I regret I cannot give you an exzact reference but the WIA
magazine Amateur Radio, some years ago had such an article
and the results thereof. It worked quite well for what it was (a tree)
and there were even suggestions as to which species were better than
others! AFAIK it wasn't an April edition.

Some of the gum trees here are 150+ feet high and the trick seemed to
be tapping in at the right level from the ground.

Some unhelpfull folk later suggested the 8' of coax to the matching
network was the radiator :-(

I have no way of finding this info - maybe you can search the net?

Cheers
Murray vk4aok

Claude Frantz wrote:
Many thanks for all the responses.

I remember that in the experiment I have mentioned, the coupling to the
tree was via an toroidal coil which was mounted around the tree, the
tree beeing in the axis.

Sure, a tree cannot be a good antenna. Any "real" antenna will probably
always be better. But often the question is: no antenna at all or
anything which does not seem to be an antenna. Perhaps a tree can be
such a thing. Further, in portable operation, it is not always easy to
install a "real" antenna.

Claude