Urban vs. Rural Drought Resilience in Pinus kesiya, P. merkusii, and P. oocarpa: A Dendrochronological Approach

Abstract

Climate change increasingly threatens the resilience of non-native pine plantations in Zambia by altering growth patterns and delaying recovery. This study assessed drought response and post-disturbance resilience in Pinus kesiya, P. merkusii, and P. oocarpa using 40-year tree-ring chronologies from 110 trees at a minimally disturbed rural site and 86 trees at an urban, mining-impacted site. Six master chronologies were developed, confirming dendrochronological viability (EPS > 0.85; SNR > 6.5). We applied a dual-metric framework—Relative Growth Change (RGC) and Resilience Index (RI)—anchored to seven Standardized Precipitation Index (SPEI)-classified drought years (1983, 1992, 1994, 2002, 2004, 2005, 2010), using CHIRPS data and SPI ≤ –1.0. The rural site recorded 28 RGC negative growth direction (dips) and 12 RI dips; the urban site showed 27 RGC dips and 15 RI dips, suggesting that elevated CO2 and pollution may buffer growth suppression but hinder full recovery. Species-level patterns revealed distinct sensitivities: Pinus kesiya emerged as the most climate-responsive and a reliable bioindicator, with the highest cumulative dips (RGC = 21; RI = 9) and strong climate-growth synchrony. P. merkusii showed moderate vulnerability (RGC = 17; RI = 9), while P. oocarpa exhibited site-dependent resilience, with fewer RGC dips but elevated RI dips in urban conditions. Across all species, growth correlated positively with precipitation (r = 0.38) and negatively with temperature (r = –0.20) and solar radiation (r = –0.33). Integrating SPEI-based drought classification with RGC and RI offers a robust framework for guiding the selection of climate-resilient species across environmental gradients.