A Lesson In Mashpee’s Changing Coast Emerges From The Sand At South Cape

By: Brian Kehrl
Published: 06/18/10

About 100 sections of juniper tree stumps, about a quarter of which are above the low-tide line, surfaced late this spring after storms washed away two or three feet of sand that had been covering them.

“What you can see is only a fraction of what’s here,” Christopher Weidman, research director at the Waquoit Bay National Estuarine Research Reserve (WBNERR), said in an interview at the site during low tide on Wednesday morning.

The dark brown stumps look like craggy model mountain ranges sticking out of the sand and the flat layers of peat that were also uncovered.

Dr. Weidman said initial estimates, based on their height relative to the current sea level, indicate that the trees may range in age from between 200 and 1,000 years old. Preparation is underway for radiocarbon dating tests of some of the wood, but the reserve is seeking funding for the approximately $500 needed for each of several planned tests, he said.

The wood, which is remarkably solid, has been well preserved underground, surrounded by peat and sand, Dr. Weidman said. Juniper contains high amounts of resin, which helps it remain intact, he said.

But if it remains exposed in the surf zone, the wood will not last long, he said.

The beach itself is not roped off, but signs put up by WBNERR staff say swimming from the roughly 500-foot-long stretch of beach is prohibited. Dr. Weidman said the reserve’s primary safety concern is the stumps underwater, which could pose a danger to someone swimming or diving into the water, or even wading, if their feet were to become tangled in the finger-like roots. 

WBNERR oversees South Cape Beach State park, as well as hundreds of acres of other conservation area in Falmouth and Mashpee. In addition to managing it for recreation, the reserve conducts scientific research in the area.
From the state parking lot at South Cape Beach, the stumps are to the left, about a quarter mile down, directly in front of Flat Pond.

The area will remain closed to swimming for as long as the stumps remain exposed, Dr. Weidman said.

He said he expected natural coastal processes to re-cover the wood, since late winter and early spring typically brings erosion from storms but the beach tends to build back up in late spring. But so far the erosion seems to be continuing, he said.

“We’ve seen more erosion here in the last winter than we’ve seen in at least the last 10 years,” he said.

Dr. Weidman said the tips of one or two small stumps have been exposed previously, so the reserve staff knew there was something underneath the beach. But until this spring, they did not know how extensive it was.

The stumps that are farther out, underwater even at low tide, are likely the oldest, he said. They sit about three or four feet below the tide line.

The junipers probably started growing when they were about five feet up from the high tide mark, he said, so based on general understanding of sea level rise in the area, he figures they were alive about 1,000 years ago.

As sea levels have risen, the shoreline has retreated, likely killing the trees with increasingly heavy infusions of saltwater.

“It is a classic demonstration of shoreline retreat,” Dr. Weidman said, illustrating a phenomenon that is explained in every basic coastal geography textbook.

“It tells you that the beach has gone that way,” he said, gesturing away from the coast.

Beyond being a clear illustration of coastal changes, the scientific value of the discovery is twofold, Dr. Weidman said. It could be used to help researchers develop a more detailed history of sea level rise in the area, and it could be used to figure out the history of major storms, hurricanes in particular, back to the time of the trees, he said.

Using the radiocarbon dating to pinpoint the age of the trees and measuring their height against current sea levels could give a more specific view into sea level rise over time, he said. That historical information could be used in planning for the expected changes to sea level from climate change, he said.

“Trees are a great tool for dating,” he said.

Likewise, the sand interspersed between layers of peat, which is old marsh, can be used to determine when and how much sand was washed into the marsh by large storms. Marshes naturally build up, then, when a storm washes sand in over the top, rebuild again.

Dr. Weidman said a researcher from the Woods Hole Oceanographic Institution may take core samples of the dunes upland from the beach to determine if it can be used for more in-depth research on storm history.

Dr. Weidman said it may be tough to tell what took down the trees, but the process of junipers being overtaken by saltwater and slowly dying can be seen over around Sedge Lot Pond, on the other side of the town parking lot from the stump site. Some junipers can be seen down in the marsh, completely or nearly dead. Others can be seen just upland from the marsh, barely hanging on. Still another level can be seen far enough from the marsh to be perfectly healthy.

“You can see the whole process up there,” Dr. Weidman said. “What we have down here is just the end.”