Trees in cities 'live fast but die young' compared to rural forests, warns a new study.
Researchers found that trees in urban areas die faster than ones in the countryside as higher levels of carbon dioxide make it harder for the plant to survive.
City-dwelling trees suffer a net loss of carbon storage which means trees produce less energy from the air.
Now researchers say more must be done to tackle the environmental impacts of urbanisation.
Ian Smith, a PhD student of Boston University in the United States, said: 'Cities are at the forefront of implementing climate mitigation policies including urban greening, to combat rising temperatures and atmospheric CO2 concentrations.
'We find that tree planting initiatives alone may not be sufficient to maintain urban canopies in older cities like Boston.
'Due to the age and size structure of the existing canopy, efforts to aid in the establishment and preservation of tree health are imperative for increasing urban tree cover and maximising the wide range of ecosystem services provided by the urban canopy.'
The research team used a model to forecast short-term changes among street trees for several planting and management scenarios.
Researchers applied the model to estimated tree growth, mortality and planting rates both among trees in Boston city and forests in rural Massachusetts.
It was discovered that rates of carbon cycling and mean diameter growth rates among urban trees were nearly four times faster in the city than the countryside.
But the positive findings were outweighed by net loss of carbon storage and high mortality losses - which are more than double than trees in rural forests.
The study, published in the journal PLOS ONE, has prompted scientists to urge communities to do more to establish and preserve trees which are essential to increasing street-tree canopy cover and carbon storage in vegetation.
Researchers say strategic combinations of planting and maintenance will be needed to secure urban sustainability but more needs to be done to develop understanding of urban trees and their ecosystems - which may differ from rural forests.