It basically comes down to the rules in terms of what's defined as farming income for income tax purposes. Nurseries providing seedlings for reforestation--woodlots, that type of thing--are not eligible. It all involves the care and nurturing of the seedling. As an example, Christmas trees, ornamentals, and fruit trees are eligible for CAIS.
So it's basically a distinction in terms of what's defined as farming income for tax purposes.