When we think of soil we all picture what is beneath our feet, but researcher Camila Tejo Haristoy is studying soil that forms in forest canopies, referred to as canopy or arboreal soil. Canopy soil develops when epiphytic plants(a plant that grows above the ground, supported non-parasitically by another plant or object, and deriving its nutrients and water from rain,the air, dust, etc.; air plant; aerophyte) begin to decompose. The formation of these soils, as with ground soils, is also aided by bacteria and microorganisms. Epiphytes, such as bromeliads, ferns and moss, and the trees themselves are able to derive nutritional benefit from arboreal soils.
Epiphytic plants grow on trees in a symbiotic relationship that can be beneficial to both plants. Trees sometimes develop “canopy roots” to uptake nutrients from soil produced by decomposition of epiphytes.
Recently published with the Soil Science Society of America, Haristoy’s research, entitled “North American Forest Soils Conference Proceedings”, focuses on canopy soils in the Queets River watershed in Olympic National Park in Washington. The research team is primarily characterizing arboreal soils forming on bigleaf maple (Acer macrophyllum) and Sitka spruce (Picea sitchensis) trees. Describing these soils will aid in fully identifying their impact and contributions to the ecosystem.
The results from Haristoy’s study revealed that soils formed on bigleaf maples was thicker than the soil layer found on Sitka spruces. The team believes this is due to the nutrient rich leaf litter built by the maples leaves dropped; this creates an optimal environment for epiphytes to grow and cycle nutrients into soil. The maples in this area are generally shorter than their surrounding community, leaf drop from nearby trees contributes to the leaf litter layer. Sitka spruces are taller, and their stands are less dense, only their own leaf drop comprises the canopy leaf litter. Additionally age is a factor in the canopy soil thickness and density, older trees had more arboreal soil because there was more time for decomposition and accumulation. Interestingly the Sitka spruces studied were an average of 300 years old, while maples were younger at approximately 200 to 250 years old.
Canopy soil in a bigleaf maple, 60 feet above the ground is colonized by licorice fern, moss and leaf litter.
Soil types found in the canopy of both trees were “Histosol”, however there were obvious differences due to the amount of time allowed for decomposition. Soil in the canopy of bigleaf maples was more fibrous and less homogenous than that found in the Sitka spruces. Canopy soil composition and contribution requires further investigation, but this research certainly provides useful data it also raises many more question.
