2024 Annual Report of the Arnold Arboretum by Arnold Arboretum of Harvard University

2024 ANNUAL REPORT

The Arnold Arboretum of Harvard University

About Us

Founded in 1872 and governed by a landmark partnership between Harvard University and the City of Boston, the Arnold Arboretum is a scientific research enterprise at Harvard, stewarding one of the world’s most comprehensive collections of temperate woody plants for research, conservation, and public education. It is also a public park, a crown jewel in Boston’s Emerald Necklace, and a National Historic Landmark. Designed by pioneering American landscape architect Frederick Law Olmsted, it remains one of the best-preserved Olmsted-designed landscapes in the United States.

The Arboretum’s extensive collections of temperate woody plants have a particular focus on the floras of eastern North America and eastern Asia. The living collections, herbaria, and library and archives support research in our laboratories at Weld Hill and by scientists around the world, advancing scholarship across a range of disciplines and across community and professional audiences. Meanwhile, the Arboretum’s 281-acre landscape is an urban oasis and outdoor classroom that provides free access and learning opportunities for the public every day of the year.

Harvard’s Museum of Trees, A Boston Public Park, Free and Open Every Day

Chris Copeland, manager of plant production, offers a tour of the nurseries at the Dana Greenhouses for a Harvard Graduate School of Design class.

Cover: Aerial view of the Arnold Arboretum landscape by Alex MacLean.

From the Director

For 153 years, the Arnold Arboretum of Harvard University has served science and humanity as a vital and expansive resource both locally and around the world. Here at home in 2024, we made significant progress in making our landscape and collections more accessible and welcoming to the Boston community as an outdoor museum, nature preserve, and urban oasis for all. At the same time, the sanctuary we offer here in Boston for the preservation and study of trees has global importance through our historical work to study biodiversity and protect species from extinction. Through both lenses, we remain a leading steward of Earth’s botanical heritage and continue our millenial quest to foster deeper connections between people and plants.

Our Sesquicentennial Campaign reflects the Arboretum’s local and global consequence. Launched in 2022, our $35M fundraising effort—the first major philanthropic campaign at the Arboretum in a generation—focuses on reaffirming our founding values as a free public health and education resource and as an international center for the study and conservation of temperate woody plants. In terms of our public mission, the Campaign is catalyzing our aspirations to renovate the many entrances that serve as neighborhood portals to our museum of trees—making those entrances more beautiful, welcoming, and accessible to communities that need access to nature now more than ever. The first phase of our Entrance Improvement Project launched in 2024 with renovations to the Poplar Gate entrance to Peters Hill, a primary point of access for Environmental Justice Neighborhoods in Roslindale. We are committed to making the Arboretum more central to the lives of people along our perimeter and throughout Boston. The Campaign reached half of its $35M goal in 2024 through the generosity of members and donors.

On the global front, the Campaign and additional philanthropic engagement is strengthening the Arboretum’s historical role as a leading research center and partner in the preservation and conservation of temperate biodiversity. This includes the creation of a new Global Change Fellowship to support Harvard’s expansive efforts to study and remedy our imperiled biosphere. Fellows will join other staff and visiting researchers at the Arboretum who have dedicated their careers to exploring the impacts of climate and global change on plants and providing valuable insights that inform global conservation strategies. In 2024 we also expanded our cooperative efforts with scientists and botanical institutions in China to protect vanishing species through the China Conservation Collaboration Initiative. Increasingly, our partnerships with botanical institutions worldwide are instrumental to our botanical and research missions and were key to the success of collecting expeditions to Japan, South Korea, and (perhaps surprisingly) the panhandle of Florida in the past year.

This report offers glimpses into the many ways that the Arnold Arboretum engaged, informed, and inspired Boston and the world in 2024. We extend our heartfelt gratitude to our members and donors who activate our mission and sustain our positive impact on the lives of both people and plants. Thank you for being an essential part of what makes this landscape and this institution so extraordinary and meaningful. Together, we can continue to make a difference both near and far for centuries to come.

William (Ned) Friedman Director of the Arnold Arboretum Arnold Professor of Organismic and Evolutionary Biology, Harvard University

KATHLEEN DOOHER

Reviewing and

Renewing

the Leventritt Garden

TIn spring 2024, horticulture staff planted nearly 140 shrubs and vines in the garden.

he M. Victor and Frances Leventritt Garden thrives in a sunny location just north of the Dana Greenhouses and Nurseries. In 2024, staff mounted a comprehensive curatorial and horticultural review of the garden, facilitating the most significant changes to holdings there since the garden opened more than two decades ago. Acknowledging the garden’s popularity as a visitor destination and space for Arboretum programming, the review focused on improving the beauty, structure, and utility of a landscape conceived as a formal horticultural display garden for sun-loving shrubs and vines.

