Short and Spreading Oak

Nearly anywhere you go in the United States you will find oak trees. They are often large and common, so they can often contribute significantly to the look and feel of a place. The effect reaches consciousness if you are a plant nerd. During the year I lived on the Central Coast of California, I was somewhat distracted by the fact that several species of oak did not lose their leaves in the winter. And what could be more different than the spreading, moss-draped live oaks of the Southeast versus the upright, austere red and black oaks of the Northeast?

Spreading post oak in Texas
Spreading post oak in Texas

I have been reading that before the European settlement period Martha’s Vineyard was not as heavily dominated by oak forest as it is now. (When I repeated this statement to a naturalist in the employee of The Nature Conservancy, she contested it. And David Foster’s book A Meeting of Land and Sea indicates that it is a lot more complicated than that.) Supposedly, the up-island portion of Martha’s Vineyard, which is higher, rockier, and less sandy than down-island, was once more of a northern hardwoods assemblage, characterized by beech, maple (mostly red), black tupelo (locally called beetlebung).

But clearing of the forests for sheep raising between the 17th and 19th centuries led to erosion of organic-rich top soil, so when animal husbandry and farming faded and the island became a site for second homes, the forest that returned was one more adapted to drier sites with more mineral-dominated soils. In the Northeast, this tends to be the preferred habitat of the post oak (Quercus stellata).

I am not familiar with this species. It is a common oak in the South and southern Midwest, but is confined to marginal areas in the Northeast: sand barrens and rocky ledges. In Massachusetts it is found in Bristol and Barnstable counties on the mainland (Buzzards Bay and Cape Cod) and on the Islands. This represents the northeastern corner of its range; it extends southward along the Connecticut coast and on Long Island.

"Maltese cross" shape of the post oak leaf
“Maltese cross” shape of the post oak leaf

It is a famously slow-growing species and the wood is rot-resistant. It gets its common name from its sturdiness as a component of fence construction. It often takes a spreading form, the branches assuming sinuous shapes, and generally reaches the height of 50 feet, although it can grow to twice that height in a suitable location.

It is in the white oak group, so the lobes of the leaves are rounded and without the terminal ‘pins’. The acorns mature in one year and are sweet tasting. White oaks also readily hybridize among species, making identifying characters somewhat variable from tree to tree. The post oak usually has leaves that are said to resemble a Maltese cross; they are narrow at the base and have three broad, squared off lobes at the distal end. The underside of the leaves are covered with fine hairs called trichomes. In the post oak these have a star-shaped cross-section, hence the trivial name stellata.

Allen's Farm, Martha's Vineyard
Allen’s Farm, Martha’s Vineyard

Oak leaves are poisonous to sheep and goats, so it seems odd that they are so common on this island, where sheep raising was such an important part of the economy. Apparently the sheep won’t each the leaves if there is enough grass around. Sheep are consummate grazers, even less likely to browse than cattle or horses.

When you wander the conservation lands of Martha’s Vineyard, you frequently encounter stone walls that now wend their way through the woods, but once delimited the boundaries of sheep meadows. Amid the younger trees you find larger, spreading trees — they are occasionally post oaks — that must have been there to provide shade for sheep and shepherd. I still have some questions about whether eating oak leaves was a concern, but it is a pleasant picture to conjure.

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A New Kind of Ancient

Ancient woodlands path on Martha's Vineyard. Photo: David R. Foster
Ancient woodlands path on Martha’s Vineyard. Photo: David R. Foster

I recently learned a new term to describe a forest ecosystem. The water district of Oak Bluffs, a town on the northern tip of Martha’s Vineyard, proposed going “green” at the site of their pumps and wells. They would add solar panels to the site to make electricity to power the pumps that supply the town center with drinking water. The plan was shot down by the Martha’s Vineyard Commission, the regional planning council, on the grounds the project would entail entirely clearing between 6 and 10 acres of the site to build the frames that hold the panels. David R. Foster, the director of Harvard Forest, which is in central Massachusetts, happens to live in West Tisbury, which is on the island. He told the commission that “ancient woodlands” would be destroyed should the project go forward.

Ancient woodlands” was initially a baffling term to me (although I found it is used routinely in the United Kingdom). The forests of the island date from the 19th century, generally speaking. As is the case for much of New England, particularly the southern portion, the land was almost entirely cleared for agriculture, pasturage, and for firewood, between the 17th and the 19th centuries.

