Measurement of Lichen Growth

Abstract

Growth of an organism can be defined as the increase in its living biomass. In lichens, biomass increase is presumed to be manifest in an increase in linear dimension, area or weight, which are convenient to measure (Table 1). However they do have different interpretations. For a lichen, an increase in lobe length, or thallus diameter, may not exactly reflect increase in area or mass; conversely, biomass increase may, for example, occur without an increase in the apparent linear size of a lichen thallus (e.g. a thallus confined in a mosaic may grow only in thickness). The rate of growth, which is expressed as increase per unit time, may give very different rates over different time spans, if it varies with different sized thalli, and, especially, with differing environments. The time span can be predetermined and the size of thallus can be allowed for in the analysis of the data. The growth form of the thallus is also important in deciding what parameter to measure. The type of data analysis planned and the aim of the study may also determine the type of measurement chosen. It should be decided whether the actual direct measurement itself is required or a derived measure, such as a proportional increase or the value of a growth rate coefficient.