COS 182-3 - The effects of pre-planting treatment strategies on understory vegetation in urban forest patches

Abstract: Urban forest patches often consist of a mixture of invaded and healthy forests. These forests encounter a wide variety of anthropogenic and environmental pressures, including frequent canopy gap-creating events, herbivory pressure, and invasive species. Forest restoration strategies to overcome these stressors often rely on enhancing natural tree regeneration or tree-planting. However, pre-planting treatment strategies are a crucial preparatory step in establishing site conditions to ensure successful long-term natural and artificial tree regeneration. Here, we evaluated the response of invasive and other understory plants to three pre-planting treatment strategies: mechanical removal, synthetic herbicide use, and organic herbicide use. Our objective was to determine which pre-planting strategy was most effective at controlling invasive plant species and enhancing native plant cover. We hypothesized that organic herbicide would yield the lowest understory response, particularly with invasive plants.


In collaboration with Philadelphia Parks and Recreation, we conducted a study in Pennypack Park, located in Philadelphia, Pennsylvania. The study was installed in a 40-acre upland oak-tulip forest with a deer exclosure. In this stand we identified 15 naturally occurring canopy gaps and established 36 plots within those gaps, each of which was assigned a pre-planting treatment (mechanical = 20; synthetic = 8; organic = 8 plots). To monitor plant understory response to pre-planting treatments, we established 5-meter diameter subplots at the center of each of the 36 plots. Initial vegetation surveys were conducted in July 2021, prior to any treatment. Vegetation surveys were conducted an additional three times and concluded in September 2022. Mechanical and herbicide treatments were employed between each of the four surveys.


Our pre-planting treatments targeted plants such as Alliaria petiolata, Lonicera japonica, Microstegium vimineum, Persicaria perfoliata, and Rosa multiflora. Mechanical removal yielded the highest understory percent cover reduction rates (average decrease of 111%) with synthetic (average decrease of 97%), and organic herbicide (average decrease of 21%). Of these, mechanical removal had a decrease of 94%, synthetic herbicide had a decrease of 88%, and organic herbicide a decrease of 21% in invasive understory cover. Native understory responses varied likely due to the reduction in invasive cover and reduced competition. In conclusion, mechanical and synthetic herbicide use may have the greatest impact on understory vegetation and at controlling invasive plants during pre-planting stages. Future work will monitor the effects of these treatments on planting success.