Codominant Silver Maple With a Cracked Union

What the defect is

• Two codominant stems of nearly equal size with a V-shaped union and included bark means there is no strong wood connection - the stems are held largely by bark and a wedge of compressed wood. This is a structural defect present since the tree was young, and it does not improve with age.
• A 40 cm longitudinal crack in that union is not a cosmetic feature. It indicates the union is already separating under load - the failure process has started, not merely been predicted.

Why the proposed plan does not address the problem

• Cables and braces are supplementary: they limit the spread of a union under dynamic load. They do not restore strength to decayed or included tissue, and a cable installed above a union does not prevent failure below the attachment point. A crack in the union means the failure plane is at or below where you would install the hardware.
• Static (through-rod) bracing in a cracked union of this size in a species with weak wood is a high-risk intervention. It can hold a stem together while the crack continues to propagate internally, and it gives the client a false sense of security.
• Thinning 30% 'to let the wind through' is actively harmful: see the next task.

What I would actually do

• This warrants an advanced (Level 3) assessment before any commitment: resistograph or sonic tomography through the union, plus a close look for decay and for any cavity, and a decision on whether the crack is active (check for fresh wood, callus, staining, and measure and record the crack width for later comparison).
• If the crack is active and targets cannot be moved, removal is the defensible recommendation. Endorse the cabling quote only if an advanced assessment shows the union retains substantial sound wood and the client accepts defined residual risk, monitoring, and a written limitation.
• A cable installed by anyone other than a qualified arborist working to ANSI A300 Part 3 is not a mitigation; it is a liability transfer.

Objectives

• Reduce end weight and leverage on the leaning stem without removing live crown volume that the tree needs, and remove only material that is dead, broken, or a genuine hazard.

What to cut

• Dead, broken, and hanging branches over the driveway and sidewalk - always the first pass, and the only work that is unambiguously justified.
• End-weight reduction on the leaning stem: reduction cuts back to a lateral branch or scaffold that is at least one-third the diameter of the piece being removed. Target the longest, most horizontal limbs on the lean side, since those carry the greatest moment about the union. A handful of well-chosen reduction cuts on the outer third of those limbs does more for the union than any number of small cuts elsewhere.
• Remove any coarser subordinate stem or included sprout in the union zone that adds weight without contributing.

What NOT to cut

• No lion-tailing (stripping interior and lower laterals). It moves the crown's mass outward, increases sway at the ends of limbs, and stimulates a flush of epicormic shoots along the stripped limbs - the opposite of the goal.
• No topping or heading cuts into large-diameter wood; no stub cuts; no flush cuts.
• Do not remove more than about 15-25% of live crown in one operation on a tree of this age, and do not reduce the crown in a way that removes the lower live crown - the lower limbs damp sway and are the last to be sacrificed.

When

• Late dormant season, before bud break, is the practical window; silver maple is a heavy bleeder and will exude sap from large cuts in late winter/early spring, which is mostly cosmetic but worth scheduling around.
• Do not prune during active leaf expansion or in extreme heat.
• Document and date every cut and every defect observation, and set a re-inspection date (12 months, then annually) with the crack width recorded in writing so the next inspector has a baseline.

Why 'letting the wind through' is a myth

• A tree's crown is not a solid sail. Wind loading on a tree is dominated by the outer, leafy shell, and the crown already sheds wind through flexing, leaf flutter, and reconfiguration - branches and foliage streamline and reduce their own drag as wind speed rises.
• Opening the interior with 30% thinning removes the damping tissue - the lower and interior branches that slow sway and absorb energy. What remains is a thinner, whippier crown whose remaining limbs must dissipate the same energy over less wood, with more leverage at the ends. You can increase, not decrease, the load at the union.
• Thinning also removes photosynthate, and the tree typically responds by pushing a dense flush of epicormic sprouts along the limbs and trunk. Within a few seasons you have more sail area than you started with, attached by weaker shoots, plus the original defect untouched.

The correct alternative

• Reduction, not thinning. Shorten the longest, heaviest limbs back to substantial laterals. The goal is to reduce the lever arm (length) and end mass, not to open the crown. Cutting length by a third reduces the bending moment at the union disproportionately, because moment scales with distance.
• Move or harden the target. Short of removal, the most reliable mitigation is not on the tree. Reroute or lift the sidewalk/driveway use, keep parked vehicles out of the fall zone, and define the area under the lean as off-limits. Target reduction is engineering, not arboriculture, and it works without fail.
• Support and monitor as a supplement, not a solution. If the tree is retained, install hardware to specification and inspect it on a schedule; record the crack width at each inspection.
• Say the limitation out loud, in writing. With a cracked included union in a silver maple, no pruning prescription makes this tree safe. Pruning and cabling manage the risk to a defined level; they do not eliminate it. Removal and replanting with a species and structure suited to the site is a legitimate and often the best recommendation - give the client that option plainly, with a cost comparison.