Does Money Grow on Trees After All?

How can a city benefit from trees? As calculated by Dan Burden, growing trees might be the best long-term investment for a city – a single street tree returns over 80,000 € of direct benefits in its lifetime. Here’s a quick look at some of the most prominent positions for hiring trees that research has thrown light upon so far.

  1. Trees increase property values

This is not surprising as trees create a tapestry of colour, fragrance and interesting form that changes throughout the year, screen unattractive views and soften the harsh contours of buildings. Trees help residential and commercial properties to rent more quickly and to have a higher occupancy rate. They can add up to 15 percent to residential property value and where the entire street is tree-lined, homes may be worth 25% more.

  1. Trees increase business and commercial activity

An abundant tree canopy can attract new residents, tourists and businesses into a neighbourhood. Studies show that people like to spend more time and money in districts with more trees. In addition, having offices with a view of nature and access to green areas during breaks translates into healthier, more productive and satisfied employees.

  1. Trees reduce energy expenditure

Strategically placed trees around a building can reduce summer cooling costs by as much as 30%, while in winter heating costs can be reduced by a similar percentage with the use of trees as windbreaks. A tree is a natural air conditioner and can produce the cooling effect of ten room-size, residential air conditioners operating 20 hours a day. Neighborhoods well-shaded with street trees can be up to 6-10 degrees cooler.

5989410617_69969375d2_z
Urban trees provide many benefits for a city and its residents
  1. Trees reduce water management costs

Trees reduce stormwater management costs and produce better water quality. They act as natural water filters and prevent harmful land pollutants contained in the soil from getting into our waterways. They significantly slow the movement of stormwater, which lowers total runoff volume, soil erosion and flooding.

  1. Trees reduce costs for meeting regulatory pollution requirements

Trees contribute to meeting a city’s regulatory clean air requirements by capturing more than 60% of the particulate air pollution. They remove dust, particulates, absorb ozone, carbon monoxide, sulfur dioxide and other pollutants. Estimates show that over a 50-year lifetime, a tree provides more than 50,000 € worth of air pollution control. Trees also act as sound buffers and reduce noise pollution by absorbing and blocking more than 40% of urban noise.

  1. Trees reduce health care costs

Trees catch air pollutants that damage human lungs which enhances a community’s respiratory health and ameliorates respiratory problems, such as asthma. They provide protection against ozone-associated health issues. Studies show that hospital patients with a view of trees out their windows recover much faster and with fewer complications. Time spent in nature not only promotes greater physical activity, but also reduces stress, eye strain and lowers blood pressure.

  1. Trees increase security and strength of a community

Trees lower anxious and violent behaviour – the greener the neighbourhood, the lower the crime rate. In homes surronded by trees there is less domestic violence and child abuse than in barren conditions. Trees also create a physical barrier between the street and the sidewalk, keeping pedestrians, children and pets out of harm’s way. Urban nature creates popular meeting places, inviting citizens to spend time together relaxing, walking, jogging or playing. These activities encourage interaction, bring neighbours together and strengthen urban communities.

As shown, urban trees provide a wide array of solutions to a city’s welfare and resilience. A city with an abundance of trees is a rich, sociably stable, safe and healthy city.

Author: Anita Mašek, Slovenian Forestry Institute

Featured photo by star5112.

Urban Forests and Water

This year’s topic of the International Day of Forests on March 21st is “Forests and Water”. It’s a very important topic, especially in urbanizing cities, where reducing stormwater runoff by urban forests and trees has become important part of stormwater management. Read about this in a blog written by Dr. Urša Vilhar, research fellow at the Forest Ecology Department of the Slovenian Forestry Institute.

The ability to mitigate stormwater runoff in many urbanized watersheds around the globe has decreased. Stormwater runoff associated with an increased amount of impervious surfaces in the cities is the main cause of flooding, poor water quality, and deteriorating stream health.

How can urban trees reduce stormwater?

Urban forests and trees have a great potential for reducing stormwater runoff by enhancing soil infiltration and evapotranspiration, as well as regulating the amount of throughfall reaching the ground via rainfall interception by tree crowns. Trees can also absorb water in the soil by root uptake. Together, the roots and leaf litter stabilize soil and reduce erosion. Since the amount of impervious surfaces, e.g. parking lots, roof tops, driveways, and roads is increasing in many urban communities, rainwater cannot infiltrate and runs off as stormwater.

In urbanizing cities, management of urban forests and trees has become important part of stormwater management. Urban forests, trees, vegetation and pervious soils beneficially affect urban watershed hydrology by their ability to intercept, evaporate, transpire, infiltrate, and store rainfall.

Vilhar_vodnilrogWater cycle in urban forest and in the city. Canopy interception loss by urban forests or individual city trees accounts for 4 to 50 % of annual or seasonal rainfall. Trees and their associated tree pits may reduce surface runoff from asphalt by as much as 62 %.

How can urban trees improve water quality?

Research has found that water quality is strongly related to runoff. Stormwater flows into the community’s stormwater system or flows directly into the urban streams, lakes or wetlands. Before reaching a stormwater system or water way, stormwater picks up and transports loads of nutrients, heavy metals, organic pollutants, and other harmful substances from roadways, sidewalks, yards, and homes.

Tree roots, leaf litter, and vegetation can remove pollutants, sediment, and nutrients from the stormwater, lessening the amount of harmful substances reaching our ground or surface waters. Among plant types, trees have an exceptional ability to capture and filter multiple air pollutants, including ground-level ozone, sulphur dioxide, nitrogen oxides and particulate matter. Finally, tree canopy over streams and wetlands can reduce water temperatures, thereby increasing dissolved oxygen and reducing the formation of nuisance algae.

Using natural vegetation as a low impact development and best management practice can be an effective technique to control stormwater runoff on site, mitigating the impacts of urbanization on surface runoff and pollutants delivery at a local scale.

ecosystem_contribution_water

Relative contribution of different land cover classes in the City of Ljubljana to ecosystem services, related to regulation of water flow and water purification. The highest capacity to provide water flow regulation was indicated for wetlands and mixed forests. The highest capacity to provide water purification services was indicated for mixed and coniferous forests. The lowest capacity for both ecosystem services was indicated for urbanized areas. (Results of the Life+ project EMoNFUr).

Urban forests and trees are valuable parts of our urban ecosystem for the numerous benefits they provide to communities. Proper management of the urban forest reduces stormwater runoff and improve water quality. The following practices can help achieve this:

  • Maximize the amount of growing space and understory vegetation around a tree.
  • Preserve established trees and minimize soil compaction, displacement, and erosion around a tree.
  • Minimize clearing of trees and vegetation to preserve their benefits and minimize soil compaction.
  • Do not over fertilize or over irrigate trees, lawns or gardens.
  • Route excess stormwater to bioretention areas made of a vegetated buffer and a soil bed to filter pollutants, store water, and prevent erosion.
  • Include tree and vegetative strips in parking lots to collect, store, and treat the runoff.
  • Maintain and increase the amount and width of urban forest buffers around urban streams, lakes, and wetlands.

Author: Dr. Urša Vilhar, Forest Ecology Department of the Slovenian Forestry Institute