Deer, invasive plants are a grave threat to park forests in eastern U.S., study says

A new study from the National Park Service (NPS) found that long-term forest health is dependent on reducing the number of deer and the removal of invasive plants. 

Scientists with the NPS and Schoodic Institute at Acadia National Park in Maine studied the conditions of forests after analyzing data from 39 national parks from Virginia to Maine, National Park Service said in a statement. 

The study, published in the journal Ecological Applications, found that most forests in national parks in the eastern U.S. are at risk due to browsing by an excessive amount of white-tailed deer and crowding by invasive plants. 

“As deer populations grow in these national parks, they eat the understory vegetation to such low levels that canopy regeneration can’t occur,” study co-author Stephanie Perles said in a statement. “Without native seedlings and saplings, invasive plants, which deer don’t like to eat, take over. Both the forest and, ultimately, the deer and every other forest creature, suffer without enough food and no place to go.” 

The scientist focused on forest regeneration, which is “the ability of each forest to sustain itself through the growth and survival of seedlings and saplings that replace large trees as they die,” NPS said. 

The study placed each of the 39 parks into one of four categories of regeneration, including secure, insecure, probable failure or imminent failure. Only the forests in Acadia National Park were classified as “secure” while every other forest fell into the subsequent categories, NPS said. 

The study said that browsing by too many deer was the main culprit behind the lack of canopy species found in the understory, a layer of vegetation beneath the main canopy of a forest, in almost every park included in the study.  

Scientist said that pests and invasive plants, like the emerald ash borer and hemlock woolly adelgid, contributed to forest loss in the regions as well. 

Scientist said that even though most forests in eastern national parks are in a “dire state,” there is hope they can be restored back to healthy condition by reducing the amount of deer, removing invasive plants and planting native seedlings and saplings. Doing so would help the other animals that rely on forests for survival, the study said. 

To address the issue, eastern national parks partnered up with NPS on the Resilient Forest Initiative.  As part of the collaboration, 11 national parks in New York, Pennsylvania, Maryland, Virginia, West Virginia and the District of Columbia are currently reducing deer populations, while nearly as many other parks are planning to do the same.