The ability to have trees in a garden would perhaps not only be climate related, but again relate to allotment size. The gardens in terrace houses in London tend to be compact. [ http://farm5.static.flickr.com/4003/4422462390_3fd0bda264.jpg ]

So the potential for ‘green’ gentrification of existing typologies is a particular challenge for the landscape profession. [ http://www.london-architecture.info/LO-018.htm ]

In some cases perhaps communal gardens behind terraces could provide greater amenity than a row of individual gardens?

Consider if the row of terraces were connected by an edge tree lined
gravel walk [ http://austenonly.com/2010/08/09/the-georgian-garden-the-gravel-walk-bath/ ] which provided connection between individual walled/screened micro-flower gardens at a slightly higher level close to each terrace. Some terraces may provide opportunities also for roof gardens?

These gardens could be connected by (contemporary) glazed rear garden ‘conservatories’ at ground level and overlooked from the second level by (contemporary) Juliet balconies or glazed bay windows.

In the US cities can get Tree City designation if they can demonstrate a commitment to maintaining the local urban forest and tree canopy cover. [ http://www.norwalkplus.com/nwk/information/nwsnwk/publish/News_1/Connecticut-DEP-announces-Tree-City-USA-designation_np_12850.shtml ]

Four things are required:
1) A Tree Board or Department
2) A Community Tree Ordinance
3) A Community Forest Program with an annual budget of at least $2 per capita
4) An Arbor Day Observance and Proclamation

The benefits of urban trees for climate modification and energy efficiency also need to be given greater attention in this the International Year of the Forest. [ http://www.ksallink.com/?cmd=displaystory&story_id=17248&format=html ]

“Louis XIV’s minister Jean-Baptiste Colbert’s oak forest at Tronçais, planted for the future use of the French Navy, matured as expected in the mid-19th century: “Colbert had thought of everything except the steamship,” Fernand Braudel observed.”

Here is the wiki perspective on modern forest management conundrums:

“Public perception of forest management has become controversial, with growing public concern over perceived mismanagement of the forest and increasing demands that forest land be managed for uses other than pure timber production, for example, indigenous rights, recreation, watershed management, and preservation of wilderness, waterways and wildlife habitat. Sharp disagreements over the role of forest fires, logging, motorized recreation and others drives debate while the public demand for wood products continues to increase.”