Leaning trees present an interesting challenge for a couple of reasons: Aesthetically, with a few exceptions, a vertical trunk is usually preferable to a sharply leaning trunk. Structurally, a lean might indicate instability, but not always.
Here is an example from a reader in Washington state:
I saw your article on straightening a leaning tree. We had an acre of forest logged off and red alder began an aggressive invasion. I had most of them cut and left some around the border. Some have grown to about 10-12 inch diameter. I planted a silver maple and its trunk is now about
8 inches in diameter. It grew up under three alders and leans toward a clearing at about a
45-degree angle. I’d like to straighten it. I’ve removed the alders and left two stumps opposite the direction of lean at about 4 feet tall to support a bracing plan. I’ve been told to put a bolt into the maple, then attach a wire rope or chain with a come along or adjuster to the bolt, the other end to the bracing stumps, and tighten slowly. Any suggestions for me? I really want to keep the tree.
It sounds like the maple grew at a lean because of crowding by the adjacent trees. If the tree is stable, it might be better to just leave it as is, monitor stability and prune to reduce weight on the leaning side every few years.
Here are some points about hardware, according to the ISA Best Management Practices book on cabling, bracing, guying, and propping (ISA 2006):
• Tree-to-tree guying requires an anchor tree equal to or larger than the tree being guyed and carefully selected to be strong enough to provide support. I’m concerned that the alder stumps will decay.
• An 8-inch diameter tree requires a 5/16-inch forged eye bolt through the trunk. This is preferable to a “J” lag into the trunk. It must be in direct alignment with the guy cable.
• There should a heavy-duty washer on the back side and the end of the bolt should be preened to keep the nut from working off the end.
• Cable should be 5/16-inch common grade steel cable, or 3/16-inch extra high strength steel cable, commonly used by tree services. or 3/16-inch aircraft cable.
• The cable should be attached through the eye over a thimble and secured properly for the type of cable selected.
• The anchor point on the guyed tree should be at no less than half of its height.
• The anchor point on the ground or the supporting tree should be at a distance from the guyed tree equal to at least two-thirds the height of the attachment point on the guyed tree.
• Install the hardware and cable on the tree being guyed. Use a cable puller (like a Chicago Grip) and come-along or winch to start to pull the tree into a more vertical position. Finally, attach the guy cable to the anchor point on the ground or anchor tree.
• Turnbuckles in guying systems must meet the same strength requirements as the rest of the system.
• If two cables are necessary, use two anchor points on the tree being guyed, separated by a distance equal to or greater than the trunk diameter at that point.
• Guy cables can present a severe “clotheslining” hazard to people and vehicles using the area.
• Without cracking or splitting the trunk or roots, gradually adjust the turnbuckle until you are satisfied with the results.
For those interested in the status of Sudden Oak Death and how to manage it, the UC Berkeley Forest Pathology and Mycology Lab is planning two public meetings. An indoor session on 2012 SOD Blitz results is Friday, Nov. 9, at 7 p.m. in the UCCE meeting room, 1710 Soscol Ave. On Sunday, Nov. 18, at 1 p.m. is an outdoor session on prevention and management practices at the Carolyn Parr Nature Museum, 3107 Browns Valley Road.
Bill Pramuk is a registered consulting arborist. Email questions to firstname.lastname@example.org, visit his website, billpramuk.com or call him at 226-2884.