A growing forest will remove carbon dioxide and produce oxygen. Conversely, a decaying or declining forest will release carbon dioxide and consume oxygen through decomposition processes. If forest canopy cover is increased (more trees are added) and sustained through time, net carbon dioxide will be removed and oxygen produced. Given the carbon dioxide level in the atmosphere (≈0.03%) is much less than the oxygen level (21%), the relative impact of urban forests and their management are much more significant for carbon dioxide than for oxygen.