The bluffs along the Potomac River and the adjacent neighborhood in Washington, DC are known as the palisades. I measured trees occurring in wooded areas here (with a few open grown trees as well) between December 2014 and March 2015. Most of the woods occur on the steep slope between the top of the bluffs and Canal Road which runs along the bluffs’ base. An old trolley line, which had opened in 1895, used to run along the top of the slope for much of its length. It was decommissioned in the early 1960s. There has been some controversy about whether or not to make this a more formal trail. In the meantime it stays open, relatively unvegetated, and is a means of traversing the palisades. Closer to the Maryland line, the Georgetown Branch of the Baltimore & Ohio railroad climbed up along the slope. Now it is the Capital Crescent Trail. Various sections of the bluffs had been quarried in the past, leaving cliffs and rock outcroppings. Civil War fortifications had been installed on the heights above Chain Bridge. Despite the multiple causes of disturbance, some patches of older trees still occur on sections of steep slope and in some of the small stream valleys emptying into the Potomac.
As with the District portion of the Chesapeake & Ohio Canal, I measured trees that had a large cbh for the species, were uncommon, or appeared to be tall for the area. I measured a total of 147 trees consisting of 28 species. Making tree measurements in this area was often not very pleasant. The steep slopes made it necessary to walk down around some trees and back up the slope to get a tape around the trunks. There was a lot of dense undergrowth, including quite a bit of greenbrier. These conditions combined in some cases to make throwing the tape to the other side of the tree the only reasonable alternative for taking a cbh measurement. During one such toss around a tree, I gashed open my hand on greenbrier thorns, getting blood all over the tape. In another case I estimated the cbh (and noted such) as it was right at the edge of a cliff, and wasn’t worth risking maneuvers to try and measure it. Some trees were also in close proximity to traffic and people’s backyards – or at least what they might think are their backyards. While walking along the old trolley right of way, I became a bit uncomfortable the first time I saw a pack of dogs approaching. Then I saw their walker, which put me at better ease. Although the right of way is used, one comes across people infrequently.
Overall, the tree heights and girths were slightly greater than that of the Potomac floodplain below. This is mostly attributable to sections of older trees, but also to greater overall diversity. On the other hand, the open southwest facing exposure in much of the area would tend to limit girths and heights. The section with the highest concentration of big trees was the stream valley of Maddox Branch, which is easily accessible and has a footpath running through it. Many of the large trees here were growing more or less in a line along the west side of the stream. I believe some of these may have originally been semi-open grown trees along a fence line or property line. Behind this line was a small section of woods which appears to have been relatively undisturbed for over 150 years. There are a few other small areas along the palisades which may have a similar age. Other interesting sections included a grove of willow oaks on the slopes east of Arizona Avenue (what used to be Davis’ Branch) and some larger trees near the Georgetown Reservoir.
The height Rucker Index is 113.8 feet. The girth Rucker Index is 13 feet 11 inches. As is often the case, the large old tulip trees were the most impressive. What stood out most about the site though, was the number of large black cherries growing on the disturbed slopes. Cherries in the DC area are often not a very large or long-lived species, and many of the cherries along the palisades were in decline. The period since disturbance may have been about the right balance to produce trees that were large, but not quite dead yet. I measured 5 black cherries with a dbh over 3 feet. An uncommon tree I measured was a hackberry, which based on its form appeared to be Celtis tenuifolia. However, I have not yet confirmed this and it could possibly be C. laevigata or less likely C. occidentalis. Near the Maryland border, there were also a few Quercus muehlenbergii, which are not common in the area.
I previously mentioned that the palisades was not the most pleasant place to make measurements. However, it was definitely interesting, with a lot of history – and signs of history, some discoveries of nice trees, and good views of the Potomac below.