Single line trees represent one possibility to establish several trees in urban areas. As the name implies, single line trees are arranged along e.g. streets, bicycle paths and sidewalks and the trees are situated on one side. Trees have multiple effects on the local micro-climate conditions, absorb particular matter and provide shade for people as well as for buildings. One of the main positive effects for the human well-being in periods with high temperatures is the air cooling effect. The mentioned effect of street trees in general depends on different factors such as tree size, canopy coverage, planting density, tree species, tree health, location, availability of root water or leaf area index.

Basic information

Type: 
Retrofitting + Creation

Performance

Evapotranspiration 1 1
Shading 1 none
Reflection (Albedo) none
Water Conveyance none
Water Infiltration 1
Water Retention 1
Water Storage none
Water Reuse none
Water Filtering none
Water Bio-remediation none
Deposition 1
Bio-filtration 1
Habitat Provision 1
Connectivity 1
Beauty / Appearance 2
Usability / Functionality 1
Social Interaction 1
Role of Nature / Mode of Action: 
Single line trees simulate those trees growing at the edge of the woods and their effects on the surrounding environment outside the tree-covered area. The trees shade adjoining land uses. As a result the shaded surface is cooler than surfaces without a protecting tree cover. The shading effect is determined by the characteristics of the trees (tree and canopy density, season). Other effects are a reduced wind velocity; transpiration/air cooling, air purification/absorption of particular matter.
Technical & Design Parameters: 
The most important aspect is the selection of suitable trees that serve the intended purpose and are fit for the geobotanical conditions. The area of the root space for neighbouring trees can be connected in suitable conditions and if separated root space should be 12 m³ with a minimum depth of 1.5 m (FLL 2015). Depending on local climatic conditions, permanent or temporary irrigation facilities need to be considered. The distance between the trees depend on the maximum size of adult tree but also on the size of the planted tree and design ideas. Protection measures (e.g. poles, wire mesh against animals) may be needed as well.
Conditions for Implementation: 
Local circumstances (e.g. topography, route characteristics, surrounding land use, and underground uses) need to be considered when planning and establishing new single line trees. Suitable location for the establishment of trees should offer enough space for trees to grow. Depending on the site conditions and available space, suitable tree species have to be selected. The consideration of the maximum height of the trees is important to avoid space problems in the future. Trees that are not sufficiently rooted may cause accidents and constitute a danger for peoples on or beside the road. The soil and subsurface should generally be suitable for the establishment of street trees and may need to be replaced by standard soils if necessary. The selection of suitable tree species should also consider local conditions like topography: For the stabilization of banks or small hills steadfast trees are necessary. Species and sub species that are suitable for urban conditions should be planted.
Benefits & Limitations: 
Benefits: Single trees are associated with diverse benefits for urban ecosystems: - Microclimate regulation - Habitat provision - Aesthetics/recreation - Rainwater regulation (delayed runoff) It takes decades until newly planted trees fulfil the services of adult trees, individually as well as in combination. Therefore initiatives to protect existing trees are very important. Potential limitations/disservices: Disservices of trees may be the allergenic potential of its pollen and BVOC emissions, resulting in high O3 concentrations in summer.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No. 730052 Topic: SCC-2-2016-2017: Smart Cities and Communities Nature based solutions