How old is a forest? I don't have a good way of answering the question. It's one of those things I have to get at through indirection. But when I find myself surrounding by big trees (see the thumbnail), I have to ask anyway.
One kind of clue is the evidence of human use. Rockwoods Range has been used for quite a while by the Boy Scouts, who run their Green-Rock trail across the Range and into Greensfelder Park next door. I think I saw a sign that said it had been in use for 40 years. An old marker along the trail suggests such an age.
The marker's typography certainly does--I was in the Boy Scouts in the 70's, when their graphic design had gotten all hip (in the self-consciously hip way that only fundamentally square organizations can be), but there was still plenty of deliberately old-school signage around, of which the trail marker seems an instance.
I suppose that a smart forester could read time from the amount that fencing ends up embedded in trees. One example at the Range is the most deeply embedded I've ever seen--the tree must have been a foot in diameter, and the fence is burried almost through the middle. I'm surprised that the wire hasn't rusted out. Good galvanized steel, I guess.
Some facts help too. The Conservation Department says A.P. Greensfelder donated the land in 1943, almost 70 years ago, so the forest must be at least that old, since it's doubtful that the Department would have logged land donated by one of its founders, who incidently seems to have been a leader in preserving open space in west St. Louis County. A Gateway Off-Road Cyclists website says that the last significant fire in the area was in 1941. A.P. Greensfelder built his cabin on the Range in 1926, so it seems likely that some parts of the forest are at least that old, since it seems unlikely that he would have built his cabin if the place was a logged over, burnt out mess. Taking everything into account, my best guess is that the forest is at least 85 years old, with some trees older than that.
The Green Rock Trail leaves the parking lot, heads up a brushy and generally unpleasant drainage, and then cross a ridge and drops into into the head of another drainage. There, across the ridge, is a stand of especially large hardwoods. It's one of those spots where the attentive hiker will pause, surprised by the size of the trees (the picture doesn't quite do it justice). It's nice to be able to say, this is 85 years old, at least, and to speculate what it may be like in another 85.