Tree Risk Assessment Report

In Summary

Tree First was contacted by the Royal Oak Nature Society to inspect the large dead Burr Oak (Quercus macrocarpa) next to the south entrance of Tenhave Woods in Royal Oak, Michigan. The goal of the inspection was to determine if the tree poses significant threat to people or property in the tree’s vicinity. The city of Royal Oak has indicated this tree to be a candidate for removal.

The risk assessments performed were in compliance with the ISA (International Society of Arboriculture) best management practices and meets all ANSI A300 standards.

A level 2 visual tree inspection was performed at ground level, where the tree was determined safe to climb. The tree was then climbed to perform another visual inspection of the crown therein. The canopy of the tree was accessed by two climbers using stationary rope systems. No heavy equipment or spurs were necessary to perform the work. A drone was also flown above and around the tree for additional photographs and videos.

Based on all of the observations listed in this report, as well as the general characteristics of the species, the targets, and the frequency of occupancy of the targets, this tree has been given a risk rating of low for a 2 year time frame, under normal environmental conditions. The tree should be reinspected every 2 years.

Dead trees are just as important to live ones, and this is a specimen tree which provides habitat and food sources for wildlife in the area. The tree serves as an educational point on nature walks in Tenhave, which highlights its significance. Removing a wildlife sanctuary tree is to remove a vital element a what makes a nature area natural. The tree should be retained so long as it is safe, which it is currently.

Mitigation

The main consideration here is to ensure the safety of people walking beneath this tree on the sidewalk. The infrequency of people standing beneath the tree reduces this tree’s overall risk rating. Generally people walk right by this tree and do not stand beneath it. They are within the target zone for a very short time. In instances where the tree is likely to suffer from failures or breakages are during wind storms and ice storms. In either case, pedestrian traffic reduces even more.

The several branches over the sidewalk with very obvious cladoptosis should be reduced in length. Refractory cuts would be advised here in the interest of wildlife habitat and maintaining a natural appearance to the tree. This retains a safe length of branch to still allow wildlife to utilize these branches, while being safe for people to walk beneath. 

Level 2 Assessment from the ground

The Burr Oak is 51” in diameter at breast height, and approximately 100 feet tall. The crown spreads approximately 55 feet across at its widest. Approximate age between 175 and 250 years old.

Site

The oak sits right along the fence enclosing Tenhave Woods, its trunk is to the outside of the woods. 

The tree is protected from wind exposure on three sides. Other trees in the area seem to have a slightly buried trunk flare, though not significant. It has been demonstrated, however, oaks generally do not respond well to the addition of soil on top of their root systems. The tree stands among other oaks which are evenly spaced apart amongst the turf. At a cursory look around, these oaks are younger than the large dead burr oak, and look mostly healthy. 

The area around the tree to the south is entirely turf grass that is mowed, with high weed populations. No indicators of herbicide of fertilizers on this turf. To the north, its root system extends into the forest, where the canopy seems to have begun to die first, as indicated by the state of decay in the crown being more advanced on that side. 

No recent major site changes.

Soil

Only the soil’s physical properties were examined briefly by use of a small, hand soil auger.

The soil was extraordinarily compact within the dripline of the tree on the south side of the tree, where all of the turf grass is. The soil auger could not penetrate deeper than 5 inches without significant force. The soil type was inconsistent, suggesting grade alteration on the site at some point.

Soil in the forest seemed to be as expected: a darker color, loamy, with a healthy amount of organic material. The moisture was normal as well, not overly saturated. 

The soil near the trunk didn’t show any signs of soil heaving, indicating the tree hasn’t been subjected to any severe wind loading recently. The anchorage of the root system seems to still be mostly intact, despite damage from the sidewalk installation years ago and the compact soil.

Trunk

One major trunk defect was evident from the ground. A wound which began closing long ago had been impacted by two separate decay complexes. The second of which halted wound closure and prevented the formation of a full seam.

The crack/seal complex originates at the first major union, approximately 25 feet off of the ground. At the top of the wound where it originates, cavities are visible from the ground. Further probing of those are covered in the second section of this report.

Lightning strike is suspected by the Royal Oak Nature Society, however there is no obvious evidence in the upper canopy of a lightning strike. The origin of this wound is unknown.

The crack is most evident on the north-east side of the trunk. The wound is clearly visible from the gate into Tenhave Woods. This wound extends from the major union to the ground. Directly opposite the wound on the north-east side of the trunk, on the south-west side, the other part of this crack complex is visible. It has significant wound closure, the tree had almost completely sealed this side. The seal only needed to form approximately 7 feet below the major union of the tree. Below this point, the wound is suspected to be internal.

Several decay columns were exposed on the north side of the trunk flare, indicating the decay complex had likely had multiple points of entry. This decay likely extends into the trunk and into the roots, which is common for veteran trees.

