Bryophyte and macrolichen diversity show contrasting elevation relationships and are negatively affected by disturbances in laurel forests of Madeira island

Prepared by Steffen Boch, Anabela Martins, Sara Ruas, Susana Fontinha, Palmira Carvalho, Fábio Reis, Ariel Bergamini & Manuela Sim-Sim

Madeira Island belongs to the Madeira Archipelago (Portugal) and is located 600 km northwest of the Western African coast in the Atlantic Ocean. The island is famous for its unique laurel forest on the north coast that occupy altitudes of 300–1450 m a.s.l., where humidity is continuously high. Because of its exceptional biodiversity, including many endemic species, this habitat is a priority for nature conservation and has been designated as a UNESCO World Natural Heritage site.

Bryophytes (i.e., mosses, liverworts, hornworts) and lichens are important components of the Madeiran laurel forest biodiversity. 39% of all endemic bryophyte species of Macaronesia (i.e., Madeira, Canary, Azore and Cape Verde islands) are growing in the laurel forest of Madeira. Many bryophytes and lichens have narrow ecological niches with specific substrate or habitat requirements. Given their sensitivity to environmental change, they are ideal biological indicators and study objects for land-use and climate-change research. On Madeira Island, many bryophyte and lichen species are adapted to the continuously humid conditions of the laurel forest. However, although these species are sensitive indicators and contribute greatly to Macaronesian biodiversity, we know very little about their diversity patterns in Madeiras’ forests.

Madeiras’ climate projections indicate an average temperature increase of up to 3°C and a precipitation decrease of about 30% until 2100. This will likely trigger a shift in forest distribution to higher elevations and pose a threat to bryophyte and lichen diversity. Today’s warm low-elevation sites can help us to project how climatic conditions at currently colder high-elevation sites will potentially be in future. If species manage to move upward with warming, a study of species composition of current low-elevation sites might allow us to predict the potential future species composition of higher elevated sites. Hence, a study of biodiversity patterns along elevational gradients can help us to understand climate-warming effects.

In this study, we investigated macrolichen (i.e., excluding crust-forming lichens) and bryophyte species richness in disturbed stands and undisturbed stands along elevational gradients on Madeira island. Disturbed stands encompassed, for instance, former anthropogenic disturbances such as burning, logging, and agricultural areas.

Our findings confirm the value of the laurel forest of Madeira island as a bryophyte and lichen diversity hotspot. One of our novel finds was that disturbance reduced bryophyte and macrolichen species richness by an average of about 20%. This result supports calls for a strict protection status of the laurel forest and for reducing anthropogenic disturbances to a minimum, e.g., by efficient and fast suppression of forest fires.

While species richness of bryophytes, in particular of endemic bryophytes, peaked around 950 m altitude, macrolichen richness increased with elevation from the laurel to the more open tree-heath forests, which replace laurel forests at higher elevation. Given projections of a dryer and warmer climate on Madeira Island, our findings imply that bryophyte and lichen diversity will be imperiled. In particularly desiccation-sensitive species, including many endemic taxa, will be endangered because they rely on constantly humid conditions in their current habitats, the closed laurel forest at intermediate elevations or the light and very moist conditions in the more open tree-heath forests at high elevations.

The Region of Madeira has a high responsibility to protect the unique laurel forest and its biodiversity. To prevent future species extinctions, it is crucial to curb anthropogenic disturbance and promote natural forest regeneration on disturbed sites. As forest-fire frequencies might increase under the predicted climate-change scenarios, efficient and fast suppression of forest fires will be one of the most important measures.

This is a plain language summary for the paper of Boch et al. published in the Journal of Vegetation Science (https://doi.org/10.1111/jvs.12802).