by Dhanya Shree Ragunath
Long before humans roamed the earth, the dominant life form on land were trees. Trees are integral to the existence and survival of all lifeforms as they are essentially the lungs of the planet. Yet their role in our lives go far beyond their ability to provide oxygen for our respiratory needs.
Naturally, trees provide habitat, food and shelter to plants, animals and humans, increasing biodiversity and promoting a stable ecosystem. As urban cities expand, trees tend to be removed to make way for development. However, maintaining or reintroducing trees in the city through urban forestry programmes can provide numerous benefits to surrounding communities.
Trees assist in filtering out pollutants in the air i.e. particulate matter, nitrogen oxides (NOx) and volatile organic compounds (VOCs), improving air quality and significantly reducing risks of pollution-related illnesses such as asthma and other respiratory infections. Ground-level ozone, or smog, is created by chemical reactions between NOx and VOCs in the presence of sunlight, with high temperatures increasing the rate of this reaction. Vehicle and industrial emissions are the major sources of these pollutants. In a study conducted by a group of researchers at Portland State University, it was found that trees reduced local nitrogen dioxide levels by an average of 15% which consequently decreased the cases of asthma-related illnesses drastically, and saved the public US$7 million from avoided hospital visits1.
During rainstorms, water can overload drainage systems, resulting in polluted runoff and flooding, a common occurrence in major cities. Trees can reduce this problem by capturing rain; a mature tree can store 150 to 350L of water from their roots during large storms, and the soil and organic matter increases absorption and reduces runoff by 2-7%2. The network of tree roots also assists in preventing landslides and erosion by holding the soil together.
Another important function of trees is the mitigation of urban heat islands, a phenomenon with severe effects in most cities. Urban heat islands are areas that are significantly warmer than their surrounding due to radiation being trapped where surfaces are impermeable and dry (e.g. infrastructure, as opposed to earth and trees, which would absorb it). Through the natural process of evapotranspiration, trees release moisture into the air, providing a cooling effect. With proper placement around buildings, this cooling effect can also reduce air conditioning needs by 30% which reduces energy use and in turn reduces the greenhouse gases emitted into the atmosphere, thus breaking a vicious cycle. As the formation of ground-level ozone is temperature dependent, reduced temperatures also decreases the occurrence of smog.
Urban trees can play an important role in climate change mitigation; acting as a sink for carbon dioxide (CO2) by fixing carbon during photosynthesis and storing carbon as biomass. Carbon sequestration in urban areas assist in reducing anthropogenic CO2 levels. Using field data and photo-interpretation of tree cover, it was estimated that total gross sequestration in U.S. urban areas is 25.6 million tonnes C/year which amounts to $2 billion in a carbon market4.
Trees act as buffers that reduce noise and enhance the aesthetics of the area. Landscaping, especially with trees, can increase property values by 20%5. Urban parks and green spaces tend to promote community interaction and could also serve as popular tourist attractions such as New York’s Central Park and Portland’s Forest Park. Urban tourism can meet visitors’ expectations and at the same time make a positive contribution to the development of towns and cities and the well-being of their residents, as it boosts local economy.
Figure 2: Tourists and visitors at Central Park
Studies have also shown that spending time near trees improves physical and mental health by increasing energy levels and speed of recovery, while decreasing blood pressure and stress. The research demonstrates that the sight of trees bolsters the parasympathetic nervous system, that serves to ease blood pressure, slow pulse rate and loosen muscles; essentially inducing a calming effect.
With an urban population of 75% of the total population, and an annual urbanisation rate of 2.5%, Malaysian cities are rapidly growing. As part of efforts to transform Kuala Lumpur into a world-class, top liveable city by 2020, the Malaysian government aims to increase greenery in the city by planting 100,000 large-coverage trees. This initiative is championed by DBKL and the Ministry of Federal Territories and Urban Wellbeing and is undertaken together with the private sector, which will sponsor tree-planting and establish parks within KL.
Urban forestry influences local climate, carbon cycles, energy use and climate change, with the simple act of planting trees. There are undeniable benefits to having trees in the city; environmentally, socially and economically. With this in mind, Malaysia would do well to continue planting urban trees and further integrate green spaces and infrastructure (e.g. vertical gardens, green roofs etc.) as it works towards becoming a sustainable, developed country by 2020, through effective public-private partnerships.
Landskap Malaysia conducts such tree planting programmes, with the objectives of encouraging various communities to plant rainforest trees which will eventually create much needed green lungs in urban areas. The aptly named Hutan Kita, or Our Forest, programme started on 15 February 2009 at the Bukit Kiara forest, Kuala Lumpur, and has now grown to include schools, hospitals and university compounds, parks, as well as mangrove forests. There have been 72,588 trees planted to date. Together with Tropical Rainforest Conservation and Research Centre, these two NGOs are engaging various local and international partners to bring more trees and diversity into Malaysian landscapes.
Figure 3: Research shows that trees have a calming effect.