Atlantic trees will be affected the most by climate change on the Iberian Peninsula

Now, researchers from the University of the Basque Country (Universidad del País Vasco) have studied the responses to the midsummer heat of the Mediterranean and Atlantic trees and bushes of the Iberian Peninsula to conclude that the latter species will suffer most with the increase in temperatures.

Researchers from the Department of Plant Biology and Ecology from the University of the Basque Country have shown the response capacity of Mediterranean and Atlantic plants. ?We were able to notice that all species responded in a similar way, through the accumulation of photoprotective compounds (tocopherol or Vitamin E), reduction in clorophyll content and the activation of the so called xanthophyll cycle, points out José Ignacio Garcia-Plazaola, the first signatory of the study.

The study, which is published in the journal called Trees – Structure and Function, compares the effects of the summer of 2003 with the same period for 1998, 1999 and 2001. Generally, all the summers were dry, but in 2003 there was an average increase of 5o C, and this was considered to be the most stressful time for the trees, which turned yellow and the trees started to shed their leaves before the autumn.

Differences between the Mediterranean and Atlantic species

The researchers noticed a notable difference between the Mediterranean and Atlantic species. The Mediterranean species were much more plastic, having a much greater ability to stimulate the defence systems states García-Plazaola. With regard to the distribution of Atlantic species, scientists recorded the partial extinction of trees or bushes, such as the bearberry (Arctostaphylos), after the heat wave.

The study shows that the Atlantic species have less ability to respond to acute summer stress because of their responses to photosynthesis and the induction of photoprotective molecules. However, the majority of Mediterranean species, as they keep their green leaves throughout the year, are much more protected in the presence of environmental adversities and have developed mechanisms which allow them to acclimatise in an efficient way in the presence of heat waves and episodic cold waves as well.

According to the research, this phenomenon could be of special significance in the context of future global warming when the Atlantic species would be affected more. This result creates doubts about the future viability of certain Atlantic species that find their distribution limit on the Iberian Peninsula, as is the case of the beech tree (F. sylvatica), concludes García-Plazaola.

The unusually hot period that affected Europe in the summer of 2003 may have been the most extreme heat wave in the last 200 years. The plant species had to deal with an unequalled level of environmental stress (or adversity) in their entire existence, circumstances that they will have to face more and more frequently as a consequence of climate change.

Five years after the heat wave the Mediterranean species (Box and Holm Oak) remain the same but it has not been possible for the Atlantic species (Bearberry) to recover and it has disappeared. Photo: SINC/José Ignacio

Garcia-Plazaola.