Time is not the driving influence of forest carbon storage, U-M study finds
University of Michigan
It is commonly assumed that as forest ecosystems age, they accumulate and store, or "sequester," more carbon.
A new study based at the University of Michigan Biological Station untangled carbon cycling over two centuries and found that it's more nuanced than that.
The synergistic effects of forest structure, the composition of the tree and fungal communities, and soil biogeochemical processes have more influence on how much carbon is being sequestered above and below ground than previously thought.
The research, published in the journal Ecological Applications, involved the effort of more than 100 scientists from across the country who have conducted studies at the historic field station in Pellston, Michigan, over many decades.
The researchers targeted a variety of forest stands at the more-than-10,000-acre campus founded in 1909, including old reference forests that were established in the 1800s, stands that were logged in the early 1900s and have since been left undisturbed, and stands that have experienced subsequent logging or burning.
Luke Nave, research associate professor at Michigan Technological University's College of Forest Resources and Environmental Science, led the collaborative team that synthesized the decades of data.
"Time is not what drives carbon cycling," Nave said. "Time is more of a playing field, and the rules of the game on that field are things like canopy structure, tree and microbial community composition, and soil nitrogen availability. That means that changes in things like structure, composition and soil nitrogen are what control forest carbon trajectories, whether those changes happen quickly or slowly, and whether we are influencing those changes through management or letting them happen on their own terms."
The study was based on data that the team generated and compiled over decades at the U-M Biological Station in northern Michigan, including research infrastructure such as the 150-foot AmeriFlux tower, which is part of a network of instrumented sites in North, South and Central America that measure ecosystem carbon dioxide, water and energy "fluxes," and other exchanges between the land surface and atmosphere.
UMBS, one of the nation's largest and longest continuously operating field research stations, manages two towers near Douglas Lake that generate long-term data on forest carbon dynamics.
The newly published research spanned a wide variety of forest datasets in the footprints of the flux towers and elsewhere on the property, everything from soil respiration, fungal communities and root production to leaf litterfall, carbon pools and soil enzyme activities.
"It's exciting to see the results of this study. It was a lot of work and many years in the making," said Jason Tallant, data manager and research specialist at UMBS and a co-author of the research.
"At the U-M Biological Station, we put a lot of effort into data curation and digitization. It's nice to see the carbon synthesis research team leverage our historic data sets and crunch real-time carbon sequestration information to illuminate what's happening in our forests and inform future management."
The researchers said that managing forests means much more than managing their age. Directly and indirectly, managing forests means manipulating structure (above and below ground), composition (plants and microbes) and relationships between ecosystem components, including their functional and biogeochemical outcomes.
"With the rates of change we're now seeing in things like climate, forest health and disturbance, and tree species composition, management will have to contend with more challenges and constraints all the time. What was true a decade or two ago can't be assumed as truth at this point," Nave said.
"A good example for folks who know the territory is on the Burn Plots—the 1998 burn is a thriving young stand of post-clearcut aspen, and the 2017 burn is a regeneration failure. You might not think that 19 years is a long time to a tree, but it is in today's world. Researchers and managers who take a whole-ecosystem perspective like we did in the paper will have an easier time understanding what has changed over the last few decades and what we can do about it to sustain forests."
This work is supported by the National Science Foundation, the U.S. Department of Energy's Office of Science and the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory.
Collaborators are affiliated with nearly a dozen institutions including Michigan Tech, U-M, Virginia Commonwealth University, Oak Ridge National Laboratory, USDA Forest Service, Ohio State University, University of Connecticut, Purdue University, University of Texas and University of Wisconsin.
Journal
Ecological Applications
