When northeastern farmers left for the city or for greener pastures to the west in the early 20th century, their abandoned fields grew into sunlit forests marked by mossy stone walls, wolf pines, and thick red oaks. These “old field” forests are part of the region’s cultural history and are ecologically unique. They also, without further care and attention, could disappear from the northeastern landscape, according to research published in the December 2021 issue of Forest Ecology and Management.
University of Vermont scientists repeated an experiment first established in the Jericho Research Forest in 1948. Back then, researchers inventoried and measured trees in stands of mature hardwoods, recently cutover hardwoods, and a 40-year-old pine-oak forest as part of a study to evaluate saw timber management. In 2017, graduate student Peter Clark and researcher Tony D’Amato, director of the University of Vermont Forestry Program (and a Northern Woodlands board member), wanted to learn how the forests had changed over time, and what the changes might mean for the future. They were specifically interested in structural complexity – measured by the density and number of trees of different sizes and species – as an indicator of resilience to disturbances such as wind, drought, and pest outbreaks. USDA and Northeast Climate Adaptation Science Center funded the project.
Their results showed that the hardwood stands stayed fairly consistent over time, while the most change occurred in the old field forest.
“The old field pine forests in our study emerged 120 years ago from abandoned farmland,” said Clark. At first, the forest was dominated by eastern white pine and some red oak. As the forests matured, the pines and oaks grew larger, while beech, hemlock, and maples – trees that do well in shade – filled the understory. This made the forest more diverse and complex, increasing its potential to withstand disturbance and to adapt to a changing climate.
“A forest with a more complex structure or diverse mixes of species with varying life-history traits, such as oaks with carbohydrate-rich acorns, deep shade from hemlocks, and towering growth rates from white pines, may be more resilient to impacts relative to more uniform forest,” said Clark. “Compared to the hardwood-dominated forest types that we tested in our study, the pine-oak mixed woods were highly unique in that they simultaneously supported not only complex, diverse forests (high climate adaption potential), but also elevated levels of carbon storage (climate mitigation potential).”
But the forest also became less like its old self, with little to no regeneration of pine or oak. “Since the growing conditions under which these pines and oaks established have yet to be replicated, we see little to no new pine or oak regenerating in these forests today,” reported Clark. “The novel communities of the old field forests are much more ephemeral over longer time periods. Without management, these transitory forests will likely decline and trend toward a greater preponderance of hardwood species and traits.”
The authors suggested that silvicultural interventions, such as promoting growth of pine and oak, may be required to maintain the complexity and carbon storage potential of old field forests.