The response of planted trees to vegetation zonation and soil redox potential in created wetlands

We examined interrelationships among natural vegetation zones, soil redox potential (Eh), and metrics of tree seedling performance (i.e survival, growth, and photosynthesis) for planted Fraxinus pennsylvanica, Acer saccharinum, Quercus palustris, and Quercus bicolor at two created perched wetlands (two years and five years old) in Michigan, USA. Vegetation zones apparently associated with hydrology were fully developed at both sites. Wetland zones always had lower mean Eh than upland zones, indicating mostly anaerobic and aerobic root environments, respectively. Eh values for transition zones were similar to aerobic upland zones at the five-year-old site, and changed from anaerobic to aerobic conditions over the growing season at the two-year-old site. At the five-year-old site, transition zone trees of all species generally had greater height growth, survival, and were less likely browsed by deer than upland trees. They also had much greater survival and endured shorter periods of anoxia stress than wetland trees. Photosynthesis was positively related to survival and Eh, suggesting that unfavorable carbon balance may help explain low survival in the anoxic wetland zone. Management implications include: (1) vegetation zonation is a good indicator of wetland hydrological factors important to planted tree performance; (2) targeting developed transition vegetation zones for tree planting could increase the success and efficiency of efforts to create forested wetlands; and (3) transition zones extended over only a 9.3 cm vertical elevation gradient, indicating the importance of precise grading when creating perched forested wetlands.