Distribution of thalli in a population of the epiphytic lichen Lobaria oregana and a model of population dynamics and production

Data on weight-class distribution, growth rate and asexual propagule(lobule) release are used to analyze populations of the nitrogen fixing lichen Lobariaoregana in old-growth Douglas fir canopies of western Oregon. A life-table modelprepared from observed data is used to produce an estimate of net annual productionof biomass, and to analyze the response of a population of this lichen to possibleenvironmental perturbations. The weight-class distribution is similar in each of fourtrees studied and at different levels within the trees, but differed among the differentcomponents of the trees. Survivorship curves (log survivorship versus estimated thal-lus age) are similar for populations in all trees studied. Estimated net annual pro-duction is 31.1% of the standing crop of Lobaria oregana biomass. Mathematicalmanipulation of matrix formulations of the life-table model indicates that popula-tions would be stable if they recruited 10% of the lobules released each year. In sucha configuration, the model population returns to its original size and distributionwithin 30 years following a simulated storm that removes 90% of the largest thalliand momentarily increases lobule production.