An Afforestation System for Restoring Bottomland Hardwood Forests: Biomass Accumulation of Nuttall Oak Seedlings Interplanted Beneath Eastern Cottonwood
Bottomland hardwood forests of the southeastern United States have declined in extent since European settlement. Forest restoration activities over the past decade, however, have driven recent changes in land use through an intensified afforestation effort on former agricultural land. This intense afforestation effort, particularly in the Lower Mississippi Alluvial Valley, has generated a demand for alternative afforestation systems that accommodate various landowner objectives through restoration of sustainable forests. We are currently studying an afforestation system that involves initial establishment of the rapidly growing native species eastern cottonwood (Populus deltoides Bartr. ex Marsh.), followed by enrichment of the plantation understory with Nuttall oak (Quercus nuttallii Palm.). In this article, we examine the growth and biomass accumulation by Nuttall oak seedlings to determine whether this species can be established and whether it will develop beneath the cottonwood overstory. After 3 years of growth beneath cottonwood canopies, Nuttall oak seedlings were similar in height (126cm), but were 20% smaller in root-collar diameter than seedlings established in open fields. Seedlings established in theopen accumulated more than twice the biomass of seedlings growing beneath a cottonwood canopy. However, the relative distribution of accumulated biomass in seedlings did not differ in the two environments. Ten percent of total seedling biomass was maintained in leaf tissue, 42% was maintained in stem tissue, and 48% was maintained in root tissue on open-grown seedlings and seedlings established in the understory of cottonwood plantations. Though establishment in the more shaded understory environment reduced Nuttall oak growth, seedling function was not limited enough to induce changes in plant morphology. Our results suggest that an afforestation system involving rapid establishment of forest cover with a quick-growing plantation species, followed by understory enrichment with species of later succession, may provide an alternative method of forest restoration on bottomland hardwood sites and perhaps other sites degraded by agriculture throughout temperate regions.