Rosebay Rhododendron on Mill Creek

Rhododendron "(from the Greek: rhodos, "rose", and dendron, "tree") is a genus of flowering plants in the family Ericaceae. It is a large genus with over 1000 species and most have showy flower displays..."

Rhododendron maximum, also called Great Rhododendron, Great Laurel, Rose Bay, American Rhododendron or Big Rhododendron, is a species of Rhododendron native to eastern North America, from Nova Scotia south to northern Alabama.

Approximately 12,000 square kilometers in the southern Appalachians are occupied by this species (Dobbs 1995) where it dominates the understory. This species has historically been confined to riparian areas and other mesic sites but takes advantage of disturbed areas where it is present to advance onto sub-mesic sites.

It prefers deep well-drained acid soils high in organic matter where it produces a thick, peat-like humus. It prefers low to medium light conditions for optimum carbon gain, and has a tremendous capacity for avoiding cavitation during freeze-thaw cycles (Lipp and Nilsen 1997).

Where extensive overstory mortality has eliminated most of the overstory, this species forms a thick and continuous subcanopy known locally as ‘laurel slicks’ or ‘laurel hells’. Rosebay rhododendron is an important structural and functional component of southern Appalachian forest ecosystems.

What isn’t clear is whether or not we are in a period of advancement or retreat for this species. For example, on poorly drained sites on ridge or upper slope positions, large areas of rosebay rhododendron, particularly at the high elevations, have recently died out presumably due to the phytophthora fugus, or due to recent prolonged periods of below-average precipitation.

A few definitions:

riparian A riparian zone is the interface between land and a stream. Plant communities along the river margins are called riparian vegetation, characterized by hydrophilic plants.

mesic "in ecology, a mesic habitat is a type of habitat with a moderate or well-balanced supply of moisture, i.e. a mesic forest, a temperate hardwood forest, or dry-mesic prairie. The opposite of mesic is xeric.

cavitation occurs in the xylem (transport tissue) of vascular plants when the water potential becomes so great that dissolved air within the water expands to fill the plant cell

phytophthora (from Greek phytón, “plant” and phthorá, “destruction, destruction”; “the plant-destroyer”) is a genus of plant-damaging Protists of the Oomycetes (water molds).

all info from Wikipedia