What to Expect from a Tree Inspection – Advanced Assessment

Over the past few weeks, we’ve been dealing with tree inspections. There are three different types. So far, we’ve gone over a limited visual assessment and a basic assessment. Now, we’ll talk about the advanced assessment. Advanced assessment tree inspections are performed to provide detailed information about specific tree parts, defects, targets or site inspections. They are usually conducted in conjunction with or after a basic assessment if the tree risk assessor needs additional information and the client approves of the additional service.  Specialized equipment, data collection and analysis and expertise are usually required for a tree risk assessor to perform an advanced assessment. These assessments are generally more time intensive and more expensive.

The procedures and methodologies the tree risk assessor chooses to use in an advanced assessment should be selected and applied as appropriate with special consideration given to what is reasonable and proportionate to the specific conditions and situations. The risk manager/property owner should consider the value of the tree to the owner and the community, the possible consequences of failure and the time and expense to provide the advanced assessment. Advanced assessments can provide additional information that may make the difference between recommending tree retention or tree removal. The tree risk assessor should identify what additional information they need and recommend the proper technique to be used.

There are many types of advanced assessments that can be conducted, some of which we will describe in this article. Tree risk assessors are cautioned, however, that all technologies involve some uncertainty. Each technology carries its own limitations; therefore, any evaluation of an individual tree or target will not be an accurate measure but a qualified estimation. No matter what method the tree risk assessor uses to inspect the trees, they should employ safe work practices.

Aerial Inspection

An aerial inspection, aka crown inspection, is the inspection of the aboveground parts of a tree that are not visible from a ground-based inspection. This includes the upper trunk and the upper surfaces of stems and branches. Aerial inspection usually includes a visual assessment for defects, conditions and response growth. Conditions of particular importance include inspection of significant branch junctions, cracks in branches, sunscald on the tops of branches and bark damage from bird or animal feeding. In addition, aerial inspections may include an evaluation of internal decay. This type of inspection can be performed from an aerial lift, an adjacent building, ladder, or by climbing the tree. The tree risk assessor should determine if the tree is safe to climb before entering the tree. Visual inspection from the ground is not considered an advance assessment but may be part of the basic assessment.

Assessment of Internal Decay

We know that it’s difficult to estimate or quantify the location and extent of internal wood decay during most basic assessments. When it’s necessary to more accurately determine these factors, the tree risk assessor can use several decay-detecting techniques including drilling and the use of sonic devices. After estimates are made of the amount and location of solid wood present around a column of internal decay, several methods are available to evaluate the significance of the decay. Some methods are based on engineering models of pipe strength and recommended thresholds for minimum solid wall thickness. Modifications for species, locations, amount of decay, dimensions of the tree, additional defects, and site conditions should be made by adapting the thresholds, but there is little guidance for such adaptions.  Other methods adapt mechanical principles for engineering models in order to compare expected wind loads with the estimated load-bearing capacity of the tree.

So, what are these methods?


Two types of drilling tools can be used to evaluate the extent of decay. These are a hand-held electric drill or a resistance-recording drill. Both distinguish between solid wood and decayed wood by the drill’s resistance to penetration as it moves through the wood. It is important to carefully select testing locations so that the size and configuration of the decay column can be estimated. Before testing, sound or visual testing should be done to determine the best location to test. The tree risk assessor should be careful to avoid unnecessary wounding of the tree. The number of drillings should be as few as possible to avoid further damage to the tree.

Sonic Assessment

Sonic wood assessment instruments send a sound wave through the wood and measure the time for the wave to travel from the sending point to the receiving point. If a crack, cavity or decay is present, the sound travels around the defect. This increases the transmission time from the sending to the receiving point as compared to wood with no defects. The device, however, cannot determine the type of defect (decay, cracks, embedded bark or cavities).

Root Assessment

When you perform root assessment, you can do several different things. These are root inspection and evaluation, root decay evaluation, measuring the change of lean and load tests. These are very technical processes that your tree risk assessor will be able to explain to you. Basically, they are checking the roots for defects and use different tools and techniques to discover what the problems are.

We really hope that you’ve enjoyed our series or tree inspections. We want to give you as much information on tree care as we can. If you have questions, we encourage you to contact us at your convenience. We can be reached at 512-341-8888.