Introduction

The term barren is a historical one, used by settlers to refer to a landscape or landscape feature with little, if any, timber-sized trees, although tree species may have been present in smaller size classes. We use the term serpentine barren to refer to a serpentine outcrop and its associated vegetation. Prior to European settlement, serpentine barrens vegetation in much of eastern North America was composed predominately of fire-maintained communities of grassland and savanna (grassland with trees). This chapter considers the history, flora, vegetation, and physiological ecology of the serpentine barrens of eastern North America, with emphasis on the Mid-Atlantic states of Maryland and Pennsylvania. In this region, afforestation of nearly all undeveloped barrens, and more than 90% of undeveloped historic communities, has occurred during the past 50 years. The invading trees are relatively fire intolerant species such as Pinus virginiana (Virginia pine) and Juniperus virginiana (redcedar) (nomenclature follows Gleason and Cronquist [1991] unless authorities are given).

Serpentine soils are derived from ultramafic rocks, which occur in a discontinuous band along the eastern edge of the Appalachian mountain system from Newfoundland and Quebec, Canada, through New England, U.S.A., to Alabama on the Piedmont Plateau (Reed 1986; Brooks 1987). Ultramafic rocks are thermally altered and largely plutonic.

They are ferro-magnesium silicates high in magnesium and iron and low in aluminum, calcium, and silica. Serpentinite is a hydrated ultramafic rock, and it may be ultrabasic and contain heavy metals such as chromium and nickel (Reed 1986).