look out his window Arnold Arboretum At Harvard, Ned Friedman has seen 150 years of history and millions of years of history. He knows this collection of nearly 16,000 woody plants holds clues about how to navigate the future of increasingly extreme ecosystems.
Dr. Friedman, who has been Arnold’s director for 12 years, said: In his century-and-a-half history of the Arboretum (this year is a memorable year), he is only his eighth leader.
Of course, there is a timeline of seasonal changes that a tree may pass through in a given year. These include the subtle changes that Dr. Friedman urges to note, such as purple, pink and red in the early spring ephemeral female coniferous cones. As is the case, the time measured in the lifespan of a species may equal many human lifespans.
“But as an evolutionary biologist, I’m starting to see time on another scale as well,” he said.
He was referring to spans measured in thousands of years, as the last ice age displaced temperate plants hundreds and thousands of miles from their former native ranges. In the hundreds of millions of years since it began, the landmass and plant genetic pathways have shifted.
This very long field of view asks about decorative characteristics, final size and hardiness rather than what the individual gardener considers when choosing a particular tree. A more complete picture of life would be even more impressive, Dr. Friedman said.
Historically, we’ve wondered why some conifers are deciduous, dropping needles in the fall, and why some deciduous plants retain their conifers all winter, faded and seemingly useless. It helps explain what you might think.
Have you ever wondered why many of the species we call natives of the Southeast lie so far north beyond their current range?
The answers to that and many other questions can be found in Arnold’s collection of over 2,000 species, along with insight into the tenacity needed to adapt to tomorrow’s world.
let go and hold on
Perhaps your garden is home to Dawn Redwood (Metasequoia glyptostroboides), a pyramidal, fast-growing deciduous conifer that can reach 100 feet in height and has a distinctive grooved base. .
“It’s just meandering,” said Dr. Friedman. “I could see those trunks all day long.”
But until recently, 75 years ago, there were no such trees in North America.
Each species tells its own story of resilience and long-range survival strategies. The redwoods depicted in the Arboretum logo are often referred to as living fossils. This is because it was thought to be extinct until the 1940s when a living grove was discovered in China.
Seeds sent to Arnold in 1948 gave birth to these trees, the first to grow in North America in over two million years.
Why do conifers lose their leaves? Whether it’s a conifer or not, Dr. Friedman said there are many reasons why trees drop their leaves.
In the tropics, deciduous trees developed in response to the dry season. This is because the plant rests when it lacks water. For some conifers, millions of years ago it was a response to the challenge of keeping leaves alive at high latitudes during the dark and cold winters.
“This is a cost-benefit analysis,” Dr. Friedman said. “It would have been a better business model to remove the needle every year.”
It is not well understood why deciduous trees such as oak, beech and witch hazel cling to their old load all winter long. Do the faded leaves remain a barrier to deer grazing, or do they continue to fall just in time to act as mulch in the spring?
This phenomenon is known as Marcescence, which is a beautiful word, but a delicate one. To prevent the leaves from falling off, the plant must keep a very small portion of each leaf stem, or petiole, alive during months of cold weather. In one of his winter examples, Dr. Friedman’s favorite is the Chinese Spice His Bush (Lindera angustifolia), which displays pleasing tawny foliage off his season.
What was the impetus for bringing such tricky engineering into development?
“They all just marched north.”
Being deciduous isn’t for everyone. The California coastal sequoia (Sequoia sempervirens) and the Sierra giant heirloom sequoia (Sequoiadendron giganteum) are both closely related to the dawn sequoia and are evergreen trees.
But their cousins diverged from that path, Dr. Friedman said.
The trees move, you see. Yes, slowly, but it works.
It wasn’t that long ago, evolutionarily, that there were no trees where there are arboretums, or anywhere in the Northeast, north of New York City, or around it.
About 18,000 years ago, sheets of ice covered a vast northern band. “And all temperate trees in eastern North America hung in Georgia and Florida,” Dr. Friedman said. “And, amazingly, they all marched north.”
He added: They have returned in thousands of years. They just push their seed north, north, north. “
Spruce and black locust (Robinia pseudoacacia) are already making impressive moves. The fringe tree (Chionanthus virginicus) also continues its journey.
But famously, the extinct wild Franklin tree (Franklinia alatamaha) is one of those that didn’t escape its Ice Age hideout. Today it is found only in botanical gardens and private properties.
Are those trees, and popular southeastern shrubs like Fothergilla major and bottlebrush buckeye (Aesculus parviflora), hardy in the north because they once lived there? Only fossilized pollen records.
Whatever the reason, Northeast gardeners are happy beneficiaries.
modern transition
Glaciers are not a migration risk factor today, but extreme heat and drought are. Arnold’s researchers are working to preserve the genetics of stressed plants, especially in the habitat’s most hostile southern extremities.
“Species may migrate and survive, but some parts may just go extinct,” Dr. Friedman said. “And you lose those genes.”
Early on, that principle was applied to another challenge. How was Arnold’s first director, Charles Sprague Sargent, able to grow the Lebanese cedar (Cedrus libani) he coveted, even though it wasn’t hardy in Boston? ?With seeds from the Turks of the Highlands, desires have been satisfied.
Similar research is underway in the evergreen Southern Live Oak (Quercus virginiana). “You can’t grow evergreen oak here,” Dr. Friedman said.
“At the end of the day, if you plant 200 saplings and one has the genes to survive in Boston, that’s a win,” Dr. Friedman said.
family reunion
Three-quarters of the research in arboretums now focuses on how trees and forests perform in the face of “human-induced global change, including climate change,” Friedman says. He recently wrote for Arnoldia, a quarterly membership magazine.
The arboretum collection is taxonomically arranged on 281 acres and is densely populated with related trees. This is useful, for example, to study how different maple species respond to increased drought, or how certain trees handle more freeze-thaw cycles that occur during spring foliage. Ideal. stage.
Dr. Friedman says, “Just like a museum gallery that exhibits a particular kind of art, it needs that comparative context.”
Arnold is also a significant collection of what is known as biogeographic segregation. Closely related plants are very much apart in nature thanks to continental drift millions of years ago. That’s when sea levels dropped and plants started to migrate east-west across the continent. A bridge that is currently submerged.
This is why North America and Asia have so many relatives among temperate trees and shrubs, such as magnolia and viburnum.
For example, after 14 million years of estrangement, the Chinese tulip tree (Liriodendron chinense) now lives in Arnold alongside the North American tulip (L. tulipifera). The two are genetically so similar that they can cross-pollinate and the hybrid offspring will happily grow in it.
“Family reunion” — one of many rooted in the grounds and history of this place — noted Dr. Friedman.
Get to know Arnold
Dr. Friedman sees the Arnold Arboretum as part of Boston’s public health system: a place of exercise and escape. During the pandemic it was never closed.
Part of Boston’s urban park system, the landscape was designed by Frederick Law Olmsted, who turns 200 in April. It is free to use and open all year round.series selected walks Websites contain audio, text, and pictures to guide visitors directly or virtually.
Each plant has detailed origins, and the large-leaved magnolia (Magnolia macrophylla) is a tropical-looking creature with the largest flowers and simple leaves of any plant native to temperate North America. This is another tree found in the southeast today, but hardy enough to grow further north.
There is also future-oriented inspiration. The arboretum has an ambitious photovoltaic installation, designed in a higher-than-average frame to accommodate a thriving pollinator habitat all around and below.
Margaret Roach is a website and podcast creator way to the gardenthe book of the same name.
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