Exploring the science of plants, from the field to the lab

A Surprising Find in Central Park

Posted in New Plant Discoveries on August 5, 2016 by Daniel Atha

Daniel Atha is the Conservation Program Manager at The New York Botanical Garden. He leads the Botanical Garden’s collaboration with the Central Park Conservancy on the Central Park Flora project.

Pumpkin ash tree recently discovered in Central Park
Pumpkin ash tree recently discovered in Central Park (Photos: Ken Chaya)

In the middle of Central Park, in the heart of North America’s largest metropolis, one of the rarest trees in New York has begun to set fruit, making it possible to determine its true identity. Working with arborists from the Central Park Conservancy, botanists from The New York Botanical Garden recently confirmed the occurrence of two pumpkin ash trees (Fraxinus profunda), a species that is endangered in New Jersey and Pennsylvania and was only recently added to the New York flora.

As part of the Central Park Flora project—a three-year endeavor to document the wild flora of Central Park—the team has discovered white ash (Fraxinus americana), European ash (Fraxinus excelsior), two varieties of green ash (Fraxinus pennsylvanica var. pennsylvanica and Fraxinus pennsylvanica var. subintegerrima) and now pumpkin ash growing wild in Central Park.

Wedged between a large rock outcrop and the Bridle Path, west of Winterdale Arch and east of Diana Ross Playground, the newly discovered pumpkin ashes are estimated to be 30 to 40 years old, based on their trunk size. Since its founding in 1980, the Central Park Conservancy has been restoring habitat and planting and encouraging the regeneration of native species. Weeding out invasive species like Japanese knotweed and Norway maple gives native species such as pumpkin ash the space and resources to flourish.

Pumpkin ash is a medium-to-large tree native to the eastern United States in scattered locations, roughly following the Mississippi and Ohio Rivers from New Orleans to Cleveland and along the Gulf and Atlantic coasts from Biloxi, Mississippi, across the Florida Panhandle and up the Atlantic coast from Daytona Beach, Florida, to the Bronx, where Botanical Garden botanists discovered it during an intensive wild-plant inventory on the Garden’s grounds and in the surrounding community of Bedford Park. That resulted in the addition of the species to the New York State flora.

Pumpkin ash fruit
Pumpkin ash fruit

Pumpkin ash grows in swamp and river bottoms and occasionally on drier sites with oak, black cherry, and other hardwoods. Like all ash trees, it has grey, furrowed bark, opposite leaves with several leaflets, and very small flowers that may develop into paddle-like winged fruits. The pumpkin ash is distinguished from other native ashes by its fuzzy twigs and leaves and its large fruits, which are much wider than any other ash fruit. The tree is called pumpkin ash for a pumpkin-like swelling that develops at the base of its trunk when it grows in standing water.

Ash trees in the genus Fraxinus are mostly dioecious, meaning that male and female flowers are produced on separate plants—a strategy that optimizes genetic mixing. Like oaks, ashes are known for masting, whereby trees produce a bumper crop of fruits one year and little or no fruits for a year or two after—a strategy to overwhelm seed predators one year and starve them the next.

Ashes are not just interesting organisms, they are incredibly important ecologically, forming a very high percentage of the forest trees in the eastern United States. And they are useful. The wood is very hard and shock resistant—making them the ideal wood for baseball bats, tool handles, and bowling alley floors.

Comparison of green ash fruit (left) and pumpkin ash (right)
Comparison of green ash fruit (left) and pumpkin ash (right)

There are some 40 species of ash worldwide and, unfortunately, most of them are threatened by microbial diseases and insects, particularly in Europe and America. Here in the Northeast, our ash trees are being decimated by the emerald ash borer (Agrilus planipennes), an invasive insect that was introduced accidentally from Asia. The borer’s larvae burrow under the bark, which disrupts the flow of water and nutrients and kills nearly 100 percent of infested trees. First discovered in 2002 in Michigan and Ontario, the insect is moving through New York State and was recently found north of the city in the Hudson Valley. The Central Park Conservancy has taken steps to proactively protect vulnerable ash trees in the Park, particularly those with historic, landscape, and conservation value, including the pumpkin ash. (You can listen to a recent National Public Radio story about the emerald ash borer here.)

Working on ash conservation more broadly, The New York Botanical Garden is currently leading a consortium that is investigating the genetic relationships among our native ash trees in the hopes of finding resistant strains or traits that can be used to protect our remaining trees. To learn more, visit the project webpage, Strategy for Conserving Ash Trees in the Northeast: Collection, Analysis, and Outreach.