Early establishment performance of hybrid Populus and Salix in canopy gaps of a post emerald ash borer urban forest
| Authors: | Richard Hallett, Nancy Falxa Sonti, M.R. Piana, Ronald S. Zalesny Jr. |
| Year: | 2026 |
| Type: | Scientific Journal |
| Station: | Northern Research Station |
| DOI: | https://doi.org/10.1016/j.ufug.2026.129564 |
| Source: | Urban Forestry & Urban Greening |
Abstract
Urban forests face challenges from invasive species, deer herbivory, and tree mortality, creating gaps where natural regeneration fails. We tested whether fast-growing hybrid Populus and Salix genotypes could facilitate urban forest restoration in post-emerald ash borer (Agrilus planipennis) canopy gaps. We planted six genotypes of each genus using two methods—potted trees and direct-planted cuttings across five 21 × 21-meter plots in Baltimore, Maryland, USA. We assessed initial light availability above each planted tree as canopy leaf area index (LAI). From 2021–2023, we measured survival, growth, stress indicators, and photosynthetic performance for 720 trees. Potted trees significantly outperformed cuttings, achieving 59% three-year survival compared to only 14% for cuttings. Among potted trees, Populus genotypes grew 73% more than Salix counterparts with no significant survival difference. Light availability strongly influenced establishment success, Populus showed greater sensitivity to shade than Salix, exhibiting declining survival and increasing stress as LAI increased. Optimal planting zones occurred where overhead LAI remained below 1.4. Areas where established cover had an LAI > 2.7 presented elevated mortality risk. Genotype variation emerged within both genera, with superior performers identified through comprehensive multi-trait rankings via phyto-recurrent selection. These results demonstrate that Populus and Salix genotypes planted as potted stock can successfully establish in challenging urban environments when planted in canopy gaps with adequate light and when appropriate genotypes are selected. The rapid growth offers significant advantages for restoration goals, providing early canopy closure to suppress invasive species while reducing long-term maintenance requirements in urban forest restoration projects.