A data-driven evaluation of lichen climate change indicators in Central Europe

Matthew P. Nelson and H. Thorsten Lumbsch

Summarized by Anna Geldert

What data were used? For this study, researchers obtained collection data on 35 of the 45 lichen species designated as climate change indicators from the Global Biodiversity and Information Facility (GBIF). Data for this study focused on patterns found in Central Europe, and most specifically, Germany.

Methods: GBIF data on the lichen species were categorized into two age groups: before 1970, and 1970 to present. 1970 marked the year where reductions in the use of sulfur dioxide pollutants was implemented in Europe. Because pollution levels also play a role in the survival of lichen populations, it was important to create this distinction to separate this variable from other population changes due to climate change. Lichen species with fewer than 10 historical records were deemed unreliable and excluded from further analysis, leaving only 17 out of the 35 species. To determine the lichen’s preferred habitat, researchers combined historical distribution records of where the different species of lichen were found over time with a map of climate variables (temperature, humidity, soil composition, etc.). Using a computer model, they were able to predict the lichens’ preferred habitats with 95% accuracy, and generate a map to represent these predictions spatially. The map was compared to modern data to evaluate potential changes due to climate change.

Results: The results of this study revealed that approximately half of the 17 primary species studied were found in significant numbers outside their historical range, while the other half still resides primarily in the same regions as they did prior to 1970. Species other than the primary 17 did not have sufficient historical data to recognize specific trends in geographic distribution. However, researchers noted that only one third of these additional species saw an increase in abundance in recent years, while the other two thirds saw equal or reduced numbers compared to the limited historical records.

The map shows the distribution of Opergrapha vermicellifera over time. The map spans 10° of latitude, from 45° North to 55° North, and 20° of longitude, from 5° East to 25° East. The map is divided into suitable and unsuitable habitat for Opegrapha vermicellifera, which are shaded in dark green and light green respectively. The suitable habitat makes up only about 10% of the image, and is composed of a narrow, uneven band running from 46° North, 5° East to 55° North, 14° East. Approximately 11 historical (before 1970s) records of lichen distribution are marked by yellow triangles on the map, and all are contained within or along the border of the area denoted as “suitable” habitat. Approximately 30 modern (1970 to present) records of lichen distribution are shown, and are marked with purple circles. While some modern lichen records lie within the “suitable” habitat, approximately two thirds lie in the “unsuitable” area; the majority of these points lie 5° to 10° East and a few degrees South of the “suitable” range.
Fig 1. Distribution of Opegrapha vermicellifera is shown as an example of one of the maps created to analyze changes in lichen distribution over time. The map compares historical records from prior to 1970 (orange triangles) and modern records from after 1970 (purple circles). Habitat deemed suitable/unsuitable was determined using a computer model of climate variables based on pre-1970 habitat. For Opegrapha vermicellifera, over 30% of modern records lie outside historically suitable habitat.

Why is this study important? This study calls into question the usefulness of lichen as climate change indicator species. For one, the study found that there is very little data, especially historical data, on these species and the habitat they lived in originally. Therefore, it is somewhat difficult to draw conclusions regarding the degree of the lichen’s response to climate change. The study also found that, even among species with sufficient data, only about half were found outside their historical range. If climate change was truly impacting lichen populations as much as was originally thought, researchers would expect to find all populations outside of this range because they would have migrated to better suit their traditional habitat. These results pose the question as to whether other factors may be impacting the distribution of lichen even more so than climate change. For example, the rise and fall of sulfur dioxide pollutants before and after 1970 may be more significant.

The big picture: This study serves as a warning for climate change scientists, who may tend to jump to conclusions regarding migration, geographic distribution, and local extinction of many species of lichen in recent years. For many species of lichen, there is not enough data to determine whether the geographic distribution of lichen has changed, as well as whether these changes were due to climate change instead of other factors. More research and collection of historical data is needed in order to confirm the usefulness of these species as climate change indicators in future studies.

Citation: Nelsen, M. P., & Lumbsch, H. T. (2020). A data-driven evaluation of lichen climate change indicators in Central Europe. Biodiversity and Conservation, 29(14), 3959–3971. https://doi.org/10.1007/s10531-020-02057-8

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