Our student volunteers were working hard last week, dragging huge piles of privet cuttings and other shrubs down the slope toward the power chipper. More helpers were bringing plant debris out of the bamboo forest, that unique environment at the end of the Brenau campus where bamboo, planted in the 1930s, has grown into huge trees.
With a loud roar, the machine was turning all the dead plant matter into a handsome pile of mulch. As the small mountains of twigs and branches were shrinking, a student asked an innocent question: “Why don’t we burn this stuff instead of doing so much work?”
Taken by surprise, I feebly mumbled something about “carbon footprint.” But a better explanation would have been appropriate.
When vegetation is removed, the nutrients that it drew from the soil go away with it. Even if the purpose is a benign one (in this case, to build a teaching garden), clearing an area means that something is taken away. If the invasive shrubbery is burned, its substance, which is carbon, combines with oxygen in the process.
Carbon plus oxygen makes carbon dioxide. With CO2 levels in the atmosphere rising, we don’t need to make more of it.
But most significantly, these plant cuttings can add nutrients back to the soil if they are cut up into small pieces and put back as a ground cover. Gardeners have long known the benefits of putting mulch on top of the soil. It rots slowly, releasing nutrients back into the ground. It stores water during rain, which becomes available to new and desirable plants sprouting from below. It provides shade, which protects seeds underneath from getting overheated and dying in the sunlight. And it also makes a preferred home for many insects and earthworms that are beneficial to the ground because they loosen it up and mix organic matter into the assembly of minerals.
A purely mineral soil, made from clay and other products derived from rotting bedrock, isn’t a good growing base for plants. It needs generous input of organic substances such as compost, fallen leaves or, in this case, mulch made from chipped-up shrubs. This makes for a natural fertility that’s equal or better than what one gets with mineral (store-bought) fertilizer.
Foregoing the burning also saves the area from enduring clouds of smoke. And finally, no unneeded carbon dioxide is sent into the atmosphere.
Rudi Kiefer, Ph.D., is a professor of physical science and director of sustainability at Brenau University. His column appears Sundays and at gainesvilletimes.com.