Inventory scope, limitations & risk

What this is. A tree condition inventory. Each tree received a ground-based visual inspection, including a 360° walk-around where access permitted. Tree size was measured, and species, condition, visible structural defects, failure potential and recommended treatments were recorded.

What this is not. This inventory is not a tree risk assessment. No tree risk assessment — at any level defined by the ISA and ANSI A300 (Part 9) — was performed. Although the assessor took account of nearby targets when judging the urgency of treatment, targets were not systematically identified, recorded or evaluated, target occupancy was not quantified, the likelihood of impact and consequences of failure were not formally assessed, and no risk rating (Low / Moderate / High / Extreme) has been assigned to any tree. Where a tree with recorded defects stands within striking distance of a significant target, a tree risk assessment should be commissioned.

What was not done. Trees were not climbed, probed, cored, excavated or subjected to advanced diagnostic testing. Internal decay, root defects below grade, and conditions concealed by foliage, vines, snow, or restricted access may not have been detected. Assessments are founded on visual observation, experience and professional judgement, and are made with incomplete information about internal and below-grade conditions.

How to read the treatment priorities. Recommended treatments carry a priority — immediate, high priority or low priority. These express the assessor’s professional judgement of urgency, formed from the tree’s observed condition and structural defects together with the surroundings and nearby targets observed at the time of inspection. They are intended to help the Town prioritise and schedule work, and trees recommended for immediate attention should be actioned promptly.

A judgement, not a formal risk rating. While targets were taken into account, they were not systematically recorded or evaluated, occupancy was not quantified, and no risk rating was derived using the ISA risk matrices. A priority should therefore be read as the assessor’s prioritisation of work, not as a risk rating for the tree. It reflects what was apparent during a single visit — the Town’s own knowledge of site use and occupancy, which may differ, should be weighed alongside it when scheduling work.

Assessment period — one year. In accordance with ISA practice, each assessment is made for a specified time frame. The ratings in this inventory apply for a period of one (1) year from each tree’s date of inspection, under normal weather conditions. Beyond one year, a rating should not be relied upon as a current description of a tree’s condition or risk.

Inspection interval. Setting the inspection interval, and any inspection programme, is the responsibility of the Town as owner. Where the interval between inspections exceeds one year, the intervening period is not covered by this assessment, and Silv-Econ Ltd. accepts no responsibility for changes in tree condition or risk arising after the one-year period. Trees in high-use areas, trees with recorded structural defects, and trees flagged for further evaluation warrant more frequent inspection than the general tree population.

Normal weather only. Condition and failure-potential ratings describe what may be expected under normal weather conditions. Extreme events — severe wind or ice storms, saturated or frozen soils, drought, flooding, fire or vehicle impact — can cause the failure of trees rated as low risk, including trees in good condition. No assessment can anticipate such events. Trees should be re-inspected following any major storm or site disturbance, regardless of where they fall in the inspection cycle.

Point in time. Each record reflects the condition observed on its date of inspection only. Trees are living organisms whose condition changes continuously, and a rating can be overtaken by events at any time after inspection.

Recommendations are advisory. Treatment recommendations are the professional opinion of Silv-Econ Ltd. based on the conditions observed. They are not directions, and not a warranty of outcome. The Town remains the owner and controlling authority for these trees, and is responsible for deciding what work is carried out, and when.

Deciding what risk is acceptable is the Town’s decision. Under ISA practice, acceptable risk is the degree of risk within the tolerance of the owner, manager or controlling authority — not of the assessor. Silv-Econ Ltd.’s role is to identify and communicate condition, defects and relative risk so that the Town can make an informed decision. Some trees are retained with known defects. A structurally defective tree near a target may be judged unlikely to fail under normal conditions and reasonable to retain, while still carrying a real possibility of failure in an extreme event. Where a tree is retained — whether or not removal was recommended — the residual risk is knowingly accepted by the Town.

No guarantee of safety. Silv-Econ Ltd. does not warrant or guarantee that any tree is safe, that any tree will remain standing or intact, or that every defect or condition affecting any tree has been identified. Where a tree is flagged for further evaluation, or where site conditions change, further assessment by a qualified arborist may be warranted.

Intended use. This inventory was prepared for the Town of Aurora for the management of its tree resource. It is not intended for, and should not be relied upon by, any other party, and it is not a substitute for a site-specific assessment of an individual tree.

Condition and defect terminology is consistent with the ISA Best Management Practices — Tree Risk Assessment and ANSI A300 (Part 9). Risk ratings under those documents are produced by a tree risk assessment, which requires evaluation of targets and consequences and was outside the scope of this inventory.