Contemporary urban ecology assumes that urban areas are ecosystems since they have interacting biological and physical complexes (Cadenasso & Pickett, 2008). McHarg played a major role in emergence of ecological landscape design approaches in urban development. His work "Design with Nature"(1969) displays how nature and city might coexist together. However, ecology has been neglected in urban planning systems of most developing countries which mostly focus on the relationship between physical and socioeconomic aspects of an urban development. Urban green spaces are fundamental in sustaining the urban ecology. Some of the environmental and ecological benefits of the urban landscape are listed below:
• Urban green spaces provide flora and fauna with a habitat to live and therefore support biodiversity conservation.
• They also act as ecological corridors between urban, periurban and rural areas. They support movement of living organisms between these areas.
• Vegetation cover in urban landscape helps to improve micro-climate of urban areas where climate is warmer than their surroundings due to dense built environment and human activities. Vegetation cover raises humidity levels, reduces the stress of the heat island and mitigates the less desirable effects of urban climate (Landsberg, 1981). Daytime temperature in large parks was found to be 2-3°C lower than the surrounding streets (GreenSpace, 2010).
• Vegetation helps to decrease carbon emission levels in cities. Through photosynthesis process in plants CO2 in the air is converted to O2. Therefore, urban vegetation cover helps to reduce excess CO2 in the urban atmosphere. Although the degree of trees’ drawing carbon emissions from the air is affected by their size, canopy cover, age and health, large trees can lower carbon emission in the atmosphere by 2-3% (GreenSpace, 2010).
• Vegetation cover also filters out other particles and dust in the air.
• Green spaces absorb and reduce the noise generated by human activities, especially trees act like noise barriers.
• Vegetation cover and soil in urban landscape controls water regime and reduces runoff, hence helps to prevent water floods by absorbing excess water.
• Trees can also act like wind breaker.