Final answer:
The trophic facilitation phenomenon involves direct interactions between two plant species that benefit a third species indirectly.
Step-by-step explanation:
The trophic facilitation phenomenon described by Hacker and colleagues involves direct interactions between two plant species in the form of facilitation with indirect effects benefiting a third species of one of those plants. This phenomenon refers to a scenario where one plant provides resources or services that enhance the growth, survival, or reproduction of another plant, which in turn benefits a third species. For example, some plants release chemicals into the soil that promote the growth of neighboring plants, creating a positive indirect effect on other organisms.