The live oak forests of Savannah, Ga., are famous for their ghostly, gray-green curtains of Spanish moss. The moss belongs to a group of plants called epiphytes, which live in the branches and trunks of trees and get everything they need to survive from the Sun and the air. A new study reveals that epiphyte-draped forests play an underappreciated role in the local ecosystem by leaching dissolved organic matter (DOM), which mostly contains carbon, into the soil, streams, and rivers during rainstorms.
Forests contribute a great deal of organic matter to the soil and water, in part through the decay of leaf litter and dead trees. But scientists are not always able to parse the contributions of different tree species or of the organisms living on the trees. In the new study, Van Stan et al. set out to measure how much DOM—particularly, dissolved organic carbon—rainwater picks up as it hits the tree canopy and filters through moss, lichen, and other epiphytes.
Over the course of 25 storms between June 2015 and September 2016, the team collected buckets of rainwater. Some buckets were out in the open, others were under the tree canopy, and still others were at the base of tree trunks. The team compared water collected from oaks and cedars with water collected from mossy trees and “bare” trees without epiphytes. Once back in the lab, the team measured the dissolved organic carbon and other matter in each sample.
Water collected beneath all the trees contained quadruple the amount of organic matter in rainwater collected in the open. Furthermore, the team found that DOM in water from trees with epiphytes on them exceeded that in water from bare trees. Mossy live oaks produced water with the most DOM of all. The findings suggest that the trees and the epiphytes within them create biogeochemical hot spots that could have important impacts on local ecology, the team writes. (Journal of Geophysical Research: Biogeosciences, https://doi.org/10.1002/2017JG004111, 2017)
—Emily Underwood, Freelance Writer