Green tree planning for roads towards sustainable green urban development

01/07/2016

   Benefits of green trees to the environment

   Green trees are having increasing roles and becoming required criteria for roads crossing residential areas and in sustainable transportation development. This is because green trees have a function in improving the air and climate environment in roads. Green trees at roads’ sides can reduce dust in the atmosphere, up to 30-60% in upper-storeys of high-rise buildings. Green trees help reduce greenhouse gas and radiation reflex to the surrounding environment. According to recent studies, on average, 1 ha of forest or dense garden can absorb 1,000kg CO₂ and emits 730kg O₂ daily. Therefore, each urban resident needs an area of about 10m² green trees or 25m² of grass to ensure clean air for living.

   Green trees can also absorb noise depending on dense or loose, wide or narrow, high or low, thick or thin leaves, broad or small leaf tree belts, etc. Green trees have effects in antiseptic, killing germs and harmful bacteria, absorption of hazardous gas and environmental sanitation insurance.

   Regarding road landscape, green trees increase aesthetic effects and create a soft impression of colour and pleasant climatic environment.

   Green tree planning suitable with the transportation and urban system

   In the last 10 years, the transportation infrastructure system has developed towards scope expansion and quality improvement. However, up to now, in Việt Nam, the study or legal documents are not available for street green tree planning. The planting of trees along roads is subject to investors but not according to long-term planning or paying attention to environmental protection solutions.

   Tree belts along roads must not develop at a spontaneous manner but must ensure some principles: warranty of green cover, green area and green trees, etc. particularly in sections crossing residential areas - small areas of high population density that cause many issues relating to environmental sanitation. These criteria depend on population, residential distribution, manufacturing activities, construction and volumes of traffic… At the same time, green tree distribution and development must ensure environmental improvement and pay attention to the prevention of the spread of pollutants and noise from factories, enterprises, industrial zones, processing zones, semi-industrial facilities, vehicles and transportation. The continuity of green trees in the whole route should also be paid attention to. Green trees consist of those in pavements, road dividers and road slopes.

   It is important to combine with natural conditions and climatic conditions such as wind direction and speed, temperature, rainfall, soil capability, etc. in tree plantation and development for each area, based on “tree for compatible soil”, particularly noting that soil structure has changed because of construction works. It is also important to consider historical relics, cultural relics and landscape features as they are parts of entertainment, recreational, cultural and education activities for residents.

   The distribution of green trees along roads is not necessarily even but dependent on residential areas. This principle is also a “soft” motto as it should be appropriate with practical conditions of the society, particularly in urban areas - where architectural positions are fundamentally fixed. Existing green trees along roads that are not suitable with climate conditions, soils, transportation safety and residential culture, etc. should be replaced by new trees. New green trees should be planted along new or renovated roads using different tree species to create typical characters of the roads. On the roads in the city centre, green trees along pavements should be paid attention to. If condition allows, huge green tree belts should be established to separate roads and residential areas. Green trees can include not only timber trees but also shrubs, flowers and grass. They create the landscape but also contribute to prevent noise, vibration and dust and reduce negative impacts on residential areas.

   In roundabouts and traffic islands in roads in the city, mobile water works can be built in combination with flower pots or grass to increase the liveliness and create the landscape for urban areas, high trees should not be planted to affect traffic vision. Traffic islands should not be constructed with sole concrete parts. On the other hand, green tree management requires the understanding of green trees (sanitation, climatic renovation, etc.), impacts to the livings and there should be solutions to achieve long-term and sustainable objectives. Some criteria for selection of pavement trees: trees with natural straight stems, good timber, not-crisp, not-easily-broken to avoid accidents. Trees should have canopies, neat branches, taproots and majority of roots are deep down into the soil to stabilize trees and to prevent tree falling. These trees should have no or little surface roots to avoid damages to pavements, road surface and works around the tree roots. Leaves should be large, fruits or flowers should not attract flies and insects for sanitary purposes, etc.

   Tree lifecycle should be long to reduce replanting costs. Tree height develops considerably fast and not too slow in order to maximize its effects. Trees have good resistance against natural conditions and insects. Trees have possibilities to prevent bacteria in the air; trees have high economic values. Selection criteria should be flexible as it is difficult to select trees meeting all these criteria. Criteria on stem, roots and leaves should be paid attention to. It is also important to develop particular characteristics for each road using typical species and along one road or one section only one species is planted for easy maintenance, aesthetics and straight line of trees.