The Leventritt Garden is unique within the Arboretum, as it facilitates horticultural experimentation and the maximization of horticultural display within our Olmsted-designed, naturalistic landscape. The 2024 review and subsequent improvements underscore its role as a dynamic and evolving space. As part of the review, the existing collection was meticulously reassessed for plant health, aesthetic appearance, and curatorial value. Plants in the terraced beds that had become overgrown were thinned, and many redundant or less desirable individuals of original massed plantings were removed to create additional space for new plantings. In spring 2024, horticulture staff planted nearly 140 shrubs and vines in the garden. This careful approach to existing and potential holdings ensured that the garden’s plantings remained both diverse, visually appealing, and representative of the Arboretum’s collecting mission and history.

To further improve the visitor experience, new stake labels were deployed throughout the garden, providing clear and informative identification. Additionally, several vine trellises were added, and those forming an allée near the garden wall were raised to allow visitors to pass beneath them more easily. In addition to the horticultural enhancements, movable chairs were added to the garden, providing comfortable spots for visitors to relax, reflect, and immerse themselves in the beauty of the garden during the growing season. The 2024 review of the Leventritt Shrub and Vine Garden has ensured that this cherished part of the Arboretum continues to thrive and inspire, offering a delightful and educational experience for all who visit.

JON HETMAN

Interns Begin Explorers Garden Expansion

Each summer, participants in the Isabella Welles Hunnewell Internship Program at the Arnold Arboretum complete a group project as the culmination of their training in horticulture and public garden management. In 2024, interns focused on the eastern slope of Bussey Hill, home to the Explorers Garden and its plants from global expeditions and species new to North America. The project allowed the team to exercise what they had learned over the summer, while helping the Arboretum refine collections and improve the visitor experience in a key part of the historic landscape.

The trace remains of the estate of Benjamin Bussey lie below the Explorers Garden, with a mix of plantings—including native species of conservation concern and a historical lilac hedge—all in need of reevaluation. Interns removed underbrush and small trees, while Arboretum arborists removed larger specimens that were compromised or redundant to the collection. Central to the project was the removal of a small grove of American beech trees heavily infested with beech leaf disease, a step to diminish exposure to important beech accessions nearby and to create additional planting areas. Seeding straw and plant mixes were incorporated into the site to increase soil fertility and prevent erosion.

The interns assessed the state of our Center for Plant Conservation collections including holdings of Diervilla, and created planting, landscaping, and construction plans for future consideration. The microclimate shared with the Explorers Garden offers exciting options for future plantings, allowing for the extension of the garden and its capacity to shelter plants on the margins of hardiness. In consultation with Arboretum staff, interns compiled planting criteria and reviewed greenhouse inventory for potential plantings. As envisioned in their plans, the space will continue to house species of conservation concern, offer protection to cold-sensitive trees, and feature plants with seasonal interest—providing multiple layers of continuity with the Explorers Garden.

2024 Hunnewell Interns present their capstone project on Bussey Hill to Arboretum staff.

JON HETMAN

“Arnold

Selects” Spotlights

Inkberry Cultivar

Arnold Selects, the Arboretum’s Plant Introduction program, blends the art and science of horticulture to promote the cultivation of exceptional plants in American gardens. Working with partners in the commercial nursery industry, Arnold Selects marshals more than 150 years of experimentation and expertise to bring plants central to our legacy to consumers. In 2024, the Arboretum offered its second cultivar release through Arnold Selects, the Forever Emerald™ inkberry (Ilex glabra ‘Peggy’s Cove’).

Inkberry is a versatile North American native shrub, popular for its winter color, large foliage, and use as an evergreen foundation planting or hedge. The cultivar ‘Peggy’s Cove’ was discovered in 1988 by Arboretum Plant Propagator Jack Alexander in Nova Scotia and introduced as the Forever Emerald™ inkberry. The cultivar stands out for its small stature, reaching only 4 feet tall and 5 feet wide, and its low-branched, rounded habit that contrasts with the leggy branching seen in other varieties. Forever Emerald™ inkberry has dark green leaves, minimal winter burning, and produces abundant white flowers in late spring, followed by dark purple to black fruit.

