As compared to the rest of New England, Nantucket has relatively few hardwood forests. However, it appears that this was not always the case. At the end of the last glacial period, the region’s climate was considerably colder. During this time, it is believed that the island was covered with tree species typical of more northern climates, such as spruce and jack pine.
As the glacier melted and the climate warmed, the northern tree species were slowly replaced by trees that prefer warmer temperatures. Analysis of historic pollen excavated from ponds and bogs on the island has revealed that, just prior to European settlement, large areas were dominated by oak, with some beech, pine, maple, and hickory.
This situation changed when emigrants settled Nantucket in 1659 and began to cut trees for home construction, ship building, and firewood. Large areas were also cleared for growing crops and as pasture land. These activities quickly depleted the island of its forests. Several sources report that islanders began depending on firewood shipments from the mainland within several decades of settlement.
Visitors to Nantucket in the late 1700’s and early 1800’s described the island as virtually treeless. In 1854, the famous naturalist Henry David Thoreau wrote “There is not a tree to be seen, except such as are set out about houses…This Island must look exactly like a prairie, except that the view in clear weather is bounded by the sea…” Since the decline and eventual elimination of livestock grazing in the early 1900’s, tall shrubs have gradually become reestablished in many areas of the island. However, hardwood forest communities are still relatively rare on Nantucket and limited to certain areas.
There are several distinctive types of hardwood forests on Nantucket. A maritime forest occurs at Coskata, just north of the Foundation’s Haulover property. This unique area contains dry, upland soils but is surrounded by salt marsh, harbor, salt pond, sand dunes and ocean. The predominant species here are mature black and white oak trees, with huckleberry, hazelnut, bracken, and wintergreen as understory plants. During the Revolutionary War and the War of 1812, there was a severe shortage of firewood on the island because shipping from the mainland was disrupted. It was reported that islanders had to cut down trees from Coskata Woods and transport them over the ice on Nantucket Harbor to town during these times.
The northeastern portion of Nantucket is currently contains the most hardwood forest habitat on the island because the retreating glacier left behind many poorly drained depressions that developed rich, peaty organic soil. Here, forest trees can grow to be 30 to 40 feet tall before they are impacted by high winds and salt. These wooded areas are locally referred to as hidden forests because they tend to occur in depressions that are surrounded by hills, which reduces salt exposure and makes them somewhat hidden when viewed from a distance.
Some forested areas, such as lower elevations of the Squam Swamp, have standing water in them year-round. The only trees that can grow here are those with adaptations that allow them to tolerate water-logged, oxygen depleted soils. Red maples are able to survive in these conditions by developing shallow, spreading root systems that maximize the absorption of what little oxygen is available. Shrub species such as swamp azalea and high bush blueberry can also thrive in damp soils.
Some of the higher elevations of the Squam Swamp, the Masquetuck Reservation in Quaise, and the forest surrounding Stump Pond (south of the Windswept Cranberry Bog) have wet soils during only a portion of the year. These areas contain trees and shrubs that are adapted to growing under such conditions, including tupelo or black gum, sassafras, shadbush, and sweet pepperbush. Small patches of dry upland soils within these forests contain some beautiful, old examples of American beech, black oak, white oak, and American holly – all trees that are relatively rare on Nantucket.
The vegetation patterns in the forest are influenced by a variety of other factors besides soil water content. Black tupelo, sassafras, and shadbush prefer high levels of sunlight, while American beech, flowering dogwood, red maple, and American holly are understory species that can tolerate shade. Growing below the tree canopy and forming another layer in the forest are shrubs such as highbush blueberry, arrowwood, American hazelnut, common winterberry, and inkberry. Below these is a third layer of flowering plants, ferns, mosses, and ground covers, including cinnamon fern, wintergreen, jack-in-the-pulpit, starflower, and swamp candles.