Wakefield Plant Collections Research

The Wakefield Estate Arboretum plant collection offers many opportunities to observe and study a wonderful array of topics related to plant habit, plant propagation, ecosystem health, and the impacts of climate change on ecology. In 2018, the Wakefield Estate was officially certified as an arboretum by the ArbNet Arboretum Accreditation Program. The protocol for this designation includes public access and educational opportunities, a strategic plan, more than 100 labeled species, a collections policy, and a research component. This edition of our quarterly journal provides a brief introduction into research using the arboretum as the study site started by Mary "Polly" Wakefield and continued by arboretum staff, scholars, students, volunteers, and visitors. 
Renovating a plant collection
The Front Garden at the Wakefield Estate was renovated in 2016. All bricks and hardscape elements were replaced, new plant material was added and shrubs were renovated.
Between the last years of Polly Wakefield’s life and the hiring of permanent staff in 2006, the Wakefield Estate's plant collection was minimally maintained. The collection suffered from overcrowding, soil compaction, erosion, excessive deer browsing and outdated arboriculture methods. In addition, several unusual species of trees that were intentionally planted by Polly had become aggressive in the landscape and later were listed on the Massachusetts invasive species list (started in 2005).

In 2012, Debbie Merriam was hired by the Trust to manage and restore the unique cultural landscape at the Wakefield Estate, which represents 300 years of use by eleven generations of one interrelated family. Previously, Merriam had worked as a fellow at the Wakefield Estate, cataloging plant material. She then used this information as the basis of her graduate thesis in cultural landscape preservation at the University of Pennsylvania using Wakefield as the subject. Over the past 25 years, landscape preservation has been a rapidly evolving and changing field. Early land preservation methods followed the tenets of building preservation, “return it to its original state.” However, as former Arnold Arboretum Director Robert Cook points out in his article Is Landscape Preservation an Oxymoron ?: “Plants, and the wildlife associated with them, grow, move around, reproduce, die, and generally bring to the landscape a very uncooperative tendency to change. A successful effort at preservation would seem to require its own failure.” ( George Wright Forum, 1996)  Keeping this idea in mind, Merriam wondered what should the appropriate restoration approach look like? How do we deal with plant material that has become fairly invasive? How do we respond to a changing climate? What is our responsibility to surrounding land-holders as managers of this unique collection? 
View of the north facing side of the mansion before garden renovation
New dwarf conifer garden installed in 2018 and recognized in 2019 by the American Conifer Society as a reference garden for the Northeast Region.
Renovated lattice nurseries in formal gardens
The dogwood allee required several years of pruning in order to let light and air flow around the trees. New cobblestone edging was also added.
To begin to answer some of these questions, Merriam visited more than 30 gardens and arboreta and interviewed managers to learn of their failures and successes in the restoration process. She studied the history of the Wakefield Estate landscape, conducted a site conditions assessment, and formed a landscape advisory committee made up of preservationists, landscape architects, horticulturalists, and Wakefield Estate supporters. She developed a three-year strategic plan that focused on repairing damaged hardscape, removing and replacing badly damaged trees and shrubs, and restoring trees with careful pruning, weeding and mulching. While plants respond well to care, the process can be very slow. Merriam says, “You have to have the long view with plants. Polly worked on her garden for more than 40 years. I am trying to channel that level of patience.”  Patience does pay off. Several heavily browsed giant yews, (Taxus baccata) are now looking spectacular after five years of regenerative pruning and the installation of a deer fence. Most of the large trees in the collection have had careful pruning by volunteer and paid arborists. Many new plants have been added to the collection, and hardscape elements have been repaired or replaced. 

Another issue impacting the landscape is climate change. There has been a series of invasive pest infestations that are lasting longer due to warming temperatures. Fluctuating and warmer temperatures in the winter months and long periods of drought in the summer have caused damage to the collection. Fortunately, there is excellent research available on how plants are adapting and how land managers can deal with these changes. Polly Wakefield was interested in how her Asian dogwood( Cornus kousa)  collection would adapt to cold temperatures but what the staff has observed through the phenology study is their tremendous capacity to adapt to drought and warm temperatures and their ability to fend off invasive pests. These characteristics will likely aid in their survival in a changing climate.
Polly Wakefield’s collection of Cornus kousa dogwoods
 
In 1990, Polly Wakefield wrote an article for Arnoldia, the Arnold Arboretum’s quarterly journal extolling the virtues of the Cornus kousa dogwood. Polly started her collection of kousa dogwoods in 1956 after she attended a class on plant propagation with Roger Coggeshall, Arnold Arboretum’s preeminent plant researcher at the time. It was during this class that she became enamored with the Cornus kousa dogwood and the tree’s adaptability to New England climate and soils. Polly referred to herself In the Arnoldia article as an “amateur hobbyist working in her spare time without scientific skill or equipment,” yet she worked diligently and methodically for more than 35 years to develop her collection, choosing dogwood trees for specific characteristics.   By the time Polly passed away in 2004, she had propagated and planted more than 600 kousa dogwoods, all descended from three select kousa dogwoods in the Arnold Arboretum collection. Ultimately, she patented seven cultivars, developed from this careful selection, all highlighted in Andre Gayraud’s 2013 book Cornus: Monograph of the Genus Cornus.
 
