The research article states that "these results suggest that modifications of forest canopy structures are capable of affecting ... soil microbial community structure via throughfall when canopies’ biomass distribution is highly heterogeneous."
Thinking about NZ forests, it certainly isn't hard to believe that the soils in A, B & C (below) would be different. Simplified, epiphytes intercept water and nutrients from the canopy and atmosphere, transform them and deliver them in different quantities and forms to the forest floor. And this all varies depending on the flora and fauna within the epiphyte community... gets ya thinking!