Vegetation water status and topography shape drought-induced dieback of two Pinus species in Southwest China

Gao, Dao-Xiong

FOREST ECOLOGY AND MANAGEMENT

2026

616

Zhai, DL; Fan, ZX

Extreme droughts increasingly trigger forest dieback globally, yet how species-specific physiological strategies interact with local micro-environments to shape landscape-scale mortality patterns remains poorly understood. Here, we integrated unmanned aerial vehicle (UAV) surveys from 20 large plots (4 ha each; 10 per species), satellite-derived vegetation indices, and environmental data to investigate a severe 2023 die-off event of Pinus yunnanensis Franch (Yunnan pine) and Pinus kesiya var. langbianensis (A. Chev.) Gaussen ex Bui (Simao pine) in Southwest China. UAV observations revealed moderate but spatially heterogeneous canopy dieback, with rates ranging from 1.05% to 6.47% in P. yunnanensis and from 0.53% to 11.16% in P. kesiya var. langbianensis, predominantly concentrated on south-facing slopes. At the pixel level, satellite-based analyses showed pronounced declines in the normalized difference water index (NDWI) during 2023, accompanied by divergent post-drought trajectories between dieback (upper-quartile) and healthy (zero-dieback) pixels. In P. yunnanensis, dieback pixels exhibited a near-complete collapse in both resistance and resilience, indicating irreversible damage. Conversely, P. kesiya var. langbianensis showed rapid but incomplete recovery, suggesting a persistent drought legacy despite compensatory growth. These contrasting pixel-level responses were governed by distinct constraints: dieback in P. yunnanensis was primarily driven by intrinsic stand characteristics (e.g., age, canopy height) and soil potassium, whereas P. kesiya var. langbianensis was predominantly constrained by topographic conditions, especially slope. Despite these differences, dry-season NDWI anomalies consistently emerged as a robust predictor of dieback hotspots, which were disproportionately located near species distribution margins. Together, our results provide new mechanistic insight into species-specific drought vulnerability and highlight the importance of integrating multi-scale observations to improve predictions of forest dieback under climate change. These findings further suggest that effective adaptation strategies should move beyond generalized vulnerability assessments toward species-specific management interventions.