Cornus kousa dogwoods inherit characteristics of both parents, producing new one- of- a- kind flowers, fruit, leaves and bark. It is a true wonder and challenge to study these variations in the Wakefield Estate's vast collection. Some of the specimens have stunning pink hues in the bark and kousa berries as big as plums. Others have flower-like ‘bracts’ (leaves that surround the very small flowers) the size of dinner plates or tiny triangulated bracts with a pink tinge. Polly chose to patent some of her cultivars based on these traits. These patents are for cultivars known as ‘Silverstar,’ ‘Triple Crown,’ ‘Greensleeves,’ ‘Twinkle,’ ‘Moonlight,’ ‘Moonbeam,’ and ‘Fanfare’. These varieties are represented in the Wakefield Estate collection, however, we have been unable to properly identify them due to the fact that the tags were lost and no map has been found among Polly’s vast collection of notes and papers. We realized if we could determine which kousas were patented by Polly, we could begin to graft them, thus preserving the exact identity of each patented cultivar and continuing this special horticultural legacy.
Connecticut College students collecting samples for DNA testing from the Wakefield Estate dogwood collection.
Plant DNA research project: the quest to unravel the mystery of the patented kousas

In 2017, the Wakefield Estate staff approached Dr. Martha Grossel, normally a cancer and genetics researcher and professor at Connecticut College, about the possibility of doing DNA research on the kousa collection to determine which cultivars were Polly’s patented varieties. This request “blossomed” into the beginning of a long-term research project to unravel the mysteries of the Wakefield Estate Cornus kousa collection. 
Grossel explains: “Students went to the Wakefield Estate to collect samples of 15 different trees that displayed characteristics of the patented cultivars and then took them back to the lab for analysis. After an entire semester of work, two of the cultivars were identified by the students using DNA analysis. We hope that over the next few years, collaboration will continue so that we may eventually identify all of the patented trees. The value to students is that this project-based work will mimic a work environment and will meet the learning goals of my course, Molecular Cell Biology.”

In order for this project to be successful, it was necessary to seek some control plants from nurseries and arboreta that were already identified as Polly’s cultivars. This led to a fascinating search throughout the United States. Fortunately, Bernheim Arboretum in Kentucky had four of Polly’s cultivars in their extensive plant collection. The Bernheim Plant records department was eager to help and sent twig samples to Connecticut College for comparison. The Estate also purchased another "control" Cornus kousa cultivar from Rare Find Nursery in New Jersey, ‘Greensleeves’, which according to Paul Cappiello and Don Shadow (authors of Dogwoods ) is probably the most highly regarded of all of Polly’s patented varieties and considered one of the very best kousa cultivars. As this work continues, we will update the public on the efforts to unravel the mysteries of our incredible collection. In the meantime, this winter Wakefield staff will be collecting twigs from the identified cultivars for a spring grafting.
Cornus kousa 'Greensleeves' at the Connecticut College greenhouse for DNA analysis
Polly with some of her original kousa dogwood trees
Cornus DNA isolated from leaf buds and snap-frozen (2,3-10) or dessicated (2). Lane 1 is Cornus florida (flower bud), all others Cornus kousa, Plant DNA easy (Quiagen) columns were used to isolate DNA from Dogwood leaf buds. Total genomic DNA loaded varies from 50ug to 250 ug.
Wakefield Estate’s p henology study and the importance of citizen science

According to an article in the Boston Globe, on January 12, 2017, temperatures in the Northeast have already risen faster than global averages. Since 1895, Massachusetts has warmed by an average of 1.3 degrees Celsius, compared with 1 degree globally. That disparity will rapidly accelerate in the coming years for a combination of reasons, including the region’s relatively high latitude, its position relative to the prevailing winds that blow west across the United States, and the drastic rise in temperatures in the Gulf of Maine, which has warmed faster than nearly any other body of water on the planet. Understanding how these rising temperatures impact plants and animals is an important part of our ability to adapt to these changes. Engaging young people in this process will help them gain an understanding of the role that plants play in our ecosystem.

