For the most part, the rapid expansion of cities takes place without any land use planning strategy and the consequent human pressure has highly damaging effects on forests, landscapes and green areas in and around cities. The environmental effects of urbanization are often intensified by climate change and include increased pollution, decreased availability of food and resources, as well as increased poverty and the frequency of extreme weather events.
Urban trees can help mitigate some of the negative impacts and social consequences of urbanization, and thus make cities more resilient to these changes. Here are nine ways urban trees and forests help make cities more socio-economically and environmentally sustainable:
1. Trees can contribute to increasing local food and nutritional security by providing food such as fruits, nuts and leaves for both human consumption and forage. Its wood, in turn, can be used for cooking and heating.
2. Trees play an important role in increasing urban biodiversity, providing plants and animals with habitat, food and protection.
3. A mature tree can absorb up to 150 kg of CO2 per year. As a result, trees play an important role in mitigating climate change. Especially in cities with high levels of pollution, trees can improve air quality, making cities healthier places to live.
4. The strategic location of trees in cities can help cool the air between 2 and 8 degrees Celsius, thus reducing the urban “heat island” effect and helping urban communities adapt to the effects of climate change.
5. Large trees are excellent filters for urban pollutants and fine particles. They absorb polluting gases (such as carbon monoxide, nitrogen oxides, ozone and sulfur oxides) and filter fine particles such as dust, dirt or smoke from the air trapping them on the leaves and bark.
6. Research shows that living near and having access to urban green spaces can improve physical and mental health, for example by lowering high blood pressure and stress. This, in turn, contributes to the well-being of urban communities.
7. Mature trees regulate the flow of water and play a key role in preventing floods and reducing the risks of natural disasters. An evergreen or mature tree with permanent green leaves, for example, can intercept more than 15,000 liters of water per year.
8. Trees also help reduce carbon emissions by helping to conserve energy. For example, the correct placement of trees around buildings can reduce the need for air conditioning by 30 percent and reduce heating bills in winter by 20 to 50 percent.
9. Urban landscape planning with trees can increase a property's value by 20 percent and attract tourism and business.
A city with a well-planned and well-managed green infrastructure becomes more resilient, sustainable and equitable in terms of nutrition and food security, poverty alleviation, improved livelihoods, mitigation and adaptation to climate change, risk reduction of disasters and conservation of ecosystems. Trees can provide a package of benefits over their lifetime that is worth two to three times more than the investment in planting and care.