Moving Tree-of-Heaven and Earth to Conserve Native Biodiversity

Tree-of-heaven – the name suggests paradise. A tall, ethereal beauty with leaves fluttering in the sunlight of Mount Olympus, perhaps shading a brood of lounging Greek gods or a bed of Ferrero Rocher.

Sometimes, caught in the soft afternoon light on Grape Island, the image fits: tree-of-heaven will take part in divine scenes of beauty, basking in the foreground, branches stretching to the sky, high above yellow fields of flowering goldenrod, while the snaking ocean water behind shimmers and bends around the rocky edges of neighboring Slate Island.

For the most part though, the species’ presence across the Boston Harbor Islands doesn’t quite match the cherubic dreaminess that its name inspires.

NPS Photo/E. Bernbaum

Tree-of-heaven (Ailanthus altissima), or chouchun in Chinese, is a temperate species native to central and northeast China and Taiwan. In their native range, these trees offer habitat to a beautiful and economically valued silkmoth (Samia cynthia) and have historically served as ingredients in traditional Chinese medicine.

Since the introduction of tree-of-heaven across the globe, however, these trees have become one of the most widespread and harmful invasive plant species in Europe and North America. Growing and spreading more rapidly than most native plants and thriving in both nutrient-rich and poor soils, tree-of-heaven can quickly take over large swaths of land.

Soil quality also changes under tree-of-heaven stands. The species is allelopathic, meaning that these trees release chemicals into the soil that prove toxic to other plants, actively killing native life while clearing space for more tree-of-heaven to move in.

NPS Photo/E. Bernbaum

While these trees are admirably adaptable, and their strategies for spread are impressively effective, their success comes at a steep cost. When tree-of-heaven thrives, the cherished native biodiversity of the Boston Harbor Islands diminishes. The trees also change the canopy of island forests, leaving unknown impacts on plant, animal, and fungal growth.

Threats that tree-of-heaven's biology poses to native biodiversity are cause enough for concern and action. Yet, more still amplifies land stewards’ worry: tree-of-heaven is a preferred host to the spotted lanternfly, a looming shadow that strikes fear into food growers and land stewards alike.

The spotted lanternfly, again native to China as well as Vietnam, is a fast-spreading invasive planthopper who enjoys sipping saps from a variety of plant species. While feasting, the planthopper further enjoys excreting a sticky, sugary fluid called honeydew, and that honeydew, left in messy globs along tree trunk and plant stems, welcomes black sooty mold that can devastate plant communities. In fact, in one Pennsylvania State University study, researchers found a vineyard that experienced a 90% decline in grape yields due to spotted lanternfly infestation.

Fortunately, the spotted lanternfly hasn’t yet made its way to the Boston Harbor Islands. But it’s closing in; with infestations in 16 other states, the species has now been spotted in communities throughout Massachusetts. Tree-of-heaven is too tasty a tree (to spotted-lanternflies) to risk having around.

NPS Photo/E. Bernbaum

So, throughout September and October of this year and likely next year too, the National Parks of Boston’s Science and Stewardship Partnerships team and partners like the Department of Conservation and Recreation (DCR) are working toward a big goal. For the first time ever, they are endeavoring to remove all tree-of-heaven from Bumpkin Island, and about 130 trees this year.

Fall is the right time of the year to do this work. As trees move nutrients from their leaves into their roots in preparation for their colorful fall shedding, the team is able to administer herbicide most effectively. Herbicide prevents tree-of-heaven from growing “root suckers” under stress. These root suckers are baby clones of the tree that shoot up from the roots – if not for the herbicide, they'd replace felled trees in no time. Two weeks to thirty days later, after taking these chemical measures to combat recolonization, the team and its partners cut down the trees and use a woodchipper to do away with debris.

NPS Photo/E. Bernbaum

This fall, the team will spend the majority of their days bucking trunks and hauling limbs, moving tree-of-heaven and earth to support native biodiversity on Boston’s treasured harbor islands. Stewards of the Boston Harbor Islands will no doubt continue fighting tree-of-heaven for years to come too, as they have in years past. The journey to rid the islands of the species is a long one, but executing this first-ever intensive project to remove all tree-of-heaven from one Island is a powerful step, and the Science and Stewardship team is hopeful that the fruits of their labor will show in renewed ecological health on Bumpkin Island.

Read more about other invasive-removal projects, conservation efforts, and science and monitoring taking place across the islands on the National Park Service website.

Contributed by: Elle Bernbaum, Biological Science Technician

Additional Source: Rachel Vincent, Biological Science Technician, National Parks of Boston