Creating Climate Resilient Oak Forests in Cities

For urban forest managers, there are many challenges to creating and maintaining healthy and sustainable oak forests. Oak trees do not automatically thrive in many environments and may require significant time and attention to become established and grow well. However, according to climate change models, oaks may be better suited for future conditions than other tree species. For example, oaks are very drought tolerant and will survive better than other species if climate change brings longer periods of drought to the Eastern United States in the coming decades.

This project is adapting traditional oak forest management techniques for use in cities. NRS scientists and partners are using long-term field experiments in multiple east coast cities to test different strategies and, ultimately, to identify successful approaches for managing oak forests in cities. The research is taking place in Baltimore, Maryland; Philadelphia, Pennsylvania; New York City, New York; Westchester County, New York; New Haven and Hartford, Connecticut; and Springfield, Massachusetts.

This work grew out of the Northeast Urban Silviculture Workshop that was held virtually in December 2020 and January 2021. The workshop focused on adapting traditional forest management practices for cities, using oak forests as a case study. Workshop participants explored how people in urban areas and their various activities affect oak forest management. During the workshop scientists and practitioners designed long-term experiments set in oak forests in multiple cities.

Traditional forest management supports oak growth and reproduction by removing trees to create gaps in the forest canopy, and/or removing some oak seedlings to reduce competition and provide favorable growing conditions for others. However, stressors such as pollution, habitat fragmentation, land-use changes, invasive plants, animals, and diseases interact with climate change, creating environmental conditions that ecosystems have never experienced before. Because of this, there is interest in creating new forest management practices that promote healthy forests over the long term. This led to the creation of the “Canopy Gap Study” that is part of this overall project.

Another approach that can help a forest ecosystem thrive now and in the future is planting seedlings that are better adapted to expected future conditions. This strategy is called assisted migration and can include both planting species from warmer climatic zones and collecting seeds from warmer seed zones. The “Oak Orchard Study” portion of this project is testing this approach for creating healthy oak forests in cities.

In the seven study cities, forest managers identified mature, closed-canopy oak forest patches that could accommodate long-term research plots. Broadly considered healthy urban forests, or “good woods,” these sites provide high quality ecosystem services and greenspace for residents. The forests are all dominated by native trees in the canopy and midstory and have minimal invasive (non-native) species in the understory. 

These sites typically have limited natural growth and reproduction of native tree species resulting in a mismatch between the mature canopy and seedling community. As a result, today’s “good woods” are vulnerable to future disturbance, such as windthrow and pests, and may become tomorrow’s invaded and lower quality urban forests.

Additional threats and pressures influencing forest management strategies across the study region include:

• High deer abundance and browse.
• Frequent tree loss and gap creation caused by the natural death of older trees, insect pests, diseases, and storms.
• Current or future risk from pests, pathogens, and plant invasions.
• Public opposition to tree removal and/or management activities.
• Rules and regulations of the government agencies or organizations that own and manage the land.

Canopy Gap Study

The “Climate Adapted Oak Provenance - Canopy Gap” study (referred to as the “Canopy Gap Study”) is planting and tracking seedlings from six seed zones. The seeds are planted in canopy gaps in mature, oak-dominated forests that are relatively healthy and have mostly native tree species.

In Baltimore, Philadelphia, New Haven, and Springfield, the project team selected existing canopy gaps at three forest sites in each city. Each canopy gap plot was planted with either chestnut oak (Quercus montana) or white oak (Quercus alba) seedlings from the four, plus two seed zones located in Kentucky and Tennessee. The research sites were selected with the help of partners in each participating city with an eye toward areas that are unlikely to be disturbed by park visitors.

Oak Orchard Study

The “Oak Orchard - Provenance and Progeny” study (referred to as the “Oak Orchard Study”) is part of a broader research effort led by the University of Kentucky’s White Oak Genetics and Tree Improvement Project. The University of Kentucky study is identifying white oaks with genetic traits that are likely to help the trees adapt to a changing climate in the coming decades.

In Springfield, Massachusetts, Katonah, New York, and Baltimore, Maryland, the research team has planted hundreds of white oak seedlings grown from seeds that were collected in six different cities (Springfield, MA; New Haven, CT; Philadelphia, PA; Baltimore, MD; Louisville, KY; and Memphis, TN). The planting sites are located in places where it is possible to invite the general public to demonstrations and/or places that are connected to local forestry operations.

Expected Outcomes

Field operations began on this project in 2023. The research team hopes to have initial findings to report in late 2024 after the first round of post-planting data collection.