Crown

The tree had a live-crown-ratio of 0%, the tree is dead. The tree has significant peripheral dieback which has progressed for years. It should be stated these dead tips are very brittle, and are expected to fall off with little force. It should also be said the large diameter branches where these tips originate from, despite being dead, are incredibly sturdy.

Without leaves, the tree’s crown experiences virtually no wind load, which is the most common cause of tree and branch failures in living trees in our area (in addition to ice storms). With a very low wind load, the larger, potentially more damaging branches, have an improbable likelihood of failure.

The tree had begun retrenching, but it could not sustain the new epicormic growth. The epicorms died within four years of sprouting.

On several of the lowest limbs, the process of cladoptosis had begun long ago. The width and length of these branches vary, ranging from 7” in diameter to 12” in diameter. Each of these particular limbs has been dead longer than the rest of the tree, and each is on the same side of the tree where the sidewalk was installed in the past. 

Level 2 Aerial Visual Assessment of the Crown

Lower Crown

There were no significant wounds present beside the lowest, largest branch union. This is where the trunk crack wound originates mentioned in the first section of this report. Three connecting cavities are present at and slightly below the major union.

Significant response wood is present in and around this cavity complex. The damage to the bark and scratch patterns in this area indicates this cavity is or was occupied by a mammal. It is possible the source of the large crack on the northeast side of the trunk originated here. The cavities are relatively small in relationship with the size of the wood in the area. At a maximum depth, the cavity was about 1/4th the depth of the trunk at this site. A surprisingly low amount of organic material was found inside the cavity, mostly leaves of nearby trees. The interior of the cavities was dry.

The weight load at this region is significant. The position of the cavities here, along with the significant wound closure formed while the tree was alive, and the lack of wind load, together negate the risk of this structural defect. In a tree with a living crown, this may prove otherwise. In this scenario though, it has little impact on the overall tree’s risk rating.

Middle Crown

Nothing significant stood out as particularly worrisome. No structural defects were present on the major branch unions. No wounds that would impact tensile strength of the wood were present. No significant cavities were present. Tree decay in this region of the crown is minor at this point.

Uppermost Crown

As seen from the ground, the peripheral dieback is significant. During the time of the inspection, a single type of fungal fruiting body was evident in this upper 4th of the canopy. This species seemed to only be colonizing the top of the canopy on branches less than 9” in diameter. Both the habitat and mushroom suggest this species belongs to the Schizophyllum genus, which are sap-rotting pathogenic fungi. This type of fungus decays from the outside moving inwards. There is still some cross-sectional strength retained in these uppermost crown, but are more brittle than the larger branches lower in the crown.

Most of the decay organisms and detritivores present in the tree are secondary, which appear after the tree is dead or decaying. They are symptoms of the tree’s state of health, not necessarily the cause of it. Only 1 species of pathogenic fungi was apparent on visual inspection, and it is possible that more have colonized this tree. Without the presence of mushrooms, though, this remains unknown.

The lack of smaller and medium size twigs and small branches at the top are one of the indicators of how long the tree has been in decline. Branches up to 5” in diameter are rather brittle because the state of their decay is advanced. As previously stated, however, the type of decay occurring here retains some cross-sectional strength.

Bark beetle holes are present, but are secondary. No adults or larvae were seen. The number of holes in the uppermost canopy was neither abnormal nor significant.

Limitations of this Inspection

We didn’t see it necessary to investigate the interior of the tree at this time. The use of resistographs and tomography allows us to see the state of decay and wood quality within the tree. The state of decay in the largest parts of the tree are not advanced enough to warrant this magnitude of inspection at this time.

Long-Term Management

Currently, there is no justification to remove this tree from the perspective of safety. Removal of this tree would be a disservice to the wildlife in the area and those who enjoy nature in the city of Royal Oak.  Continued monitoring of this tree is absolutely necessary for risk management.

A dead tree retained for the sake of wildlife is typically called a wildlife snag. Snags have different management strategies than living trees.

As this tree continues to decay, it should be reduced with time. The tree will naturally do this either on its own or with the helping hand of arborists. Oaks decay slowly in our area, especially oaks in the Leucobalanus group, the white oaks. While alive and healthy, generally our oaks compartmentalize their decay well enough too. It will take a very, very long time before this tree is complete rotten. It is not possible to predict a time frame, as decay rates vary.

Canopy reduction makes the tree progressively smaller, which reduces its exposure to wind, and reduces the surface area upon which ice can accumulate. The tree has no leaves, so its sail is virtually non-existent. It will catch very little wind. Shorter levers (the branches) require a lot more force to break. This makes the tree safer, while still providing the educational and wildlife value. This is a more cost effective solution to reduce the risk without the massive expense of tree removal.