Functional traits and stand factors as strong drivers of radial growth response to hotter drought in a temperate forest of North China

Increasing drought associated with climate warming (i.e., hotter drought) is seriously threatening tree growth and survival across the world. Previous studies have reported that tree growth response to climate change is affected by species. Nevertheless, how functional traits and stand factors affect radial growth are not well understood. North China has experienced severe hotter drought in recent decades. We sampled the tree-ring from four typical species with mean stand ages of 40 to 60 years at altitudes of 1100–1300 m, and examined two aspects of radial growth response to hotter drought: temporal growth variability [mean sensitivity (MS) and standard deviation (SD)], and the correlations of ring width indices (RWI) with historical temperature and water availability. We also explored the relative importance of functional traits and stand factors on radial growth response to hotter drought. We found that MS and SD were the highest in Betula platyphylla with the highest leaf nitrogen (N) concentration and specific leaf area (SLA) (acquisitive strategy), but decreased with lower leaf N concentration and SLA (conservative strategy), until MS and SD were the lowest in Pinus tabulaformis. Consistent with the hydraulic limitation hypothesis, the growth of taller stands was more limited by hotter drought. Meanwhile, stands with higher wood density and lower leaf N concentration showed stronger water sensitivity of radial growth. These evidences highlight the importance of functional traits and stand factors on radial growth response to climate change. Hotter drought has caused a significant negative influence on radial growth in our study region and thus may be a severe threat in the future. Further studies need to explore how functional traits and stand factors affect tree growth response to climate change, to better guide forest management in alleviating the threat of future hotter drought.