these oaks are mature large with green leaves at the time when a strong wind will break them off 6-8' up their trunk when we cut the trunk through with the chainsaw we find a large pithy center on these trees. The bark is still intack, looks good, leaves were still green when it was blown over earlier in the year, but we have come across 4 trees now with this same condition on our land, all blackjack oaks, I blieve. any insight to this would be very appreciated.