Cobble Bar Monitoring
Affected ParksBig South Fork NRRA (BISO) Importance / IssuesCumberlandian cobble bars, or "river scour prairies" are unique plant communities endemic to the Cumberland Plateau of Tennessee and Kentucky. Ranked by The Nature Conservancy as Globally Imperilled (G2) and vulnerable to extinction throughout their range, they exist on open, flood-scoured exposures of bedrock, cobble or gravel along large rivers.
Fewer than 500 acres of Cumberlandian cobble bar habitat remain in existence, with the highest quality examples in Big South Fork NRRA and Obed Wild and Scenic River Typically thick with grasses and flowering herbs, these river prairies share many characteristics with the tallgrass prairies of the American Midwest. Whereas fire is the driving force sustaining midwestern prairies, in the bottom of the deep river gorges of the Cumberland Plateau, water is the ecological driver. Raging floods wash over these habitats on multiple occasions each year, scouring out species that are not adapted to disturbance, including most trees and other woody species. Grasses, herbs, and some low shrubs thrive under these punishing conditoins. Several extremely rare plants, including some that grow nowhere else, also flourish in these riparian prairies. Among these are two Federally-listed species - Cumberland rosemary (Conradina verticillata) and Virginia spiraea (Spiraea virginiana), as well as several dozen other globally or regionally rare plants. Protocol Development and StatusMAPPING: As of winter 2007, we have mapped 77 river miles at Big South Fork NRRA and Obed Wild and Scenic River, representing 67% and 61% of the parks, respectively. Cobble bar mapping will be completed in 2008, given sufficient water levels for access. 147 cobblebars have been mapped at Obed, and 22 at Big South Fork. 37 previously unknown populations of the Threatened Cumberland rosemary have been documented.
Hydrograph from Big South Fork, showing the river's characteristically sudden rise from 170 to 8,000 cfs (cubic feet per second) in less than 24 hours
METHODS: 30 permanent transects have been established at 6 sites and have been monitored for 2 consecutive years. An average of 1,000 data points are being taken at each site to monitor changes in vegetation structure and substrate (sand, gravel, cobble, boulders, coal sediment). Initial analyses of data indicate that we will need to establish monitoring plots on 5-10 sites in each tributary. Final monitoring sites will be selected as soon as the mapping is complete.
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Cumberland rosemary - a Federally-listed Threatened plant endemic to Cumberland Plateau cobble bars Monitoring ObjectivesThe goals of this long-term monitoring effort are to determine whether cobblebar communities are being negatively impacted by changes in natural flood cycles or degradation of water quality. If normal flood cycles are disrupted by upstream impoundments or water withdrawal, these open, grassy communities could vanish, replaced by woody species - including non-natives - that would not ordinarily be able to survive here. Specific objectives are to document: 1. Long-term trends in community structure (e.g., cover, density by height class of woody species; cover and density of grasses and herbs). 2. Long-term trends in abundance and size class distribution of selected rare, threatened and endangered plant species on the cobble bars. 3. Long-term trends in cobble bar substrate composition (sand, gravel, cobble, boulder, coal sediment). 4. Presence and abundance, by species, of invasive exotics. |
