Probably no one knows the Chattahoochee River National Recreation Area — its ecology, wildlife, plants, geology, human history — better than Jerry Hightower. He has been a naturalist/ranger with the park since Congress established it in 1978.

Its 15 individual units, covering 5,050 acres, stretch 48 miles along the Chattahoochee like a necklace of sparkling emeralds, from Buford Dam on Lake Lanier to Peachtree Creek inside Atlanta's city limits.

Hightower in the 1950s grew up near one of the units, Powers Island, near where the I-285 bridge now crosses the river. "Most of this area was farmland when I was a boy," says Hightower, who spent his boyhood days roaming the cliffs, steep slopes, hardwood forests, sloughs and coves along the Chattahoochee.

So a walk with Hightower along the beautiful trails of the recreation area can be a fascinating lesson in both the natural history and human history of the area. One minute he may be talking about the medicinal uses of a plant along the trail and the next minute describing in vivid detail a Civil War skirmish fought there.

Last weekend, we followed Hightower along the main trail in the park's Vickery Creek unit, where steep rock bluffs create a rugged and varied terrain along the creek, which is a Chattahoochee tributary.

We were there primarily to see the unit's spectacular blooms of rhododendron and mountain laurel. But along the way Hightower kept up a running commentary about the other plants and features we encountered. Here are excerpts from my notes of the day:

We spy a mullein plant, and Jerry plucks one of its huge, soft, dry leaves and holds it up. "This served as toilet paper for Colonial settlers," he says, grinning. Next is a lush growth of pokeweed, whose young, tender shoots have been used as greens — but only after being boiled at least three times, discarding the water each time. The result is poke sallet, once a staple of Southern cooking. It must be "thrice boiled" to cleanse it of toxins, since all parts of the plant are poisonous, Jerry says. Many experts advise against eating pokeweed even after thrice boiling, as traces of the toxins may remain. Purple pokeweed berries in the fall, however, are an important food source for robins, bluebirds and other birds. Colonists once used the berries to make inks and dyes.

Jerry spies a sprig of English ivy and growls, "We're trying to eradicate the ivy from the park because it's non-native." We come across a more colorful non-native, Japanese honeysuckle, whose bright white and yellow blossoms are profuse. "I hate it, but I love it," Jerry says of the honeysuckle. Hates it, he says, because it crowds out native plants; loves it for its sweet fragrance and beautiful blooms. "We used to pick the blossoms and suck the nectar from them," he says.

He points out a large tulip poplar tree. "Tulip poplar was the first choice of Native Americans for making dugout canoes," he says, then snaps off the leafy twig of a small tree and tells us to pass it around, scratch the bark and sniff it. We do so and instantly recognize the rootbeer-like fragrance of sassafras. Sixteenth-century French traders came to Georgia's coastal islands to ship large quantities of sassafras back to Europe, where it was used to make a highly popular medicinal tea. Many people today still brew a tea from it, Jerry says.

Toward the end of our walk, we come upon those thickets of mountain laurel and rhododendron in bloom. Though beautiful, they were not quite in peak bloom last weekend, so maybe I'll come back in a week or so. ...

Missing goldfinches

We get several notes this time of year from folks worried because American goldfinches have suddenly stopped coming to their feeders. Ellis Hodges of north Cobb County writes: "We had a large flock of goldfinches all winter, and all of a sudden they all disappeared."

As the breeding season approaches and the males start taking on the vivid yellow plumage of summer, the goldfinch flocks so much in evidence in winter and early spring break up by late April and seemingly disappear. Until early fall, only scattered pairs or single birds most likely will be seen. Also, says birder Lisa Hurt of the Atlanta Audubon Society, there's a lot of wild food available right now and the birds might prefer that over the feeder food. In addition, the goldfinch is a short-distance migrant, and many of them may be heading to summer grounds elsewhere.

By late autumn, though, feeders should be busy again with goldfinches.

In the sky

The moon will be full on Monday night. The Creeks called May's full moon "the Mulberry Moon," says Fernbank Science Center astronomer David Dundee. Mercury is low in the west just after dark. Mars is in the western sky just after dark. Jupiter rises out of the east at about midnight and appears near the moon Saturday night. Saturn is high in the southwest at dusk.