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

The Pumpkin Ash: An Update on a Rare New York Tree

Posted in New Plant Discoveries on November 21, 2016 by Daniel Atha

Daniel Atha is Director of Conservation Outreach for the Center for Conservation Strategy at The New York Botanical Garden.

Jim Coelho with pumpkin ash near the Bronx Zoo’s Reptile House. (Photos by Daniel Atha)
Jim Coelho with pumpkin ash near the Bronx Zoo’s Reptile House. (Photos by Daniel Atha)

I previously reported on the discovery of pumpkin ash trees in Central Park, expanding the known range of the species into Manhattan. Now, recent discoveries have expanded the range of the species in the Bronx as well, bringing the number of known populations of this rare tree in New York to five (four in the Bronx and one in Manhattan).

In 1903, Nathaniel Britton, co-founder of The New York Botanical Garden and one of the most influential botanists of the 20th Century, collected a specimen of a “wild” ash tree in what was then the Botanical Garden’s “North Meadow” (the site is now in the Bronx River Forest section of Bronx Park). Britton named the tree Fraxinus michauxii for André and François Michaux, a father-and-son team of 19th-century French botanists sent to catalog the arboreal treasures of North America. Taxonomists now consider Britton’s tree only a minor variant of Fraxinus profunda (the pumpkin ash) and not worthy of species distinction. The tree from which he collected the specimen is now gone, but its descendants are alive and well in the region, as we are discovering.

Pumpkin ash is found in swamps, river bottoms, and wet depressions, chiefly on the Atlantic Coastal Plain from southern New York to northern Florida and in the Mississippi and Ohio River Valleys to Michigan and Ontario. Pumpkin ashes were not collected in New York after 1936, and botanists assumed they had disappeared from the flora.

Then in 2010, Michael Nee—an NYBG curator at the time—and I found an unusual ash on the banks of the Bronx River, just south of the Garden’s Stone Mill. We tentatively identified it as Fraxinus profunda based on the distinctive bark, very pubescent twigs and leaves, and extremely large fruits. Guy Nesom, who is preparing the ash treatment for the Flora of North America, later visited the Bronx and confirmed the identity of the Garden’s tree as well as trees on Mosholu Parkway.

Finding the Central Park pumpkin ashes earlier this year inspired us to look more thoroughly for the species in the Bronx. This summer, Julian Campbell, a collaborator on our ash project; Ilsa Jule, an NYBG volunteer; and I found two trees not far from Britton’s original location in a forest dominated by silver maples, red maples, tulip trees, and American elms. The New York City Parks Department has worked with the Bronx River Alliance to re-water this section of the forest, formerly cut off from the river’s rejuvenating floods and now developing into a truly spectacular stand of floodplain forest unlike any other in New York City. We hope the restoration of swamp-like conditions will be good for the sustainability of the pumpkin ash.

Jim Coelho and pumpkin ash on the Bronx River. Pumpkin ash has the largest fruit of any species in North America.
Jim Coelho and pumpkin ash on the Bronx River. Pumpkin ash has the largest fruit of any species in North America.

On the last day of September, James “Jim” Coelho, Gardener at the Wildlife Conservation Society (WCS), and I visited several sites at the WCS’ Bronx Zoo, searching for additional pumpkin ash. We found white ash (Fraxinus americana) regenerating very well, but we found almost no large white ash trees. As elsewhere throughout the city, mature white ashes declined precipitously about 20 years ago due to “ash yellows,” a microbial disease that clogs the conducting tissue and eventually kills the tree. Pumpkin ashes appear to be doing better—at least here in New York City—raising hopes that they are resistant to ash yellows and the devastating emerald ash borer, an invasive beetle that is killing millions of ash trees across North America.

The oldest pumpkin ash we found on the zoo’s grounds probably predates the institution’s founding and is a remnant of the forest that once occurred across the region. This tree, near the Reptile House, is undoubtedly the same one from which a specimen was collected by George Skene in 1936. The tree is more than three feet in diameter and one of the few very large ashes remaining in the area.

On the west bank of the Bronx River, east of the Old Boston Post Road and south of the Bronx River Gate, we surveyed a beautiful remnant of native, old-growth forest containing many large specimens of red oak, willow, pumpkin ash, white ash, sweet gum, buttonbush, sweet pepperbush, sassafras, hickory, witch hazel, American basswood, American bladdernut, and others. In the wettest soil, growing with lizardtail and arrow arum, we found a medium-sized pumpkin ash. The youngest tree we found at the zoo was only about 30 feet tall and 10 inches in diameter, growing near the service gate to the Bison Range. None of these trees were planted, and Jim thinks floodwaters brought the seeds downstream from the Garden.

We are grateful to Jim Coelho, Gardener, and Todd Comstock, Assistant Director, Maintenance and Curator of Horticulture, at the Bronx Zoo of the Wildlife Conservation Society, for their cooperation and help in finding these rare and important trees.

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. Strategy for Conserving Ash Trees in the Northeast: Collection, Analysis, and Outreach is generously supported by the Sarah K. de Coizart Article TENTH Perpetual Charitable Trust. To learn more, visit the project webpage.