ISA Tree Biology & Physiology 3

Question 1

What is reaction wood and what are the two types found in trees?

Accepted Answer

Abnormal wood that forms in response to mechanical stress; tension wood in hardwoods (on upper side of leaning stems) and compression wood in conifers (on lower side)

Answer

Wood that forms in response to insect attack; sapwood and heartwood

Answer

Wood produced after pruning wounds; callus wood and barrier wood

Answer

Decorative wood grain patterns; curly wood and bird's eye

Question 2

How do trees allocate carbon resources under stress, and what does this mean for management decisions?

Accepted Answer

Trees prioritize maintenance respiration and defense over growth, meaning stressed trees have reduced capacity to compartmentalize wounds and respond to additional stressors like pruning

Answer

Stressed trees increase carbon allocation to growth to outgrow the stressor

Answer

Carbon allocation does not change during stress

Answer

Stressed trees store all carbon in roots and shut down all above-ground processes

Question 3

What is apical dominance and how does removal of the apical meristem affect tree form?

Accepted Answer

Apical dominance is hormonal suppression of lateral bud growth by auxin from the terminal bud; removing it releases lateral buds, causing bushier growth or multiple leaders

Answer

Apical dominance means the lowest branches always grow fastest; removing the apex has no effect

Answer

Apical dominance only applies to herbaceous plants, not trees

Answer

Removing the apical meristem always kills the tree

Question 4

What is the role of the Casparian strip in root water uptake?

Accepted Answer

It is a waxy barrier in the endodermis that forces water and dissolved minerals to pass through living cells, allowing the root to selectively control which ions enter the xylem

Answer

It is the outer bark of the root that prevents water loss

Answer

It is a growth zone that produces new root tips

Answer

It is a fungal structure in mycorrhizal roots

Question 5

How does phloem loading work and why is it important for understanding tree carbohydrate distribution?

Accepted Answer

Phloem loading is the active transport of sugars into sieve tube elements at source tissues, creating an osmotic gradient that drives the pressure flow of photoassimilates to sink tissues throughout the tree

Answer

Phloem loading is the passive flow of water into phloem from the xylem

Answer

Phloem loading refers to the physical weight of the inner bark on branch structure

Answer

It is the process of bark growth adding new layers each year

Question 6

What is phenotypic plasticity in trees and why is it important for arborists to understand?

Accepted Answer

It is the ability of a single genotype to produce different physical forms in response to different environmental conditions, explaining why the same species looks different in different settings

Answer

It refers to the flexibility of young branches before they lignify

Answer

It means all trees of the same species look identical regardless of growing conditions

Answer

It is a genetic mutation that causes unusual growth patterns