Right away I was reminded of a fishing spider in the genus Dolomedes, but ten feet up in a tree seemed an odd place for one of these stream and pond dwellers. Furthermore, it appeared that the spider had a nest up in the tree, and was guarding it. Indeed, as I approached, the spider moved out from the foliage as if to guard her den. Not too put off by her intimidating attitude, I moved in for photos...
Upon my return to Columbus, I cracked the books and it didn't take long to determine that the mystery spider was Dolomedes albineus (don't know a good common name, although I would suggest "Blond-headed Fishing Spider"). This species is somewhat variable, and my specimen has far more of a pale cephalothorax (head) than many or most of them.
From the information that I could glean, it seemed that D. albineus would or should occur to the south of Ohio. So I sent some images off to Rich Bradley, a spider expert and author of THIS BOOK. Rich is always helpful and he responded quickly, confirming the identification. He was also excited by the find, as this is only the second reported record of this spectacular fishing spider in Ohio! The other was also photo-documented a few years ago, in Perry County I believe.
Dolomedes albineus is one to watch for, especially in southernmost Ohio. It seems to be expanding its range northward, along with a whole host of other small animals, especially insects. Low shrubby growth in the general vicinity of ponds or other water features might be a likely place to discover them.