Certified Arborist Test Urban Forestry and Tree Selection 1

Question 1

The '10-20-30 rule' is a widely cited guideline in urban forestry species diversity. What does it prescribe?

Accepted Answer

No more than 10% of trees from one species, 20% from one genus, and 30% from one family

Answer

The 10-20-30 rule, popularized by Frank Santamour, recommends limiting any single species to 10% of the urban tree population, any single genus to 20%, and any single family to 30%. This biodiversity threshold reduces the risk of catastrophic loss from a single pest, disease, or climate event affecting taxonomically related trees.

Question 2

Which soil condition is most commonly cited as the primary limiting factor for urban tree establishment and long-term survival?

Accepted Answer

Soil compaction reducing pore space, aeration, and root penetration

Answer

Soil compaction from foot traffic, construction, and vehicle loads collapses macropores, reducing oxygen and water infiltration. Compacted soils have bulk densities that physically prevent root elongation, making it the single most pervasive limiting factor in urban tree establishment even when other conditions are adequate.

Question 3

When selecting street trees for a roadway that receives winter deicing salt applications, which characteristic is most critical to evaluate in candidate species?

Accepted Answer

Tolerance to soil sodium and chloride ion accumulation

Answer

Deicing salts elevate soil sodium and chloride levels, causing osmotic stress and ion toxicity in root tissue. Species selection must prioritize documented tolerance to soil salt accumulation, since absorbed chloride ions are transported to foliage causing marginal scorch and dieback regardless of root depth or transpiration rate.

Question 4

A minimum rooting soil volume is often cited as essential for urban tree longevity. What is the generally accepted minimum soil volume required to sustain a mature canopy street tree?

Accepted Answer

5–10 cubic meters (approximately 175–350 cubic feet)

Answer

Research, including work from the Urban Tree Foundation and international studies, consistently identifies roughly 30 cubic meters (about 1,000 cubic feet) as an ideal target, with 5–10 cubic meters representing a practical minimum below which trees rarely achieve healthy mature size or longevity exceeding 10–15 years in constrained urban pits.

Question 5

What is a 'urban forest master plan' and what distinguishes it from a standard municipal tree inventory?

Accepted Answer

A master plan is a strategic, long-term document setting canopy goals, policies, and management priorities; an inventory is a data-collection record of existing trees and their condition

Answer

A tree inventory is a systematic database of individual trees—species, DBH, condition, location—while an urban forest master plan is a policy and strategic framework that uses inventory data to establish canopy cover targets, prioritize planting and removal, allocate budgets, guide species diversity, and align urban forestry with climate resilience and equity goals.

Certified Arborist Test Practice Test

Certified Arborist Test Practice Test

Certified Arborist Test Urban Forestry and Tree Selection 1