Martha’s Vineyard is so endowed with notable wild species — the rare, the beautiful, the specialized — that I sometimes lose sight of ordinary things. But common and unspectacular plants and animals have their stories to tell, and in many cases, these overlooked residents play major ecological roles.
The sumacs provide a fine example. Members of the genus Rhus, sumacs are generally medium-size shrubs or trees characterized by pithy wood, large leaves featuring two rows of leaflets, and clusters of berries that, in most of our species, ripen to red in autumn. Taxonomically, our sumacs are related both to poison ivy and, oddly, mangoes and cashews.
Five sumac species are known on the Vineyard. One, the nonnative fragrant sumac, turns up occasionally as a cultivated ornamental and, perhaps, as an escape into the wild. Another, poison sumac, is a wetland species, white-berried and scarce on the Vineyard. But the other three, staghorn, smooth, and shining sumacs, are common, and indeed can be dominant where conditions favor them.
Staghorn sumac gets its name from brownish fuzz, resembling the velvet of developing deer antlers, which cover its twigs. Smooth and shining sumacs both lack that feature, and are distinguished by the structure of their leaves: On shining, but not on smooth sumac, the leaflets are connected by flanges of leaf tissue that run along the rib of the leaf. All three species can be found in open and edge habitats, and all three play multiple roles in supporting the Island’s ecology.
Flowers of our common sumacs are dull yellow, appearing in large, conical clusters at the ends of branches. These clusters are unremarkable except for their size, but the individual flowers, when fully developed, turn out to be highly attractive to insects. Bees, butterflies, wasps, flies, and beetles visit sumac flowers in large numbers, and it’s not unusual to find dozens of individuals representing multiple species sharing a single flower cluster.
In settings in which sumac is abundant, the total volume of pollen and nectar that these flowers represent must be astronomical. For many sumac plants, the peak of bloom falls in mid- to late July, a period when relatively few other native flowers are blooming. So these shrubs offer an important resource to a wide range of pollinators.
Fewer insects eat the plant itself, as opposed to the pollen; I don’t often notice leaf damage from herbivory on sumacs. But one interesting butterfly uses a curious strategy to feed on sumac leaves. Larvae of the red-banded hairstreak, a primarily Southern butterfly that has colonized the Vineyard over the past decade or so, feed on sumac leaves — but generally on decomposing ones on the ground, not living leaves.
I speculate that this approach makes the leaves more consumable and digestible by breaking them down partially before they’re eaten. And this ground-feeding strategy may allow the caterpillars to feed actively and constantly, while staying concealed from most predators. In any case, red-banded hairstreak produces three generations per year on the Vineyard, and numbers have steadily grown since this butterfly was first detected here in September 2016. Banded hairstreak, a related butterfly, is also known to use sumac as a larval host plant, though they may not do so on the Vineyard, where oaks appear to be the usual choice.
While the subject has not been studied here, sumacs undoubtedly offer nesting sites to a variety of bees, wasps, and flies. The wood of sumac branches and twigs is soft, with a foamlike pith that must be easy to burrow into. A surprising number of insects nest inside stems, a choice that offers relative safety from predators as well as insulation from extremes of temperature or moisture, and sumacs offer a congenial substrate.
Finally, as sumac flowers mature, morph into berries, and then ripen into clusters of red, beadlike fruit, these shrubs offer an important late fall and winter resource for birds. A quirky but useful volume published in 1951, “American Wildlife and Plants: A Guide to Wildlife Food Habits,” has some details.
Alexander Martin and his two co-authors point out that sumac berries remain firmly attached to the plant deep into the winter, making them accessible at a season when many other avian food sources have become hard to locate. Dozens of game and songbird species are listed as known to feed on sumac berries, along with mammals including chipmunks, rabbits, and deer.
Its ecological value notwithstanding, I can’t wholly endorse sumac as a choice for eco-friendly landscaping. These vigorous shrubs can be aggressive to the point of invasiveness, and are hard to eradicate if you decide you’ve made a mistake. But in their natural setting, that vigor is just one more factor making these plants an indispensable part of our local ecology. Keep an eye on them and watch how much they contribute.
