High temperatures vary the rhythms of many plants, which in mild autumns and winters bloom earlier and can even do so twice.
This January, Javier Cano, head of Aemet's Getafe (Madrid) meteorological office, came across, for the first time in 44 years of uninterrupted observations in the Community of Madrid, a specimen of almond trees in bloom still with green leaves from the season. past, which should have disappeared by late fall or early winter.
“It is an anomaly that he had never seen and it may be due to the fact that there is hardly any frost, which is necessary for the tree to shed those leaves,” he explains.
In addition, the first flowers have emerged 16 days before February 7, the average flowering start date, taking the last three decades as a reference.
Cano's data confirm that this advance in the almond trees in the south and center of Madrid - one of the species that blooms first - has become a trend: in four decades the petals appear five days earlier.
Changes in flowering have been detected for years in different species, and it is not only due to specific episodes of heat in the middle of winter like the one we are experiencing in Spain, in which 68 temperature records have been broken.
Catalonia is a clear example.
The temperatures of September and October last year, much warmer than usual, turned autumn into a second spring, indicates the public Center for Ecological Research and Forestry Applications (CREAF).
The plants decided to return to their spring attire: the Penedès and Garraf vineyards sprouted, the fall of the leaves of the deciduous trees was delayed and a multitude of wild plants and fruit trees bloomed for the second time from the Terres de l'Ebre to Catalonia North.
In 2022, the maelstrom was similar and the mountain rose bushes in interior areas of Catalonia bloomed four or five months earlier than usual, an unprecedented fact, which was collected by volunteers from the RitmeNatura observatory, a citizen science initiative managed by CREAF and Servei Meteorological of Catalonia.
“Even,” CREAF highlights, trees such as pear or cherry trees produced fruit “for the second and even third time.”
The effects that the current heat episode may have caused have not yet been studied.
Second flowering of a wild rose bush the same year in Colmenar Viejo (Madrid). Pablo Vargas
They are not harmless anomalies, warns Ester Prat, coordinator of RitmeNatura.
“Although the second blooms are more discreet, the plant needs water and can cost resources that it will need in spring,” she warns.
It may also happen that the flowers open before the insects appear, "which would affect fruit production due to the lack of pollination, in short, the survival of the species," adds Joan Pino, director of CREAF.
And the danger of the dreaded late frosts is accentuated, because they can cause greater damage than in previous decades, when plants suffered, but not with such intensity by not waking up early from their winter retreat.
Andrés Bravo, researcher at the National Museum of Natural Sciences (CSIC), raises the need to investigate in depth the effects of high winter temperatures, which have not been given as much attention as summer temperatures as they are less common.
“These disturbances respond to global factors and must be analyzed together,” he comments.
He gives as an example the impact on the growth of a tree.
“If it does not rain in winter or spring and the temperature is higher than normal, there may be a collapse in its growth and, most likely, mortality will increase,” says Bravo.
It is a combination of heat and lack of precipitation, "if this occurs it is catastrophic in terms of its development and if a late frost is added to this, the problem is amplified."
Bravo adds that it is time to “consider forest management that allows competition for water to be reduced with better adapted species when repopulation is carried out.”
Because these periods of winter heat will become more and more frequent, and they are episodes that bring the problem to light.
“They are very striking, people are more aware that something is happening if there are high temperatures in winter, because if it were cold, but not raining, they would not have the same perception,” he says.
Agriculture on alert
The situation generates great concern in agricultural operations.
The research group at the Center for Scientific and Technological Research of Extremadura (CICTEX) works on the reproductive biology and cold needs of fruit trees.
María Engracia Guerrero, member of the team, explains that they are developing “several projects, because the winters are somewhat milder and trees that were flowering perfectly 20 years ago now have problems because each species needs a few days of cold that is not covered now and Some flowers do not bear fruit,” he details.
When the leaves fall from the fruit trees, the tree falls into rest and collects reserves, at the same time that the bud is forming, something that is imperceptible from the outside.
To do this they need a few hours of cold, and then heat, and when this cycle is complete they revive and bloom.
But, nowadays, “heat is easy to cover, but cold is not.”
Researchers make future projections, 50 and 80 years into the future, studying the genes related to this need for low temperatures and the varieties that are genetically compatible.
“In some, like the cherry tree, we know what gene it is,” he says.
It is about farmers knowing which variety they should choose.
There are some, such as the Japanese plum, that have been traditionally grown and "that will not be able to be planted within 50 years if it is not replaced by a variety that needs to accumulate less cold to flower properly."
One of the darkest futures looms over high mountain plants, says Pablo Vargas, researcher at the Madrid Botanical Garden (CSIC).
“They are the best bioindicators of climate change, especially those of the Mediterranean summits that are already in very bad shape,” he maintains.
The quickest escape for a plant, which does not have time to evolve to adapt to new conditions, is to migrate to areas with a similar climate.
It is not easy for them, because the suitable habitats are reduced, there is no more land to continue climbing.
This occurs, for example, in Sierra Nevada (Granada), with the spur (
Linaria glacialis)
and the
Sierra Nevada poppy (
Papaver lapeyrousianum)
.
“The other option for a harassed plant is to resist, to activate its capacity for endurance, as happens with the holm oak or the wild olive tree, but that depends not only on the specific species, but also on the individuals,” he points out. .
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