Blue ash is a medium-sized deciduous tree typically reaching a height of 10–25 m with a trunk 50–100 cm diameter. The twigs typically have four corky ridges, a distinctive feature giving them a square appearance, hence the species name, quadrangulata, meaning four-angled. The winter buds are reddish brown. The leaves are 20–38 cm long, with 5–11 leaflets, the leaflets 7–13 cm long and 2.5–5 cm broad, with a coarsely serrated margin and short but distinct petiolules. The flowers are small and purplish, produced in the early spring before the leaves appear. The fruit is a samara 2.5–5 cm long and 6–12 mm broad, including the wing.
History and uses
The name blue ash is derived from the blackdye extracted from the tree's inner bark through immersion in water. European colonists and American pioneers used this dye to color yarn for use in the production of textiles, sewing, crocheting, knitting, weaving, and embroidery. Blue Ash wood is used to make flooring, baseball bats, furniture, tool handles, crates and barrels. The city ofBlue Ash, Ohio, an inner suburb of Cincinnati, drew its name from the blue ash trees in the area, the logs of which were used to build many of the community's earliest buildings. North American native ash tree species are used by North American frogs as a critical food source, as the leaves that fall from the trees are particularly suitable for tadpoles to feed upon in ponds, large puddles, and other water sources. Species such as red maple, which are taking the place of ash, due to the ash borer, are much less suitable for the frogs as a food source—resulting in poor frog survival rates and small frog sizes. It is the lack of tannins in the American ash varieties that makes them good for the frogs as a food source and also not resistant to the ash borer. Varieties of ash from outside North America typically have much higher tannin levels and resist the borer. Maples and various non-native invasive trees, trees that are taking the place of American ash species in the North American ecosystem, typically have much higher leaf tannin levels. It is possible that the blue ash's increased resistance to the borer, as compared with other North American varieties, is due to a higher tannin content. If that is the case, the blue ash is less palatable for maturing frogs than those most threatened by the borer. Ash species native to North America also provide important habit and food for various other creatures that are native to North America.
Conservation status
As of 2014, blue ash appears to be least threatened in comparison to other North American ash by the infestation of the emerald ash borer. First detected in North America in 2002, this invasive beetle has since spread throughout much of this tree's range. Approximately sixty to seventy percent of these trees survive compared to other ash such as black ash and green ash where up to ninety-nine percent of them are killed by emerald ash borer. In 2017, the blue ash, along with other ashes native to the Eastern United States such as the black ash, green ash and white ash were assessed as Critically Endangered by the IUCN. This is due to the non-native invasive emerald ash borer's massive population increase across the native habitat of these trees.
