Thursday, January 14, 2010
Because they're evergreen, this is a great time of year to look for hemlocks, when other trees have lost their leaves. The needles of hemlock will help you distinguish this tree from other evergreens in our area: they are flat, about 3/4 of an inch long, and grow in a plane off the twigs. The overall form of hemlocks can also be distinctive: branches grow horizontally from the trunk, but are floppy on the ends as the twigs haven't hardened up yet. Up close, you may notice very small cones on the trees -- they look like pine cones, but much smaller.
It wasn't until the 1980's that people started noticing that the adelgid had spread from ornamental plantings in Richmond to native trees in York River State Park and Shenandoah National Park. By the mid-90's, the adelgid had spread to Connecticut and Massachusetts, and it is now considered established throughout the hemlock's eastern range, from Maine to Alabama. Experiments are being done with the release of adelgid-eating beetles from Japan, but results don't seem very promising, and many stands of hemlock have already been lost. (To see some of the destruction to old growth hemlock groves, see this video from the Charlotte Observer.)
In the wild: We're not aware of any really large hemlocks in the DC area (do let us know!) but there are still some small hemlocks scattered in our local forests. The most we've noticed are at Scott's Run Nature Preserve in McLean -- they grow right along several of the trails there (like the one shown here).
In your yard: It's probably better not to bother planting hemlocks unless and until someone figures out how to control the adelgids. Too bad, because they're beautiful trees.