Friday, October 23, 2009

Carbon foot prints

From Lawn & Landscape (see the full article here)

Trees + Turf = Carbon Storage
Plants grow by removing carbon dioxide from the air during photosynthesis and incorporating the carbon into above and below ground tissues. In the eastern and northwestern regions of the U.S., trees often are a major component of the urban landscape and the most obvious potential reservoirs for carbon storage. It has been estimated by the journal Oecologia that healthy trees store about 3,200 pounds of carbon per acre annually, or about 7.4 pounds per 100 square feet of space.

It has just recently been recognized that turfgrasses also play an important role in carbon sequestration. In many urban settings, turfgrasses are the major part of the landscape, particularly when recreation areas are considered. It is estimated that turfgrasses occupy about 165,000 square kilometers in the continental U.S, according to the Agronomy Journal and Environmental Management. Healthy turfgrass can store almost 800 pounds of carbon per acre below ground in soil each year, the Agronomy Journal also reports, which equates to almost 1.85 pounds per 100 square feet of lawn or about one-quarter the rate for trees.

Keeping plants in a healthy state is essential for carbon storage to occur, though. Photosynthesis and growth are the carbon generators. To operate at high efficiencies, they require plants to have minimal problems with diseases and have adequate fertility. With turfgrass, for example, maximal productivity has been linked with regular mowing and leaving clippings in place, reports J. Environ Quality. At the same time, it’s important to manage fungal diseases and insect pests because they can negatively impact the potential of turfgrass to sequester carbon. While less is currently known about the ability of horticultural landscape plants to store carbon, one can safely assume they too will contribute to the carbon storage pool but must be kept in a healthy condition.

Homeowner Help
Healthy, growing landscape plants can offset some of the carbon being generated by individual homeowners. Here is a hypothetical example: A typical gas-powered automobile driven 12,500 miles annually might be expected to release about 2,500 pounds of carbon a year, according to Environmental Protection Agency Emission Facts. A half-acre residence with roughly 50 percent covered in trees could store about 800 pounds of carbon a year. If the remainder of the landscape were turfgrass, it would store another 200 pounds. So, this hypothetical homeowner could offset 1,000 pounds of carbon – 40 percent of their automobile footprint – just by maintaining a healthy landscape.

A common question being posed about green spaces is whether the release of carbon dioxide during maintenance will negate the carbon storage advantages gained with landscapes. With turfgrasses, for example, would gas-powered mowers generate substantial amounts of carbon dioxide and compromise below ground carbon storage? Estimates of carbon use by the Outdoor Power Equipment Institute indicate about 50 pounds of carbon dioxide would be released with frequent mowing over the span of a year. That is a quarter of the carbon being stored in the turfgrass, and a fifth of the total 1,000 pounds of carbon sequestered in the hypothetical lawn cited previously. Bottom line, the system stays positive on balance.