Balancing Forest Carbon Storage and Wildlife HabitatApr. 7th 2022
Forests are a critical natural climate change solution. Carbon stored in trees and soils lessens atmospheric carbon dioxide, a greenhouse gas that contributes to a warming world.
A tree stores carbon in the form of wood, bark, roots, and leaves, so it stands to reason that if we cut fewer trees and allow them to grow, forests will store more carbon. But, if all forests across the landscape become, what forest managers call, late successional or mature in age and structure, this habitat is not beneficial for all wildlife species. Many animal species require early successional habitat made up of young trees, shrubs, and openings created by natural or human-caused disturbances.
In the Northeast’s spruce-fir habitat, the imperiled Canada lynx relies on its prey, snowshoe hare, which often prefer young forest stands. Many other mammals and birds depend on adjacent patches of both mature and early successional forests.
How can we balance the carbon storage of old forests with the young, more open habitat needed to conserve many of our wildlife species?
One answer, according to University of Vermont (UVM) researchers, is to create a mosaic, or patchwork, landscape. Managing for a diversity of forest, shrub, and grassland habitats for vulnerable wildlife species forms a heterogenous landscape.
“The importance of diverse habitat conditions across the landscape may be increasingly overlooked, especially by the public, as forest carbon storage takes center stage,” said Caitlin Littlefield, a recent Research Associate in the UVM Rubenstein School of Environment and Natural Resources. “As more attention is focused on maximizing forest carbon, we risk unintentionally compromising the long-term sustainability of other objectives, such as maintaining important habitat for at-risk wildlife species.”
In a new paper published in Conservation Science and Practice, Caitlin Littlefield, Lead Scientist at Conservation Science Partners, and Anthony D’Amato, Professor in the UVM Rubenstein School, recommend practicing forest management through a lens of climate adaptation to help maintain forests for carbon benefits while also providing refuge for wildlife. Climate change adaptation prioritizes landscape diversity, complexity, and connectivity.
The authors examined four forest and open woodland habitat types in the northern half of the United States. This region transitions from New England’s hardwood forests and more northern spruce-fir forests to grasslands and oak savannasinthe Midwest and to the sandy pine barrens of the coastal Northeast. These habitats supportsomeofthegreatestwildlifediversity inthe temperatezone—between the tropics and the arctic.
Following glacial retreat, natural disturbance agents—beavers, flooding, wind, hurricanes, ice, and fire—as well as Indigenous people maintained open meadows, shrublands, and early successional habitats scattered throughout the otherwise forested landscape. In modern day, many of these open habitats have begun converting to late successional conditions due, in part, to fire exclusion, beaver trapping, flood-control dams, and insect suppression. Loss of small- to moderate-scale natural disturbances has contributed to homogenization of forests across the region.
In each of the four ecosystems, the authors found that managing only for mature stands of trees fails to provide critical habitat for sensitive wildlife species. Restoration of these four habitats across the widespread landscape will support biodiversity, increase resilience to change, and may ultimately store more carbon over time by resisting carbon loss from catastrophic disturbance like severe wildfires and drought-induced stress on trees. Restoring these habitats often involves reintroducing natural disturbances and practices such as controlled burning.
“Characterizing trade-offs and consequences of alternative management options can help avoid practices that may ultimately reduce the complex ecological structure of forests and their capacity to adapt to change,” said D’Amato. “This sort of critical evaluation of forest stand-level management actions can then facilitate landscape-scale planning that supports a diversity of habitats while also suggesting where we ought to invest in maximizing forest carbon.”
Early successional habitat in New England’s northern hardwoods
There is currently less early successional forest—and less old forest—across New England, and Vermont, since forests rebounded from European settler clearing. Wildlife species that rely on early successional habitat have declined—including American woodcock, ruffed grouse, and most notably breeding songbirds.
The golden-winged warbler has experienced one of the steepest declines of any North American songbird. The bird nests near the ground in early successional patches of two and a half acres or more and often relies on surrounding mature forest for foraging.
“Wildlife that require early successional habitats in the Northeast include nearly 90 different kinds of birds, mammals, reptiles, and insects, many of which are ‘species of greatest conservation need,’” said Jim Oehler, Wildlife Habitat Program Supervisor for New Hampshire Fish and Game Department. “Strategic, carefully planned and carried out forest management is critical to restoring and maintaining healthy populations of these species, particularly in light of climate change.”
Relative to mature forests, early successional forests store less carbon overall, but they do sequester, or capture and store, carbon at relatively high rates. This, in combination with a mix of wildlife habitat across the landscape, would compensate for the trade-off of not pursuing maximum carbon storage.
“This paper affirms the value of conserving and maintaining an array of forest conditions, including early successional forests, on public and private lands and reinforces the importance of not focusing on a single objective, like simply maximizing on-site carbon storage,” said Michael Snyder, Commissioner of Vermont Forests, Parks and Recreation. “As demonstrated by this work and by initiatives like Vermont Conservation Design, wildlife habitat restoration and active forest management are becoming more critical for conserving and connecting a diversity of habitat types across the New England landscape.”
Open woodland and grassland habitats
Three open woodland ecosystems—the tallgrass aspen parklands of northern Minnesota, the oak savannas of southern Michigan, and the Northeast’s coastal pine barrens—are further examples of critical habitats that are diminishing in the region. Exclusion of natural fires has allowed for encroachment by less fire-resistant tree and invasive plant species and a loss of open conditions, patchy vegetation, and native plants essential for many vulnerable wildlife species.
In addition to reducing important habitat conditions for at-risk wildlife species, the increase of less fire-tolerant trees and shrubs makes forest stands more susceptible to drought and pests and increases fire severity, which can release a large pulse of carbon. Restoring low severity, prescribed fire helps alleviate drought stress, reduce invasive vegetation, reestablish critical wildlife habitat, and prevent higher severity fire risk, which keeps more carbon out of the atmosphere.
In a conservation success story, resource managers are restoring and maintaining Minnesota’s tallgrass aspen parklands through mowing, tree harvest openings, and prescribed burns. These strategies supported return of elk populations after regional extirpation in the early 20th century. Sharp-tailed grouse and sandhill crane have also largely recovered from dramatic declines.
“It is critical to recognize that climate change itself is one of the most serious threats facing wildlife in this region and globally,” said Littlefield. “We don’t have the luxury of unlimited time to devise the ‘perfect’ balance of maximizing carbon storage and wildlife habitat across the landscape. Assessing vulnerabilities and risks, acknowledging trade-offs, and prioritizing ecological complexity and landscape heterogeneity may well be the best way to keep carbon out of the atmosphere while protecting wildlife and hedging our bets in an uncertain future.”
This work is supported by the Northeast Climate Adaptation Science Center, which is managed by the National Climate Adaptation Science Center of the U.S. Geological Survey.