Key messages Since 2008 and for the first time in history, more than 50% of the world’s population lives urban areas, and this percentage is expected to swell to 70% by 2050. Particularly in lower- and middle-income countries, this rapid urbanization process has been translated into depletion of natural resources, outpacing the capacity of most urban settlements to provide dwellers with services and goods essential for their livelihood. Well-planned and managed tree and forest resources in and around cities can play a key role in responding to the needs and threats posed by an increasing urban population. By providing ecosystem services, products and public benefits they can help facing local and global challenges, thus contributing to make cities economically, socially and environmentally more sustainable and resilient. In particular, they can: Improve human health and well-being Properly designed and managed urban and peri-urban forests and other green spaces can play an important role in ensuring healthy lives and promoting well-being through diseases prevention and faster recovery from illness. - Children living in areas with good access to green spaces have been shown to spend less time in front of television screens, computers and smart phones ant to have 11-19 percent lower prevalence of obesity compared with children limited or no access to green spaces (Dadvand et al., 2014).
- In the United States of America, trees help reduce or prevent more than 670 000 cases of severe respiratory diseases per year and thereby save more than 850 lives annually (Nowak et al., 2014).
Contribute to mitigate/adapt to the effects of climate change Forests in and around urban areas can contribute to climate-change mitigation, both directly by sequestering carbon and indirectly by helping saving energy for cooling and heating, thus contributing to reduce the urban heat island effect. - Urban trees in the conterminous United States of America store 770 million tons of carbon, valued at US$ 14.3 billion (Nowak and Crane, 2002).
- Shade from trees can reduce utility bills for air-conditioning in residential and commercial buildings by 15-50 percent (Parker, 1983; Huang et al., 1987).
Protect biodiversity and landscapes If well-managed and protected, urban forests can contribute to halt the loss of biodiversity, reduce the degradation of natural habitats and prevent the extinction of threatened species, thus ensuring the provision of ecosystem services to cities and the preservation of natural landscapes. - Urban forests provide habitat for many species of birds, insects and other wildlife. For example, there are approximately 200 000 trees in Amsterdam’s open spaces, and the mosaic of interconnected landscapes provides a home for 140 bird species, 34 mammal species, 60 fish species and six frog and salamander species (UNEP and ICLEI, 2008).
- On average, 70 percent of the plant species and 94 percent of the bird species found in urban areas are native to the surrounding region (Secretariat of the Convention on Biological Diversity, 2012).
Provide economic benefits and foster green economy Urban and peri-urban forests provide many economic benefits - including through green branding and marketing strategies - which help cities build dynamic, energetic and prosperous green economies. - Urban trees in the conterminous United States of America remove some 784 000 tons of air pollution annually, at a value of US$3.8 billion (Nowak, Crane and Stevens, 2006).
- UPF supports an estimated 15 500 jobs in Manchester City, United Kingdom of Great Britain and Northern Ireland, in areas such as the processing of forest products, tree-related tourism, and professional forestry-related services (Connor, 2013).
- In the United States of America, the appraised values of homes adjacent to naturalistic parks and open spaces are typically 8-20% higher than comparable properties without such amenities (Crompton, 2001).
Mitigate land and soil degradation By protecting soils and increasing their fertility, urban and peri-urban forests help combat desertification, restore degraded soils and lands, prevent drought and floods and strive to achieve a land degradation-neutral world. - In a medium-sized city, the tree cover can save more than 10 000 tonnes of soil from degradation and erosion annually (Coder, 1996).
- Properly designed shelterbelts have been estimated to reduce the erosive force of winds by up to 75 percent (Agriculture Victoria, 2003).
Protect and regulate water and watersheds By protecting watersheds, filtering waters and increasing soil permeability, urban and peri-urban forests can greatly contribute to a successful and sustainable urban and peri-urban water and watershed management. - Ninety percent of sediments and nutrients can be prevented from entering waterways by maintaining strips of riparian vegetation (Schultz, Isenhart and Colletti, 2005).
- Since 2006, the City of Philadelphia has reduced combined sewer overflow and improved water quality through green infrastructure policies and pilot projects, savings approximately US$ 170 million (Boyle et al., 2014).
Increase food and nutrition security By providing food, woodfuel for cooking, and non-food products to be sold on markets, urban and peri-urban forests can contribute significantly to food and nutrition security in urban and peri-urban environments. - In Indonesia, homegardens can contribute up to 56 percent of the total income of owners (Soemarwoto, 1987).
- The value of shelterbelts in raising agricultural productivity has been demonstrated in many countries, suggesting potential improvements in crop yields (25 percent) pasture yields (20-30 percent), and dairy milk production (10-20 percent) (Tisdell, 1985).
- City Fruit harvested 12 700 kg of unused fruit from Seattle’s urban fruit trees in 2014 and donated 10 000 kg to 39 local groups, including food banks, schools and community organizations. The value of fruit donated to meal programmes and food banks is estimated at US$ 44 112 (City Fruit, undated).
Enhance wood security By providing additional sources of wood and wood-fuel, urban and peri-urban forests can play a key role in responding to urban needs in terms of wood provision while contributing to protect natural forests and woodlands from depletion and over-exploitation. - Wood energy supply for a city of one million inhabitants in Central Africa represents annual harvesting of 10,000 ha of productive plantation, and up to 100,000 ha of degraded natural forests, according to stands’ natural productivity and land use pattern (Marien, 2009).
- The estimated demand for wood fuel in Dhaka, Bangladesh, was 11 553 million m3, meaning a shortage of 3.81 million m3. The shortfall had grown significantly from 1993, it was 2.14 million m3 (Uddin, 2006).
Maintain and enhance socio-cultural values The protection of the urban and peri-urban forests can help communities maintain cultural identities across generations, provide dwellers with community spaces where to socialize and decrease the gap between rich and poor neighbourhoods. - In China, buildings were undermining the roots of a 4 700-year-old, 50-metre tall tree. The government spent more than US$ 300 000 to relocate nearby residents in order to preserve the tree (Xinhua, 2015).
- A study conducted in Baltimore, United States of America, showed that a 10 percent increase in canopy cover was linked to a 12 percent decrease in crime (Troy, Grove and O’Neil-Dunne, 2012).
To minimize the risks associated with urban and peri-urban forests and maximize their benefits, urban forestry risk management should be fully integrated into urban planning and management, emergency response protocols and public education programmes. Residents often mention tree loss as one of the greatest impacts of storms – including more than 30 percent of residents in the wake of Hurricane Hugo in 1989 (Miller, Hauer and Werner, 2015). Studies in the United Kingdom of Great Britain and Northern Ireland estimate that there is a one in ten million chance of an individual being killed by a falling tree (or part of a tree) in any given year (Watt and Ball, 2009). |
