Tracking Phenological Changes over 183 Years in Endemic Species of a Mediterranean Mountain (Sierra Nevada, SE Spain) Using Herbarium Specimens

Abstract

Phenological studies have a crucial role in the global change context. The Mediterranean basin constitutes a key study site since strong climate change impacts are expected, particularly in mountain areas such as Sierra Nevada, where we focus. Specifically, we delve into phenological changes in endemic vascular plants over time by analysing data at three scales: entire massif, altitudinal ranges, and particular species, seeking to contribute to stopping biodiversity loss. For this, we analysed 5262 samples of 2129 herbarium sheets from Sierra Nevada, dated from 1837 to 2019, including reproductive structure, complete collection date, and precise location. We found a generalized advancement in phenology at all scales, and particularly in flowering onset and flowering peak. Thus, plants flower on average 11 days earlier now than before the 1970s. Although similar trends have been confirmed for many territories and species, we address plants that have been studied little in the past regarding biotypes and distribution, and which are relevant for conservation. Thus, we analysed phenological changes in endemic plants, mostly threatened, from a crucial hotspot within the Mediterranean hotspot, which is particularly vulnerable to global warming. Our results highlight the urgency of phenological studies by species and of including ecological interactions and effects on their life cycles.

Keywords: Mediterranean mountain; endemic plant; flowering; fruiting; global warming; herbarium sheet; phenology.

Figure 1

Regression plot showing phenological trends of flowering and fruiting phases over time for different phenophases (from flowering onset to late fruiting) for the assessed period (p-value: <2 × 10⁻¹⁶ ***; Pseudo-R2: 0.06572040). Lines show negative linear trends for most of the phenophases during the assessed period (1837–2019). The shaded area shows the standard error of the mean.

Figure 2

Regression plot showing the linear relationship between Julian date and collection year in each altitudinal zone (alpine vs. non alpine). Note that the trends for both altitudinal zones were negative, yet more pronounced for the non-alpine zone (pseudo-R² = 0.105) than for the alpine zone (pseudo-R² = 0.044).