Based on the apparent lack of reports of any allelopathic activity of this species, I'd guess that, if there is any negative-allelopathic activity associated with this plant, it is not significant. Some Rhus species are known to have some moderate to low-level allelopathic activity, so I wouldn't be surprised if there was some (just not lots) for this species too.

Have seen them growing next to other trees and do not remember having seen the effect you are describing. Will pay more attention to this in the future.

I have the same question. There is a clump of several Rhus lancea in my yard, and I recently planted three different varieties of cold-hardy avocados among them, hoping the microclimate created by the Rhus foliage would protect the avocados during their first couple of years. Then, when and if the avocados are well-established, the plan is to keep pruning the Rhus back and eventually remove them altogether. I also used the carpet of dead leaves under the Rhus to mulch the avocados, but then began wondering if they might have any allelopathic effect. Guess I'll find out!