Growth rates and responses to climate and aridity of Algerian Atlas pistachio populations

The Atlas pistachio (Pistacia atlantica) is a minor hardwood species threatened due to overexploitation in some regions of the Maghreb, but it shows an extraordinary ecological plasticity inhabiting sites subjected from Mediterranean humid to arid conditions. To assess the drought tolerance of this understudied species, we sampled three Algerian populations along a N-S gradient of increasing aridity: Theniet el Had (sub-humid site, H), Djelba (semi-arid or dry site, D) and Béchar (arid site, A). First, ring-width chronologies were built. Second, correlations between ring-width indices, climate variables, a drought index and teleconnection indices (NAO, North Atlantic Oscillation; MOI, Mediterranean Oscillation index; SOI, Southern Oscillation Index; SaOI, Sahara Oscillation Index) were calculated. A high precipitation in the previous autumn and winter enhanced radial growth of Atlas pistachio and also high June precipitation in the wettest site H. In the driest site A, high maximum temperatures in spring constrained growth. High minimum temperatures in late summer and early autumn enhanced growth in sites D and A, which showed similar year-to-year growth variability (r = 0.426, p = 0.015, period 1980–2011). Correlations with a drought index peaked in the driest site A from September to December. Positive relationships between growth and drought indices in spring and autumn suggest a bimodal growth pattern. The three sites showed positive correlations between growth indices and the April MOI. However, negative relationships were found for January NAO or MOI and spring indices (June NAO, May SOI) in site H. Here, growth rates were negatively related to the SaOI. The Atlas pistachio shows a remarkable drought tolerance and its climate-growth relationships indicate plastic growth responses to precipitation variability.