Wednesday, March 23, 2005

Natural (and un-natural) history notes

It was a fine spring day for birdwatching at the Onion Creek greenbelt close to my house. But the birds didn’t want to be watched. I did see a red shouldered hawk make a wingfolded thunderbolt drop on something, but I couldn’t see what happened.
The greenbelt is a kind of wilderness now, but in the early 1900s was part of a thriving cotton-farming community called Bluff Springs, which is now gone. In my walks I have located one of the springs--but the people have all disappeared. There was at one time a post office, a one room school, and a cotton gin--now no trace of any of them. Cotton farming declined steadily until by WWII it was gone for good.
The problem was really that Austin is too dry for reliable un-irrigated farming. The farmers slowly went broke and got jobs in town and the fields reverted to pasture, and then to tracts now for sale as eventual subdivisions, except land closest to the creek which is subject to catastrophic floods, which is why the greenbelt exists.

So the greenbelt is all secondary vegetation, except the land that never got farmed that is right next to the creek and thus is the way it has always been, with big baldcypress trees right at the creek's edge, and pecans in the bottomland to the inside of the oxbows. The oldest abandoned cotton fields beyond the creek bottom have grown up into a thick forest of mainly hackberry and cedar elm, with a few introduced species like chinaberry. The most recently abandoned fields, which were cow pastures 15 years ago, are now dense thorny mesquite thickets, with small cedar elms underneath now struggling for light, but destined to eventually triumph.

Most of the area is underlain by cretaceous chalk, but a few miles away we have a small, unobtrusive volcano called Pilot Knob, defunct now, which spumed and thundered in the cretaceous sea but whose eruptive output never kept ahead of wave erosion--an atoll formed around it, but no permanent island stood above the central cauldron of boiling smoke and steam. Only now 65 million years later with the seas gone does the small basaltic knob stand a couple hundred feet above the surrounding limestone. The atoll still rings the hill, and Onion Creek cuts through some of the volcanic outcrops, where it forms a waterfall.

There was a human succession, like a vegetation one, in the abandoned cotton fields. Caved-in shacks mark farmsteads that were simply abandoned, and sold at auction. Lots of people held on but worked in town, running a few cows on their land. The auctioned-off land usually ended up as rental property with a single-wide trailer and and an illegal septic system. In the 60s and 70s some pretty rough people lived out here: the manufacture of speed was a cottage industry, and I remember reading about one dope dealer who lived in the shadow of the volcano who was beheaded by business associates, but the killers felt it was the humane thing to do to release the pet monkeys owned by the deceased so they would not starve, and the murder was only discovered when neighbors found the monkeys rolling the head around in the yard.

Nowadays it is very different. Subdivisions are on the march, and 3-bedroom 2-bath, nearly identical tract houses appear almost overnight in neat rows and columns, and a month later have people living in them, watering spindly so-called "Spanish Oaks" (Quercus texana Buckl.) replacing the bulldozed out hackberries.

Meanwhile, the greenbelt is slowly and eventually reverting to an as yet unknown climax wilderness, almost under their noses. The subdivision folks never walk here. Off in the distance the crows are mobbing a hawk.

Horse trail across Onion Creek
Horse ford

Under the volcano

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