Question
I have been reviewing a landscaping specification for a construction project and see that it requires placement of trees in the same orientation to north (by flagging the north side of the trees) as they were in the nursery.  I've been involved in forestry and environmental science for nearly 30 years and have never heard of this and haven't been able to find a single hit on the web about this subject.  Have you heard of this?  If so, is it really necessary to get good establishment of trees in a landscaping project (not my experience)?  Do you know of a literature citation for this?  Thanks for any info or thoughts on the subject.

Answer
I found out one possible source for this specification:  The Saguaro Cactus of the Southwest is sensitive to rotation after being transplanted.  The developers would lose most of the cactus planted if the side formerly facing north (in the shade) was suddenly placed in full sun, causing the potential for damage and parasitic infection.

A horticulture friend of mine says they now spray-paint a big "X" on the north side, so it is oriented in the installation properly.

Sounds plausible.

-Marc