Microclimates act as climatic refuges and protect biodiversity

Pieris napi Foto: Vlad Dinca
Pieris napi Foto: Vlad Dinca

Two studies led by Jofre Carnicer, CREAF researcher and professor at the University of Barcelona-IRBIO, show that natural areas that maintain microclimates are more resilient to climate change and biodiversity loss. Both studies conclude that microclimates (areas of natural space with different temperature, shade or humidity) become climatic refuges when there are extreme conditions, and that they should be studied in detail to assess the real impacts of global warming on nature.

The study closely links climate change with biodiversity loss, two crises that must be addressed jointly and urgently, as the two main world scientific panels on climate and biodiversity, the IPCC and IPBES, warned in 2021. 

Studies such as this one show that thermal refuges or microclimates are key for species in an ecosystem to survive and escape the threat of climate change. Conversely, natural areas that lack these spaces have seen their populations decline drastically.“The study closely links climate change with biodiversity loss, two crises that must be addressed jointly and urgently, as the two main world scientific panels on climate and biodiversity, the IPCC and IPBES, warned in 2021. Climate change is driving the decline of biodiversity, but it does so through very complex mechanisms,” according to Jofre Carnicer.

Studies such as this one show that thermal refuges or microclimates are key for species in an ecosystem to survive and escape the threat of climate change. 

The studies led by this researcher study, on the one hand, natural spaces with climatic refuges, such as forests, and compare them with open natural spaces, such as wetlands and coastal areas, which have a microclimate that is more exposed to heat waves. On the other hand, they analyse how conditions vary within the same forest ecosystem when it occupies a heterogeneous territory, comparing microclimates in valley and ridge areas, with north and south orientation. In both cases the results emphasise that species do not all react in the same way to extreme drought episodes or heat waves, but respond differently depending on the microclimate in which they are found.

“Some models that analyse the impacts of climate change on biodiversity consider homogeneous territory scenarios. Our studies show that it is necessary to take microclimates into account, and carry out detailed analyses with very precise measurements to understand these differences and predict future scenarios,” says Jofre Carnicer

Drought pushes butterflies into decline

The results are clear: there is an evident climatic signal in this decline, and mechanisms interacting with butterflies are local and very complex.   

The first article, published in the Journal of Animal Ecology –by Jofre Carnicer together with researchers Constanti Stefanescu and Maria Vives-Ingla– concludes that drought and the lack of climatic refuges are to blame for the decline of butterflies that open spaces have experienced over the last thirty years in the Mediterranean, These results were included in “Estat de la Natura a Catalunya 2020,” a 2020 report on the status of nature in Catalonia. Data show that natural areas with climatic refuges, such as La Fageda d’en Jordà (Olot, Girona), maintain the most stable butterfly populations. This is due to the fact that, under the canopy of the beech trees, temperatures 5 ºC lower than the ambient temperature are maintained, thus keeping the vegetation more hydrated, more capable of dissipating heat and with higher quality leaves, which protects the food and the survival of the larvae of these insects during droughts and summer heat. In contrast, in open areas without microclimates, such as the coastal areas of the Llobregat Delta (Tarragona) and the Aiguamolls de l’Empordà (Girona), insect larvae grow under stressful thermal conditions and often with poor quality food. This causes the insects’ body size to decrease, shortens their wings as the summer heat progresses and puts the butterflies’ survival at risk.

Infographics showing the study results. Author: José Luis Ordóñez.

The work has taken field measurements of four different populations of the Pieris napi butterfly, popularly known as the fragrant blanquita because it gives off a strong lemon scent on its wings (see picture). The same process was then successfully replicated in the laboratory to isolate and compare the influence of climate and other environmental factors,something that is often very difficult to document and separate from others. The results are clear: there is an evident climatic signal in this decline, and mechanisms interacting with butterflies are local and very complex.

Microclimates, the lifelines of the Mediterranean forest

The research team found that the north-facing areas of the forest and the valleys withstood episodes of extreme heat and drought much better. In contrast, the ridge areas, with thinner and more bare soil, were more vulnerable and suffered from summer decay. 

The second study is also convincing: climate change scenarios predicting that Mediterranean forest ecosystems will undergo disruptive and uniform change are not real. Data show that Mediterranean forest ecosystems are very heterogeneous and that trees respond extremely differently to drought episodes or heat waves, depending on the microclimatein which they are located. Altitude and orientation, for example, modulate climatic conditions, although the study also takes into account other differences that can be found within an ecosystem, such as soil thickness (topography), or other new pressures such as an unprecedented increase in tree-shoot-eating herbivores such as roe deer and wild boar, an increase that is explained by the lack of predators and limited hunting pressure.

Sant Llorenç del Munt and Obac Natural Park Roy Tack at Unsplash

Findings have been published in the Journal of Ecology and were carried out in a large-leaved oak forest in the Sant Llorenç del Munt and Obac Natural Park (Barcelona), that occupies a heterogeneous area, from the bottom of the valley to the top of the ridge, with different north and south orientations. The research team found that the north-facing areas of the forest and the valleys withstood episodes of extreme heat and drought much better. In contrast, the ridge areas, with thinner and more bare soil, were more vulnerable and suffered from summer decay. “These are examples of results that support the previous idea: in the Mediterranean we cannot work exclusively with macroclimatic impact models. We have to add local and detailed studies on microclimates, topography and the heterogeneous response of living organisms in microclimates, because these are the key factors that are driving the resilience of forests and the carbon stored in global warming.”

In the Mediterranean we cannot work exclusively with macroclimatic impact models. We have to add local and detailed studies on microclimates, topography and the heterogeneous response of living organisms in microclimates 

Both studies have involved a multidisciplinary research team from Catalan institutions such as CREAF, the University of Barcelona, IRBIO, the Museum of Natural Sciences of Granollers and the Institute of Evolutionary Biology of the Pompeu Fabra University, among others. The study of microclimatic impacts on ecosystems is an active line of research at CREAF within the framework of the MICROCLIM project, led by researchers Jofre Carnicer and Adrià Barbeta.

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