Sunday, August 4, 2013

Saving Our Trees from the Alien Invaders

English Ivy (Hedera helix) is flowering plant in the family Araliaceae, native to most of Europe and Middle East.

In the United States, it’s been prized for over two hundred years as an ornamental evergreen. The nation’s oldest and most prestigious universities, including Harvard, Yale and Princeton are called the Ivy League in reference to their stately ivy-covered buildings.   

But what looks nice in a garden or college campus can wreak havoc when it spreads to the woods. English ivy is now found in 32 states, and is one of the greatest threats to forests in DC.  Its sale and import is outlawed in the state of Oregon.  

Why is it so bad? According to our friends at the Rock Creek Conservancy:

      • English ivy holds onto green leaves year-round, and it's heavy. It causes branches to break, and it even uproots whole trees when the wind blows or heavy snow accumulates.                                                                               
  • English ivy attaches to the bark of the tree, which keeps the bark wet underneath. This rots the bark and attracts fungus and insects that cause tree decay.                                                   
  • English ivy starves trees by taking nutrients and water from the soil that the trees need. When the vines grow out onto branches, the leaves block sunlight from reaching tree leaves on lower branches.                                                           
  • English ivy is a "reservoir" for Bacterial Leaf Scorch (Xylella fastidiosa), a plant pathogen that is harmful to elms, oaks, maples and other native plants.                                                                                                                                                                                                                         
  • English ivy only flowers and makes berries once it grows up a tree or wall, and some birds, especially the non-native English sparrow will eat these berries, which are a bit toxic, and they spread the seeds all over parks and neighborhoods.                                                                                                                                     
  • Invasive plants, such as English ivy, replace the native plants, eliminating food and habitat for the wildlife of the park.                                                                                                                                        
  • Wildlife has adapted over millions of years to the delicate and specific ecosystem of the park that is now being radically and suddenly altered by these plant invaders.                                                                                                                                                                                                                             
While our efforts to restore Shepherd Parkway have so far focused primarily on removing trash and debris, saving out trees from English ivy is equally urgent.

Fortunately, the vines get their water and nutrition from the soil, so cutting them off at the ground causes all of the upper branches to wither and die.  

In 2012 volunteers removed ivy from nearly 100 trees in the park north of Malcolm X Avenue, and in recent months we’ve been tackling the massive infestation just south of where South Capitol Street crosses the park.

Thousands of trees face illness and death if we don’t get to them in the next few years! Help us slay the alien invaders, just like in the movies.