CATS Urban Tree Risk Assessment & Mitigation 3 — Questions and Answers
Question 1: Which failure mode is described as the separation of a branch or stem at a point other than a union or attachment point?
- Attachment failure
- Root failure
- Stem failure (Correct answer)
- Crown twist
Correct answer: Stem failure
Stem failure (also called mid-stem or trunk failure) occurs when wood fractures along the stem rather than at a branch union or root plate.
Question 2: When calculating the modified Mattheck ratio (t/R) for a hollow tree, what minimum wall thickness ratio is generally considered the threshold for structural concern?
- 0.10
- 0.20
- 0.30 (Correct answer)
- 0.50
Correct answer: 0.30
A t/R ratio below 0.30 (wall thickness less than 30% of the trunk radius) is generally considered a threshold where structural integrity is compromised.
Question 3: A large Siberian elm on a residential street in Albuquerque shows signs of lion-tailing. Which risk does this create?
- Increased crown density blocking sunlight
- Weight distribution shifted to branch ends increasing failure risk (Correct answer)
- Reduced evapotranspiration causing root stress
- Accelerated heartwood decay
Correct answer: Weight distribution shifted to branch ends increasing failure risk
Lion-tailing removes interior foliage and shifts weight to branch tips, creating lever-arm stress that increases the risk of branch failure.
Question 4: Which type of wound closure pattern best indicates a tree's capacity for compartmentalization?
- Flush, smooth callus roll with uniform width
- Rapid formation of reaction zone and woundwood (Correct answer)
- Formation of epicormic shoots around the wound
- Discoloration extending well beyond the wound margin
Correct answer: Rapid formation of reaction zone and woundwood
Rapid formation of a reaction zone and expanding woundwood callus indicates active CODIT (Compartmentalization of Decay in Trees) response.
Question 5: An arborist notes a sudden lean in a previously upright Albuquerque tree after a monsoon rainfall event. The most urgent concern is:
- Crown imbalance from past pruning
- Root system failure (Correct answer)
- Trunk decay at the base
- Epicormic growth attracting pests
Correct answer: Root system failure
A sudden lean following soil saturation indicates possible root plate failure or soil heave, requiring immediate assessment and likely removal.
Question 6: Which condition most significantly increases wind-induced tree failure risk in an urban forest setting?
- Trees growing in dense clusters
- Open-grown trees suddenly exposed by neighboring removal (Correct answer)
- Trees with deep taproots on clay soils
- Trees with symmetrical crowns
Correct answer: Open-grown trees suddenly exposed by neighboring removal
Trees previously sheltered by neighbors develop wood adapted to low wind loads; sudden exposure significantly increases failure risk in subsequent wind events.
Question 7: In Albuquerque's urban environment, alkaline soil pH most directly contributes to tree stress by:
- Promoting excessive nitrogen uptake
- Locking up micronutrients like iron and manganese (Correct answer)
- Encouraging root pathogens like Phytophthora
- Reducing soil compaction around roots
Correct answer: Locking up micronutrients like iron and manganese
High pH soils in the Southwest cause micronutrient immobilization, leading to chlorosis and weakened trees more susceptible to pathogens and structural decline.
CATS Urban Tree Risk Assessment & Mitigation 3
Which failure mode is described as the separation of a branch or stem at a point other than a union or attachment point?