   The green tree planning should not only be appropriate with the transportation system, it should also be appropriate with urban areas in Việt Nam. Currently, the area of public green trees in urban areas is very small compared to QCXD 01:2008 of the Ministry of Construction, as well as compared to other big cities of other countries as shown in the below table.

   To achieve the above objective, green trees in urban areas must be timber trees with large dense leaves and few leaf falls which are the key trees in street green tree arrangement. Each urban area should plant same tree species creating typical features of each street in the urban area.

   In main roads of the urban area, tree gardens can be arranged along highways or roads. In tree gardens, timber trees with canopies must be mixed with shrubs, flower pots and grass. In these areas, mobile water works can be distributed with green trees to create the vivacity. In the square centre where crowded meetings are regularly organised, the usage of grass instead of concrete surface or asphalt surface will significantly reduce air temperature and radiation in the square.

   In large squares, green trees and water surface are needed. In pavements surrounding the square, tree gardens can be arranged with the principle of street green tree arrangement. For the traffic island within the square, the principle of green trees and water surface is totally different. To avoid vision limitation, high trees are not allowed in traffic islands; therefore only flower pots and grass can be allowed with an ascending slope to the island centre. In large traffic islands, mobile water works (water spray or water running) can be arranged in the island centre in combination with surrounding flower pots and grass. Nowadays, trends to arrange statues in traffic islands do not exist as mobile water works help diversify the square landscape and reduce air temperature as well as dust in the square.

Table 1. Public green tree space in urban areas in Việt Nam and in the world

 

No.	Domestic urban areas	Green tree target (m2/person)		No.	Foreign urban areas	Green tree target (m2/person)
		Status	QCXD 01:2008
1	Hà Nội	2	≥ 7	1	Paris (France)	10
2	Hồ Chí Minh City	3.3	≥ 7	2	Moscow ( Russia)	26
3	Huế	3.5	≥ 6	3	Washington (USA)	40
4	Đà Nẵng	0.9	≥ 6	4	New York (USA)	29.3
5	Hải Phòng	2.0	≥ 6	5	Nanjing (China)	22
6	Nam Định	1.5	≥ 6	6	Guilin (China)	11
7	Hạ Long	3.1	≥ 6	7	Hangzhou (China)	7.3
8	Vĩnh Yên	3.2	≥ 5	8	London (UK)	26.9
9	Hải Dương	3.7	≥ 5	9	Berlin ( Germany)	27.4
10	Bắc Ninh	2.7	≥ 5
11	Hưng Yên	3.2	≥ 5

   Orientations on policy development for green tree planning towards sustainable green urban development

   First, the Government needs to promulgate policies and specific regulations on arrangement of green trees on roads to ensure the harmony between the landscape and the transportation system; regulations on planting methods and criteria, maintenance of transportation and urban area green trees. The urban green area should not only be considered as a land area that is covered green but also pays attention to aesthetic and artistic values so the green field in harmony with architecture and natural landscape and at the same time to create the uniqueness and attention of the work.

   Second, enhancing the monitoring of the society on green tree protection and maintenance; provide human resources with scientific knowledge and experience in planning and development of urban green trees, identifying land for green trees; developing works linked with protection of existing green trees; strict management of land used for green trees; developing and specifying “green” criteria in assessing and classifying urban areas; regulating clearly which trees are promoted or prohibited for planting in urban areas.

   Third, the Government should request domestic and international organizations and individuals to invest in urban green tree development for environmental protection and response to climate change project. Developing a financial supporting mechanism for protection and development of green trees such as materials, seedlings, etc.; having policies supporting the development and construction of infrastructure to protect green trees. In addition, promoting and mobilizing all resources of the society to participate in development and protection of green trees.

   Fourth, propagating all citizens to enhance awareness on protection and development of green trees along roads; mainstreaming in the education for primary students to understand and to protect green trees.

   Fifth, complying with principles of green tree planning; ensuring transportation safety and environmental sanitation and having the acceptance of local people.

   Sixth, selected trees must be appropriate with ecological conditions, soil and environment of roads and urban areas; having mechanism to promote individuals and organizations to participate actively in planting, caring and protecting street trees.

Lê Xuân Thái

The University of Transport Technology

Lê Văn Khoa

The University of Science, Vietnam National University