The cover image for our March issue shows Letharia vulpina, a lichen typical of high‐altitude forests in the Alps. Author and photographer, Juri Nascimbene, and lead author, Hugo Saiz, share the story behind this image and their related research article “Networks of epiphytic lichens and host trees along elevation gradients: Climate change implications in mountain ranges” by Saiz, Dainese, Chiarucci & Nascimbene.
Lichens are among the most sensitive organisms to climate, particularly to ambient temperature and moisture. Our cover image represents this as it shows a thin film of water on the thallus of Letharia vulpina (Th. Fr.) Zahlbr., a lichen typical of high-altitude forests in the Alps. Without this water layer, this lichen would find it hard to survive. Thus, it is not difficult to imagine that lichens are among the species that are most threatened by climate change.
In our article, we carried out a natural climate change experiment in the spruce forests of the Sothern Alps. We surveyed epiphytic communities along a 1000m elevation gradient, and evaluated how the organisation of lichen species on their host trees depended on environmental and biological attributes. The fieldwork was carried out during Summer 2012 and 2013 and we were lucky to be helped by several young collaborators to achieve the difficult task of sampling lichen communities, even in very inaccessible areas of spruce forest in the province of Bolzano. The campaign included a lot of walking on steep slopes, without any trails, chasing the point of our GPS and then a team effort to collect all the necessary data. However it wasn’t just getting to the sampling sites that was challenging. A good lens around the neck was mandatory and it took lots of patience examining the presence of less evident species on the bark of trees. Our hard work continued in the lab (with around 800 specimens examined!), but it allowed us to discover several species still not recorded for this region or even for the lichen biota of Italy. It was very satisfactory being able to give a name to some really enigmatic crusts!
(Top Left) Hypogymnia physodes – probably the most common foliose lichen in spruce forests. It is mainly dispersed by vegetative propagules. (Bottom Left) Calicioid lichens, also known as pin lichens, are ecologically specialised to establish their populations at the driest, underhanging, parts of the trunks that do not receive rain or stemflow. (Right) Fruticose lichens, especially those with a filamentose thallus (also known as hair lichens) are mainly found in well-lit conditions, exposed to both rain and wind. For this reason, they are mainly bound to the higher parts of the trunks or to tree branches. This Evernia divaricata, was photographed on a spruce branch in the Dolomites. Hair lichens of high elevation forests are extremely sensitive to climate and nitrogen deposition and may be useful indicators for mapping the impact of global change. Photographs: Juri Nascimbene.
This work allowed us to unravel some novel findings about epiphytic lichen communities. On one hand, we found that epiphytic lichen communities are dominated by local segregation, probably due to different micro-habitat preferences between lichen species. Importantly, a decrease in precipitation exacerbated this segregation, as only few stress-tolerant and micro-habitat specialist lichens are able to persist. On the other hand, lichen biological traits played a major role in lichen organisation. For example, foliose, asexually reproducing lichens behave as habitat generalists and interact with multiple micro-habitat specialist species (i.e. network hubs). These lichens are able to rapidly form a dense lichen cover on trunks that may improve the water retention capacity of the substrate, providing more suitable micro-habitat conditions for species with low water holding capacity. In contrast, crustose, sexually reproducing species, as well as fruticose lichens, behave as habitat specialists and interact only with those species that occur in the same micro-habitats.
Looking back, we feel that we have learned many things from this study. Not only that epiphytic lichens gather a lot of information about how ecological communities respond to climate change, but also that hard work will always be rewarding. After all, not everyone can finish their working day by enjoying the sunset on Italian Alps!
Juri Nascimbene University of Bologna, Italy
Hugo Saiz University Rey Juan Carlos, Spain & University of Bern, Switzerland
You can read the full article by Saiz et al. here: Networks of epiphytic lichens and host trees along elevation gradients: Climate change implications in mountain ranges