Is Climate Change an Emerging Risk for Cedrus Libani?

How is our beloved Cedar growing with the increasing drought and a decline of precipitations in the Levant during the 20th century as a result of Climate change?

Is Cedrus libani growing better at low or at high altitudes in Lebanon? Does it prefer the northern, the mid or the southern parts of Mount Lebanon range?

Are humid western slopes and dry eastern slopes the same for Cedar growth?

To answer all of these questions, we have conducted a “dendrochronological” study to assess the radial growth of Cedrus libani within its ecological niche, i.e., natural habitat, in Lebanon.

What do we mean by “dendrochronology” and “radial growth”?

Dendrochronology is the dating and study of annual growth rings resulting from radial tree growth or enlargement of a tree trunk (dendro = tree, chronos = time, & logos = science). Each “Annual growth ring” represents a single yearly flush of growth which begins in the spring and ceases in the summer or early autumn. One ring is produced every year; that’s why we count tree rings on wood stamps to determine the age of trees.

Tree growth is frequently affected by variations in climates, and the yearly sequence of favorable and unfavorable climate (wet and dry or warm and cold years) is faithfully recorded by the sequence of growth rings during the lifetime of trees growing in a given geographic region.

Thus, tree rings are considered as natural archives of trees’ histories. When examined closely, wide rings indicate optimal growth (moist, abundant resources), whereas narrow rings reflect restricted growth (drought, heat, competition). After assigning a calendar year to each identified ring from all trees sampled in a forest, tree ring width and climate relationships (precipitations, temperature) are established, and trends in radial growth over long periods of time are built.

This pioneer study is a collaborative work is a collaborative work between the Faculty of Sciences at Saint Joseph University of Beirut (USJ) and the National Institute for Agronomic Research “INRA” (France).

We have assessed all the known natural forests and stands of Cedar from its Northern expansion in Lebanon (Akkar) to its southernmost limit in Lebanon and the world (Niha, Shouf), sampling thus 17 forests and 439 trees (May 2018 to July 2019).
The sampling consisted of extracting wood cores from the trunk, using an increment borer.
The close study of growth rings of sampled cedar trees will demystify the trends of radial growth for Cedrus libani over the last century and will detect any potential risk of forest decline due to climate change. In fact, tree growth is an indicator of tree vitality (health).

Declining radial growth is linked to forest decline and mortality, the imminent risk for drought-prone forests throughout the world in a drastically changing climate.

The findings of the study are important for Jouzour Loubnan and will be used at national level as guidelines for reforestation and conservation policies of Lebanon Cedar to ensure proper management of cedar forests and the sustainability of reforestation projects.

Author: Rana El Zein – PhD Biodiversity Conservation Initiative – Lebanon Faculty of Science USJ - Jouzour Loubnan