The outward appearance of an old tree may indicate what happened to it during recent years but seldom more than that. If it is cut down with a saw, those rings can be counted and compared. All trees are truthful but some kinds tell their stories more plainly than others. That is true of most cottonwoods. Oaks, hickories, walnuts and sugar maples leave complete records but, because those are slow-growing trees, they are rather difficult to read and interpret.
Pines are the best.
In 1947 a big white oak in one of the preserves was removed because it was dead and a public hazard. It had 430 annual rings. Those made in 1934 and 1930 were so narrow they scarcely could be distinguished. Weather bureau records show that those were years of extreme drought. Those made in 1909, the early 80's and 1857, abnormally wet years, were extremely wide.