During the Nantucket Biodiversity Initiative Conference on Nov 1-3rd, 2013, a large group of conference attendees joined me to visit some of the largest, and likely some of the oldest, trees at Squam Swamp. These exemplary trees may provide clues to Nantucket’s land use history, teaching us more about how the forest has grown and changed over time. As mentioned in last winter’s “Forests at Sea” blog post, the contorted trunks and wind-sculpted crowns of Squam’s trees indicate some of the hardships growing trees face on our exposed little island. As if to underscore these challenges, high winds prevented all ferry traffic the day of the field trip. Conference participants and speakers made quick changes to their travel plans, fortunately all touching down safely at the Nantucket Airport.
By the time we all assembled in the Squam Swamp parking lot off of Wauwinet Road, the winds had diminished, which made the walk through the forest much more pleasant.We made our way off the main trail onto a deer path to visit three very unusual trees that the science staff discovered during our forest research project over the last two summers. By this point in the season, the sassafras and tupelo stands which dominate the upland portions of the forest have shed most of their leaves. So have the understory shrubs like sweet pepperbush, blue dangle, and swamp azalea. This opens up views throughout the forest and coincidentally highlights Squam’s largest trees, which include scattered American beech, black and white oak, and red maple. These species tend to retain their leaves later in the season, so they stand out as patches of color in a gray and brown landscape.
Our first stop was at a very large black oak (Quercus velutina), pictured below during the summer. This tree is wider than it is tall: its canopy spreads 63 ft, but it is under 50 ft tall. Its enormous main branches emerge from the trunk near the ground, rather than a more typical 10-20 ft above the forest floor. Measuring the tree’s diameter at the base shows that it is 52 inches across! Due to this remarkable form and size, I nicknamed this tree “Hydra” after the multi-headed creature of Greek Mythology. In fact, all of these trees were so unusual that they ended up with nicknames.
Hydra’s odd growth form and large size suggest that it is quite old, but began growing in an open setting without surrounding trees to shade it out or shield it from the wind. Hydra’s stocky base and ability to grow new trunks as needed improve the odds of surviving in these conditions. In the picture at right, you can see that the lowest trunks have been “shut off” and the tree is sealing off the dead stems with new healthy bark. This is a process known as “self-pruning” and it’s a way for trees to stop using limbs that have been shaded out, so active growing and photosynthesis can occur in the best places on the tree, where there is a jackpot of sunlight.
Our next stop was at a very strange old American beech (Fagus grandifolia), nicknamed “Ganesh.” American beech is known for its smooth gray elephant-skin bark, and in this case, a few additional features that further enhance its resemblance to a pachyderm: at the base, which is 42 inches across, the trunk is scalloped, making it look like elephant legs fused together. Above this impressive base, ten large trunks form a basket-like shape that is filled with humus (decomposing leaves and twigs) that the tree is thriftily tapping into with adventitious roots. This tree basically has it’s own compost pile! Talk about recycling.
Like the black oak Hydra, this beech has a canopy wider than it is tall, allowing it to capture the most sunlight possible, while still hunkering down enough in the landscape to minimize wind damage. Situated at the very edge of a vernal pool, Ganesh has grown a large trunk that extends in a great arc–nearly 50 ft out over the pool–capturing the sunlight that the gap affords. In a mainland forest, a tree like this beech would simply grow more upright, maintaining its spot in the sun by outgrowing the surrounding trees. But on Nantucket, wind is the great leveler–a big old tree must grow outwards however it can, since it can’t really overtop its fellows. Even the burliest trees in Squam Forest can’t afford to outgrow the much more slender tupelo and sassafras.
Taking this low lying growth habit to the extreme was our final tree along the walk, an enormous white oak (Quercus alba) nicknamed Titania. This tree has two enormous main bases that spread outward in a low vee shape. It appears to have split in half at the base in recent years, but the two main trunks remain growing horizontally a few feet off the ground, with healthy foliage. While they were once a bit more upright, it’s clear that this tree always grew very prostrate.
Drawing on the NCF Science Staff ‘s Squam Forest research, and spurred by conversations on this NBI walk, we are hoping to work with Aaron Ellison, David Foster, and David Orwig (researchers at Harvard Experimental Forest) to determine the age of these remarkable trees. Using an increment borer to obtain a tiny core sample of a trunk near a tree’s base allows you to count annual rings and estimate the age of the tree. It could be that Squam’s big weird trees are some of the first to grow on Nantucket following the deforestation of the colonial era.
So what will future oaks and beeches look like in the forests of Squam? Walking along, we found a number of medium sized mature oaks and beeches with canopies that begin 5-10 ft from ground level. Still a strange place for a canopy to start, but likely the shelter afforded by the surrounding forest allows the trees a bit of head space before they grow tall enough to be strongly affected by the island’s strong winds. We will continue measuring trees in plots scattered throughout the forest, and this will help determine the species composition and structure of the forest as a whole. It will also allow us to assess some potential impacts on the forest, such as deer browsing and spreading invasive plant species.