The variability of heavy metal concentrations (Pb, Cd, Zn, and Cu) of the terrestrial moss Orthotrichum lyellii on single trees was evaluated at two sites in the Pacific Northwest, one relatively unpolluted and the other polluted. In addition, a reciprocal transplant of O. lyellii between the unpolluted and polluted sites was used to evaluate the response of moss tissue metal concentrations to translocation to sites with higher or lower atmospheric deposition of
metals.Transplanted moss samples were collected at 1, 3, 6, 9, and 12 months. The position of moss sampling (interior, middle, exterior) and transplant hanging (interior and exterior) were documented in order to determine the spatial variability of heavy metals within a tree. The starting concentrations of all metals were higher at the SRDP site. In general, heavy metal concentrations in moss transplanted from the unpolluted site to the polluted site increased and reached in situ levels after 3-6 months. In some cases, moss transplant heavy metal levels surpassed in situ moss levels. In contrast, moss concentrations of heavy metals in transplants from the polluted site to the unpolluted site did not decrease substantially in metal levels. Therefore, will mosses can rapidly acquire metals when moved to more polluted sites, they tend to tenaciously hold metals when moved to less polluted sites. Furthermore, this study demonstrates the need for positional consistency and large sample size when collecting moss samples as well as when hanging transplants. We conclude that transplanted moss needs to be in place for at least 6-12 months to accurately represent metal atmospheric deposition at the transplanted site. In addition, metal levels of transplants to less polluted locations are unlikely to be representative of the transplanted site, even after 12 months.