I was wandering the campus of Lasell College today collecting building energy use data and I noticed the landscaping company we hire to maintain our property. These men were blasting away at leaves with loud leaf blowers in an effort to eliminate every fallen leaf from our campus. The energy and carbon cost of landscaping is frequently a number that escapes campus carbon footprint estimates but they are not insignificant.
Through the process of photosynthesis, trees sequester carbon dioxide from the atmosphere which accumulates in the biomass of the tree. When calculating carbon footprints, many institutions will quantify the number and size of trees on their campus and use a reasonable estimate for sequestration rates to determine how much carbon dioxide the vegetation offsets. This process seems straightforward but is filled with several flaws.
Trees on a campus are much different than trees in a forest. When forest trees suffer damage or die, the dead branches decay in place. On a college campus damaged trees are maintained and branches are removed. Maintaining and removing dead trees or damaged branches requires the use of fossil fuels. Arborists use trucks, chainsaws, and chippers to do this work. Further the process of decomposition may occur at a faster rate depending on how the waste is disposed of.
David Nowak and others found that trees that are not maintained and allowed to decompose in place are sinks for carbon dioxide. Although the decomposition and sequestration nearly balance out, trees will still act as a sink of carbon. As soon as trees have maintenance the carbon gains are lost to the atmosphere as the machines burn fossil fuels. This suggests campus trees plantings might not be the answer to reducing carbon footprints. However as Nowak et. al (2002) suggest, there are management strategies that can be put in place to maximize benefits of campus forestry. These suggestions include planting long-lived and low maintenance species, use maintenance strategies that maximize longevity, minimize fossil-fuel use related to maintenance, plant trees in energy conserving locations, and consider the use of dead wood material.