In tropical and subtropical urban areas roofs can be a collecting site.
Pedro Morales of Puerto Rico has trees collected this way.

Billy on the Florida Space Coast
BSF Annual Convention May 28 - 31, 2004 Radisson Hotel, Cape Canaveral,
Florida
Sponsored by The Bonsai Society of Brevard and the Treasure Coast Bonsai
Society
http://www.bonsaisocietyofbrevard.org/2004/2004.html

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++++Sponsored, in part, by Ken Rutledge++++
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