After more than 35 years of testing in the Arboretum landscape (where it has become a staff favorite), Forever Emerald™ inkberry deserves wider use in home gardens. In April 2024, Arboretum plant production staff shared rooted cuttings of the shrub with commercial nursery partners in Massachusetts, Connecticut, New Jersey, Ohio, and Oregon. Promoting this unique cultivar with nurseries through the Arnold Selects program will give this choice plant greater visibility in the marketplace, while celebrating the Arboretum’s continuing legacy of exploration, horticultural testing, and plant introduction.

Pictured above, flowers and foliage of Ilex glabra ‘Peggy’s Cove’ #500-2007*A.

KYLE PORT

New Bonsai Created from Historical Accessions

Plant production staff launched a project in 2024 to propagate five new bonsai for the Arboretum’s renowned collection from historical Arboretum accessions. These new additions represent the Arboretum’s history of plant exploration and introduction through the art of bonsai. The plants were propagated in the landscape by air layering, a technique that encourages the development of roots on a wounded stem to create a new plant genetically identical to the original. The air layers were started in May 2024 and harvested in August 2024 by bonsai specialist Jun Imabayashi.

Two exciting new bonsai created from this project are a Japanese tree lilac (Syringa reticulata 1111*A) cloned from the Arboretum’s oldest lilac accession and a Fuji cherry (Prunus incisa forma serrata 172-95*B) originally collected by Ernest Henry Wilson in Japan in 1915. The lilac—grown from seed sourced from the wild in Japan in 1876 by Professor William Smith Clark of Sapporo Agricultural College—blooms a few weeks later than most tree lilacs with creamy white flowers. The Fuji cherry selected for air layering grows in the Bradley Rosaceous Collection and is a scion of the original Wilson accession dating to 1995.

The Arnold Arboretum’s bonsai collection is one of the finest and oldest collections of dwarfed, potted trees the United States. It began with the donation of the Larz Anderson Collection in 1937 by Isabel Anderson and has grown over time with additional specimens created by Arboretum staff or donated by private collectors. On view from mid-April through mid-November, the collection comprises 71 masterfully curated specimens representing a range of evergreen and deciduous species, including compact Hinoki cypress (Chamaecyparis obtusa ‘Chabo-hiba’), Japanese white pine (Pinus parviflora), trident maple (Acer buergerianum var. trinerve), Japanese maple (Acer palmatum), and cedar elm (Ulmus crassifolia).

Jun Imabayashi, Arboretum bonsai specialist, works on one of the Hinoki cypresses in the collection.

264 accessions were added in 2024

Arnold Arboretum

Living Collections 2024

305 plants were removed from the permanent collections

525 plants were planted into the permanent collections

115 seed accessions added in plant production

1,506,541 specimens in the Herbarium of the Arnold Arboretum

124,733 specimens in the Herbarium of Cultivated Plants

484 total number of accessions in plant production

196 repropagations of historical accessions

As of December 2024, the living collections comprised 17,391 individual plants (including nursery holdings) belonging to 10,980 accessions representing 3,898 taxa of woody plants.

EQUITY, COMMUNITY, AND ENGAGEMENT

Poplar Gate Renovations Begin Entrance Improvement Project

The Arnold Arboretum marked a significant milestone in 2024 as renovations to the historic Poplar Gate entrance began in late summer. A groundbreaking ceremony on October 9 officially launched the construction phase of the Arboretum’s Entrance Improvement Project, aimed at enhancing accessibility, connectivity, and horticultural aesthetics across key entrances to the Arboretum. Poplar Gate renovations were championed by Arboretum benefactor RoAnn Costin, who dedicated the renovation in honor of her father, former Lynn mayor Thomas P. Costin, Jr., a champion of civil rights and green space preservation. The Poplar Gate entrance renewal underscores the Arboretum’s commitment to equity and welcoming all visitors, particularly those from Environmental Justice Neighborhoods.

The Poplar Gate, a cherished entry point to the Peters Hill landscape, has long served as a vital connection between the Arboretum and its surrounding communities. The renovation aims to create a more inclusive and beautiful environment by improving accessibility and connectivity, reducing paved surfaces, increasing plantings, and enhancing the overall horticultural display and its connection to the greater landscape. The City of Boston has also committed to funding additional improvements to the interior road extending from the Poplar Gate entrance, including restoring its cobblestone gutters and repaving the spur road to Poplar Gate with permeable pavement to reduce stormwater runoff.

