ISA Certified Arborist Practice Exam

A tree species is defined as "disease-resistant" primarily by its ability to withstand specific pathogens without significant health decline. This characteristic indicates that the tree has developed or possesses inherent mechanisms—such as physical barriers, biochemical responses, or an effective immune response—that allow it to fight off diseases more effectively than other species. Disease resistance can be the result of genetic traits that have evolved over time, enabling the species to survive in environments where certain pathogens are present.

The other options, while they describe important attributes of trees, do not directly relate to disease resistance. For example, the ability to grow in diverse environments pertains to adaptability rather than immunity to disease. Unique leaf formations can be a result of genetic variation but do not indicate resistance to pathogens. The capacity to produce more seeds speaks to reproductive success and does not correlate with how well a species can fend off diseases. Thus, the focus on the tree's ability to resist specific pathogens is what fundamentally defines disease resistance in tree species.