ISA Certified Arborist Practice Exam

What might happen to trees if they undergo excessive stress?

1. They may grow faster

2. They may become more resilient to diseases

3. They may be more susceptible to pests and diseases

4. They may produce more leaves

The correct answer is: They may be more susceptible to pests and diseases

When trees experience excessive stress, such as from environmental factors like drought, pollution, pest infestations, or physical damage, their physiological functions can be significantly impaired. Under such stress, a tree may divert resources away from growth and reproductive activities, prioritizing survival instead. This can lead to weakened defense mechanisms, making the tree more vulnerable to pests and diseases. Stress alters the tree's ability to allocate nutrients effectively. For example, when a tree is stressed, it might produce fewer defensive compounds, which are essential in combating attacks by pests or pathogens. Additionally, the tree can become less able to recover from minor injuries or infections, leaving it open to further complications. The other options—such as increased growth rate, enhanced resilience to diseases, or increased leaf production—are often misconceptions. While trees can sometimes exhibit adaptive traits under specific stress conditions, excessive and prolonged stress typically leads to vulnerability rather than strength. Therefore, the correct understanding is that excessive stress tends to increase the susceptibility of trees to pests and diseases, highlighting the importance of maintaining optimal health and conditions for tree growth.