Yakir Preisler, Fyodor Tatarinov, José M. Grünzweig, Didier Bert, Jérôme Ogée, Lisa Wingate, Eyal Rotenberg, Shani Rohatyn, Nir Her, Itzhak Moshe, Tamir Klein and Dan Yakir
The frequency and intensity of drought events are expected to increase in the Mediterranean and other parts of the world. This, in turn, will increase drought-related tree mortality, with impacts on forest ecosystem functioning, wood supply, water runoff, and the global carbon budget.
We studied the unusual spatial patterns of tree mortality observed in a semi-arid (280 mm annual precipitation) Aleppo pine forest at the edge of the Negev desert, Israel, following five non-consecutive drought years. The distribution of dead trees was highly patchy with parts of the forest showing >80% mortality, and others almost no mortality. To identify possible causes of this unusual pattern, we examined a wide range of ecophysiological and geomorphological aspects of the forest.
Tree-rings analysis indicated increased sensitivity of dead trees to drought events as long as 25 years prior to mortality, reflecting inferior tree micro-habitat. Further investigation showed that the only identifiable characteristics in the small-scale habitats of the dead trees was a lower frequency of both surface rock cover and stones in the soil profile. It appears that the higher level of ‘stoniness’ in the low-mortality plots resulted, first, in the concentration of precipitation water into the stone-free soil, and second, its protection from surface evaporation. These effects extended the time that soil moisture was above the trees’ wilting point by more than a month during the long seasonal drought period in this region.
Such findings provide new insights into tree survival in the local harsh conditions and could assist forest managers and modelers when considering climate change adaptation strategies.