Collecting mountain magnolia on the slopes of southwestern Virginia, John Berryhill asks, what do the plants need from us?
One could say my path to a wooded Virginia mountainside started with a stroll through the Arnold Arboretum accompanied by Michael Dosmann, the Keeper of Living Collections. My career at the Botanic Garden of Smith College had recently taken a turn away from a primary focus on arboriculture and toward the world of curation, and it seemed wise to connect with someone with Michael’s vast experience. The question of how to build collections and serve institutional missions is not as straightforward as it once was. Simply believing that “more is better,” or that a token example of a rare species will suffice, ignores what has been learned by the public garden and arboretum communities as we study our past and envision our future—to act as a voice for the plants, rather than just as collectors of them.
One manifestation of this shift can be seen in the work of Botanic Garden Conservation International (BGCI) and the Global Conservation Consortia (GCC). With around 60,000 described tree species (of which approximately a third are at risk of extinction), arboreta must urgently determine how to apply their resources to achieve the greatest impact on the conservation of biodiversity. That goal is central to the work of BGCI and the GCC, arising from the recognition that while some genera of trees are rich in rare or small-range species, their genetic diversity cannot be conserved through seed-banking alone. The seeds of these “exceptional species” do not remain viable over time. They must instead be held in carefully planned living collections that adequately represent the complexity and resilience of each species’ genome while also incorporating an appropriate amount of redundancy in case of tree loss. A conservation collection could require hundreds of trees, giving rise to the idea of a “meta-collection” (or collection of collections) with the effort being shared by a coordinated network of institutions. The GCC model has flipped the traditionally competitive idea of collections-building that viewed plants as “collectibles” into a more collaborative approach that asks, “what do plants need from a collector?”
During my graduate studies it was my good fortune to be partnered with Dr. Jesse Bellemare of the Smith College Department of Biological Sciences. I was grappling with the big questions surrounding the purpose of botanical collections. Jesse is a plant ecologist who researches the condition of native magnolias in the southeastern United States under climate change. My thesis investigated whether the recruitment dynamics (the capacity of a species to add new members to a population) of mountain magnolia (Magnolia fraseri) were being affected. Jesse’s prior work with umbrella tree magnolia (Magnolia tripetala) showed a trend of declining recruitment along the warm (southern) range margin. As its name suggests, mountain magnolia is a montane species, happiest at about 2,000–4,200 feet in its native southern Appalachian range. We suspected that a similar trend would play out along the elevational gradient that this species occupies.
Our efforts brought us to the heart of mountain magnolia’s range—the Mount Rogers National Recreation Area in southwestern Virginia. This botanically rich region holds the legacy of the refuge it provided from the reach of glaciers during the last ice age. Our surveys and seed collecting expeditions carried us through the familiar—the maples, birches, and viburnums we knew so well from New England forests—to the dazzling array of plants that make the southern Appalachians so special to botanists. Walls of rosebay rhododendron (Rhododendron maximum) and greenbrier (Smilax rotundifolia) were simultaneously beautiful and daunting to crash through. Crane-fly orchids (Tipularia discolor), heartleaf (Hexastylis minor), and wandflower (Galax urceolata) were exciting to behold, but quickly overshadowed by bright blazes of red, orange, and purple courtesy of the fungal kingdom. Some mushrooms were so vibrantly colored that, for an instant, they could be mistaken for litter. One of our trips brought us to the area in early October, where the prize for “lasting impression” went to the sourwood trees (Oxydendrum arboreum). Their display of electric red would put even the proudest red maple to shame. All of this made the long days of zig-zagging over steep terrain, sloshing through downpours, and meticulous attention to detail endlessly invigorating.
The data we brought back was astoundingly clear. Ecological data are often messy and require advanced statistical analysis, but this was not the case here. Our work aimed to detect a difference between the average elevation of mature trees and that of seedlings. The elevational distribution of mature canopy trees would indicate the past climate envelope that had supported their recruitment. Seedlings are far less tolerant of extremes and variance in climate and would be expected to show a distribution that had shifted or contracted upslope in a quickly warming/drying climate. This is exactly what we found. The average elevation of the more climate-sensitive seedlings was more than seven hundred feet higher than the mature trees. Furthermore, there was almost no recruitment in the lower two-thirds of our survey area. The elevation of most efficient recruiting was, in fact, around the single highest tree we could find—historically where mountain magnolia meets the limits of its cold tolerance. Aging seedlings by counting bud scars on the stems, we confirmed that this was a sustained trend. Further investigation of growth rings from core samples revealed a similar trend of significantly declining growth rates for mature trees in the warmer (lower) elevations.
Arboretum trees are not just objects in a museum but rather representatives of living communities that require advocacy and understanding.
The picture painted by these observations is not apparent with just a quick glance. A range map shows a species with a modest distribution from the mountains of northern Georgia up through West Virginia. For the most part, a walk in those mountain forests would reveal healthy-looking trees. A peek at the IUCN Red List shows that Magnolia fraseri is regarded as a species of least concern for conservation, further noting that populations appear stable and not threatened. That assessment is hard to square under close inspection. If mountain magnolia were on the verge of largescale extirpation from much of its range because of a shift in the climate envelope, the first signs would be declining growth and failure to recruit on the leading edge of that change.
Getting out into the forests reminds us that our arboretum trees are not just objects in a museum but rather representatives of living communities that require advocacy and understanding. As a curator, it has been invigorating to think of collections-building at the Botanic Garden of Smith College with this story, and others like it, in mind. Our aim is to bring students at Smith into the multidimensional work of modern botanic gardens—where not just botanists are needed, but storytellers, politicians, artists, data scientists, and new voices that can help us determine how a plant collection “for the plants” should really look.
John Berryhill is the landscape curator for the Botanic Garden of Smith College, where he is working to bring conservation horticulture to the forefront of the collection-building priorities.