How to quantify differences in epicuticular wax morphology of Picea abies (L.) Karst. needles

SUMMARY Because researchers seldom possess unlimited resources, planning is needed to maximize the ratio of information gained to work needed. The aim of the present study was to find reasonable sampling and observation schemes for documenting regional differences in the impact of air pollution on the morphology of epicuticular needle wax. One‐year‐old Picea abies (L.) Karst. needles were collected in Southern Finland at two sites with different air pollution levels. In both sites, samples were taken from four trees, and within each tree, from three heights and four compass directions. The epicuticular wax of the needles was investigated under a scanning electron microscope (SEM) by estimating the relative abundances of eight wax types representing both tubular and degraded forms. Two ways are proposed to convert these data to index values, and the usefulness of this approach is evaluated. The differences between the two sites were significant, the needles from the urban site showing, on average, less‐preserved wax types than those from the rural site. Variation among individual trees within each site was pronounced, which proved the necessity of sampling several trees. There was also marked variation among the needles taken from the same tree, but this showed no consistent pattern with respect to sampling height or compass direction. Analysis of the variance at different hierarchical levels (among trees, among needles and within needles) suggested that the sampling effort is better invested when it is spread among several tree individuals than when it is concentrated on the detailed study of fewer trees.