Bridging the gap between microclimate and microrefugia: A bottom‐up approach reveals strong climatic and biological offsets

Abstract

In the context of global warming, a clear understanding of microrefugia-microsites enabling the survival of species populations outside their main range limits-is crucial.Several studies have identified forcing factors that are thought to favor the existence of microrefugia. However, there is a lack of evidence to conclude whether, and to what extent, the climate encountered within existing microrefugia differs from the surrounding climate. To investigate this, we adopt a "bottom-up" approach, linking marginal disconnected populations to microclimate. We used the southernmost disconnected and abyssal populations of the circumboreal herbaceous plant Oxalis acetosella in Southern France to study whether populations in sites matching the definition of "microrefugia" occur in particularly favorable climatic conditions compared to neighboring control plots located at distances of between 50 to 100 m. Temperatures were recorded in putative microrefugia and in neighboring plots for approximately 2 years to quantify their thermal offsets. Vascular plant inventories were carried out to test whether plant communities also reflect microclimatic offsets. We found that current microclimatic dynamics are genuinely at stake in microrefugia. Microrefugia climates are systematically colder compared to those found in neighboring control plots. This pattern was more noticeable during the summer months. Abyssal populations showed stronger offsets compared to neighboring plots than the putative microrefugia occurring at higher altitudes. Plant communities demonstrate this strong spatial climatic variability, even at such a microscale approach, as species compositions systematically differed between the two plots, with species more adapted to colder and moister conditions in microrefugia compared to the surrounding area.

Spatial resolution impacts projected plant responses to climate change on topographically complex islands

“…Percentages are shown in boxplots, showing the 1st and 3rd quartiles (upper and lower bounds), 2nd quartile (centre), 1.5 × interquartile range (edges of the box), and extreme values (stars). and viability of these putative areas to actually persist or play a role as microrefugia for the Macaronesian bryophyte flora under ongoing climate change (Finocchiaro et al, 2023;Greiser et al, 2020).…”

“…by using the latter as boundary conditions and resolving local climate processes at a higher spatial resolution). An increasing number of studies have compared the accuracy and performance of species distribution models depending on the spatial resolution of the climate data (e.g., Ashcroft et al, 2012; Chauvier et al, 2022; Finocchiaro et al, 2023; Lenoir et al, 2017; Potter et al, 2013). Even if the idea that finer scale models lead to an improvement of model accuracy has not been consistently supported (e.g.…”

“…Connor et al, 2018; Guisan et al, 2007; Manzoor et al, 2018; Moudrý et al, 2023; Stark & Fridley, 2022), the need for fine‐scale climate data becomes evident in mountain areas, where climate can vary at short scales of 10–100 m. In such rugged areas, topographic variation locally brings about suitable conditions for the existence of small, sheltered areas against climate change. These areas, whose local conditions are to some extent decoupled from the prevailing macroclimate (Dobrowski, 2011), can play an important role as microrefugia, namely for warm‐ and drought‐sensitive organisms in a warming world (Finocchiaro et al, 2023; Hylander et al, 2015; Suggitt et al, 2018).…”

myClim: Microclimate data handling and standardised analyses in R

“…The rapidly increasing number of microclimatic studies (e.g. Finocchiaro et al, 2023;Greiser et al, 2020;Macek et al, 2019) and the establishment of local microclimate monitoring networks (e.g. Aalto et al, 2022;Dickerson-Lange et al, 2015;Lundquist et al, 2016) facilitate the creation of global microclimate database SoilTemp, aggregating data from thousands of localities (Lembrechts et al, 2020).…”

Climate change impacts on Mediterranean vegetation are amplified at low altitudes

“…However, studies from high altitude and latitude areas highlight that vegetation changes might be slow compared to changes in abiotic and other biotic factors (Alexander et al, 2018; Elmendorf et al, 2012; Løkken et al, 2020; Virtanen et al, 2010; Vittoz et al, 2009; Wilson & Nilsson, 2009). Soil and terrain patterns can slow down the impacts of global climate change locally (Finocchiaro et al, 2022; Graae et al, 2018; Rota et al, 2022; Scherrer & Körner, 2011) and successional or trophic changes as well as spatial connectivity can further complicate migration patterns, with up‐ and downward shifts of plant distributions (Lenoir, Gégout, Guisan, et al, 2010; Merle et al, 2020). Increased droughts in lowland areas might favour xerophytic species (Liu et al, 2017), a ‘xerophytization’ with different dynamics and patterns than thermophilization, notably in the much less studied Mediterranean areas (Pauli et al, 2012).…”