According to the tooltip for rapid resource regrowth, it will grow fast enough for more than 10 harvesters to harvest from 1 tree. When combined with the Instant Harvester Unload option, the amount of income you can get off of 1 tree should be significantly faster. Attached is a screenshot to illustrate. I believe this resource patch has a 3-cell invisible spreader in addition to the regular tib tree that has a 1 cell radius. It is indeed enough to sustain 10 harvesters.
You can simply enable rapid resource regrowth in the client options menu.