Lichen Communities Serve as Canary in the Coal Mine for Air Pollution
The heavily urbanized Los Angeles Basin in southern California has experienced poor air quality since the early 1940s and forest structure in the region has been shaped by severe smog incidents and chronic nitrogen deposition. Lichens are highly responsive to nitrogen, and monitoring species changes is an inexpensive method for evaluating local air-quality effects on forests.
In 2008, Forest Service scientists looked at species composition of lichen communities growing on trees in the Cleveland National Forest, San Bernardino National Forest, and Angeles National Forest to assess the current state of air quality. These sites were previously inventoried in 1976 and 1977. At that time, researchers concluded that more than 50 percent of lichen species were locally extinct since the lichen flora was first documented in the early 1900s.
Researchers found in this recent study that lichen communities in all three forests showed symptoms of worsening of air quality. No sensitive lichen species had recolonized trees since the 1976 and 1977 inventory, and the abundance of nitrogen-loving species associated with polluted areas had increased, in some cases dramatically.
Declines were most severe for the Palomar region of the Cleveland National Forest, which was formerly determined to be relatively clean in 1976 and 1977, based on its lichen communities. This information can be used to help guide future air-quality monitoring activities planned for southern California.