When we talk about carbon storage, we are talking about carbon dioxide (CO2) that is temporarily not in play in the atmosphere. This may be because the CO2 is tied up in living organisms, primarily green plants and trees; or it is stored away in the soil as organic debris; or it is buried under sufficient layers of sediment that it is inactive for an indefinite period in the way that fossil fuels once were.
Before the Industrial Revolution began, there was a relative balance between CO2 released by humans’ combustion of fuels such as wood, peat, and small amounts of coal and oil versus the CO2 picked up and stored by plants during photo- synthesis, sequestered by geologic processes, or absorbed by the oceans.
But after the late 1700s, the invention of the steam engine and, later, the internal combustion engine opened the way for fossil fuel exploitation and a new trend in Earth’s carbon cycle. With dramatically increased burning of coal, the CO2 captured by the plants of swampy woodlands many millions of years ago and long-buried under deep layers of sediments was released to join the CO2 of the current era. So too, was CO2 contained in the fossil petroleum produced by oil-rich algae that collected on sea floors millions of years ago. Pumped up to Earth’s surface and combusted, this ancient oil also released a huge volume of CO2 that had been out of circulation for millions and millions of years.
To restore some balance to Earth’s carbon cycle—and to the climate to which humans are adapted—we must reduce use of fossil fuels. But we also need to strengthen the carbon-storing capacity of modern ecosystems wherever possible. Soil carbon storage and sequestration through plant photosynthesis offer the possibility of large-scale capture and storage of greenhouse gases from the atmosphere. Additionally, carbon storage in soil has the potential to be continually renewed and recreated. In Wisconsin we are rich in land resources. The ways in which we manage these lands can offer advantages in sequestering or storing carbon.
Status & Strategies
Forests are thought to be the most important terrestrial sinks for CO2. Trees take CO2 from the air and convert it to sugars and cellulose, binding up CO2 in their leaves, roots, and woody trunks and branches. Forests across north central and north- eastern North America historically have been responsible for most of the continent’s biological carbon storage, helping to slow atmospheric CO2 increases. Most carbon is stored long-term in wood or in soil. Soil storage is more permanent than storage in living vegetation. In soil, decomposing and finely fragmented plant material can accumulate over hundreds of years and become deeply buried in cool, wet earth where decay and release of CO2 are greatly slowed.
As forests in our region age—resulting in fewer but larger trees—and as forest pests and pathogens spread, there has been concern that the forests’ rate of carbon sequestration will diminish. However, studies of forests in the Great Lakes region have shown an increase in sequestration; even with decline in leaf area, these forests actually have higher wood production. In fact, the more biologically diverse and structurally complex the older plots are, the more resilient they are to production declines with age.
Innovative forest management can accelerate the development of forest complexity in terms of number of species, range of ages, and layers of vegetation. With this comes improved carbon storage capacity.
In grass and grazing lands the majority of carbon storage is in the soil, where the extensive networks of fibrous roots penetrate deeply and enrich the soil with organic matter in death. The world’s cultivated soils have lost between 50 and 70 percent of their original carbon stock. That includes North America’s vast grasslands, which nurtured deep, fertile soils, and have been largely transformed into agricultural lands. Through intense cultivation of these former prairies over the last two centuries, massive amounts of carbon once held in their soils have been released into the atmosphere.
Researchers are studying how land restoration and regenerative agricultural practices—such as planting fields year-round in crops or other protective plant cover, and practicing agroforestry that combines crops, trees, and animal husbandry—can reduce atmospheric CO2 while boosting soil productivity and resilience to floods and droughts.
No-till farming has long been advocated as a means of minimizing soil erosion and maintaining soil fertility, and has been on the rise. It also has the advantage of less soil disturbance and less release of stored CO2 and methane. A drawback is heavier reliance on chemical herbicides to control weeds, but use of cover crops and other techniques are helping in this area. Researchers are also studying how landform characteristics and ecosystem processes can influence the soil and vegetative cover and, in turn, the carbon storage potential.
Protecting wetlands, old growth forests, and woodlots, and improving management of pasture and croplands are important strategies not only for protecting habitat, but also for maintaining carbon storage and other ecological services provided by nature. Studies are underway to identify where the greatest advantage for carbon sequestration in plants and soils may be. The findings will help us better understand and take advantage of this potential.
Research in northeast Wisconsin has identified land areas that are not optimal for agriculture and would more suitably be dedicated to biofuel source crops such as perennial grasses or woody shrubs. These studies have evaluated economic and environmental outcomes of converting poorly drained, marginal agricultural areas into perennial, biomass yielding grasslands for electricity and heat generation in that part of the state. These are areas where planting annual row crops is often delayed, prevented, or unprofitable in wet years. Spring soil saturation is expected to maximize warm season grass production by providing ideal moisture availability during the more commonly water-limited summer.
The wetter conditions and finer textured, high-clay content soils characterizing lowlying areas in northeast Wisconsin should maximize carbon-sequestration rates since wet clay conditions delay organic decomposition. Establishing perennial grasslands in these wet areas will not only maximize carbon sequestration per unit of lost agricultural productivity for food or fiber but also serve as a buffer between agricultural uplands and aquatic systems, reducing nutrient and sediment loading into waterways—an additional ecological benefit for the same land conversion costs.
Resources in Natural Carbon Storage
- Great Lakes Climate Webinar: Predicting Carbon Storage of Great Lakes Forests
- NOAA – Natural Carbon Sequestration & Storage