Staying alive on an active volcano: 80 years population dynamics of Cytisus aeolicus (Fabaceae) from Stromboli (Aeolian Islands, Italy)

Abstract

Cytisus aeolicus is a narrow endemic species restricted to the Aeolian archipelago (SE Tyrrhenian Sea, Italy) and it is one of the most evolutionarily isolated plants in the Mediterranean flora. Historical and literature data suggest that both metapopulations and isolated individuals of C. aeolicus are gradually shrinking. Field investigations and drone images demonstrate that the C. aeolicus metapopulation from Stromboli experienced a strikingly fast increase during the last decades. As of 2019, more than 7000 ± 3000 mature individuals occur on Stromboli, i.e. 14 to 20 times more than those counted during the last census, 25 years ago. The diachronic analysis of aerial photos concerning last 80 years and the analysis of the growth rings of some selected plants pointed out that the surface occupied, the demographic structure and the distribution pattern of the subpopulations of Stromboli has been highly fluctuating during last decades. Moreover, data issuing from field observations in permanent plots placed in a transect between two isolated mature individuals showed that, under natural conditions, the germination rate of the seedlings of C. aeolicus can be very high and their establishment rate may exceed 40%. By contrast, seedlings mortality is subject to strong annual fluctuations. Additionally, the pollen morphology of the Strombolian metapopulation of this rare and isolated species is studied here for the first time. Contrary to what is stated in recent literature, the C. aeolicus metapopulation from Stromboli is healthy and very dynamic, albeit frequently damaged by the volcanic activity. Regular and repeated field surveys carried out during 3 years (2017–2019) allowed improving our knowledge on the life cycle of C. aeolicus and a new extinction risk assessment of the species, according to IUCN criteria, is presented.

Species–area relationship and small‐island effect of vascular plant diversity in a young volcanic archipelago

“…rockfalls triggered by local earthquakes, extensive wildfires, accumulation of ashes, frequent fall out of burning debris and huge lava bombs) linked with active volcanism (Marsella et al, 2012). Basically, plant diversity on these islands is negatively affected by volcanism, but at the same time, volcanism may be considered a key trigger and driver of local‐scale plant evolutionary processes, so that some species were able to develop specific adaptations to live on active volcanoes, as in the case of Cytisus aeolicus (Zaia et al, 2020).…”

“…While only few data—and usually the same—have been used to test biogeographical theories on the Aeolian Archipelago, these islands have been recently subjected to a fairly high amount of botanical and ecological studies. Some of them refer to single species, such as the narrow endemic Cytisus aeolicus , a small tree that is perfectly adapted to life on active volcanoes (Zaia et al, 2020). Many others are floristic, phytosociological or bryologic contributions (Lo Cascio & Pasta, 2004 and references therein, Puglisi et al, 2006; Troia, 2012; Troia et al, 2012).…”

Plant Biogeography and Vegetation Patterns of the Mediterranean Islands

“…Already cited by the Greek botanist Theophrastus in the fourth century BCE, Cytisus aeolicus is a strikking example of extreme persistance for a tree under permanent volcanic activity (Fig. 33b); the metapopulation of Stromboli is surprisingly healthy and very dynamic despite recurrent eruptions (Zaia et al, 2020).…”

Metabolomic Study of Dactylis glomerata Growing on Aeolian Archipelago (Italy)

“…The average annual rainfall in Stromboli amounts to 570 mm, with a relative humidity of 75.0% in winter and 60.8% in summer. However, the only weather station in Stromboli is located at an elevation of 4 m a.s.l., and there is a strong baric gradient between the coastline and the top of the volcano, buffering the summer drought stress with relevant condensation of atmospheric humidity [36,37]. Additionally, the hydrothermal system of Stromboli [38] causes a conspicuous degassing along the eastern slope of the volcano, where our samples were collected.…”