Forest Management Promotes Resilience in Iconic American Landscapes

Written by Lillie Hoffart, Science Communication in the Parks Fellow

While walking through the forests in northeastern National Parks, you’ll encounter towering oaks, stately ashes, and rugged hickories. Their broad trunks rise high into the canopy, and their roots tangle underfoot, embodying a timeless connection to the landscape. It’s easy to feel like they will be here forever, right?

Resilient forests have enough tree seedlings in the understory to replace mature trees that die or fall.

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An analysis of five regional Inventory & Monitoring Networks datasets collected by the National Park Service (NPS) showed concerning, region-wide trends that indicate forests’ inability to sustain themselves. While many national parks have numerous large, mature adult trees, there are not adequate numbers of young seedlings and saplings to replace them when they die.

“We’ve known for a while that deer overabundance and lack of regeneration were problems in many of our parks.” said Kate Miller, a quantitative ecologist for the NPS Northeast Temperate Network. “The surprise for us, which took a couple of monitoring cycles to see, was that in the absence of deer management, it keeps getting worse just about everywhere.”

Miller and other NPS ecologists analyzed conditions of northeastern forests in National Parks and found that these forests are not regenerating on their own. There are not enough tree seedlings in the understory to replace mature trees in the future. For example, at Gettysburg National Military Park, mature oaks make up almost 60% of the canopy but only 7% of the seedlings.

“[As NPS Ecologists], we didn't sign up to document the decline of the forest,” Miller said. “We're not just here to be observers that don't actually do anything. We’re here to make a difference.”

That decision led to the Resilient Forests Initiative, an alliance of park managers and scientists who share knowledge and resources to ensure healthy forests persist. While forests are essential for the ecosystem services they provide — soil stabilization, wildlife habitat, carbon sequestration, and more — forests provide the additional service of adding historical context to the landscape when they surround a cultural site.

The topography of the landscape at Saratoga National Historical Park is key for understanding why the battles occurred, as it is located at a pinch point in the Hudson River. At that time the landscape was a mosaic of forests and fields which played an important role in troop positioning. Likewise, at Gettysburg National Military Park, troops moved through the forest and used the rocks and hills for cover and high ground.

Preserving the mosaic of forests and fields at Saratoga National Historical Park is key for understanding troop positioning and how the battles occurred.

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“The landscape tells a really important part of this history,” said Leslie Morlock, superintendent at Saratoga National Historical Park. “Having that sort of visual understanding of the landscape and what it looked like helps interpret [history for] the public. As a bonus, we have this amazing open space that is preserved now for the public.”

The mission of preserving and protecting cultural sites goes hand-in-hand with preserving and protecting the landscape, and maintaining healthy and sustainable forests fits well within that role.

“The contemporary view of how we manage the landscape is trying to find a balance between preserving the aesthetic quality of the battlefield while enabling sustainable and functioning ecosystems,” said Christopher Davis, supervisory biologist at Gettysburg National Military Park and Eisenhower National Historic Site. “It’s easier said than done.”

Another component of managing landscapes to aid in cultural interpretation is taking into account the long history of human influence on the landscape.

“Every inch of this park has been touched and used and manipulated in some way,” Davis said.

A healthy oak-hickory forest should have understory, midstory, and mature canopy-height trees throughout. But that was not what the oak-hickory forests, historically called “woodlots,” looked like in 1863 when the Battle of Gettysburg was fought.

“If you look at some pictures of the historic woodlots and the way they were managed, they're wide open,” Davis said. “That's obviously not sustainable, right? Around here we need regeneration.”

Decades of deer and forest management at Gettysburg National Military Park have allowed tree seedlings and saplings to flourish in some of the park’s woodlots.

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In 1863, the open understory was caused by farmers moving cattle into the woodlots to graze, stunting subcanopy growth. Today, many parks are also experiencing forests with open sub-canopies because of heavy deer browsing. However responsible stewardship for future forests means promoting the regeneration of native seedlings and saplings in the understory.

The Gettysburg park management team had to find a balance when setting forest management goals.

“Are we managing for a historic look and feel? Or are we managing for ecosystem health and promoting regeneration to replace canopy trees? We want [forests] to thrive and self-perpetuate and be resilient to climate change and pests and invasive species,” Davis said. The park management team has found ways to strike that balance.

Current projects within the Resilient Forests Initiative are focused on maintaining forests that are robust into the future. Parks are sharing expertise on invasive species treatments and shrub management and beginning projects to limit deer from over-browsing young trees and planting young native species in canopy gaps, with early successes, as Miller put it, “beyond our wildest dreams.”

“I think parks were empowered to want to do something about the problems in their forests, and the region saw it as a priority,” Miller said.

While preserving entire forests is important to maintain cultural sites, some individual trees play an especially important role. Stately “witness trees” stood at the time of the event and survive today, such as dozens of white oaks (Quercus alba) which are iconic to Gettysburg’s forests. These trees are identified through historical photographs and documentation.

Whether focused on a park for historical interpretation or the ecological landscape, maintaining resilient forests places these two goals hand-in-hand.

“Having that healthy ecosystem improves the visitor experience to allow visitors to come to the park and enjoy it the way they want to enjoy it, whether they're coming here to take a walk in the woods or to study the history in-depth,” Morlock said. “You have this chance to walk on a paved path and look at a waysign and learn about history in that important period of time. You can also walk through the woods and hear the birds and hear the frogs in the spring. And, you know, they don't have to be mutually exclusive.”