"Tree trails are inexpensive to create and maintain, and provide lots of interest and curiosity for young and old alike," it said.
"We are looking to identify potential trails and we need your help - whether you work in aboriculture, education in the outdoors, or are an enthusiastic tree hugger, we want to hear your suggestions and reocmmendations."
These can be emailed to email@example.com.
Rethinking Cities has also been asked by the Greater London Authority (GLA) to run two "walkshops" around the Ice Age Tree Trail in the south London borough of Southwark.
The GLA is also launching a heritage tree app linking tube stations to nearby heritage trees during London Tree Week (24- 31 May).