A Walk Through Time, Part 1

Glimpse an ancient landscape on Hemlock Hill reminiscent of what you might have seen just after the last Ice Age about 9,000 years ago.

“Hemlock arrived in the northeastern United States about 2,000 years after white pine and 2,000 years before American beech, even though today it frequently grows alongside both these species, and we often think of them as members of the same plant communities.”

-David Foster, in Hemlock: Forest Giant on the Edge

As we walk along Valley Road from South Street Gate, it is worth reflecting on the name of this area. Hemlock Hill refers to the outcropping and hilly topography that lies southwest of your walk. In order to take in the full spectacle of this immense glacial pileup, cross over the wooden footbridge tucked between the Rhododendrons: you will come face-to-face with a Canadian hemlock (Tsuga canadensis), and glimpse into the last glacial period and beyond.

The majestic hemlock is called a “foundation species,” which means that it has a strong role in structuring other species around it, controlling biodiversity and landscape processes. It can also serve as a bellwether for its community, heralding disruption of its ecosystem. This specimen holds stewardship concern because it represents one of few historic hemlocks in the Arboretum that has resisted the hemlock wooly adelgid.

After the last Ice Age, hemlocks were an early species that appeared in the wake of the retreating ice sheet. They clung to the rocky puddingstone outcrops. The Arboretum sits upon Roxbury puddingstone, or more properly, Roxbury Conglomerate. This form of rock was formed about 580 million years ago and is composed of clast-supported pebbles and cobbles.

Nestled on a rise above two brooks is a reminder of the old New England forest, a majestic sweet birch.

Proceeding along Hemlock Hill Road, you will see the landscape rise towards a distinct feature at the juncture of the two streams that curve through this part of the Arboretum, Bussey Brook and Spring Brook. As you journey across the footbridge, you climb to “Spring Brook Village,” the site of an ancient Indigenous camp.

Before you stands an old sweet birch that resists the classification of provenance because it may have been rooted by the time Sargent and landscape architect Frederick Law Olmsted began their designs. This tree is distinctive because it reminds us of the beauty and character of spontaneous plants. Because it was left relatively undisturbed, it gives us some clues about ancient Indigenous habitation in the Arboretum.

In 1934, Arboretum botanist collector Ernest Jesse Palmer wrote a report on the prehistory of the Arnold Arboretum. His studies reached across various sites on our grounds including that adjacent to our sweet birch. Palmer and Arboretum horticulturists unearthed stone tools, spearheads and projectile points. The artifacts show that ancient Indigenous people used this land as long ago as 6,000 years before the present.

What emerges from the past helps us explain the responsibilities of the present. Sweet birch is also called black birch, cherry birch, and red birch. Birches are a boreal species, occurring from northern North America to Europe to Asia, in what is considered the largest land biome.

As a young forest dweller, sweet birch has smooth, shiny, non-peeling bark. Through age and weathering, the bark begins to split, peel, and flake. The wide gray-toned splits, characteristic of an aged tree, are visible in this specimen.

This white oak along Hemlock Hill Road is a silent witness to the changing landscape at the Arboretum.

This magnificent white oak represents a species that was growing at the Arboretum when it was designed. It has stood proudly through disturbances from road construction to great hurricanes, transitions from forest to agriculture, from field to city.

Many of the trees on the grounds predate the mass plantings, accessioning processes, and curatorial recordings. Look at the tree’s tag: the number 2011 means that the tree was only added to the plant records 10 years ago as part of an effort to record old, spontaneously growing trees of the Arboretum. At the landscape scale, the decision to integrate the white oak is a form of recognition of past use.

White oak might be best known as a timber or fuel tree, in both settler societies and in Indigenous traditions such as Ojibwe and Haudenosaunee (Iroquois). But this specimen has neither been burned nor felled, a reminder of life each season as smooth, bright green leaves emerge and cast deep shade until they turn wine red in the fall.

Telling oaks apart is always easiest with the leaves. White oaks have rounded lobes, and red oaks have pointed lobes. White oaks also have very deep grooves in the bark, by comparison. A feature so distinct in this specimen, you can see the grooves from the path. Notice the impressive spread of the canopy, and the notable girth of this venerable witness to history.

The stately Nikko fir is an evergreen species that comes from the mountains of Japan.

At the Arboretum, it is impossible not to be awed by this specimen. It attracts visitors from schoolchildren to downy woodpeckers. The leaves are needle-like, but surprisingly flat and wide. They are glossy above and whitish below, indicating stomatal bloom, a waxy coating around stomata. In Japanese, this species is called urajiro-momi or “a fir tree with white undersides.”

This tree was grown from seed received in 1908 from the Imperial Forest School in Tokyo, Japan. This seed was among the 68 packets of seed received from various sources in Japan that year. During his 1892 visit to the country, Sargent networked with Japanese botanists in addition to collecting plants. John George Jack continued the practice during his 1905 expedition, spending time with Professor Kingo Miyabe at the Sapporo Agricultural College (now Hokkaido University) and in the field in Hokkaido. Ernest Henry Wilson, during his two expeditions to the country in 1914-1915 and 1917-1919, collaborated extensively in the field with Japanese colleagues, and it is safe to say that his expedition would not have been as successful had they not had such a fine working relationship.

Sargent described the Nikko fir in his book, Forest Flora of Japan: “The Fir of which we saw the most in Japan is the Abies homolepis… It is the common Fir of central Japan, and abounds on the Nikko Mountains between 4,000 and 5,000 feet elevation above the sea… It is a massive although not a very tall tree, apparently never growing to a greater height than eighty or ninety feet… The pale bark, the long crowded leaves, dark green above and silvery white below, and the large purple cones make this a handsome tree.”