The environment is changing: As witness, one only need look about. If that sounds familiar to the photographers among us, it should, since it is our daily ritual to soak in the aroma of the visions with which we are greeted. But when I saw this mushroom on a tree little more than a quarter mile from my front door, I halted. Here was evidence that all is not right. Why? Although it’s perhaps common to find mushrooms of all sorts in Nebraska and the Great Plains, this one is special: It’s larger than a human brain, and weighs in at more than three pounds, the product of an abnormally rainy and humid summer.