Cambium production pattern in Q. ilex growing at a dry site in Southern Italy

Survival of forest tree species in semi-arid environments such as the Mediterranean area is threatened by the increase in harsh drought conditions. Therefore, better knowledge of the eco-physiology of Mediterranean species and their growth responses to climatic factors is needed to develop strategies for sustainable management.

The studies of cambial activity and wood formation can provide information on tree growth and physiological responses to variations in intra-annual climatic parameters, helping to answer questions related to tree performance and plasticity under changing environmental conditions.

Our aim was to investigate cambium production in holm oak (Quercus ilex L.) as one of the most widespread evergreen oaks in Southern Italy. We studied the response of cambium activity throughout the particularly dry year 2017. We collected tissues from tree stems every two weeks by sampling microcores containing phloem, cambium and xylem. For the analyses, thin cross sections of the microcores were analysed under a light microscope to identify the timing of cambial production, xylogenesis and phloem formation. We detected the period in which the cambium was active, as well as the period in which the cambium was not productive. We interpreted the cambial response to climatic conditions at the site during the period of observation.

The observed pattern of xylogenesis differed from the expected bi-modal pattern typical for Mediterranean species which usually results in Intra-annual Density Fluctuations (IADFs) in tree-rings. In Q. ilex we observed only one peak of cambial activity, likely due to the low water availability during the year 2017.

The obtained results provide useful information supporting the forecasting of the wood-growth responses to expected climate change. Moreover, we gained technical experience on optimal preparation of thin sections of problematic tissues, which is especially challenging in Q.ilex due to high hardness of the peculiar wood structure making the investigations of xylogenesis very challenging in this species.