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WEATHER

Reader question: Why are the leaves falling in summer and does that mean my garden is dead?

It might look like fall outside in certain parts of France, but it certainly feels like summer. So why are the leaves falling from the trees? And what does that mean for your garden?

Reader question: Why are the leaves falling in summer and does that mean my garden is dead?
This photograph taken on August 3, 2022, shows early fall of leaves at the Buttes chaumont park in Paris as France experiences a heatwave. (Photo by BERTRAND GUAY / AFP)

Reader question: It’s only the middle of August and already the leaves have fallen from most of the trees – my lawn is covered with dead leaves like it’s the middle of autumn. Why is this happening and does it mean the trees are dead?

France is having a hot, dry summer and humans and animals are not the only ones suffering amid the heat. Plants and trees are looking pretty sickly in many areas and you may have noticed an unexpected sprinkling of dead leaves on the ground – one that you might normally expect for the fall months. 

The short answer is that the trees are thirsty too. As a result of a lack of water, trees can lose their foliage, but if you’re a gardener you don’t have to worry too much: this is a self-protection mechanism. 

While seeing leaves falling in early August might be surprising to you, it actually is a natural reaction from trees that are just trying to protect themselves from high temperatures. 

Nathalie Breda, the director for research at the National Research Institute for Agriculture, Food and Environment (INRAE),  said trees are a lot like humans when it comes to heat: they sweat when it is hot.

“Transpiring is an active part of temperature regulation,” said Nathalie Bréda to French radio service FranceInter. “This is the first step the tree takes when the temperature is high – it pumps water through its roots, which eventually turns into water vapour once it reaches the foliage, later being released into the atmosphere.

“The tree will pump water through its roots, which will turn into vapour once it reaches the foliage, and which will be released into the atmosphere.”

This helps to keep the tree at a lower temperature than the air. The tree does this by ‘opening its stomata’ (similar to pores) – which allows the plant to release water. 

However, once temperatures get even higher, and there is less water for trees to draw upon, then they ‘sweat’ less. 

“Once the tree feels that there is less water in the soil, it limits the opening of the stomata to conserve water and preserve itself,” said Bréda. 

This means that the tree gives up on its foliage to help conserve water, causing the leaves dry out and fall to the ground. 

Do gardeners have to be worried?

While conserving water in this way can weaken the tree in the long term, it does not mean that the tree dropping leaves in your garden is dead. Most trees should recover, even if it takes several years after a drought to do so (as it did, for instance, with the years 1976 and 2003).

Trees shed their leaves in the fall when they sense cold, unsuitable weather is coming. It is the same principle where they seek to conserve water and energy. 

That being said, when the tree loses leaves prematurely, this means it has finished growing prematurely for that season. Practically, trees need to open their stomata in order to photosynthesise, as this is the part of the tree that allows the entry of carbon dioxide. Failing to do this can put the tree at risk, as the plant needs to photosynthesise to remain healthy and protect itself against insect attacks and frost waves. 

Bréda explained to FranceInter that “after the 2018 heat wave, all the spruce trees in Eastern France were killed by bark beetle insects. This happened because they were weakened.”

It also takes plants one or two seasons to be able to recover and build back up their reserves. Experts worry that with recurrent climatic distress, the plants will not “have the time to recover from one year to the next.”

A sign that the tree is suffering amid severe drought might be ‘weight loss,’ Bréda explained to FranceBleu. “When drought becomes very severe, we even see that trees lose weight. Meaning, they use the water in their elastic tissue to compensate for the lack of water in the soil.”

What can I do to protect my trees?

For gardeners or home owners looking to protect their trees, another idea is to trim the branches back – this would allow them to reduce their foliage and better conserve their water. The quick answer would typically be to simply water the tree, but with most of France on some level of drought alert – water restrictions are in place almost everywhere across l’Hexagon. 

READ MORE: MAP: Where in France are there water restrictions and what do they mean?

For urban areas, Bréda recommends that cities reconsider the way of planting vegetation in the city: it is necessary to “review the size of the tree planting hole, and move the road (asphalt) away from its roots a little. This would allow the soil around it to better rehydrate when it rains.”

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CLIMATE CRISIS

Paris officials to run emergency exercise simulating a 50C day in the city

As the climate crisis pushes temperatures ever higher, officials in Paris are preparing a simulation of the day when the mercury tops 50C, in order to prepare the city's emergency response.

Paris officials to run emergency exercise simulating a 50C day in the city

This simulation, which was announced on Wednesday, is set to take place in October 2023, and it would plunge two parts of one arrondissement (which has not yet been decided) into the fictitious scenario to test the city’s capacity to respond to such a crisis. 

The current temperature record in Paris is 42.6C, which was set during the heatwave of 2019, but experts predict that the record is unlikely to remain unbroken for much longer.  

According to Deputy Mayor of Paris, Penelope Komitès, the city wants to be able to anticipate the next disaster.

“[Paris] has withstood various crises in recent years,” she said to French daily Le Parisien. The public official referenced past disasters, such as the flood of the Seine in 2018, Notre-Dame catching on fire, along with widespread protests and social movements.

“What will be the next crisis?” she said.

Public authorities hope to expand upon and move beyond the city’s first “action plan,” which was adopted in 2017.

The heatwave simulation would allow the city to test its emergency response capacity, namely deployment of cool rooms, shaded areas and other measures. It would also allow public officials to gauge and predict the reactions of Parisians amid a disastrous heatwave of 50C. 

READ MORE: ‘Over 40C’: What will summers in Paris be like in future?

“We have survived crises, but they can happen again,” Komitès said to Le Parisien. Her goal is not for the simulation to provoke anxiety, but instead to prepare the city to mobilise in such an event. 

According to RTL, on Wednesday, the greater Paris region also presented its plan to adapt the community “to the effects of climate change”.

Valérie Pécresse, the regional representative, referenced plans for “1,000 fountains” and the creation of “a network of climate shelters.”

Additionally, the region has set a target of increasing its green space by 5,000 hectares by 2030. The targets of this plan would include priority urban spaces: schoolyards, parking lots, squares, as well as cemeteries.

In 2003, the country suffered a historic heatwave that resulted in at least 14,000 heat-related deaths. Since then, France and its cities have begun adapting to rising temperatures by working to increase green space, provide ‘heat

An analysis from the BBC in 2021 found that “the number of extremely hot days every year when the temperature reaches 50C has doubled since the 1980s.”

READ MORE: Trees to trams: How French cities are adapting to summer heatwaves

This will not be the first simulation activity to anticipate or help the public become aware of rising temperatures. 

In 2014, meteorologist Evelyne Dhéliat gave a ‘fake forecast’ pretending that the year was 2050. The temperatures on her map however, ended up being eerily close to those France has seen regularly since 2019.

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