Hydrology and soil magnetic susceptibility as predictors of planted tree survival in a restored floodplain forest

Flooding in floodplain forests is an important abiotic constraint on tree recruitment, as well as on planted tree survival and growth in restorations. Nevertheless, trees are often planted in floodplain restorations without regard to a site's hydrologic context, resulting in poor survival. There is a need for improved tools for identifying critical abiotic factors that control tree growth and mortality at reforestation sites. We planted 400 bareroot tree seedlings of four commonly planted species in plots along five 100-m transects along a hydrologic gradient in a recently restored wetland to determine the effect of hydrology on planted tree survival. We evaluated the effect of exposure to flooding on survival and growth for two growing seasons. We also evaluated the use of soil magnetic susceptibility (MS) as a proxy for soil drainage and predictor of tree survival and growth. Soil MS is easily measured and mainly reflects the concentrations of ferrimagnetic minerals, which can dissolve with iron reduction in poorly drained soils. In the first year, the overall survival rate of the planted seedlings was 61%. By the end of the study period, survival had declined to 25%. Of the four species planted, Quercus bicolor survived best, followed by Quercus palustris and Carya illinoensis. No Juglans nigra seedlings survived to the end of the study. Duration of inundation and species identity were important predictors of growth and survival; as duration of inundation increased, height growth and probability of survival for each species decreased. Soil MS was not strongly correlated with either flood duration or elevation and was not an effective predictor of tree survival at this site, but might be a useful tool to guide planting in areas with a more pronounced hydrologic gradient. This research can help provide higher precision tree planting in accordance with species’ natural distribution across soil moisture gradients, ultimately leading to greater planting success in restorations.