a lot of trees use sap to heal thereselves hence finding amber . its quite natural and should be fine .

Possible damage to the stems after last winter (especially January). Though nosey is correct in some ways, it tends to be trees such as conifers (resin), Eucalyptus (gum) or various trees and shrubs from various other disparate families that produce latex that have this ability to seal wounds. I'm not so sure about Rhus having any of these capabilities though I may be wrong!

If the worst comes to worst, at least Rhus can regrow quickly from lower down below the effected area.

Thanks for your help much appreciated

your welcome x