Innovations in afforestation of agricultural bottomlands to restore native forests in the United States
Establishing trees in agricultural bottomlands is challenging because of intense competition, flooding and herbivory. A summary is presented of new practices and management systems for regenerating trees in former agricultural fields in the eastern USA. Innovations have come from improvements in planting stock and new silvicultural systems that restore ecological function more quickly than traditional afforestation with single-species stands. Advances in nursery production of large (e.g. 1–2 m tall; 1.5–2.0 cm basal diameter) bareroot and container seedlings with well-developed root systems have led to increases in survival and growth, and early seed production. In addition to planting high-quality seedlings, managing vegetation is critical to regeneration success. Planting seedlings with cover crops such as redtop grass (Agrostis gigantea Roth) may improve tree survival and growth by controlling competing vegetation and reducing animal herbivory. An innovative strategy that simulates natural succession involves interplanting later seral species such as Nuttall oak (Quercus nuttallii Palm.) in young plantations of pioneer species such as Populus deltoides Bartr. ex Marsh. Populus L. acts as a nurse crop for Quercus L. by reducing biomass of competing vegetation without seriously limiting Quercus L. seedling growth or function. Harvest of the short-rotation Populus L. crop releases the well-established Quercus L. trees. Success in afforestation requires planting high-quality seedlings using management practices that promote survival and growth. Restoration based on ecosystem processes, using tree species that have complementary ecological requirements, will be more successful and affordable than other methods.