Confluence Valley

This BDA is designated around an open floodplain forest near the confluence of the Youghiogheny and Casselman Rivers that supports a population of Carolina tassel-rue (Trautvetteria caroliniensis), a plant species of state concern. Carolina tassel-rue is a widespread and common species within its range that includes the eastern U.S. except for New England. In Pennsylvania, the plant has only been documented in three counties – Somerset, Fayette, and Allegheny (Rhoads and Klein 1993) and is considered vulnerable. Habitats for this species include streambanks, mesic slopes, moist woods, wooded seepages slopes, and bogs. At this site, Carolina tassel-rue was found along the shoreline of the Youghiogheny, a high gradient river with rapids formed at locations of Pottsville Sandstone shelves and boulders. Dominant species at the site are oak (Quercus sp.), dogwood (Cornus sp.), maple (Acer sp.), rhododendron (Rhododendron maximum), mountain laurel (Kalmia latifolia), milkweed (Asclepias sp.), wild sweet-william (Phlox maculata), and St. John's-wort (Hypericum sp.). Immediate landscape includes gravel roads and residences north of the river.

Threats and Stresses: The greatest threats to Carolina tassel-rue are altered flooding regime that leads to changes in natural communities within the floodplain of the river and residential/industrial development along the river corridor. Periodic flooding and its accompanied scouring and deposition of sand, rock and gravel keep the rock-sand-cobble alluvium bars, islands and banks open to colonization by a number of unique species that require open habitats yet free of invading woody species and aggressive weed species. Any changes to the flooding/deposition would threaten this rare species’ habitats (NatureServe 2005). Increased competition for resources by invasive exotic plant species, which typically colonize disturbed habitats, also poses a major threat to this plant species. Invasive species such as Japanese knotweed (Polygonum cuspidatum), Japanese spirea (Spirea japonica), reed canary grass (Phalaris arundinacea), multiflora rose (Rosa multiflora) and garlic mustard (Alliaria petiolata) are present in many spots along the river. In addition to outcompeting rare species, these exotic species, especially Japanese knotweed, shade out nearly all other vegetation, decreasing the stability of stream banks and creating conditions that make these compromised areas more susceptible to erosion. Direct impact from recreational use is of concern in specific areas. Frequent or intensive use of riverside areas could impact plants of special concern and lead to changes in vegetation cover that would encourage colonization by aggressive exotic species.

Recommendations: Water levels in the Youghiogheny River are now, to some large extent, regulated by releases from the Youghiogheny Reservoir. Municipal water supplies downstream demand water and growing recreational use on the river may play a role in coordinating water releases. Along with the imperatives given to these uses, the maintenance of natural communities and ecological systems need to be taken into consideration with the release of water from the reservoir. The requirements of these natural systems will need to be better researched and evaluated. The frequency and duration of flooding prior to dam construction may provide guidance in efforts to reestablish some approximation of natural hydrological cycles. Any further development in the near vicinity that directly disturbs floodplains or introduces invasive species should be avoided. Measures should be taken to control any non-native, invasive species present within the site.