On December 18, more than two inches of rain and wind gusts exceeding 50 miles per hour wreaked significant damage to trees in the Arnold Arboretum. Nearly 40 accessioned plants were lost across the landscape, many uprooted or—in the case of nearly a dozen hemlocks—snapped in half. While the storm was formidable in terms of tree loss and the enormity of the continuing clean-up effort, the immediate and coordinated response of the Arboretum’s horticultural team ensured safety for visitors and renewal for the plants either lost or severely compromised.

It was an unusual event in many respects, breaking records for highest minimum and maximum temperature for the day and generating some of the strongest winds—outside of thunderstorms—seen in Boston in a decade. “When intense wind is accompanied by heavy rain—which softens the ground and further compromises the ability of older or compromised trees to anchor themselves—we tend to see the most damage inflicted on the collections,” said Rodney Eason, Director of Horticulture and Landscape. “The fact that even more trees weren’t lost is a testament to the exceptional care and attention our horticulturists and arborists provide to plants in our collections every day.”

Rachel Brinkman and Michael Dosmann survey storm damage in the conifer collection following the December 18 storm.
Rachel Brinkman (right), Manager of Horticulture, and Michael Dosmann, Keeper of the Living Collections, survey damaged and uprooted trees in the conifer collection.

When forecasts for December 18 predicted high winds and heavy rain, the horticulture team shifted into high alert to respond to potential damage. To maximize public safety, the Arboretum posted visitor advisories about potential storm damage at its entrances and on its website that day. “When a storm hits, safety is our first concern,” Eason continued. “Once it passes, our staff put on hard hats and fan out to scout for damage.” Staff characterized what they discovered by placing affected trees into three response categories—total losses requiring removal, plants that survived but incurred significant damage and may require additional intervention or monitoring, and plants either lost or damaged that may need to be regenerated. For the latter category, plant production staff from the Dana Greenhouses are notified so that genetic material (typically cuttings for rooting or grafting) can be retrieved before it is removed from the landscape.

Storm damage centered primarily on mature specimens growing on south-facing hillsides. The conifer collection suffered the most losses—15 trees, primarily aging firs and spruces. Ten trees were lost on both Peters Hill and Hemlock Hill, two on the South Street slope of Bussey Hill, and one on the State Lab slope near the Forest Hills Gate. Many more plants were damaged by falling trees, including a Tatarian maple on Peters Hill that was in the path of a large oak trunk that snapped. Most of the plants sustaining collateral injuries stand a good chance of surviving, but only time will tell. Part of the Arboretum’s responsibility in caring and maintaining its tree collection is monitoring how plants that are structurally compromised will respond to attempts to keep them alive and healthy, and not posing any danger to public safety.

As clean-up proceeded—an effort still underway in parts of the Arboretum—individual members of the team were assigned to manage clean-up and recovery actions for specific lost and injured trees. Dead trees and details of significant damage were recorded in the Arboretum’s extensive plant records database. Those determined to be a total loss required additional communication with the Arboretum’s curatorial department to determine whether the plant could or should be repropagated to preserve its lineage in the collection. Until this determination is made, felled or uprooted trees must be left in place in order not to lose track of their identity, which is tied to their map locations.

“Although we lost some incredibly large, stalwart trees—such as an 85-ft tall Nordmann fir accessioned in 1903—the good news is that we did not lose anything irreplaceable from a research or conservation perspective,” said Michael Dosmann, Keeper of the Living Collections. Fortunately, all losses of high value to the collection (plants key to the Arboretum’s research mission due to their rarity, conservation value, or provenance) had already been duplicated at the Arboretum through ongoing repropagation efforts. “In fact,” notes Dosmann, “one of the lost trees—the rare Korean fir—was placed on the “reprop” list in 2018 and successive years of collecting have yielded a number of young plants in our nursery.”

Snapped trunk of an Eastern hemlock on Hemlock Hill
Ten trees were lost on Hemlock Hill, primarily hemlocks (Tsuga canadensis) but also one accession of Eastern white pine (Pinus strobus). This hemlock, its trunk snapped in half, is believed to predate the founding of the Arboretum in 1872.

Another bright spot in recovering from a storm of this magnitude is the renewal it engenders for the entire Arboretum collection. Germplasm of key plants may be preserved and refreshed through repropagation, and the spaces they inhabited offer new planting opportunities. The perpetual need to find locations for valuable new acquisitions in a finite space makes losses through seasonal storms a natural part of refining and renewing the collections. “Experimenting and growing new things here speaks to our mission as a research collection of trees,” Eason continued. “Storms and the damage they cause are certainly disruptive, but it’s one way that a collection of long-lived trees stays dynamic.”

Reminders of the storm may be evident for some time, particularly on Hemlock Hill and the conifer collection. In recent years, horticulture staff have left some tree snags (dead trees left standing) and felled trunks in place across the landscape when it is safe and appropriate to do so. This contributes to the ecological health of the Arboretum and provides wildlife habitat, offering another way that Arboretum plants contribute to the collection and landscape beyond their life span. In addition, data recorded by Arboretum staff about this storm and the trees lost and injured will contribute to our understanding of how extreme weather and environmental change are affecting trees at the Arboretum and across the Northeast.

For further reading: Michael Dosmann, Keeper of the Living Collections, shares his perspectives on the dynamic nature of plant collections at the Arnold Arboretum in the summer 2023 issue of Arnoldia. Read it here.

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