Green ash trees (Fraxinus pennsylvanica) are among the earliest trees in our area to show fall color. Leaves are arranged on stems about 9” long, with 5 to 9 oblong, pointed leaflets with serrated edges. In summer, leaves are a lustrous medium to dark green above, pale green below, turning in early fall to a bright yellow gold. Their fall foliage puts us in the mood for enjoying seasonal treats like colorful mums, pumpkins and other late season produce from our gardens or farmers’ markets.
Ash trees are medium to large size trees, growing 40 to 60 feet tall with an upright, spreading habit and a somewhat irregular shape. Branches often bend down and then up at the ends, and can have a coarse, twiggy appearance. Ash trees produce winged seeds, called samaras, that droop downward and often persist into winter.
Green ash is native to eastern and central North America, from Nova Scotia to Florida and west to Texas. It grows naturally in moist woods, along the edges of swamps, streams and rivers, providing important habitat for wildlife. Green ash was once one of the most popular trees for planting in cities and towns because it has a fast growth rate and tolerates pollution, road salt and other urban stressors. Ash was widely planted in the 1950’sand 60’s as a replacement for millions of American elm trees that were decimated by Dutch elm disease.
Ironically, green ash has itself faced an epidemic of another invasive pest called emerald ash borer (EAB). EAB is a beetle that was accidentally brought to North America from Asia. Ash trees have no natural resistance to this pest, which has killed millions of ash trees across the U.S. and will undoubtedly reach Massachusetts in the near future.
The lesson of the elms and the ash is that our forests, both the natural type and “urban forests”, must include a diversity of species for maximum protection against invasive pests and diseases. In Medford, the majority of our street trees are Norway maples, which themselves have become invasive and are no longer legal to sell or plant. Instead, we now plant over twenty species and varieties of trees in Medford, up from just three species about 10 years ago. (Norway maples have been severely affected this summer by a leaf fungus called tar spot. Tar spot does not harm the long term health of a tree, but it is very unsightly. The unusually wet conditions this spring was a major factor in the outbreak of tar spot on Norway maples.)
The green ash trees in the photo make a lovely presentation along Yeomans Ave and provide shade to the playground at Morrison Park. Other green ash in full fall color sparkle on sunny fall days along City streets, down the center island of the Fellsway and at Wellington Circle by MacDonald Park.
– Aggie Tuden, Tree Warden