I was curious if anyone has some publiced proof that protection of tree-inhabiting species actually helps protecting the host tree. Especially in the case of old, large (veteran) trees. Intuitively this would make sense, but also often a surrogate-habitat (nest boxes, snags or replaced tree features) are being used to maintain a species in a habitat.
It would also be great to hear about different cases in which the protected insect species serves as a umbrella for the host plant!