I really have no idea the crowns on my jack maple look real good in the summer. Never hit any bad spots tapping them either. All I know is 5 years in a row they maybe yeild a cup of sap to every full bucket on the trees next to them. I think I will tap them with the chainsaw this spring and let the young trees growing close to them get a fighting chance. Hate to do it but heck jack don't make syrup but will heat the house.