| MadSci Network: Botany |
Cutting an automobile tunnel through a big tree trunk does harm the tree but the tree may survive for decades afterward because most of its leaves, stems and roots remain. The famous Wawona Tree tunnel through a giant Sequoia (Sequoiadendron gigantea) was cut in 1881 as a tourist attraction. It fell in 1968-69 during a severe winter. We really do not know for sure if the Wawona tree would have survived longer if it had not been tunneled. "When it fell, the Wawona Tree was approximately 2100 years old, 234 feet high (71.3 meters), and 26 feet in diameter at the base (7.9 meters). The famous tunnel was 7 feet wide, 9 feet high and 26 feet long at the base (2.1 meters by 2.7 meters by 7.9 meters)." (last reference). A dead tree was tunneled before that and still stands! There are at least three ways the tree may be harmed. 1. Cutting the hole destroys a significant amount of bark, which may reduce the amount of water and mineral nutrients that flow from roots to shoots in the xylem. It also reduces the amount of phloem that transports sugars and other substances to the roots from the leaves. The tree may be able to compensate for the lost xylem and phloem by increasing the rate of flow in the remaining xylem and phloem but I do not know if this has been confirmed experimentally. 2. The loss of the wood in the center of the tree may not be a serious loss because inner wood no longer functions in transport and hollow trees can still be structurally strong. The more serious problem may be the large surface area that is exposed to entry of diseases or fungal attack and decay. 3. Autos that use the tunnel and road paving may cause soil compaction, which damages the roots. People that are attracted to the curiosity also can cause damage. In nature areas, such as Muir Woods National Monument in California, wooden walkways are sometimes built to prevent foot traffic from compacting the soil and harming tree roots. Today, cutting tunnels in large trees is not considered desirable because of the strong possibility that it may shorten the life of trees that have lived for over a thousand years. At least three privately-owned redwoods (Sequoia sempervirens) in California have old tunnels through them. People can pay to drive through them if their car is small enough to fit the tunnel. They are Klamath Tour Thru Tree, Myers Flat Shrine Tree, and Leggett Chandelier Tree. References Muir Woods National Monument California Tree Tunnel in Mariposa Grove of Bigtrees, Yosemite National Park, California The Tuolumne Grove of Sequoia Gigantea - The Big Trees 1939 Wawona Tree Photo Big Tree Drive-Thru "Where is the tree you can drive through?"
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