Designed by Michael Van Valkenburgh and Associates, the Poplar Gate renovation project aligns with Frederick Law Olmsted’s original landscape vision, extending a sense of welcome and wonder beyond the Arboretum walls. The next projects will be the renewals of the Washington Street entrance to the Bussey Brook Meadow and the Walter Street Gate entrance that provides access to the landscape for neighboring health care facilities. The project is central to the Arboretum’s civic commitments. It is about improving infrastructure with beautiful design, but of equal importance it is about building community: welcoming every member of the public to the Arboretum and fostering a deeper appreciation for the natural world.

Pictured at the groundbreaking ceremony for the Poplar Gate entrance renovations are (left to right) Boston City Councilors Ben Weber and Enrique Pepen, State Representative Rob Consalvo, State Senator Mike Rush, RoAnn Costin, Director William (Ned) Friedman, Thomas Costin Jr., and State Representative Sam Montano. (Not pictured but present, State Representative Bill MacGregor.)

ETHIOPIAH

AL-MAHDI

Preservation Work Enhances the Hunnewell Building

In 2024 the Arnold Arboretum embarked on a significant renovation project for the historic Hunnewell Building, a cornerstone of the Arboretum’s landscape since its construction in 1892. One of three facilities in the Arboretum landscape and home to its visitor center, library and archives, and education and horticulture operations, the Hunnewell Building required significant repairs to its exterior and upgrades to its roof and drainage systems. Funded by the Powder Mill Foundation in memory of Josephine and Louis J. Appell, Jr., renovations aimed to preserve and sustain the Hunnewell Building for its next century of service.

An envelope study completed by engineering consultants in 2019 identified critical restoration needs and recommended a phased approach to halt further deterioration. Renovations in 2024 focused primarily on essential exterior work, including membrane roof replacement, slate replacement and repair, copper gutter replacement, masonry restoration at the building’s cornice, select window lintel replacement, and selective repointing at all elevations. Sourcing the right materials, such as the “North Country Black” slate for the roof from Quebec, helped maintain the quality and historical integrity of the renewal effort. Sustainable building methods were employed whenever possible, including salvage of original materials and replacement of membrane roof surfaces with reflective white PVC to reduce solar absorption and thermal radiation.

The Hunnewell Building has long served as the home of our educational and outreach activities, and its preservation is key to sustaining and amplifying this important work in the future. Its ongoing stewardship and improvement reflect our dedication to protecting its historical legacy while adapting a nineteenth century structure to contemporary needs, uses, and environmental realities. Importantly, its renewal ensures that our critical efforts to teach the world about plants and our connection to the natural world can continue unabated in decades to come.

Scaffolding surrounds the façade of the Hunnewell Building during exterior renovation work in 2024.

JON HETMAN

Arboretum Celebrates 40 Years of Science Education for Kids

At a special event for volunteers in December, the Arnold Arboretum proudly celebrated the fortieth anniversary of providing free and enriching educational opportunities for Boston Public School (BPS) students through the Field Study Experiences (FSE) program. Since its inception in 1984, FSE has provided hands-on, nature-based learning experiences to over 100,000 BPS students, fostering a deep connection with plants and the natural world and igniting students’ curiosity in the wonders of life science. The program teaches students to explore science in the outdoors through the collaborative efforts of dedicated educators, Arboretum staff, and community partners.

FSE offers a variety of seasonal activities that align with school curricula, allowing students to explore the Arboretum’s diverse plant collections and ecosystems. Activities are designed to enhance students’ understanding of science, ecology, and conservation while promoting critical thinking and observational skills. Programs also emphasize the importance of environmental stewardship, encouraging students to cultivate a deeper understanding of nature and the importance of preserving biodiversity. In recent years, the model of hands-on, outdoor explorations of science pioneered by FSE has been extended to middle school students through the donor-funded Arboretum Young Scientists program, which welcomed its third summer cohort of BPS students in 2024.

As the Arnold Arboretum looks to the future, it remains committed to expanding and enhancing the Field Study Experiences program and the Arboretum’s ladder of learning to secondary and higher education. By continuing to provide high-quality, nature-based education, the Arboretum aims to inspire the next generation of environmental stewards and foster a lifelong appreciation for nature. The fortieth anniversary celebration marks a key milestone in the program’s enduring legacy and its vital role in science education in Boston.

