One of my favorite plant communities are Floodplain Scours -- areas of relative bare rock that occur along the banks of major rivers where rock outcrops are subject to winter ice scour and high-velocity flooding. Along the Youghiogheny River in Fayette County, PA these communities occur along bedrock shelves and boulders. The ice and flooding removes competition from many plant species allowing a number of threatened and endangered species such as rock grape (Vitis rupestris), Carolina tassel-rue (Trautvetteria caroliniensis) and large-flowered Barbara's buttons (Marshallia grandiflora) to survive.
Last weekend, my colleague Pete Woods and I went down to the Yough to check out these scour zones during ice conditions as we figured it would be a good time to check out the ice conditions as this region of the country had been in a multiweek deep freeze. In fact, the thermometer on the car read as low as -15F on the way down (it did warm up to nearly 20F by the time we left shortly after lunch.
Floodplain Scour communities are most likely declining due to destruction of plant populations and the alteration of ecosystem processes needed to maintain these populations. Alteration of the natural flooding regimes through construction of dams and other impoundments has greatly impacted the plant composition. As the amount and frequency of flooding and ice-scour are the most critical factors maintaining the quality and persistence of this community, factors that can change these attributes such as the effects of global climate change is the potential loss of ice scour as the climate warms.