New Clark study on clearcuts shows surprising trends in carbon, water
A new study by Clark University scientists, released today in Global Change Biology, is the first detailed account of how carbon, water, and energy balances shift in the three years following the clearcut of a deciduous forest. The study, conducted by Clark University Professor Christopher Williams and colleagues in a 20-acre clearcut in Petersham, Mass., reveals a steady loss of carbon dioxide to the atmosphere, despite rapid recovery of plant growth.
Clearcutting, an extreme approach to forest harvesting in which all trees are cut and removed from a sizable area, comprises only a fraction of harvests in Massachusetts but could become more widespread as invasive insects and other forest threats expand in the region.
Williams, lead author of the study, explains, “Forest harvest alters a host of processes important to the local and global climate system, such as carbon storage and uptake, water use, and absorption of solar radiation.”
“Overall, the study demonstrates the remarkable ability of forest to recover after even severe disruption.” ~ David Foster, director of the Harvard Forest
Carbon was a major focus of the study because of its important role in controlling the climate. In stark contrast to a clearcut area, intact forests are able to pull carbon dioxide from the atmosphere and store it in trees, creating a carbon “sink” that helps to offset greenhouse gas emissions released by fossil fuel combustion and other sources. The clearcut area studied gave off more carbon dioxide than it stored, with nearly half of the CO2 rising from exposed, disturbed soils and an additional 18 percent from decomposing wood. Williams adds, “The cleared area will only become a significant sink for atmospheric carbon after a decade or more, and full recovery of forest carbon stocks requires many decades of regrowth.”
Meanwhile, the picture on the ground is one of very rapid recovery of vegetation. The team tracked plant regeneration, documenting the rapid growth of many native species, including ferns, sedges, blackberry, starflower, red maple, and pin cherry. This surge in plant growth, says Williams, provides valuable habitat and food for wildlife.
After forest harvest, water runoff is a chief concern for land managers. Although there was an immediate increase in moisture on the site due to the decline in water released by trees, the study revealed a surprise. Vigorously growing plants in the clearcut quickly recovered the rate of ecosystem water use through evaporation, thereby allowing only a modest, short-lived increase in the amount of water that runs off to lakes, streams, and rivers. According to Williams: “By the second and third years of forest recovery, the amount of water released to the atmosphere by evaporation in the clearcut was similar to that of neighboring hemlock and red oak forests.”
The study’s findings are expected to increase accuracy in future models of climate and global change.
The study required intensive effort by a host of graduate and undergraduate students from Clark University, with funding from NASA, the National Science Foundation’s Long-Term Ecological Research Program, and student support through the Harvard Forest Summer Research Program. This research offers an example of the use-inspired learning communities that are hallmarks of Clark’s LEEP (Liberal Education and Effective Practice) model of higher education, Williams noted.
Clark doctoral students Melanie Vanderhoof and Bardan Ghimire (Ph.D. ’13), and postdoctoral research scientist Myroslava Khomik are co-authors on the paper. The study also involved a large cast of Clark undergraduate students who worked on the project, including Graham Twibell (BA ES ’10/MS ES&P '12), Michelle Smith (BA ’11/MA CDP ’12), Angela Marshall (BA ’11/MS ES&P ’12), Krittika Govil (BA ’11), Marcus Pasay (BA ’12/MS ES&P ’13), and Alexander Kappel (BA ’13/MA GIS expected ’14).
Trained as a land surface hydrologist and terrestrial ecosystem ecologist, Professor Williams investigates how earth's biosphere responds to natural and human forces such as severe drought events, bark beetle outbreaks, fires, harvesting, and land cover changes.
For more information or an interview with Professor Williams, contact Jane Salerno at Clark University (508-793-7554). Click here to see more photos.
The Harvard Forest, founded in 1907 and located in Petersham, Mass., is Harvard University's outdoor laboratory and classroom for ecology and conservation, and a Long-Term Ecological Research (LTER) site funded by the National Science Foundation. Its 3,700 acre property is one of the oldest and most intensively studied research forests in the U.S. Open to the public year-round, the site includes educational and research facilities, a museum, and recreational trails. More information can be found at http://harvardforest.fas.harvard.edu/.
Founded in 1887 in Worcester, Massachusetts, Clark University is a small, liberal arts-based research university addressing social and human imperatives on a global scale. Nationally renowned as a college that changes lives, Clark is emerging as a transformative force in higher education today. LEEP (Liberal Education and Effective Practice) is Clark’s pioneering model of education that combines a robust liberal arts curriculum with life-changing world and workplace experiences. Clark’s faculty and students work across boundaries to develop solutions to complex challenges in the natural sciences, psychology, geography, management, urban education, Holocaust and genocide studies, environmental studies, and international development and social change. The Clark educational experience embodies the University’s motto: Challenge convention. Change our world. www.clarku.edu