FSE has provided hands-on, nature-based learning experiences to over 100,000 BPS students.

Kindergarten students from Boston Public Schools draw autumn leaves and identify their colors in an Explorations field study program.

Arboretum Families Project Builds Neighborhood Engagement

The Arboretum strengthens relationships with residents and ensures its landscape is a welcoming resource for all.

Katie Fox, manager of youth education, helps kids learn about plants at Archdale Family Day in Roslindale.

The Arnold Arboretum is committed to fostering meaningful connections with its surrounding communities, particularly those historically underrepresented in public green spaces. Through targeted outreach initiatives and community events, the Arboretum strengthens relationships with residents and ensures its landscape is a welcoming resource for all. In 2024, Public Programs staff developed new programs to foster environmental appreciation and strengthen connections with the Arboretum’s Roslindale neighbors.

Collaborative work with the City of Boston and the MBTA to open a new entrance to the Bussey Brook Meadow at Arboretum Road provided an opportunity for the Arboretum to build deeper engagement with abutting communities. The Arboretum Families Project provides outreach to families from two neighboring Boston Public Housing developments—South Street Development and Archdale Village—through family-centered nature activities designed in collaboration with residents. By working with both children and caregivers, the program helps families build confidence in exploring nature together while reinforcing the Arboretum as a community-centered educational resource that is welcoming to all.

Beyond structured programming, the Arboretum has begun partnering in community events such as Archdale Family Day to increase awareness about the Arboretum and all it offers. Larger community-wide events in the year ahead will further extend the Arboretum’s outreach, intentionally welcoming underserved communities and creating inclusive spaces for engagement with plants and nature.

ANA MARIA CABALLERO

3,051 students and adults served from Boston Public Schools

21,300 attendees to Lilac Sunday and public events

5,226 volunteer hours for docents, interpreters, and guides

16,000 users of Expeditions app

Arnold Arboretum Public Programs 2024

344 tours provided to the public

947,376 visitors to the landscape

575,782 reach on Instagram

69,774 visitors to the Hunnewell Building

1,738,206 reach on Facebook

130 hours in the landscape Mobile Visitor Center

3,515 scans of Wonder Spots in the landscape

A Multifaceted Response to Beech Leaf Disease

In 2024, our beech collection faced significant challenges and the loss of many accessioned trees due to the spread of beech leaf disease (BLD) across the Northeast. Caused by a foliar nematode, BLD was first observed at the Arboretum in 2022 and since then its impacts have been profound across our nationally-accredited collection of beeches. The Arboretum’s response to BLD reflects our historical commitment to horticulture, integrated pest management, and collaborative study to protect our botanical heritage.

Beech leaf disease manifests as dark banding on leaves, leading to leaf deformation, reduced photosynthesis, and, eventually, decline and death of the tree. In response, our Horticulture staff adopted a comprehensive management plan aimed at preserving the health and resilience of the beech collection. This plan includes extensive research and collaboration with experts and institutions—including the US Department of Agriculture, University of Massachusetts Cooperative Extension, and Bartlett Tree Research—to investigate the disease and explore potential management strategies. Our team also engaged in active monitoring and assessment of our beeches to track the progression of BLD and evaluate the effectiveness of various management and treatment regimes. Additionally, we participated in broader research efforts by sharing plant material with institutions like the Holden Arboretum in Ohio, where BLD has been decimating beeches since its discovery there in 2012.

Restoration efforts in 2024 focused on improving resiliency of the beech collection. Since July 2023, 40 accessioned beeches have been removed/deaccessioned to help prevent the spread of the disease to healthy individuals. The Arnold Arboretum’s multifaceted response to BLD—involving collections monitoring, select removals, treatments, research, and cross-institutional collaboration—will continue in coming years as our team learns more about the disease and our trees’ response to treatment regimes. Public engagement and education have been integral to these efforts and included sharing information about BLD on the Arboretum website, in Arnoldia, and on signs and tours in the landscape.

Beech leaf disease can be identified by the interveinal discoloration of infected beech leaves.

Field Expeditions Mounted in Korea, Japan, and Florida

Chris Copeland, Manager of Plant Production (second from right) collects plants on Baegunsan, a mountain in South Korea, with Professor Hui Kim (far left) from Mokpo University and Hak Gi Park and Jae Jun Kim from Seoul National University’s Nambu Research Forest.

