Historical American elms line the Mall and the Park's perimeter along 5th Avenue. In fact, the Mall is home to one of the largest and last remaining stands of American elm trees in North America. The Conservancy monitors the trees for Dutch elm disease, a devastating fungus spread by elm bark beetles that has wiped out large numbers of elms worldwide. In addition, the Conservancy plants elm cultivars that are resistant to the disease whenever possible. American elms tend to have twisting, upper branches that form an elegant silhouette against the winter sky. This can be one way to distinguish an American elm from its European cousins. Elms tend to have shallow root systems and the trees are easily stressed, or even damaged, by soil compaction. This is why many of the Park's elm trees, including those along the Mall, are fenced in. We thank you for helping us protect these living treasures by staying on the outside of this protective fencing.