Shrub encroachment in lichen heath - a general summary

Submitted by editor on 12 April 2022.

In our March issue, Stefanie Reinhardt and her co-authors published their study entitled "Shrub encroachment interacts with environmental variation to reduce the albedo of alpine lichen heaths: an experimental study". Click on the title to view the full Open Access paper for free! Or continue reading below for a general summary of their findings!

Due to climate change, the vegetation composition in alpine and Arctic areas is changing. Large areas of lichen heaths are overgrown and outcompeted by shrubs. The replacement of these light-coloured lichen heaths by dark green shrubs will have consequences for the reflection of the sunlight. When the light-coloured lichens are replaced by darker coloured shrubs, less sunlight gets reflected and this could enhance warming.
With this study, we wanted to measure the difference in the reflection of sunlight between three lichen species and one shrub species. Moreover, we want to investigate how environmental variables, for example clouds, the zenith angle of the sun, and the aspect (e.g. north- or south-facing) of a lichen surface affects the reflection. To achieve this, we collected lichen and shrub specimens in the mountains of southern Norway, and set up an experimental study design.
We found that two light-coloured lichen species reflect 35% of the sunlight, while a dark-coloured lichen species and the shrub species reflect only 15% of sunlight. Next to that, we showed that the albedo of a lichen heath decreases when it is getting overgrown with an increasing amount of shrubs. We also found that the reflection of sunlight by lichens was relatively low when the sun was high on the sky or during cloudy conditions. Next to that, we showed that measurements on a north-facing lichen area led to a lower albedo than measurements on a south-facing lichen area. Our results demonstrate among others the decrease of sunlight reflection when large amounts of lichen heath are overgrown and replaced by shrubs. This decrease in the reflection of sunlight has the potential to further increase the warming of alpine and Arctic areas.
Photo by Ann Cecilie Henriksen