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Dendroecology: not everything is caused by climate change

A research team in which Universidad Politécnica is participating has assessed the causes of growth decline of a pine forest of great ecological interest in Spain.

Researchers from Universidad Politécnica de Madrid (UPM), INIA and Aix-Marseille Université bring out the irreversible changes in the structure of the Hoyocasero pine forest by using techniques of dendroecological analysis. Results suggest that the lack of pine regeneration does not stem from climate change, but it does the action of man on forest stand, therefore it is possible to establish protecting measures to guarantee its survival.

As in many other locations of the Iberian Peninsula, the valuable natural heritage of Hoyocasero Pine forest can be in danger. The richness and interest of the plants in this forest located in Ávila have been attractive to national and international naturists such as Heinrich Moritz Willkomm since the 19th century. In fact, various new species for Science were described in this location. Besides, some Mediterranean species are preserved due to their rarity in this area of the Central System.


Samples of 'Pulsatilla alpina subsp. Apiifolia' in the  Hoyocasero pine forest and a flowered  'Rhaponticum exaltatu', one of the taxa described for the first time in this pine forest. / Agustín Rubio Sánchez.

Professor Agustin Rubio Sánchez from School of Forestry Engineering and Natural Resources of UPM, along with a multidisciplinary team of researchers, has assessed this pinewood comparing to colonization by other more drought-tolerant tree species such as rebollo. This study has combined dendrochronology, climate and dasometric data.

The age patterns observed on the trees suggest a natural origin for the two species present in the forest, pine and rebollo. According to age structure and historical references, it is likely that this pine is the last vestige of a large pine forest that should occupy this region. However, while natural regeneration has been constant since 1950 for rebollos, there has hardly been natural regeneration of pines since 1870.

The used analysis techniques have allowed researchers to identify higher affection to high temperatures from spring to autumn as well as increased pine sensitivity to drought in recent years. Nonetheless, the pinewood structure established in the 19th century does not show yet symptoms of decline attributable to climate change.

As lack of pine regeneration is not a new process and has been existed since before evidences of climate change, this situation can direct or indirect affect on management of forest stand. The growth of rebollos seems to be linked to an intensity reduction of anthropic management since the mid-twentieth century. This is likely related to the decline of the local population and the abandon of firewood as the main source of energy in rural areas.

Stand dominated by 'rebollo' (foreground) at a clear place by forest management in the mature pine forest (background).  / Agustín Rubio Sánchez.

The action of man on forest stand with modifications on vegetation and soil properties (changes in pH and nutrients) could be playing an important role in forest dynamics.

As long as we do not take specific actions that guarantee the conservation of the Hoyocasero pine forest as we know today, we will keep asking ourselves when it will be the end of its precious natural heritage.

GEA-IZQUIERDO, G., MONTES, F., GAVILÁN, R.G., CAÑELLAS, I. & RUBIO A, 2015. “Is this the end? Dynamics of a relict stand from pervasively deforested ancient Iberian pine forests”. European Journal of Forest Research, 134: 525-536.  DOI 10.1007/s10342-015-0869-z.

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