I think the cedars in areas with more surface rock produce others not so much. The areas in Okl and Kansas I have picked on cedar all had thin soil but a lot of dolomite. I literally picked out of nothing but needles on to of rock in many cases. The Ozarks have a similar setup. Of course I could be totally full of it also.I'm east of Springfield, MO in Douglas Co. I still have some elms scattered around. Some older ones around old homesteads on my place. Never find any Morels with them. I can find them in rocky/cherty hillsides under almost every variety of tree so long as there is some reasonable amount of good soil with it--not real sandy. Generally have Oak forests w/ Hickory. Never find Morels or anything under Black Walnut for obvious reasons. Move from S-facing slopes early onto N-facing slopes late season. Particulary interesting is that cedar woods give up very nice tall/large morels in the late season if the ground can stay some moist. Never found a morel in northerly MO under a cedar. I lived a while in OKC, OK and almost couldn't find a morel unless you were looking under cedars.