A species patchiness is explained by many biotic and abiotic interactions. These researchers studied the transitional zone where two ecosystems meet, also known as an ecotone. This willow-meadow ecotone in the central Rocky Mountains (Park County, CO, USA) is where the distinct willow (Salix sp.) tree line ends, and the patchy growth of understory plants and smaller, Salix individuals coincide. This area is a perfect place to utilize multiple competing hypotheses to better understand how aboveground and belowground interactions drive species distributions.

The first thing we need to nail down are the different mutualists associated with these alpine plants. Salix species live symbiotically with ectomycorrhizal fungi (ECM), while the meadow species form mutualisms with arbuscular mycorrhizae (AMF). The first hypothesis was synthesized along with the notion that the taller more robust Salix trees may limit sunlight reaching the understory plants, which reduces their photosynthetic output, ultimately limiting the amount of sugar reaching their nutrient sequestering AMF. With less sugar resources to offer, these plants fungi should return less nutrients to their hosts, and AMF colonization should decrease.