separate broad classes: areas with extensive evaporating or transpiring surfaces (parks); wide treeless areas that are exposed to the sky but are very dry (parking lots); and narrow streets and courtyards surrounded by relatively tall buildings. A study by Kratzer on Vienna (1956) found that treeless areas are hot at noon but cool in the evenings; the heavily planted areas are generally cooler and have less diurnal temperature variation; the narrow streets are significantly cooler at noon but do not vary in temperature from the other microclimates at night. Trees can be used to moderate sun, wind, precipitation/humidity and air temperature. The buildings and streets that comprise much of the urban environment are constructed of materials that have highly reflective surfaces. Asphalt, brick and concrete will reflect between 15 and 50 percent of the radiation that they receive. Trees cn intercept this radiation if they are planted close to the reflective surfaces. Trees with darker foliage are more effective in reducing surface reflection.
Management of trees in the city
Whilst trees provide many beneficial qualities to the urban city, it is necessary that they are carefully managed. Some of the liabilities of trees in cities include: the costs of planting, maintaining and removing trees; the safety hazard of falling limbs; the shielding of night crime; potential excessive shadowing of houses, the destruction of utilities, sidewalks, curbs and other man-made feature by tree roots.
A holistic approach to establishing management policies would be best handled by tree commissions composed of interests representing all facets of a community. Issues covered should be: control of tree planting, maintainance and removal; autonomy for financial and policy matters; a tree commission to advise on policy; financing on a continual city budget item; and public relations to promote the environmental, social and economical values of trees in the city.
Environmental stresses on urban trees
Physical conditions in the city create extremely harsh growing conditions. Buildings reflect heat, and at the same time channel winter winds causing extreme temperature variations. changes in grade caused by construction often change the water table and can severely injure the roots and trunk. Leaking gas, road oils, de-icing compounds, fumes and other industrial or urban wastes create additional problems for trees. Harsh urban environments weaken trees, thus promoting the spread of tree diseases.
Insect problems and trees
There are two main categories for insects that attract street trees: sucking and chewing insects. Sucking insects are controlled generally through the use of contact insecticides. Chewing insects are more complex to eradicate and the insecticides used on urban trees have often been suspected of creating adverse environmental effects. During the scientific period of arboriculture’s development, emphasis in managing urban trees has shifted to control to prevention of problems. Many problems such as tree diseases invade weakened trees. Hence one of the best preventions is directed towards stimulating optimum growing conditions. A common problem in this regard is that trees are considered as an afterthought in the development of cities. They are frequently relegated to the spaces that remain after all the buildings, roadways and plazas have been constructed.
The English Common
In England and Wales, common lands are seen as features of their heritage – seen as a residue of land that has been kept open by and for the people since the first days of village settlement, hence they are symbolic of the fight for democratic freedoms. A ‘common’ represents a space or landscape that has never been enclosed or cultivated, which still contains natural habitats that have not been cleared and where continuous natural regeneration has not been unduly restricted.
It is on an urban common where urban man can still find his kinship with nature through the site of an ancient grove of gnarled and rugged oak woodland…. he can walk or play in sheltered surroundings. It is from the landscape of the urban common that many fortunate townspeople find it possible to live with more contentment and satisfaction within the city. (pp 231 ‘Nature in Cities’)
Whilst the history of the common is primarily English, the idea behind their existence is noble and universal. The commons which now exist in the towns and cities were formerly ‘held in common’ (ie. privately owned land with common rights for the community) and were located in the countryside beyond the urban boundaries. With the spread of towns a few commons were kept and encompassed by the new towns. Although still grazed, they were still recreational parks long before the 19th Century town park movement in Europe and America.
Furthermore, their landscape was entirely different from the formal ornamental country parkland of the Renaissance design tradition which had influenced the new designs for the town parks. Essentially, the urban common represents in the ‘rus in urbe’ – country in towns. As such, they provide the best and largest range of natural habitats we have in single units to represent much of what is implied in the term ‘nature in cities’.
Visual character of commons: contain sizeable woodlands, rough grass fields and open glades of mown grasslands. Visually, the woodlands provide dense masses of vegetation – the ‘solids’ to balance the ‘voids’ of the clearings, glades and other open areas. The urban commons provide for a variety of activities, absorbing large numbers of people yet still providing for those who seek isolation. As for the ecological character of these commons, thy are balanced in the sense that they largely keep their natural state, with self-generating life cycles of nature maintained within the artificial ecosystem of the city. Bird life is dependent on the shelter and food largely provided by vegetation and all three commons contain natural woodlands with considerable cover in the tree, shrub and ground layer for birds.
The Urban Park
To impark an area of land is to enclose it with a barrier, which may be permeable or semi-permeable. The barrier defined what was safe, beyond this was seen as the unknown. Later, when communities erected more extensive barriers to protect groups of families, the first settlements came into existence. Kings then began to think about private parks for their own families. When grand cities came to be planned, spatial ideas were often developed in the rulers parks and passed though to the streets and spaces of the cities in which their dictate ran. As mentioned in the tree history, in the 17th century France and 18th Century England, the rulers parks burst from their imparkments; Louis XIV projected the avenues of Versailles outwards and opened the park to his subjects. In the 19th Century, special spaces, known as “public parks” were provided for the poor. These spaces were initially bounded and locked, strictly controlled. Later they were linked by parkways. From here on, the “parkland” was no longer bounded, green space leaked out, challenging the ancient idea of a compact protected city.
The history of the park
Land was originally divided into four non-agricultural uses. The Egyptians made domestic gardens and temple gardens. The Assyrians also made hunting parks. The Greeks added public gardens, as meeting and market places protected within city walls. Th Romans continued to make public meeting spaces, bu the other three types of parks became fused in the imperial villa and its progeny. Parks were made for domestic pleasure, for exercise, for hunting, for the fine arts and for celebration of the emperor’s god-like status. The classical park prototype can be somewhat revelled in modern parks, but in a much diffused state. Most urban park space is non-domestic garden, non-temple garden, non-hunting park. The large of expanse of greenery that is featured in planner’s plans and new housing estate development placards provide questionable value to the public. Many bounded, green public spaces are designed to provide human-oriented themes. It is perhaps safe to say that in large cities green space is insufficiently diversified it is paved, gardened or managed to death, limited by grass and concrete.
Text Reference:
Laurie, Ian C. (ed) Nature in Cities: The Natural Environment in the Design and Development of Urban Green Space, 1979, London.
Image References:
http://www.lnhs.org.uk/surveys.htm
http://www.edinphoto.org.uk/0_MY_P_F/0_my_photographs_hong_kong_-_tree_in_the_city_hy18_1024.jpg
http://www.brusselspictures.com/wp-content/photos/BoisdelaCambre/bois.de.la.cambre.gazon%20(2).JPG
