This depends on the "Harvest" ability. Go to the abilities tab, search for (Ctrl + F) Harvest and go to the field "Data - Damage dealt to Trees". This ability will define how much damage you deal to the tree and up to the max health of the tree it will fall by a factor of Health/Damage.
You can make a tree give gold, but you need custom trees. Just get a destructible and go to the Stats - Targeted as -> tick something that only a worker unit can touch. Then, a trigger will run that checks when that destructible dies and, when it does, you will attach an integer value on the worker unit, so that when it returns the resources, it will provide the player with the attached via hashtable integer value.