Succession in Loblolly Pine Plantations Converted from Second-growth Forest in the Central Piedmont of Virginia

Abstract

Vegetation composition and structure were quantified in 21 pine stands converted from second-growth hardwood-pine forest at two state forests in Virginia. These stands included three replications each of seven developmental stages ranging in age from 1-22 years. Species richness and vegetation cover in the ground stratum showed the same trend: high values in stands 1-5 years of age followed by a decline from 5-15 years, at which point canopy closure was complete, and these variables were relatively stable for the next 7 years. A peak in transgressive stratum richness in the 9th year was followed by a similar decline and leveling off. Evenness (J') values over time were nearly constant for these understory strata, except in 3-year-old stands where a decline in ground stratum evenness occurred due to dominance by Andropogon virginicus. Increasing richness and evenness in the overstory stratum was due to growth of hardwoods. Trends in richness and evenness differed from the old-field successional model due to a high diversity of seeds and sprouts at the start of succession. Despite such differences, the seral stages typical of old-field succession were discernible in converted stand succession. However, they were somewhat abbreviated and masked by the abundance and variety of reproductive units and the rapid closure of the canopy by codeveloping pines and sprout hardwoods. INTRODUCTION The central Piedmont of Virginia is part of the Oak-Pine Forest Region delineated by Braun (1950). Young forests are characteristically dominated by Pinus virginiana and P. echinata and are gradually replaced during succession by an oak-hickory complex (Braun, 1950). From the 1700s to the early 1800s Piedmont lands were cleared, intensively farmed and abandoned (Gottmann, 1969). Abusive crop farming depleted soils and led to severe and extensive topsoil erosion (Culbertson, 1948; Gottmann, 1969). Much abandoned cropland reverted to native forest through succession. The end of the 19th century marked the beginning of a new period of deforestation when most of the commercially valuable forest of the Piedmont was harvested (Gottmann, 1969). Pinus taeda (loblolly pine) has been the principal species planted in the central Piedmont since the 1930s, even though it is incapable of natural regeneration throughout much of this region (S. F. Warner, pers. comm.). Up to the mid-1950s, most planting of P. taeda was in old fields. Owing to a decline in agricultural land abandonment, hardwood and pine-hardwood forests have been directly converted to P. taeda plantations at an accelerated rate. Whereas much is known about the vegetation dynamics of old-field succession in the Piedmont region of the Southeast (Crafton and Wells, 1934; Billings, 1938; McQuilkin, 1940; Oosting, 1942; Keever, 1950; Nicholson and Monk, 1974, 1975), little is known about such changes associated with the establishment and development of pine plantations on sites converted from second-growth forests. Thus, the objective of this study was to examine temporal changes in the composition and structure of vegetation in loblolly pine stands converted from such forests. 1 Present address: 435 Jackson Street, Fall River, Massachusetts 02721. 2 Present address: Department of Biology. 3Department of Biology.