0007-2745/00/449–454$0.75/0 The Bryologist 103(3), pp. 449–454 Copyright q 2000 by the American Bryological and Lichenological Society, Inc. Tethered Transplants for Estimating Biomass Growth Rates of the Arctic Lichen Masonhalea richardsonii JERILYNN E. PECK Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331-2902 U.S.A. e-mail: jeri@strengthinperspective.com Current address: Offenburger Strasse 83, D-79108 Freiburg i. Br., Germany JESSE FORD 1 Department of Fisheries and Wildlife, Oregon State University, Corvallis, OR 97331, U.S.A. e-mail: fordj@ucs.orst.edu BRUCE MCCUNE, AND BILL DALY Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331-2902, U.S.A. e-mail: mccuneb@bcc.orst.edu Abstract. Air quality studies often take advantage of the ability of lichens and mosses to accumulate certain contaminants in their tissues. In order to evaluate the rate of contaminant accumulation from concentrations in tissues, the age of the tissue must be known. Our objective was to develop and test a method for estimating annual growth rates and thallus ages for Ma- sonhalea richardsonii, a vagrant clonal lichen abundant throughout its Beringean range. The annual growth rate of healthy individuals from Arctic Alaska, based on the 75th percentile of a cumulative frequency distribution, was 11.6% (90% confidence interval: 11.2–13.3%). This growth rate suggests that the biomass of a healthy M. richardsonii individual doubles within a period of approximately 6.3 years (90% confidence interval: 5.6–6.5 years). Average ages for the thalli in this study were estimated at 5 to 41 years using a negative compound interest formula and assuming initial masses of thallus fragments. Calculations and their appropriate application are shown and the methodology is discussed. Lichens absorb and sequester several airborne contaminants. Gathering regional data on the dis- tribution and impacts of arctic air pollution through lichen and moss tissue analysis was one goal of the U.S. Environmental Protection Agency’s Arctic Contaminant Research Program (ACRP; Ford & Landers 1991; Ford et al. 1995; Landers et al. 1992). Under this program, contaminant concentra- tions were determined by tissue analysis of mosses and lichens, including the vagrant lichen Mason- halea richardsonii (Hook.) Ka ¨rnef. These data pro- vide a spatial understanding of the status and extent of contaminants present in arctic Alaskan ecosys- tems. Ideally, species used for monitoring contaminant deposition should be well-characterized with re- spect to contaminant uptake and retention. In prac- tice this is seldom the case. The primary species used in the ACRP was the moss Hylocomium splen- dens (Ford et al. 1995), precisely because the pro- cesses of contaminant uptake and retention are well understood (Ru ¨hling & Tyler 1970). A major strength of using H. splendens is that this species adds recognizable increments of growth each grow- 1 Corresponding author. ing season. Thus, it is possible to define precisely the period of exposure. The Nordic and European monitoring protocols call for revisiting the spatially dispersed network every five years, and for analyz- ing only the past three years growth in each sam- pling campaign (Ru ¨hling & Steinnes 1998). For a practical goal, if the period of exposure cannot be precisely defined for a potentially useful monitoring species on morphological grounds, it would be useful to estimate bounds for the likely exposure period based on an understanding of bio- mass growth rates. Knowledge of factors affecting net retention of target contaminants is also desir- able. This paper contributes toward the first of these goals. Discussions with workers in tundra ecosystems revealed large discrepancies in the presumed age of Masonhalea thalli. Therefore, we sought to make the tissue analysis more informative by determining the biomass growth rates of Masonhalea. Further- more, growth rates combined with standing crop measurements can be used to estimate lichen pro- ductivity, which is of particular interest in lichen- dominated communities in the arctic. In a few species, growth can be measured on the basis of annual markers (Lechowicz 1983; Stone &