Urban Forests

Construction of cities comes with many planning challenges such as clearing trees and failing to put up effective replanting strategies. ‘Urban forests’ are important and should be set out close to residentials and along major highways where high pollution has been documented. Currently, there is a lot of urban construction and road expansion going on in Kenya. These projects come with environmental degradation effects. For instance, the Nairobi Expressway construction led to a loss of trees - an undertaking that put the Marabou storks at risk. Not only did the project impact lives such as the storks, but also biodiversity along the stretch of 27 km highway at large. Similar scenarios are expected in numerous road and town expansion projects across the country. Therefore, there is a need to adopt suitable and sustainable urban policies, and where they do exist, a better implementation plan is pivotal. One of the most reliable and sustainable approaches to controlling pollution and preserving biodiversity in urban areas and along the major highways is tree planting. 

 

Why urban forests?

Urban forests mean an increase in the number of trees in towns and cities. Major highways and urban areas are endemic regions where toxic emissions from automobiles, industries and other human activities occur, hence, the presence of trees in these areas is necessary for the reduction of toxic material build-up. Trees are indirectly or directly involved in improving air quality. By shading surfaces, trees indirectly reduce temperatures and emission of greenhouse gasses associated with it by regulating ground-level ozone that commonly spikes on hot days in urban areas. Directly, they reduce pollution through absorbing ‘unwanted’ gasses and compounds such as Lead, Sulphur Dioxide, Nitrogen Dioxide, Nitrogen Monoxide and Ozone thus, acting as ‘lungs and liver’ in this case. Besides, they extract particle matter (tiny particles of organic chemicals, acids, metals and dust) emitted from fossil-fuel-powered vehicles and construction sites. During photosynthesis, trees extract carbon converting it to biomass, consequently playing the role of carbon sinks.

 

Trees intercept surface run-off which normally carries much of litter and chemicals into rivers, streams, lakes and oceans. The surface run-off perhaps negatively impacts aquatic life, human health and the entire ecosystem. Therefore, planting more trees in urban areas would intercept rains through leaves, barks, and branches to serve as mini-reservoirs to curb soil erosion. In addition, plant roots would provide a further alternative to soil erosion mitigations by working as bio-infiltrators to surface run-off. Trees are also best known to prevent noise and sound pollution by absorbing vibrations likely to be caused by heavy commercial vehicles and fierce industrial activities. Besides, biodiversity is also correlated to the amount of land vegetation as trees are homes for birds and animals. Finally, trees are properties and sources of income for the community – income from trees improves livelihoods. 

 

Pollutants are harmful to life in general. For instance, noise is likely to cause changes in sleep patterns and hearing impairment. According to the World Health Organization (WHO) noise is a common cause of disruptions in learning centres, an obstruction to communication and a likely causal agent in shifting productivity and social behaviours. Continuous exposure to dust and emissions from automobiles, for example, Lead compounds, Nitrite Oxide and Sulfur Dioxide are associated with health problems such as cardio-respiratory systems diseases, and skin and eye ailments. They are also destined to cause abdominal colic pain, bloody diarrhoea, and kidney failure. Children born under constant exposure to these pollutants experience retarded physical and mental growth. Moreover, these pollutants are potentially harmful to the central nervous system. It is approximated that there are 8.9 million deaths globally attributed to exposure to outdoor fine particulate matter yearly. Nitrogen oxides, for example, would most likely lead to indirect concerns such as poor visibility, a situation likely to elevate disasters on roads and airports. Food insecurity is not spared either as pollutants constrain agriculture and crop production.

 

Right trees for urban dwellings

Not all trees are effective in reducing air pollution. The extent of their performance depends on canopy size, leaf size and leaf structure. Bigger canopies are better in regards to the provision of a larger surface area for absorption of pollutants than small canopies. Trees with rough leaf surfaces, rugged and hairy surfaces make better pollutant filters; leaf hairs trap solid and liquid particles components of particle matter.

 

Research has shown that conifers are better adapted to improving air quality. They are known to reduce air allergens and volatile organic compounds (VOCs). VOCs are a set of substances that interact with gases emitted by vehicles in the presence of sunlight and contribute to ground-level ozone. Conifers thus are a fantastic canopy. Other than the species, the orientation of trees is a major contributing factor to pollution reduction. Positioning trees with the direction of air movement would influence the rate and extent of pollutant absorption. Pollutants are known to move in the direction of the winds. Therefore, improper positioning of trees would result in greater health risks as a result of entrapping and accumulating hazardous agents within residentials and places of work. This calls for a proper planning system, for instance, incorporating hedges between buildings and tall trees along major highways.

 

Let’s go green, breathe clean.

Several countries have adopted this simple, cheap and sustainable approach in their quest to reduce pollution along highways and urban areas. In January 2019, the mayor of London announced that 7,000 trees would be planted before the end of the following year. Similarly, China’s Hebei Province, the home to Beijing, has been working on a “green necklace” to mitigate industrial pollution. Paris is also planning an urban forest that will encompass its most iconic landmarks to adapt to climate change, and also improve the city’s air quality. Therefore, it is integral for Kenya to adopt sustainable urban/major highway environmental improvement programs and economic empowerment schemes such as tree planting. Trees are important in achieving #1, #2, #3, #6, #11, and #13 Sustainable Development Goals to transform our world. 

Justus Obara, Egerton University

Email: justusanyieni@gmail.com

 

Sudhir Otieno, founder SudhirNet

Email: sudhirkalando@gmail.com

 

22 May 2022