Beeches on Gay Head Moraine terrain. Photo: David R. Foster
Beeches on Gay Head Moraine terrain. Photo: David R. Foster

Martha’s Vineyard was settled by Europeans after 1641 when Thomas Mayhew purchased the island from the Earl of Sterling and Sir Ferdinando Gorges. The Wampanoag had (and have) inhabited the place since you could walk to it on dry land after the last Ice Age. Like other coastal tribes they burned the land to keep it clear for agriculture and for hunting. Parts of the Vineyard, the portion that is glacial outwash plain, was also open heathland (home to the heath hen), perhaps even before the Wampanoag began burning it systematically, and not forest at all. But in a March 2016 letter (included in an August 2016 letter) to the commission Foster, the author of a monograph about the island’s forests, stated that 40 percent of the Vineyard’s woodlands had come through the historical clearances intact, and the Oak Bluffs water district site was within the largest remaining tract.

Foster explained that an ancient forest is not really about the age of the trees; it is about the age of the ecosystem. The parcel owned by the Oak Bluffs water district turned out to be a piece of land that had never been tilled. The soil architecture and its attendant microbial and invertebrate ecosystems had never been disturbed. It therefore supports a sub-aerial floral communities that is similarly continuous. These are not majestic, old growth forests with towering trees and haunted silences. Instead it is a scrubby-looking tract populated by several species of oak in the canopy and a sub-canopy somewhat oversubscribed with ericads. There is, of course, more to it than that, but that is definitely what meets the eye of the casual observer.

The carbon cycle
The carbon cycle

This is an ecosystem distinct from an old-growth forest. Old-growth as defined by non-foresters includes the idea that the mature trees in a stand have never been felled by a lumbering operation. Old-growth forests presumably share a lot of sub-surface characteristics with ancient forests, but the sub-aerial expression is quite different. No one claimed that the trees at the water district site were hundreds of years old, but Foster said that the ecosystem had been undisturbed by human activity for millennia:

These ancient woods are particularly important because their soils are intact, their vegetation has continuity on the landscape going back thousands of years, the resprouting trees on these sites are many hundreds of years old, and the habitat that they provide is globally rare and valuable to many unusual as well as common species. (excerpted from Foster’s March 6 letter)

Foster and other opponents argued that the forest was doing its job sequestering carbon and keeping it out of the atmosphere, and it was “counterintuitive” to remove it and build solar panels, which were after all meant to contribute to the switch away from carbon-based fuels. Although there is a difference between the short-term storage of carbon in a forest and long-term in a coal deposit, we have little hope of actively creating or maintaining long-term storage (although Freeman Dyson and some others do feel otherwise) and maintaining our ancient woodlands where we still have them seems prudent. Especially, as Foster points out, there are so many roof tops, gravel pits and other disturbed sites where solar panels can be erected.

Gathering the Laurels

I grew up enjoying the site of mountain-laurel blooming in profusion each June. It is a common understory shrub in the Hudson Highlands, one of the northeast-southwest-trending chains of mountains that make up the northern Appalachians through downstate New York. Kalmia latifolia is an evergreen member of the Ericaceae (heath family), but it is definitely most noticeable when it flowers. The pink-tinged white blossoms are arranged in corymbs; the petals are attached to form pentangular bowls. The corymbs are several inches across; each flower is about an three-quarters to an inch in diameter. It is a showy plant.

Mountain-laurel in flower in Maryland.
Mountain-laurel in flower in Maryland.

In addition to their large size, the flowers are set against glossy, dark green foliage. K. latifolia has the tendency to form large, continuous thickets, sometimes covering part of an acre on rocky, well drained hillsides. In the southern Appalachians, they can attain the size of a small tree (over 20 feet tall), but in the northeastern states they are usually five or six feet tall.

I haven’t seen any mountain-laurel on Martha’s Vineyard yet, but it does occur here and is likely to be found “up-island” in the towns of West Tisbury, Chilmark, and Aquinnah. The Gay Head and Martha’s Vineyard Moraines create a series of northeast-southwest-trending ridges that form the upland portion of the island. The terrain is dotted with large boulders (especially in the Gay Head Moraine areas) and was apparently originally forested with more beeches and maples (Northern Hardwood assemblage), tempering the dominant Oak-Heath presence that still dominates the down-island portion of the island, which a sandy outwash plain formed by the erosion of the moraine.

Sheep-laurel. (Photo: Bob Cunningham)
Sheep-laurel. (Photo: Bob Cunningham)

The most common member of the heath family in the outwash plain is the sheep-laurel, Kalmia angustifolia. This is a much smaller plant than K. latifolia, getting only about three feet all, but it has the same tendency to grow in extensive thickets. It is a common part of the Oak-Heath assemblage wherever it is found. It has evergreen leaves that hang down at a sharp angle. As its trivial name implies, the leaves of sheep laurel are narrow. It can also be distinguished from other Kalmia species because its branches end in terminal whorls of leaves, while the flowers emerge from the stem beneath the terminal leaves. The flowers resemble those of mountain laurel, but are a deep pink and much smaller.

