This Thursday night, Denver Botanic Gardens is hosting an independent film screening of the movie The Real Dirt on Farmer John. Acompanying this event will be a “Local Food Open House” featuring local farmers, farmer’s markets, co-ops, bakers, community gardening organizations and more. (if you’re coming, please pre-register! We’re expecting a full house).

A couple of our participants represent farms that raise grass-fed beef. What does this have to do with plants and botanic gardens? Grazing has co-evolved along with grasslands to produce an ecosystem that is totally dependent on the specific relationship between grazing animals and plants for its vitality, health and diversity. Farms, with their substantial acreages, can also play an important role in sequestering atmospheric carbon and thus mitigating the effects of global warming. The following essay by Sara Puharich of  The Farm at Sunrise Ranch explains this in greater detail.

Grasslands and Carbon Sequestering: Feel Good About Eating Grass-fed Meat

Global climate change entered the mainstream media in 2006 and 2007. Less well publicized is the role agricultural practices play in releasing CO2 and the potential present in agriculture to sequester CO2 from the atmosphere. 

Current agricultural methods cannot sequester carbon. In fact, today’s common practices of chemical use and exposing bear ground are contributing to the increase of atmospheric CO2.  Allan J. Yeoman, Australian author of Priority One: How We Can Beat Global Warming, cites the enormous contribution to the build-up of greenhouse gases in our atmosphere by the use of agricultural chemicals. Dr. Christine Jones, Australian soil scientist and founder of Carbon for Life, explains that anything that causes bare ground results in the loss of organic carbon. Both of these practices are extensively used in farming today. Picture the planting of corn and soybeans, the two most prevalent crops in America. Looking across the fields, there seems to be a plentiful number of plants; but from a birds-eye-view, about 90 percent of the ground is left exposed. Both corn and soybeans are seeded and harvested in less than half of the year and in many cases the ground is left bare between plantings. To ensure that the ground is left bare, extensive herbicides are used to kill weeds. With the resulting singular species of plant remaining in the fields, referred to as monoculture, pests that feed on these plants need to be sprayed in order to decrease the damage they cause. Again, farmers are emitting carbon, instead of securing it. 

The potential positive impact of land stewardship to affect global climate change lies in the ability of the soil to sequester carbon. To sequester carbon, the excess carbon dioxide in our atmosphere causing global warming must be transformed through photosynthesis by grassland plants.  Then it can be stored through the decay of plants by soil life into stable soil organic matter. Dr. Jones explains that for photosynthesis to optimize the sequestering of CO2, soils must be covered with living plants that are green for as much of the year as possible. Through photosynthesis, organic carbon is added proportionally to the soil by the volume of plant roots per unit of soil, and the growth rate of those plants. Plant roots add carbon to soils as they decompose, and the decomposition of fibrous roots is also an important source of carbon in soils.  The decomposition of roots combined with maintenance of photosynthesizing ground cover is well accomplished in grassland ecosystems.

Grasses developed in ecosystems characterized by large herds of ruminant animals tightly bunched together against pack hunting predators. The grazing habits of ruminant herds stimulate the soil’s ability to sequester carbon. When leaves are removed from the plant, carbon in the form of stored carbohydrate is mobilized to the crown of the plant. This assists in the production of new leaves. Some carbon is released to the soil in the form of roots shed by the plant as a result of sending energy for re-growth to the leaves.

In the ecosystems in which grasses evolved, animals would be closely bunched while grazing as part of their defense against predators. As a result, animals deposited a large uniform track of manure, which they would then avoid until it had been incorporated into the soil. Because animals avoided their dung, plants that had been grazed were able to reestablish leaves from the root reserves and then re-grow root structures before being grazed again. Additionally, the impact of trampling loosened capped soils, promoting the growth of new plants while incorporating the minerals locked in dry material along with the minerals consumed and excreted through manure. The animal impact on grass lands promoted and continues to promote the conditions that build the soil’s concentration of carbon: healthy ground cover, high root biomass and high levels of microbial activity. These conditions lead to carbon sequestering, or an increase in soil carbon levels. Our management can mimic the conditions that foster perennial grassland.  Through the use of electric fencing, high stock density, and recovery periods between animal grazing and impact, land managers can create the conditions ripe for increasing the levels of carbon in our soils, thereby decreasing the levels of CO2 in our atmosphere. Hooray for grass-fed meats!