Arabia Mountain is a dome of granite about 12 miles from the house. It’s like Stone Mountain, but its ecosystem has been much less disturbed. It’s now preserved as a National Heritage Area.
If I were a teacher of ecology, I think I’d just invite students on a hike. Most ecosystems are complex, and it’s easy to get lost. But these granite outcrops are such harsh places that relatively few species live in them. The system itself is simpler.
Biologists talk of “primary succession,” the process by which bare rock becomes a place that supports life.
Over eons, water has eroded the granite domes, making small, shallow pools. Rainwater collects and small plants grow: elf-orpine, grasses and mosses. So do lichens, which are a community of organisms — commonly a partnership between a fungus and an algae — rather than a single plant.
When these die, the decayed organic matter in these pools forms little islands of soil in a sea of granite.
The textbook succession looks like this: in the first stage, the dominant species is elf-orpine, a little red succulent. The second stage is marked by communities with lichens and annual herbs. The third is marked by communities with annual and perennial herbs with haircap moss.
These plant communities are primitive and ancient.
Elf-orpine is pollinated by ants. This plant evolved before bees were around.
Walking around these granite outcrops will give you sense of what at least part of the earth looked like millions of years ago.
• Sources: Leslie Edwards, Jonathan Ambrose and L. Katherine Kirkman, The Natural Communities of Georgia; Athens, Ga.: The University of Georgia Press, 2013. You can find a photograph of elf-orpine here:
https://arabiaalliance.org/themes/natural-systems/diamorpha-blooms/
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