What does it take to grow and sustain Harvard’s tree museum for research, horticulture, and education in the twenty-first century? Since becoming director in 2011, William (Ned) Friedman has become increasingly concerned with this question, particularly in terms of protecting the Arboretum and its accessioned plants from threats and challenges posed by global change. Scientists predict that incidents of drought are likely to become more frequent and longer in duration, and if so, the consequences could be catastrophic for the living collections. In response, the Arboretum has completed the first stage of a plan to bring water where and when it’s needed through an automated irrigation system.

“The fundamental imperative of our work as an Arboretum is to safeguard the living collections so they continue to inform and inspire, from generation to generation,” said Arboretum Director William (Ned) Friedman. “We expend a tremendous amount of effort and resources to provide the best environmental controls for our trees, shrubs, and lianas for their entire lifespans. Just as a museum of art must protect its treasures with the right environmental controls, the Arboretum must act now to shield ours from the growing threat of extreme drought.”

Throughout the Northeast, spring is arriving earlier and bringing more precipitation, though our summers are trending hotter and drier—a warning shot being the brutal summer of 2016, the hottest and driest yet recorded in Boston. Among the collections hardest hit that season were the beeches (Fagus), as the drought forced a final reckoning for several specimens severely compromised by beech bark disease. As this misfortune illustrates, several successive years of inadequate rainfall could devastate many Arboretum collections, as drought-stressed plants are more vulnerable to pests, disease, and the long-term effects of issues like poor soil health. Irrigating our plants during drought emergencies is part of a larger set of strategies aimed at improving growing conditions across our landscape.

Irrigation as a tool for drought-mitigation is not new to the Arboretum but was previously limited in scope to high-maintenance areas like the Bradley Rosaceous Collection and the Leventritt Shrub and Vine Garden. With this new initiative, the Arboretum is investing in a multi-phase expansion of this infrastructure. And while the system will be thoroughly automated and synchronized for efficiency, it is not intended to be used under normal conditions. Instead, it is envisioned as an essential safeguard—insurance against calamity—when dry spells become a danger.

Emma Hahn and Jed Romanowiz in the Explorers Garden
Staff irrigation specialists Jed Romanowiz (right) and Emma Hahn bring automation technology to the new irrigation system in the Explorers Garden on Bussey Hill, an area with a large concentration of high-priority accessions. Danny Schissler

“Our goal isn’t to use more water, but in fact, water more with less,” said Andrew Gapinski, head of horticulture. “Our current means of responding to drought are highly inefficient and labor intensive. Through new points of access and use of automated irrigation systems where appropriate, we will be able to fine tune our water use during extreme drought and maximize the effectiveness of every drop.”

Until now, the Arboretum has responded reactively to extended periods of dry weather as the typical homeowner does: by supplemental watering. In a 281-acre landscape, this requires pulling horticulture staff away from their usual tasks to deploy water cannons and position miles of hoses to hydrate the collections. Unfortunately, this means application occurs during the heat of the day, a process that loses a significant amount of water to run-off or evaporation before it can reach the roots. The new system will bring water directly to the plants and collections that need it most and reschedule watering to night when it is more likely to saturate the soil.

Planning and design work for the project began in late 2018, with an extensive process for permitting following last spring. Ground was broken in autumn 2019 in an effort that Gapinski calls unprecedented in scope. While typically irrigation systems of this kind are installed in advance of plantings, the Arboretum and its collections are well established, demanding meticulous care during installation. Air spades were used to excavate soil without disturbing root systems, and consultation with irrigation consultants and contractors led to a revision in the design of the pipes, making them more flexible to avoid damage or disruption to the root systems of nearby trees.

“The beauty of the project is that it brought together both internal and external experts to design and implement an extensive state-of-the-art system using the latest materials and installation technologies,” explains Gapinski. “We were literally able to thread-the-needle with the piping to go under and around the critical root zones of our mature and irreplaceable trees with minimal impact. The lessons learned through the trials and error of this phase will pave the way future projects of its kind.”

Airspading around tree roots
Bartlett Tree Experts work alongside Arboretum staff using an airspade to excavate around the critical root zones of mature trees. Andrew Gapinski

As installation work proceeded over the autumn, horticulturist and irrigation specialist Jed Romanowiz and irrigation apprentice Emma Hahn began installing automated systems in the viburnum collection near the Centre Street Gate and in the historically significant collections in the Explorers Garden. By year’s end, the Arboretum had received permission to commission the new water service at the Centre Street Gate, feeding nearly 13,000 feet of newly installed piping through adjacent collections. Comprehensive mapping of the irrigation infrastructure has also commenced under the direction of Kyle Port, manager of plant records, as a new layer in our mapping

Thus far the donor-funded project has proceeded on schedule, with some thirty acres of high-value collections receiving access to automated irrigation and another seventeen gaining new access to water infrastructure. With momentum gained the Arboretum has launched plans for next steps, including up-dating existing systems and bringing them online with the central controller. Lessons of the past year have allowed horticulture staff to refine the Arboretum’s remaining irrigation needs to parts of three additional areas: Meadow Road, Hemlock Hill Road, and Peters Hill. With the assistance of a team of civil, hydrogeological, and irrigation engineers, conceptual planning for systems in these areas should be complete by the fall, when the Arboretum will begin fundraising for their design and construction.

With this initiative, the Arboretum takes an enormous step toward improving stewardship of the living collections and boosting its prospects for survival in a rapidly changing environment. When needed, our automated irrigation systems will dramatically increase the efficiency of watering our plants and recover thousands of hours of horticultural labor, reduce compaction caused by moving equipment through the landscape, and uphold our commitment to sustainable development and practices. With this and other critical work underway to respond to changing conditions and the uncertainties of the future, the Arboretum continues to pursue innovative thinking and ambitious means to protect and preserve our trees.
Originally published in Silva, Fall/Winter 2019-20. Silva is available biannually as a benefit of membership in the Friends of the Arnold Arboretum.