Eastern red cedar (Juniperus virginiana) has become one of the dominant tree species of Nantucket’s open lands, increasingly abundant in our more recently abandoned farm fields. These areas that remain undeveloped are often managed with mowing to maintain open savannah-like habitats. While frequently called a cedar, this species is actually a member of the juniper genus and is named for its reddish wood and cedary scent. On Nantucket it’s mainly a shrubby species when young, but grows into small trees, often forming groves where it’s allowed to remain undisturbed. The prickly awl or needle shaped leaves of seedlings and young saplings are less attractive to deer, allowing it to survive and grow above the reach of deer with upright trunks in areas that aren’t exposed to the worst winds; in contrast the leaves of the mature trees are compressed along the twigs, presenting a smoother surface that resembles a braided cord.

The dense juniper canopy fills out above the deer browsing line and spreads outward, often flat-topped due to the pressures of winds and salt spray. In winter, the greenish blue foliage turns a tarnished reddish color in the harsh conditions of salt spray and desiccation. But come spring, the canopy greens up again and new branch tips are rapidly extended. The trees bloom in early spring, with males producing copious amounts of pollen, and females beginning the process of producing the characteristic fruits.

Juniper berries (actually cones in disguise) range from a pale white to a dark blue, with a waxy outer coating. Photos: K.A. Omand

You’d think that these waxy bluish fruits are berries – and in fact, they are commonly called juniper berries – but they are actually dark blue fleshy cones with a waxy coating that gives them a lighter bloom, their color ranging from deep blue to almost white among different trees. These berries, like bayberries (Morella caroliniensis), are a vital food for birds migrating through in the fall, or overwintering. They are full of fats, carbohydrates, and other nutrients that are so vital as the days grow colder and insects become scarce. Cedar waxwings (Bombycilla cedrorum) are drawn in flocks to the abundant fruits along with a variety of other birds. The dense canopies of these conifers are also a great nesting habitat for birds such as Cooper’s hawks (Accipiter cooperii), which are abundant on Nantucket, and the tiny saw-whet owl (Aegolius acudicus). The branching pattern of these trees offers great perches for hunting, and the abundant foliage offers wonderful cover.

A dense red cedar shrubland at the edge of a salt marsh on Five-fingered point, with groundsel bush (Baccharis halimifolia) at left. Photo: K.A. Omand

But red cedar juniper is not just a bird magnet! It’s also a creator of beneficial micro-habitats that nurture other species of native plants.  Widespread on the low sand dunes of Coatue, juniper is vital to dune stability and tolerates even harsher conditions than it does farther inland on Nantucket. While surveying for prickly pear (Opuntia) cactus on Coatue this fall, we enjoyed a close-up view of the juniper in all its glory. This year was a fairly heavy fruiting year for this species; like bayberry and beach plum it has boom years and bust years for fruit production. In 2020, the upper branches of Coatue’s female trees (often only 4-12 feet tall) were laden with the frosted blue berries (2015 was another recent notable year for a heavy fruiting, which I wrote about in an earlier blog article about fall berries).

Red cedar juniper on Coatue helps stabilize dunes; when sand moves in storms, or accumulates over time, the shrubs grow new foliage on top and the older parts of the plants remain below ground, helping to hold the sand in place. Photo: N.P. Foley

In addition to its beauty and wildlife food value, juniper’s shrub cover and soil stabilizing effect provide a mix of sun and shade that benefits many native plant species on our great sandspit, including the wildflowers blunt-leaved grove sandwort (Moehringia lateriflora) and herb Robert (Geranium robertianum).

Blunt-leaved grove sandwort grows in profusion on stabilized dunes around red cedar and among other coastal heathland species on Coatue. Photo: K.A. Omand.

In the more sheltered micro-habitats formed in the stabilized dunes, there are extensive patches of the tiny 5 petaled white flowers of grove sandwort, which on Nantucket is only common on Coatue. The delicate grove sandwort flowers look a bit like chickweeds, but they have a more graceful form and when growing in large numbers are particularly beautiful, similar to windflower anemones. It seems that they really appreciate the open shrubland and miniature juniper forests and sandy soil forming the backbone of our sandy scalloped barrier beach, true to their name, “grove sandwort.”

Herb robert, a native cranesbill geranium, is only found on Coatue, out of all of the habitat offered on Nantucket, where it thrives in the shelter of the red cedar shrublands. Photo: K.A. Omand

Hidden in smaller clumps in the juniper maritime shrublands and woodlands are the pink flowers of herb Robert, one of our native cranesbill geranium species. Another common name for this species is “mountain cranesbill,” which I find particularly amusing, because the only habitat this species inhabits on Nantucket is the low sand dunes of Coatue! It resembles the more common woodland geranium, spotted cranesbill (Geranium maculatum), which is common in the moist forested edge habitats of Squam and Norwood Farm, but its leaves are more finely cut into a fernlike pattern and the blossoms are a deeper pink than the spotted geranium.

A native prickly pear cactus growing sheltered behind a red cedar juniper on the north side of Coatue near Third Point. Photo: K.A. Omand

Ironically, the same juniper covered rolling sand dunes and hollows that support these open woodland wildflowers also are home to Nantucket’s only cactus species, the prickly pear. Listed in the Nantucket Flora as eastern prickly pear (Opuntia humifusa), our native American cactus of sandy eastern habitats from Texas to the East Coast and into Canada near the Great Lakes. In recent years we have been wondering if our native better fits the description for (Opuntia cespitosa) because our plants have the distinctive red centered flowers of that species, but they are both considered members of the Opuntia humifusa group…in other words, it’s complicated, and this is a nomenclatural digression to be discussed another time…check out this article on the genetics of the prickly pear clade to feel your head spin.

Close-up view of prickly pear pads and fruit growing in the open on Third Point. This is the type lacking spines, and the color is much lighter than on the shade-grown prickly pear found under red cedars, and appears a bit dehydrated after a long summer. Photo: K.A. Omand

In this context, what we found most interesting was that the prickly pear on Coatue appeared to be benefiting from the partial shade provided by the juniper. Tucked into dappled shade or small openings the large flat clusters of prickly pears seemed to flourish, while plants out in the open on sandy expanses appeared more shriveled and had lots of browned wrinkled pads. The accumulation of dead leaves and twigs under cedar trees in these sandy micro-habitats increases the soil organic matter and likely helps hold nutrients and moisture from rain and dew, giving partly shaded wildflowers and prickly pear a boost.

From sandy dunes to old field, the common red cedar juniper contributes a surprising amount to the biodiversity and ecology of the island. While considered a pest species in some habitats, like the prairies, and managed here on Nantucket to maintain open areas of early successional grassland and low coastal heathland, this small but mighty tree is a vital food and habitat provider for a network of species in different communities.