Jun 3, 2010

upriver from Nashville

The same storms that flooded Nashville filled the banks of Big South Fork, the major eastern tributary of the Cumberland River. Most of the rocks in this photograph were submerged during the flood, and their surfaces were scoured of soil. Riverbank plant communities took a hit, but these plants are adapted to floods and should rebound before rains that improbable strike again.

Yesterday along Big South Fork, recently deposited debris marked high waters 20 feet above current flow. Tree trunks were submerged at the edge of the gorge's forest, but not much evidence of uprootings or other damage was apparent. Among the rocks along the bank, alders, viburnums, birches, sycamores and other woody plants remained firmly rooted and full of leaves. Royal ferns were abundant; what was missing were last year's fronds.

When this river flooded last month, plants along its banks would have been flush with tender new growth. Shrubs and saplings may have lost leaves, and smaller herbaceous plants may have lost all their above-ground growth. Trees above flood stage had maturing, waxy leaves while those in the river had newer leaves.

Judging from what the riverbank looks like a month later, I would guess the early May flood stripped leaf litter, fresh growth and topsoil, but was not strong enough to cause major damage. Rainfall totals east and north of Nashville were not as epic. An epic Big South Fork storm would tumble most rocks in the photograph a bit further downriver and completely reset riverbank ecosystems.

One plant that may have suffered setbacks in the flood is the Cumberland rosemary, one of several endangered or threatened species found only in the Cumberland and Emory river systems. Yesterday I had the privilege of accompanying professional botanists on a search for rare and endemic plants, and we checked two known populations of rosemary. One population was but a dozen plants in a small span of a large boulder field. The second was not found; we may have misunderstood our map. My guess is the rosemary and other smaller plants got a setback that will limit this year's seed set, but they will recover within a year or three.

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