Throughout our history, the Arnold Arboretum has explored wild environments across the temperate world to collect examples of woody plant diversity. By acquiring germplasm, herbarium vouchers, and knowledge about plant populations around the world, the Arboretum enhances its living collections and contributes to global conservation. The Campaign for the Living Collections—a multi-year effort to obtain nearly 400 taxa of plants to enhance the depth and research value of the Arboretum’s holdings—ramped up collecting activities in 2024 with collaborative expeditions to South Korea, Japan, and the panhandle of Florida.

In recent years the Arboretum has worked to increase its engagement with South Korea, a region with significant floristic similarities to China and Japan and a key destination for Arboretum plant collectors since the storied work of Ernest Henry Wilson. Arboretum Director William (Ned) Friedman visited South Korea in May to build relationships and sign collecting agreements with local botanic gardens and universities. In mid-September to early October, Keeper of the Living Collections Michael Dosmann and Manager of Plant Production Chris Copeland made their own trip to South Korea, conducting botanical surveys and collecting seeds from plants in collaboration with in-country botanical partners. These efforts marked the Arboretum’s first major fieldwork on the Korean Peninsula since 1977 and promise a new era of cooperation to conserve plants.

In mid-October to early November, Assistant Curator Miles Sax and Propagator Sarah Shank undertook an expedition in Japan, the Arboretum’s fourth collecting trip there since 2018. Hosted by Dr. Hiroyuki Iketani of Okayama University of Science, the team focused on collecting endemic species in Kyushu and Okayama, including the rare apple species Malus hupehensis and the newly described Malus roseotakanabensis. Also in October, but closer to home, Director of Horticulture and Landscape Rodney Eason led an expedition in cooperation with the Florida Plant Conservation Program to Florida’s panhandle. Florida’s biodiversity hotspot provided opportunities to collect rare species like buckwheat tree (Cliftonia monophylla), bay starvine (Schisandra glabra) and scrub hickory (Carya floridana).

MICHAEL DOSMANN

The Arboretum has expanded irrigation systems across 140 acres of landscape, serving about half of accessioned holdings.

Protecting Our Plants From Drought

The potential for hotter and drier summers driven by global change poses significant challenges to the caretakers of our living collections. The prolonged effects from extreme drought—which Boston experienced in 2020, 2022, and 2024—compound harm caused by pests, pathogens, and human-induced impacts including soil compaction and pollution. Since 2016, the Arboretum has worked with leading engineering firms and irrigation consultants to develop a master plan for irrigating the entirety of our collections. The Arboretum continued to make progress in 2024 on this essential infrastructure for protecting the Arboretum’s renowned collections.

In recent years the Arboretum has expanded water infrastructure and irrigation systems across 140 acres of landscape, serving nearly 8,000 plants or about half of our accessioned holdings. With the first two phases of this work completed in 2023, horticulture and operations staff focused on finalizing the planning, design, and installation of the third phase of this infrastructure with a team of leading irrigation experts, civil engineers, and consultants from Harvard Capital Projects. This final phase will replace and upsize the existing water service to the Dana Greenhouse, improving efficiency for that critical facility while also providing capacity for expansion of irrigation zones.

New zones coming online through Phase 3 will protect 60 acres of treasured collections along Hemlock Hill Road and Meadow Road, including the Arboretum’s nationally accredited collections of maples, hemlocks, and beeches; our famed cork trees, lindens, horse chestnuts, and tulip trees; and the azaleas, rhododendrons, and mountain laurels growing along the foot of Hemlock Hill. Construction is anticipated in late summer 2025. Once completed, the Arboretum’s comprehensive in-ground irrigation system will bring water to all parts of the Arboretum during drought conditions.

Emergency irrigation systems engaged on Peters Hill during the late summer 2024 drought.

DANNY SCHISSLER

Collaborating for Biodiversity Exploration and Conservation

Through a generous multi-year donation from friends and Harvard alumni in China, the Arnold Arboretum established the China Conservation Collaboration Initiative (CCCI). The CCCI provides cooperative support between the Arboretum and botanical institutions and scientists in China to enhance plant conservation efforts and foster global collaboration for the study and preservation of biodiversity. Activities include monitoring and documenting natural plant populations, establishing ex-situ collections of wild-collected plants in China and the United States, training the next generation of botanical scholars, and exchanging horticultural knowledge between professionals in Chinese and American gardens.

