Plants require water to survive. Drought makes plants more vulnerable to pests and pathogens. In 2016, the Arnold Arboretum experienced a record-breaking high temperature season. This drought episode lasted for eleven weeks. A considerable number of trees died or required removal. The impacts of prolonged drought require significant attention from our horticultural staff. We expect climate change to cause hotter temperatures in New England over the coming decade, making prolonged droughts more frequent. We are concerned with the consequences that increasing pressures of drought will have on the health of our living collections.
Manual watering practices involve transport of heavy hose and water equipment across the grounds. These practices contribute to soil compaction and unnecessary carbon emissions. The practice of hand watering during the daytime is ineffective because of the loss of water due to evaporation. In 2015, we reviewed our strategy for preparing our living collections for the challenges of climate change. Our long-term strategy involves increasing water access, building out of automated irrigation systems in high-priority collections, and improving overall water infrastructure and irrigation systems to increase water use efficiency.
Centre Street Irrigation Project (Phase 1, 2019-2021)
In 2019, we completed the first phase of a large-scale initiative to improve our response to drought with the Centre Street Gate Project. This donor-funded project includes automated irrigation across 30 acres of plant collections, and water access to another 17 acres. This covers our oak collection, viburnum collection, Explorers Garden, hickory collection, and birch collection. From 2021 through 2023, we expanded the Centre Street system with thousands of feet of irrigation, providing additional water connections and sprinkler capacity throughout the conifer, hickory, birch, ash, elm, and Oriental oak collections, extending the reach of the system to over 4,200 plants.
These new, automated irrigation systems help alleviate the detrimental effects of manual watering practices. Our systems water at night to minimize water loss in the day from evaporation and reduce the amounts of soil compaction and fossil fuel emissions caused by watering vehicles and manual watering.
Peters Hill Irrigation Project (Phase 2, 2021-2023)
Moving forward from the first phase of our large-scale drought preparation initiative, we will continue to upgrade water infrastructure across our grounds for improving water accessibility and conservation.
Phase 2 aims to bring water access to over 55 acres and more than 2,700 accessions on Peters Hill—the area least accessible to sources of water in the Arboretum. Among these organisms are the Arboretum’s ginkgo collection, nationally accredited by the Plant Collections Network and holding the greatest genetic diversity of any collection of wild collected ginkgoes in the world. Two other high-value collections that stand to benefit from this new system, the crabapples and hawthorns (a favorite of the Arboretum’s founder and first director, Charles Sprague Sargent), provide year-round interest and draw thousands of visitors each spring with their showy blossoms. Atop the Peters Hill summit, the honey locust collection includes dozens of majestic specimens, adorned in brilliant gold each October.
Due to the varied terrain and elevation of the tract, transporting and deploying supplemental water throughout the entirety of this area will require the use of electrical booster pumps. Instead of utilizing expensive and unsightly above-ground structures in the historical landscape, the Arboretum will retrofit and soundproof the concrete garage of its property at 163 Walter Street to hold a new 4” water service, three-phase electrical service, and pumping station.
Construction of Phase 2 is ongoing, with substantial completion anticipated in June 2023.
Meadow Road Irrigation Project (Phase 3, 2024-2025)
Looking ahead, the Arboretum is setting its sights on a third and final phase of the project to safeguard an additional 36 acres of treasured collections along Hemlock Hill Road, Meadow Road, Conifer Path, and Weld Hill, including the Arboretum’s prized national collection of maples. This phase will also require the construction of a freestanding booster pump station to move water across both sides of Bussey Hill. Design of Phase 3 is ongoing, with construction anticipated in 2024.
Once completed, the Arboretum’s drought mitigation initiative will represent the most comprehensive infrastructure project designed to protect the living collections in our 150-year history. Most importantly, this effort embodies a key component of the Arboretum’s strategy to mitigate the effects of climate change on the plants we grow and treasure—and signals a strong reaffirmation of our founding promise to protect and preserve biodiversity for generations to come.
We are thankful for the donors who have supported the Arboretum Drought Preparedness Initiative. If you are interested in supporting the Arnold Arboretum’s future sustainability initiatives, please check our Support Page.