The third member of the genus that is found in the northeastern U.S. is Kalmia polifolia, the bog-laurel. While the other two species are associated with mesic or even dry habitats, K. polifolia lives up to its name and is strongly associated with hydric conditions, although not necessarily bogs. K. polifolia is distinguished from K. angustifolia by the position of its flowers, which are terminal rather than growing further down the stem like the sheep-laurel’s. K. polifolia also blooms in the spring (April or May) rather than in the early summer.

Bog-laurel
Bog-laurel

All Kalmia prefer acidic soil conditions. But while sheep-laurel grows on a variety of sites ranging from wet sphagnum bogs to dry jack pine forests, bog-laurel is confined to wetlands (it is also called “swamp-laurel”). Mountain-laurel, on the other hand, prefers drier sites, but can tolerate moist soils at the edges of wetlands. While the sheep-laurel is widespread on Martha’s Vineyard, the bog-laurel is not found here at all.

The fourth member of the heath family found in the Northeast is Kalmia procumbens, the alpine-azalea, but as its name suggests, it is confined to the tundra-like areas on the higher peaks of New Hampshire and Maine and grows to be only 4 inches tall.

All parts of all members of the genus are poisonous to many mammals. The sheep-laurel gets its name for its morbid effect on that species, but the plant is poisonous to all livestock, as well as to humans. Some mammals, caribou for example, can tolerate it, and many birds depend on the fruits for winter forage.

Red Versus White

Oak holding onto leaves.
Oak holding onto leaves.

This time of the year—late October—most of the deciduous trees have dropped their leaves. Prominent exceptions are members of the family Fagaceae, which includes the American beech (Fagus grandifolia) and all the oaks (Quercus). They hold on to their leaves through the winter, a phenomenon called “marcescence.” The oaks are among the more diverse genera in the northeastern forest. They are dominant species in the “oak-heath” and “oak-hickory” communities that cover the drier, warmer, south-facing slopes of temperate eastern forests. There are about 90 species in the U.S., and many of them are important economically, mostly for building interiors and for furniture, and more esoterically, for boat building.

The oaks are divided into five “sections.” The first has the same name as the genus, Quercus (synonyms Lepidobalanus and Leucobalanus), which is also referred to more colloquially as the “white oak group.” Another is the Lobatae (synonym Erythrobalanus), which is usually called the “red oak group.” There is another North American section, the Protobalanus, which includes the canyon live oak and its relatives in Mexico, and two Eurasian sections, the Mesobalanus, the Hungarian oak and its relatives, and the Cerris, the Turkey oak and its relatives.

The Quercus section is Holarctic; its species are distributed in both the Old and New World in the Northern Hemisphere, but the Erythrobalanus species are confined to the New World north of northern South America.

Red versus white oaks
Red versus white oaks

The “white oak group” is distinguished from the “red oak group” by leaves with rounded lobes that lack a terminal bristle on each lobe. The acorns of the white oaks ripen in one year and tend to be sweet and quite edible. Red oak species have leaves with angular lobes and a small terminal bristle. Their acorns take 18 months to ripen, and they are full of tannins, which give them a bitter taste. Squirrels and birds that collect the red oak acorns will bury them and let the tannins leach out of them for weeks or months to make them more palatable.

Each group has an eponymous species that demonstrates the characteristics of the classification clearly. The white oak (Quercus alba) can get to be an enormous spreading tree when it grows in the open. The crown can be wider than the height of the tree, which can approach 85 feet. It tends grow taller in the forest, but is still a massive tree. It doesn’t begin to produce acorns until it is at least 20 years old, and after it reaches 50 years, it produces more every year.

Tyloses in white oak wood
Tyloses in white oak wood

The xylem cells of white oak have tyloses, obstructions that cause the lumber to be very water-tight. Consequently, white oak is used for boat building and the construction of barrels, notably those for storing wine and bourbon whiskey. Quarter-sawn white oak was the signature material of Mission-style furniture made by Gustav Stickley.

The northern red oak (Quercus rubra) is large tree, like the white oak, but it tends to be less massive and when grown in the open forms a narrow round-topped crown. While white oak bark is gray with irregular raised plates separated by narrow furrows, red oak bark is darker, with narrower ridges and broader furrows. The ridges of the northern red oak appear to have shiny stripes down the center.

Red oak acorns are larger than those of the white oak. The inside of the cupule that covers the nut is also fuzzy in red oaks and smooth in white oaks. The red oak acorns display epigeal dormancy; they have to be exposed to three months of temperature below 40°F before the germinate. They over-winter on the tree and fall during the following growing season.

Red oak is used for building, but the wood lacks the tyloses of the white oak, which makes it much more permeable. Most hardwood floors made of oak, however, are made from trees of the red oak group. Q. rubra is the highest quality wood in the group, but flooring sold as “red oak” may include pin oak (Q. palustris), black oak (Q. velutina), scarlet oak (Q. coccinea) and other “red oak” species.