Climate warming shortens the time interval between stem-girth and wood biomass production in twelve temperate tree...

Climate warming is reshaping the phenology of plants in recent decades, with potential implications for forest productivity, carbon sequestration, and ecosystem functioning. While the effects of warming on secondary growth phenology is becoming increasingly clear, the influence of environmental factors on different developmental phases of xylem remains to be quantified. In this study, we investigated the temporal dynamics of xylem cell enlargement, wall-thickening, and the interval between these events in twelve temperate tree species from Northeast China over the period 2019-2024. We found that both cell enlargement and wall-thickening advanced significantly in response to climate warming, with species-specific variations in the rate of advancement. Importantly, the advancing rate of wall-thickening was greater than that of cell enlargement, leading to a shortening of the interval between these two events. Linear mixed-effects models revealed that photoperiod, forcing temperature, and precipitation were the primary environmental drivers influencing the timing of both cell enlargement and wall-thickening, with photoperiod emerging as the most important factor. These results suggest that climate warming accelerates the heat accumulation required for the transition from xylem cell enlargement to wall-thickening, thereby shortening the time interval between these two developmental stages. Beyond contributing valuable multi-year xylem phenological data, our results provide mechanistic insights that enhance predictions of wood formation dynamics under future climate scenarios and improve the accuracy of forest carbon models.