From
http://plants.usda.gov/plantguide/pdf/pg_prse2.pdf
"The leaves, twigs, bark, and seeds produce a
cyanogenic glycoside. Most livestock poisoning
apparently comes from eating wilted leaves, which
contain more of the toxin than fresh leaves, but
white-tailed deer browse seedlings and saplings
without harm. The inner bark, where the glycoside is
concentrated, was used historically in the
Appalachians as a cough remedy, tonic, and sedative.
The glycoside derivatives act by quelling spasms in
the smooth muscles lining bronchioles. Very large
amounts of black cherry pose the theoretical risk of
causing cyanide poisoning. "
From Wiki:
"The foliage, particularly when wilted, contains
cyanogenic glycosides, which convert to
hydrogen cyanide if eaten by animals.
[17] Farmers are recommended to remove any trees that fall in a field containing livestock, because the wilted leaves could poison the animals. Removal is not always practical, though, because they often grow in very large numbers on farms, taking advantage of the light brought about by mowing and grazing. Entire fencerows can be lined with this poisonous tree, making it difficult to monitor all the branches falling into the grazing area. Black cherry is a leading cause of livestock illness, and grazing animals' access to it should be limited."
I burn a fair bit of black cherry and love it. I'll let you know if I get poisoning.