500 years of May temperature variability in Balochistan reconstructed from Juniperus excelsa tree rings: heat stress, growth-collapse extremes, and implications for an endangered relict forest

Abstract The Ziarat juniper forest of Balochistan, Pakistan—among the oldest juniper woodlands documented in the Hindu Kush–Himalayan (HKH) system—provides a valuable proxy archive for reconstructing pre-instrumental climate variability in this data-sparse western arid zone. Using 101 ring-width series from high-elevation Juniperus excelsa , spanning 1523–2023 CE, we developed a master chronology (EPS = 0.971; SNR = 33.4) restricted for robust climate interpretation to the post-1700 CE window, where sample depth exceeds the 10–15 series threshold required for EPS ≥ 0.85 (Wigley et al., 1984). A 14-month climate-growth correlation analysis identifies current-year May mean temperature as the single strongest and most coherent driver of radial growth (r = − 0.66, p < 0.001), providing both a statistical and physiological basis for selecting May as the reconstruction target. May mean temperature was reconstructed back to 1523 CE via a calibrated Simple Linear Regression model validated with Leave-One-Out (LOO) cross-validation (R² = 0.43; r = 0.66; RE = 0.51; RMSE = 1.56°C; p < 0.001), with robust climatic interpretation confined to the post-1700 CE period and the pre-1700 CE interval treated explicitly as exploratory (EPS < 0.85; Supplementary Fig. S3). Over the robust period, the reconstruction reveals a secondary warm phase during 1700–1770 CE, renewed cooling through much of the eighteenth and nineteenth centuries consistent with Little Ice Age and Dalton Minimum forcing, and a modern warming trend accelerating after ca. 1980 CE that reaches the highest sustained 30-year values in the robust record. Pointer Year Analysis, using a > 70% synchronous growth-collapse threshold applied consistently across the full chronology, identified thirteen extreme events, with the most severe collapses occurring in 1767, 1761, 1801, 1910, and 2010 CE—several of which align temporally with documented regional famines, Dalton Minimum forcing, and monsoon failures, though we treat these as temporal correspondences rather than demonstrated causal links. A 31-year moving correlation analysis shows that the negative temperature-growth relationship strengthened progressively after ca. 1985 CE (r approaching − 0.6 to − 0.66 for May mean temperature), consistent with, but not conclusive proof of, a warming-driven physiological threshold response that we discuss alongside the alternative and non-exclusive possibility of compounding anthropogenic disturbance (grazing, fuelwood extraction). These results provide the first multi-century climate reconstruction from the Ziarat ecosystem and a quantitative, appropriately bounded baseline for evaluating this critically endangered forest’s vulnerability to continued warming.