Hollow Public Trees

Town Manager, PW Director, Urban Forester etc. Approved

The fattest oak in Europe has a cavity large enough to hold a council meeting. Trees have many strategies for coping with cavities, like shedding unneeded limbs and adding support.

To the left, a new root grows at the margins of the cavity. To the right, a column of new wood is formed inside the cavity.

The Crying Tree, Marion VA

Inspecting the structure, pruning branches, and invigorating roots

improves health, safety, and longevity.

Open cavities between buttress roots are not uncommon in old oaks, and interior decay is typical. Healthy trees are supported by their buttress roots, and wall off the spread of decay.

The cavity is in a sinus and strong response growth, woundwood, is visible (orange lines). The yellow lines indicate a second line of defense.

The open areas appear to be 3" x 5" and 2" x 4“, in a non-supporting sinus area. This activity is starting to affect one buttress root.

. Using a trowel to get a look below ground on the Crying Tree may reveal this type of response growth.

This type of inspection can provide an idea of the structural significance of those openings.

On the north side of the trunk, trunk tissues have cracked apart after the loss of limbs.

The crack stops at a growth point, where tissues are strengthened. Even after the branches are cut off, the protection zone remains.

A small hole in the upper left appears to be one of several access points for squirrels and other creatures.

These are typical in older oaks.

The loss of limbs on this one vascular column of this tree restricts the flow of nutrients to the area around the crack. This starvation contributed to the cracking, and slows closure.

The BMP and the TRAQ form guides the assessor to document response growth. The tree’s response growth is an important factor.

The ANSI A300 standard calls for inspection before pruning, or installing lightning protection.

The crack and the openings were probably observed at those times or before.

Response growth is visible on both sides of the tape

measure.

Its thickness indicates the crack has been there for

5+ years.

The Crying Tree sprawls toward the parking lot. This imbalance puts a lot of strain on the supporting tissues on the opposite side of the trunk that faces the building.

Reducing the sprawl will reduce the strain on the trunk, and risk of failure.

The red line shows a gap in the crown. It could be related to the loss of a limb in 2012.

The yellow line may point to the wound created by the removal of a broken limb.Closer inspection will guide the adjustment of pruning specifications.

Reducing branches will reduce the distance that water and nutrients must travel, redirecting the tree’s energy to foliage that is easier for the tree to support .

CONCLUSION: The reduction of branches will reduce the risk associated with this tree to or below the level of risk associated with the average mature tree in the urban landscape. SPECIFICATIONS for Care:Flare: Remove soil >6” away from the trunk. Avoid damaging roots. Expose and measure any roots that arise near wounds. Replace soil with stalite or another sterile aggregate.

Roots: Eliminate turf >6’ from trunk by spraying contact herbicide per need and suffocating with cardboard. Spread woodchip mulch 4” deep. Beyond 6’, modify soil by aerating and inoculating per need.

Trunk: Clean dead material away from wounds. Document and monitor response growth—”scar tissue”-- in the form of woundwood. Assess strength.

Branches: Reduce horizontal and downward growth to improve crown symmetry and lessen crown movement. Make cuts <4”, to laterals that grow upright or in a favored direction. Remove 10%-15% of the crown.

Monitoring: Review images of the crack and the cavity and the crown annually. Return in 3 years to inspect the tree and perform other treatments as specified.

Invasive testing causes excessive damage to structure and health. Future inspections will involve sounding, probing, and recording images of the interior with a camera.