Effects of a willow overstory on planted seedlings in a bottomland restoration

Four bottomland tree species (green ash, bald cypress, water tupelo, and swamp chestnut oak) were planted under four levels of willow canopy (intact canopy, 60% thinned with herbicide, complete control with herbicide, and complete mechanical removal plus control with herbicide). Through age 5, species selection rather than canopy control treatment was the dominant factor in determining regeneration success. About 55% of the cypress and green ash seedlings were surviving at age 5, versus 17 and 27% of water tupelo and swamp chestnut oak, respectively. Green ash was significantly taller (at 3.7 m) than all other species at age 5. The willow canopy provided minor growth benefits during the first 2 years by ameliorating herbaceous competition, hydrology, and soil temperature. However, by age 5, there were no significant differences in seedling heights among the canopy treatments. We believe that an improved strategy would involve removal of the willow canopy 2 years after planting, when the seedlings begin to exhibit substantial height-growth potential and are, thus, better prepared to respond.