Introduction

Scattered within the oak-hickory forest of southern Illinois and at Land Between The Lakes (LBL) in western Kentucky and northwest middle Tennessee are a variety of woodlands that have evolved from a barrens or savanna community of pre-European settlement time (before ca. 1820). In the present context, a barren is a community of widely scattered, short trees growing on relatively thin but continuous cover of extremely rocky soil; a savanna is dominated by scattered trees interspersed with prairie vegetation and located on somewhat deeper soil that may not have a large rock component. Trees commonly found in these communities are drought-tolerant scrub oak species (post oak, Quercus stellata; chestnut oak, Q. prinus; scarlet oak, Q. coccinea; southern red oak, Q. falcata; blackjack oak, Q. marilandica).

Woodland represents a late (successional) stage in the development of barrens and savanna communities and results from an extended period of protection (i.e., absence of disturbance, specifically fire). Like a barrens or savanna, it is a community dominated by extremely slow-growing, usually short, trees. The community has a higher tree density and a more closed (although still relatively open) canopy structure than a barrens or savanna. The generally gnarled, large, twisted limbs and crowns result from a combination of the open character of the overstory canopy, extreme temperatures (40 °C; Fralish, unpublished data) and low soil water-holding capacity, which produce high stress.