Microclimate can save plant species from population migration

Global warming would force plant species to move dozens of kilometres north at breakneck speed to still find suitable habitat. “A failure for flora,” was the scientific consensus for a long time. Recent research suggests that such population relocation would not be necessary in many cases. Plants could seek refuge in ‘microrefugia’: oases in the landscape where the climate is relatively cooler than in the surrounding area.

Those who look at the climatology models hold their breath. Global warming is pernicious for greenery in this world. In fact, temperatures would rise so fast that plants would not have the chance to seek cooler places in time.

Although two recent papers in the journal Nature Climate Change outline a less grim prospect. “So-called microrefugia, such as a dense patch of forest where temperatures under the canopy are much lower than in the open areas around it, can provide (temporary) shelter for species fleeing rising temperatures.” explains ecologist Jonas Lembrechts (University of Antwerp). Lembrechts is the author of one of the papers and helped note that so far the consequences have turned out to be less severe than expected. “Thanks to those cooler locations, plants over the last 20 years eventually had to move no more than one km northwards, Maclean and Early calculated, while traditional models indicated another 50 km or so.”

One type of warming is not the other

“The temperature as perceived by plants, close to the ground or under the canopy of a forest, is very different from what we are used to from our weather stations,” Lembrechts explains. For instance, trees form an insulating layer above the forest, and photosynthesis in leaves causes water to evaporate, drawing heat from the environment.

Now it gets really interesting when those microrefugia are not only cooler than their surroundings, but also heat up more slowly. This makes them a buffer against climate change for much longer. “Such slower warming now also appears to be effectively possible,” Lembrechts explains. “For instance, in previous research, we showed that temperatures warm up more slowly in forests than in the surrounding countryside, because the cooling effect of (healthy) forests increases even more when temperatures rise.”

The influence of microclimate. A representation of the rate of microclimate change resulting in species range shifts. Three scenarios are shown: increased urbanization, unchanged land use, and increased forestation. The macroclimate will warm by 2 °C between 2020 and 2040. Each microhabitat may experience a unique rate of warming, ranging from 0 °C to 4 °C per pixel. Increased urbanization accelerates microclimate warming and requires faster species range shifts, while increased forestation slows microclimate warming and may maintain viable species populations. Protecting natural areas and creating new ones, especially in urban settings, is essential. The graph (bottom right) shows microclimate temperature increase variation over the 20-year period in different land-use scenarios (red, yellow, and blue).

Smart nature management as a solution

Such findings show that local nature can play an important role in combating the effects of global warming. At the same time, it is also fragile and human intervention can cause significant damage. Lembrechts: “Cutting down a forest will kill that local air conditioning, resulting in a local rise in temperature. That warming process can be much faster locally than what we expect from global climate change.” As a result, plant species will still have to rush off to cooler places.

But things can be different: smart nature management is able to firmly slow down warming at the local level. “So from nature’s perspective, it is not just about to what extent we can limit climate change by reducing our CO2 emissions, for example,” Lembrechts stresses. “Certainly as important is what we do with our limited green space. If we let it become more and more urbanised, the temperature in the microrefugia will rise much faster than if we bet on more forests, marshes, and other greenery.”

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