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.
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