Phenology is the leading indicator of climate change impacts on ecology. “Phenology” refers to key seasonal changes in plants and animals from year to year—such as flowering, emergence of insects and migration of birds—especially their timing and relationship with weather and climate. Because not all parts of the world are impacted the same by climate change, this can lead to mismatches in bloom time and migration patterns. Phenology impacts nearly all aspects of the environment, including the abundance, distribution, and diversity of organisms, ecosystem services, food webs, and the global cycles of water and carbon. To get started collecting phenological data and become a Nature's Notebook "observer," click here .

These changes can be tracked using the citizen science platform, Nature’s Notebook. This phenology monitoring tool can help us determine how our Cornus kousa collection is adapting to climate change. In the first year of the study, we focused on 30 kousa cultivars then expanded to include 15 more each year. This research creates a standardized, long-term dataset for use in multiple types of research. Once we understand the ability to collect data on our own property, we will expand this project to the surrounding community by becoming a sponsor of a network of organizations that track phenological changes in the northeast. To read the Globe article on the Northeast experiencing faster warming, click here .
To join Nature's Notebook, click here .
Dogwood phenology sheets used for tracking growth patterns.
Thatcher Montessorri school students recording data on kousa dogwood trees using the phenophase photo guide.
photo by Patrick O'Connor
Measuring dogwood fruit
Nature’s Notebook is a software application that allows students, educators and land managers to input and interpret collected data, analyzing the impacts of climate change. Observers following a status monitoring approach visit the site regularly to check the phenological status of marked individual plants and animal species. Life stages, or phenophases, are reported as a series of yes/no questions. This approach ensures the capture of negative data (when the phenophase is not occurring), repeat events (for example, a second wave of blooming after a rain event), and allows for an estimation of the uncertainty around the beginning or end date of a life stage. Other data is collected including soil and air temperature, soil moisture and ph, and the overall health of the tree.
 
Nature’s Notebook offers opportunities for place-based, hands-on learning which is another way that we can fulfill the Wakefield Estate's mission to promote lifelong participatory learning. Middle school-aged students from the Thacher Montessori school participate in the monitoring project. After working on the project for a few months, the staff noticed that the students more readily observe other naturally occurring events in the garden and are interested in learning more about the fascinating world of botany, ecology, and horticulture.
Invasive plant species research by Debbie Merriam

In 2015, I was driving on route 138 in Milton and noticed a very unusual plant on the side of the road. It had very large leaves similar to a Sugar Maple, however the trunk was covered with large scary looking barbs. This tree, Castor-aralia, Kalopanax septemlobus, is relatively rare. Arnold Arboretum's first Director Charles Sprague Sargent collected seed of the species during his first excursion to Japan in 1892, propagating and planting the plants on the grounds of the Arboretum in Jamaica Plain where two plants from this collection still survive. Only a few arboreta and gardens have this plant and Wakefield Estate is one of them. Castor-aralia produces copious amounts of fruit that birds love so that the plant is quickly distributed throughout the landscape, growing rapidly and shading out native species.

Castor-aralia provides us insight into how invasive plant species move in the landscape and disrupt native plant ecosystems. Because of its unusual appearance, the Wakefield Estate staff had recognized that the species had self-sown in the estate's successional woodland. It is now listed as an invasive species.  An Invasive species is defined by the USDA as a non-native (or alien) to the ecosystem under consideration and whose introduction causes or is likely to cause economic or environmental harm or harm to human health. There is much debate about how to effectively control/manage invasive species and whether or not some invasives may be more suitable than natives in a changing climate. 

In our effort to be responsible stewards of the land, our first goal was to launch an invasive species study to better manage our landscape and eradicate any species that may originate at Wakefield Estate and move into the surrounding landscape crowding out natives. We focused on 13 species that are particularly problematic in New England yet widely planted until they were banned from sale in the nursery trade in 2009. Some of these species were barberry (Barberis thunbergi), bittersweet ( Celastrus orbiculatu), black swallow-wort (Cynanchum louisea), and garlic mustard ( Alliaria petiolata) . An intern interested in plant studies set up transect plots on Wakefield Estate and the abutting properties then quantified species in the plots and extrapolated the information to determine which species were most dominant.
Castor-aralia flowers and leaves
The results of this study revealed some helpful information. First and foremost, the Castor-aralia was indeed migrating to the surrounding woodlands and it was likely that the Wakefield Estate was ground zero. Second, we learned that many invasive species including burning bush, bittersweet, and barberry were most likely being carried down through the property as seeds in our stream bed from neighboring properties that were doing little to control these species. Seeds could be seen visibly moving down stream. This meant that in order to control the species on our property, we would have to work with the property owners that also had land along the stream. 

It became clear to us that our individual landscapes do not exist in a bubble and are part of a larger mosaic. It is important to work together with landholders and government entities to manage the impacts of invasive species in our collective landscapes. We hold yearly seminars on invasive species and have partnered with Master Gardeners, The Trustees of the Reservations, and Friends of the Blue Hills to spread the word and take management steps to control these plants and pests.