The CCCI became fully activated in 2024 with partner organizations in China beginning plant collections, regional surveys, and research projects. In April, Keeper of the Living Collections Michael Dosmann and Assistant Curator Miles Sax visited China for botanical fieldwork, marking the Arboretum’s first visit for botanical exploration since 2018. While expeditions have historically been mounted in autumn for seed collection, the spring visit enabled the Arboretum team to experience China’s rich floristic biodiversity in a new way, identifying populations that could be revisited by CCCI partners to collect targeted species. The team visited gardens and diverse floristic areas across Zhejiang and Anhui provinces, as well as field sites where the conservation and floristic projects of CCCI partners are ongoing.

In October, CCCI partners Drs. Pan Li and Yun-Peng Zhao from Zhejiang University visited the Arboretum and the Harvard campus. Meetings with Arboretum leadership and staff included conversations about recreating botanical field opportunities for Chinese students in the US with the Arnold Arboretum as a primary partner. Interactions in Cambridge focused on strengthening ties between Zhejiang and Harvard Universities and creating new opportunities for future collaboration in teaching and research.

Colleagues from CCCI partner Zhejiang University visited the Arnold Arboretum in October 2024. Pictured (left to right) are Pan Li, Yunpeng Zhou, Peter Del Tredici, Michael Dosmann, and Zhechen Qi.

PAN LI

Arnoldia special issue on Collections, Extinction, & Abundance

Arnoldia, the magazine of the Arnold Arboretum, explores the nature of trees through various lenses, including tales of plant exploration, behind-thescenes glimpses of botanical research, and explorations of the history of gardens and landscapes. First published in 1911 as the Bulletin of Popular Information, Arnoldia was fully redesigned during the Arboretum’s sesquicentennial in 2022 to make the magazine more engaging and accessible, reflecting the institution’s commitment to education and thought leadership. The four issues of Arnoldia published in 2024 continued to expand the depth of topics and multiplicity of voices featured in its pages to enrich global conversations about trees and the natural world.

The summer 2024 issue of Arnoldia was published as a special edition devoted to the pressing question of extinction and conservation in botanical collections. With biodiversity loss and climate change profoundly altering our natural world, this issue highlights compelling stories of botanical gardens and herbaria fighting extinction and cultivating resilience in the face of global change. The culmination of nearly two years of planning, the issue brings together the diverse viewpoints and experiences of scientists, artists, humanists, and horticulturists to explore the many ways that institutional collections can provide perspective and action on preserving species threatened with loss.

Perfoliate bellwort (Uvularia perfoliata) artwork by Leah Sobsey on the cover of Arnoldia 81-2.

Research in the Living Collections

The living collections of the Arnold Arboretum comprises a valuable genetic resource representing a large subset of the combined woody floras of the North Temperate Zone. Arboretum plants and associated collections are utilized by an extensive network of scientists to support comparative studies across a wide range of disciplines including morphology, phylogenetics, physiology, ecology, and biodiversity. The curatorial department provided collecting permits, plant material, and research support for more than 87 research studies in 2024, including 41 projects continuing from previous years.

Among the investigations launched in the Arboretum landscape in 2024 was a research project by Miles Schwartz Sax, assistant curator of living collections, focusing on the reproductive strategies of the endangered Malus spontanea. First collected for Western gardens by Ernest Henry Wilson in 1919, this crabapple species grows on a single volcanic mountain in Kyushu, Japan, and faces extinction with fewer than 300 individuals left in the wild. Because its reproductive cycle extends over multiple months, the living collections facilitate sustained close observation—conditions difficult to achieve in the field. Miles hopes to discover the barriers limiting its capacity to flourish in the wild, information critical to developing conservation strategies for M. spontanea both in the wild and in cultivation.

John Kress, research scientist at the Smithsonian Institution, received a 2021 Sargent Award from the Arnold Arboretum to advance work on a guidebook to trees of North America—a topic pioneered by the Arboretum’s founding director, Charles Sprague Sargent. His resulting work—published in 2024 as the Smithsonian Trees of North America—provides an authoritative reference on the native and non-native trees of North America, offering an unprecedented appraisal of more than 325 common species. Through his Sargent Award, Kress used the Arboretum’s living collections as a source of material for composing high-resolution color images of dozens of species of trees for the book.

The curatorial department supported more than 87 research studies in 2024.

The rare Malus spontanea (accession 10796-2*A on Peters Hill pictured here) is the subject of a research study by Miles Schwarz Sax, assistant curator.

