University of Minnesota study: Planting trees, restoring prairies help reduce C02 -- but not enough to make a difference
Contacts:
Becky Beyers, College of Food, Agricultural and Natural Resource Sciences, bbeyers@umn.edu, (612) 626-5754
Patty Mattern, University News Service, mattern@umn.edu, (612) 624-2801
MINNEAPOLIS / ST. PAUL (01/29/2010) —Promoting activities such as planting new forests and restoring prairies will have little effect on offsetting carbon dioxide emissions, because there simply isn't enough idle land available to add up to significant carbon sequestration, a new study from the University of Minnesota shows.
The study is currently available online in the journal Frontiers in Ecology and the Environment.
Plants take up carbon dioxide from the atmosphere to build leaf, stem and root biomass, some of which is then transferred to soil, where it can reside for decades before eventually being broken down by soil organisms and returned to the atmosphere as carbon dioxide. Some scientists and policymakers have viewed carbon sequestration by plants and soil as a possible way to offset, in part, increasing carbon dioxide emissions that cause global warming.
Such enhanced carbon sequestration would require long-lived plants like trees or perennial grasses to be grown in areas now used for growing annual crops. But it has been unclear how much carbon sequestration reasonably could be achieved by changing management practices to promote carbon storage.
The study was led by Cinzia Fissore, a research associate in the Department of Soil, Water and Climate, with contributions from Javier Espeleta, a former University of Minnesota research associate; Ed Nater, professor in the Soil, Water and Climate department; Sarah Hobbie, professor in the department of Ecology, Evolution and Behavior and Peter Reich, professor in the department of Forest Resources. The team estimated how much carbon different plant types and management practices can remove from the atmosphere and store in biomass and soil upon conversion from cropland. Among the possibilities they considered, planting forests and perennial grasslands such as prairies led to the greatest carbon storage for a given area.
However, the potential to offset substantial emissions is constrained by the lack of large areas of idle land available for conversion to forests or grasslands. Achieving substantial offsets would require taking large areas of land out of agricultural production. For example, converting even 10 percent of current cropland in an 11-state Upper Midwestern region into a combination of new forests and grasslands, along with planting more trees in existing forests, would offset less than 5 percent of total carbon dioxide emissions for the region.
Although changes in vegetation cover could provide other environmental benefits such as improved water quality and wildlife habitat, achieving appreciable carbon sequestration would require taking significant land out of agricultural production, which may be impractical given increasing demand for food and biomass for energy.
Although this study shows that shifting land use practices to store meaningful amounts of additional "new" carbon is likely impractical, losses of massive amounts of stored "old" carbon could be lost from peatlands and wetlands if they are drained. Thus, making sure that land use practices are chosen that maintain our historical carbon stores is likely a much higher order goal, and more feasible, than trying to store additional carbon in carbon-depleted lands.