Evaluation of the Index of Atmospheric Purity in an American tropical valley through the sampling of corticulous lichens in different phorophyte species

[Display omitted] •IAP Index is applicable for sampling of lichens in different phorophyte species.•Zonal classification by using lichens is similar with one or more phorophyte species.•Air pollution and thallus heterogeneity of lichens are correlated with each other.•Coverage of corticulous lichens vary in response to air pollution levels.•Richness of corticulous lichens are correlated with air pollution levels. Lichens have been widely used worldwide as bioindicators of air quality and also integrated into national programs and protocols in several countries. The Index of Atmospheric Purity (IAP) has been a commonly used tool for the diagnosis of air quality using corticulous lichens. However, its implementation is recommended when phorophytes with similar characteristics of the bark are used. Therefore, many studies are restricted to the use of a single supporting phorophyte. This criterion makes it difficult to implement this index in areas with limited number of individuals and species of phorophytes. This research evaluates the functionality of this index without differentiating among carrier phorophytes for the classification of areas with differences in air quality. For this, the lichens were mapped and collected, along with bark samples to determine the pH bark of phorophytes close to air quality monitoring stations located in Medellín City. A total of 148 lichen species were identified, belonging to 26 families and 52 genera. In addition, indicators such as thallus heterogeneity, richness (with correlations coefficients r = 0.52 with no phorophyte differentiation and for the tree species F. uhdei and T. rosea, r = 0.578 and r = 0.777; respectively) and total coverage of corticulous lichens (r = 0.76) vary in response to air pollution levels, no matter if their evaluation is carried out on a single phorophyte or in a diversity of phorophytes. This research also revealed that the evaluation of IAP in the biomonitoring zones is functional, resulting in positive correlations between the IAP and the air quality classification when this index is evaluated without differentiation of phorophytes (r = 0.78) and for T. rosea (r = 0.94) and F. uhdei (r = 0.99). In this sense, the uniformity criterion in the selection of the phorophyte use for the application of this index can be complemented taking into account the possibility of using a heterogeneous sample of phorophytes.