ISA Certified Arborist Practice Exam

A tree species is considered "disease-resistant" primarily due to its ability to withstand specific pathogens without experiencing significant health decline. This resistance often results from the tree's genetic makeup, which may include certain biochemical pathways or physical defenses that enable it to fend off infections or mitigate the effects of pathogens. These trees can maintain their health and vitality even when exposed to diseases that affect other species, demonstrating resilience in their overall growth and functionality.

The other options relate to different aspects of a tree's characteristics but do not specifically address disease resistance. Thriving in poor soil conditions pertains to environmental adaptability rather than disease-related factors. A tree that grows faster could simply be a growth characteristic without any relation to its ability to resist diseases. The presence of thicker bark may offer protection from physical injuries or pests, but it does not directly equate to resistance against biochemical pathogens or infections that cause disease. Therefore, only the ability to withstand specific pathogens truly defines what makes a tree species disease-resistant.