Robin Hopkins earned tenure at Harvard and promotion to full professor in 2024.

Spotlight on the Robin Hopkins Laboratory

For more than a decade, Professor Robin Hopkins has taught, mentored, and inspired Harvard University students as a member of the faculty for Organismic and Evolutionary Biology and has coordinated investigations of adaptation and speciation in plants at Weld Hill as a Faculty Fellow of the Arnold Arboretum. She earned tenure at Harvard and promotion to full professor in 2024. During her time at Harvard, Dr. Hopkins has received multiple major federal research grants, including the National Science Foundation’s prestigious CAREER award. Her dedication to teaching and mentoring earned her two teaching awards for excellence in science and undergraduate teaching, as well as an award for excellence in graduate mentoring from The Harvard Graduate School of Arts and Sciences.

In 2024, the Hopkins lab conducted a major study on how natural selection drives divergence between species and within populations. Published in Nature Communications, this three-year field research by Dr. Ben Goulet-Scott documents how a wide range of selection pressures simultaneously act on populations to cause divergence across different biological scales. Another significant project by Dr. Austin Garner—along with Drs. Andrea Berardi, Felix Wu, and Patrick McKenzie—identified the genetic basis of flower color variation in Phlox drummondii, revealing the mechanisms driving speciation and divergence in phlox investigated in Dr. Hopkins’ previous research.

The lab also explored using artificial intelligence to understand biological diversity. Led by Dr. Patrick McKenzie and published in Current Biology, the team used community science data from the website iNaturalist to test if flowering time differs between plants with different flower colors—and if this variation is, in part, predicted based on pollinator. Using GPT-4 with Vision, they processed over 1.5 million observations of nearly 12,000 species, finding that red-flowered plants have delayed flowering, corresponding to the migration patterns of hummingbirds who serve as their dominant pollinators.

JEFF BLACKWELL/HARVARD COMMUNICATIONS

Professor Robin Hopkins teaching students in the lecture hall at the Weld Hill Research Building.

Supporting Discovery: 2024 Research Fellowships and Awards

To foster both independent and collaborative work, the Arnold Arboretum offers fellowships and awards to students, post-doctoral researchers, and professionals of the biological and horticultural sciences as part of its mission to discover and disseminate knowledge of the plant kingdom. The following individuals and their research proposals were awarded funding by the Arnold Arboretum in 2024:

ASHTON AWARD FOR STUDENT RESEARCH

Promish Adhikari, Undergraduate Student, Tribhuwan University, Nepal: “Status of orchids diversity, distribution, and threats in Panchase Protected Forest, Nepal.”

Rishiddh Jhaveri, PhD Candidate, The Centre for Cellular & Molecular Biology, India: “How plant chemistry shapes seedling community dynamics in a tropical humid forest.”

CUNIN-SIGAL RESEARCH AWARD

Oluwatobi Oso, PhD Candidate, Yale University: “Unraveling the influence of biome transitions, bud-packing, and cellular processes on leaf margin development and evolution.”

PUTNAM FELLOWSHIPS IN PLANT SCIENCE

Michael LaScaleia, PhD Candidate, University of Connecticut: “Quantifying the physical, chemical, and phenological defenses that allow invasive exotic plants to escape their natural enemies.”

SARGENT AWARD FOR VISITING SCHOLARS

Vidya Vuruputoor, PhD Candidate, University of Connecticut: “Elucidating genomic mechanisms of hemlock woolly adelgid resistance through transcriptome profiling.”

SINNOTT AWARD

Alaina Bisson, Research Assistant in the Taylor Lab, Harvard University: “Assessing rhizobial communities amongst native and introduced legumes within the Arnold Arboretum.”

Alaina Bisson, research assistant in the Taylor Lab at Weld Hill, received a Sinnott Award in 2024 to support her studies of nitrogen-fixing rhizobia bacterial communities associated with Arboretum plants.

Faculty Fellows

Faculty Fellows of the Arnold Arboretum of Harvard University contribute significantly to one or more of five areas central to our mission: leading or collaborating on research based at the Arboretum; mentoring students and postdoctoral fellows based at the Arboretum; teaching Harvard courses based at the Arboretum; providing input on living or archival collections and landscape management; and creating outreach programs to share science and scholarship with the public.

William (Ned) Friedman

Arnold Professor of Organismic and Evolutionary Biology

Director of the Arnold Arboretum of Harvard University