Critical minimum temperature limits xylogenesis and maintains treelines on the southeastern Tibetan Plateau

Abstract

Physiological and ecological mechanisms that define treelines are still debated. It has been suggested that the absence of trees above the treeline is caused by low temperatures that limit growth. Thus, we hypothesized that there is a critical minimum temperature (CTmin) preventing xylogenesis at treeline. We tested this hypothesis by examining weekly xylogenesis across three and four growing seasons in two natural Smith fir (Abies georgei var. smithii) treeline sites on the southeastern Tibetan Plateau. Despite differences in the timing of cell differentiation among years, minimum air temperature was the dominant climatic variable associated with xylem growth; the critical minimum temperature (CTmin) for the onset and end of xylogenesis occurred at 0.7±0.4 °C. A process-based modelling chronology of tree-ring formation using this CTmin was consistent with actual tree-ring data. This extremely low CTmin permits Smith fir growing at treeline to complete annual xylem production and maturation and provides both support and a mechanism for treeline formation.

Climate change jointly with migration ability affect future range shifts of dominant fir species in Southwest China

“…However, accounting for additional factors, apparent differences exist in the importance of solar radiation and temperature seasonality between our “North” and “South” species (Figure ). Temperature‐related variables, such as pre‐growing season temperature (Guo et al, ), minimum air temperature (Li et al, ) and summer mean and minimum temperatures, have been reported as important factors for the growth and regeneration of fir species on the QTP (Yin et al, ), and further affect their large‐scale distribution pattern (Benito‐Garzón, Ruiz‐Benito, & Zavala, ). On the other hand, solar radiation indirectly determines the precipitation and temperature patterns on the Earth's surface and regulates the composition, productivity and distribution of ecosystems through photosynthesis (Piedallu & Gégout, ).…”

Chilling and forcing temperatures interact to predict the onset of wood formation in Northern Hemisphere conifers

“…Thus, heat‐sum models mimic the progress of cambium through the ecodormancy phase, making the implicit hypothesis that the endo and ecodormancy phases are sequential, and that endodormancy stops at the date when heat accumulation starts (Delpierre, Vitasse, et al, ). In practice, a degree‐days accumulation is calculated by summing temperatures above a threshold (“base temperature”) of typically +5°C (or more rarely lower values, e.g., 0–1°C, see Antonucci et al, ; Li et al, ) from a given day, fixed a priori, before the onset date of cambial reactivation. However, there is no consensus concerning the day or period of year from which the cambium becomes sensitive to forcing temperatures.…”

Species- and Elevation-Dependent Growth Responses to Climate Warming of Mountain Forests in the Qinling Mountains, Central China

“…In our study, L. chinensis growth was favored by warmer conditions prior to the growing season but also during the spring of the growth year, whereas A. fargesii growth negatively responded to warm and dry summer conditions. The responses of L. chinensis correspond to a direct control of temperatures on radial growth through xylogenesis, as in other treeline-forming species, but may also be explained by a higher synthesis of carbohydrates during the previous autumn and winter [29,[34][35][36][37]. Warmer spring temperatures would advance the onset of growing season by increasing the melting of snow cover and warming soil and stem meristems at higher elevations [35].…”