ISA Certified Arborist Practice Exam

Which term describes the orientation of tree growth in external cells?

1. Internal Growth

2. Concurrent Growth

3. Excurrent Growth

4. Decurrent Growth

The correct answer is: Excurrent Growth

Excurrent growth describes the orientation of tree growth where the main trunk of the tree continuously extends upwards and outward, producing a cone or pyramid shape. This term is specifically used for trees with primary growth, meaning they grow from the tips of their shoots and branches. In contrast, decurrent growth is when the growth is oriented downwards, such as in a weeping willow tree. Internal growth refers to the growth within the tree, such as the expansion and thickening of the trunk and branches. Concurrent growth is a term that is commonly used to describe plants with indeterminate growth, where new growth occurs at the same time as older growth. While internal, decurrent, and concurrent growth may have some relevance to the growth of a tree, they do not accurately describe the orientation of tree growth in external cells, making them incorrect choices.