EDITION: Ferbuary - April '08


Vicente Cleries

In order to develop well, plants need both heat and cold throughout the different seasons of the year. Cold is in fact more decisive than heat in their life cycles, since frosts can stop many species from surviving. Some lose their leaves when temperatures descend below 10 ºC; these are deciduous plants. Those who do not lose their leaves are called evergreen plants. In tropical climates, plants do not lose their leaves as temperatures never descend below 5 ºC.

Lately, and due to climate change, flowering cycles are changing as the summers get shorter and cooler, while the autumns are milder and not as windy. In winter there are warm days, and rarely as much cold as we used to have, and the spring arrives sooner.

Deciduous trees are an example: the leaves come out ealier and take longer to fall. “The most surprising is how deciduous plants grow their leaves before usual, and then lose them later”. Proof of this, in Ibiza, is the almond tree. Years ago it lost its leaves in October, while nowadays it doesn’t lose its leaves until almost Christmas, and in the beginning of the year it starts to flower again, which indicates there is a change in its biological cycle.

It has been observed that Mediterranean plants are growing their leaves an average of 16 days earlier, and losing them 13 days later than they should… in a warmer environment. Various studies confirm that global warming is bringing forward our springtime: eight days sooner in Europe between 1969 and 1998, and six days in North America between 1959 and 1993.

Observations via satellite suggest that the growth period of plants has become 18 days longer in the last two decades in both Europe and Asia, and 12 days longer in North America.

Spain now has 23 more days of heat a year compared to three decades ago: spring arrives two weeks earlier and autumn takes nine days longer to arrive than before. This information is underlined by a study carried out at European level in which investigators from 17 countries took part. After analysing the evolution of 561 species, it found “conclusive evidence” that climate change is making plants flower earlier in spring and lose their leaves later in autumn. Spain is the European country in which this phenomenon is happening more markedly.

Of the species that flower in the Spanish countryside, one which has most suffered the effects of climate change is the oak tree, which is flowering now seven days early, and whose acorns are appearing almost a month and a half sooner.

The tomato plant has also flowered over 20 days early, an imbalance in harvesting times that has provoked an exit to European markets of tomatoes grown in greenhouses. Another of the crops which has suffered big changes is wheat, which is appearing up to 19 days before it should according to its biological cycle.

Insect appearance has also been affected, which can give way to new problems. In Ibiza during the summer of 2007 the presence of a new pest that attacks tomatoes was detected. The most natural way to combat pests is the “biological” way, with the appearance (or introduction) of another insect which is the natural predator of the problem insect. Extreme cases where all else fails will require the use of insecticides.