Pinus halepensis response to drought in Israeli planted forests
This winter, following a year with abundant rainfall, the Aleppo pine forests surrounding Jerusalem were covered in snow for some days; a rare phenomenon for the Middle East. However, this has not been the case during previous years, as from 2009 to 2011 the region was affected by a severe drought that put into jeopardy some of the most southern planted pine forest in the Mediterranean that reach out to the Middle East desert.
Supported by EFIMED’s Short Scientific Visit Grant under the project “Pinus halepensis response to drought in Israeli planted forests”, Dimitris Sarris explains how he had the unique opportunity to study these forests that experienced extensive mortality during the recent severe drought (Photo 1). response to drought in Israeli planted forests.
Using the quasi-manipulation experiment (experiment by nature), my aim was to work together with colleagues from the region to improve our understanding of how wood productivity responded to drought in extreme conditions and to identify the climatic thresholds causing the increased tree stand mortality. Photo 1: D.Sarris
We selected one of the most southern Pinus halepensis plantations in the Mediterranean; that of the Lahav forest from the semi-arid region of Israel at the northern edge of the Negev desert. The plantation had evident signs of high pine mortality rates (Photo 2). A 40x80 m sampling plot was established and out of the 49 trees in the plot (planted in 1961), 28 living and dead trees were cored (mean mortality in the plot being 78% in 2012). Annual increment to the nearest 0.01 mm was measured and after dedrochronological analysis the year of mortality for each tree was determined. 26 trees were found to be alive until 2008, so they were used in correlations with climate to determine what precipitation integration period drives their growth in this region.
Photo 2: D. Sarris
We found that trees receiving the average annual (Nov-Oct) precipitation of around c. 300 mm (the “normal” rainfall for the region) rely on a moisture input of two to three years for annual growth. However, when this average rainfall falls below the c. 300 mm threshold, longer integration periods of rainfall are needed for pine survival. As observed, extensive mortality in low density stands on low elevation slopes of southern aspect can be expected if the average rainfall falls below c. 250 mm for six years in a row. This increase in the accumulating rainfall that is needed to sustain tree growth under drought intensification fits very well with other findings from very drought stressed pine sites in the Eastern Mediterranean.
The visit did not only focus on producing research outputs but also included an educational aspect. Michael Dorman, a PhD Student at the Dept. of Geography and Environmental Development (Ben-Gurion Univ. of the Negev) had the chance to receive the basic training in dendrochronology and dendroclimatology in order to continue the investigation of how planted forests respond to drought in terms of his thesis (Photo 3).
Modeling future responses for the species in the Mediterranean under the expected increase in aridity may consider thresholds such as those identified through this work in predicting future forest productivity levels. Our findings may assist in determining where afforestation will have better chances of success for areas of the Mediterranean experiencing similar conditions, either now or in the future under global warming.
Photo 3: D. Sarris and M. Dorman
I am most grateful to EFIMED for providing the financial support for the visit, as well as to my hosts Prof. Perevolotsky (Dept. of Natural Resources, Israeli Agricultural Research Organization), Prof. Svoray and Mr. Dorman (Dept. of Geography and Environmental Development, Ben-Gurion Univ. of the Negev) for their kind hospitality. My hope is that other colleagues may also have a chance to gain knowledge and experience through EFIMED’s support in the future in caring for Mediterranean forests.
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