Is my mulching mower a greenhouse gas emitter?

As I was reading an article about carbon taxes from the New York Times web site (nytimes.com) titled The Carbon Calculus that I found via a link from A Musing Environment, I realized that I had to ask myself – is mulching a source of greenhouse gas emissions that should be avoided or is it a beneficial addition to any gardening or farming plan?

Here is the passage from the article that got me thinking:

For example, Range Fuels, of Denver, plans to open a plant in Soperton, Ga., next year to make ethanol from pine tree waste. About 25 percent of the tree cannot go to a lumber mill or paper mill, the company says, and is usually left behind when the forest is clear-cut. If it is burned, it produces carbon dioxide. If it rots, it produces methane, an even more potent greenhouse gas.

Range has a thermochemical method for turning the waste — bark, cones, treetops, needles and small branches — into ethanol. Burning ethanol creates carbon dioxide no matter how it was made. But the economics could vary if Range got credit for producing a fuel by using material that was going to turn into a greenhouse gas anyway.

In contrast, corn ethanol is made using natural gas or coal that also contains carbon, but could have stayed in the ground if not for the ethanol manufacture. Ethanol advocates say that some gallons of corn ethanol have twice as much closet carbon as others. One new approach to ethanol uses algae; in Arizona, a utility is testing a process to fertilize algae with carbon dioxide captured from an adjacent power plant. The algae can be grown and processed into fuel.

Ever since I was a little guy, I have thought that rotting vegetation was a good thing – that the residues left behind were the materials that would allow soil to grow additional plants. At home, we always had a compost heap in the back yard and we kept a small bucket on the kitchen counter where we would put fruit peels, potato skins, and citrus membranes for eventual disposal in the compost heap. Dad directed us to dump the grass catcher into the heap and also added cut up branches and leaves that fell out of the citrus trees that he grew on our small suburban lot. According to Dad, one of the key ingredients for the pile was the droppings from the rabbits that he also raised. (Dad grew up on a small dirt farm in southern Georgia and carefully maintained some of the habits that led to survival there throughout his life.)

He had convinced me that compost was good – I enjoyed the results of effort by eating plenty of wonderful fruit and appreciating the look of the rest of the plants where we spread the compost. I never managed to develop that kind of composting habit on my own, but I have been using a mulching lawn mower for many years. I always felt pretty good about that – the grass clippings do not end up in a landfill and I avoid the need to add commercial fertilizer to keep the grass looking fairly nice. We do not have the greenest lawn on the block, but I always felt like it was a pretty “green” way to keep it from being a disgrace to the neighborhood.

I have also generally considered that the leaves and branches that fall from deciduous trees are a good thing for the soil and add to the richness of the forest. In a similar fashion, I always figured that the residues from crops are best plowed back into the soil to contribute to the next year’s harvest.

What do you think? Perhaps Al Gore has published something about this – as I recall, soil erosion was one of his big issues when he was a Congressman from Tennessee. Maybe I have been thinking about this part of the cycle of life all wrong and that we really should be turning all of that plant “waste” into ethanol instead of letting it rot. (In case you do not see it, there is a hint of sarcasm in that last sentence.)