Climate Control on Tree Growth at the Upper and Lower Treelines: A Case Study in the Qilian Mountains, Tibetan Plateau

Abstract

It is generally hypothesized that tree growth at the upper treeline is normally controlled by temperature while that at the lower treeline is precipitation limited. However, uniform patterns of inter-annual ring-width variations along altitudinal gradients are also observed in some situations. How changing elevation influences tree growth in the cold and arid Qilian Mountains, on the northeastern Tibetan Plateau, is of considerable interest because of the sensitivity of the region’s local climate to different atmospheric circulation patterns. Here, a network of four Qilian juniper (Sabina przewalskii Kom.) ring-width chronologies was developed from trees distributed on a typical mountain slope at elevations ranging from 3000 to 3520 m above sea level (a.s.l.). The statistical characteristics of the four tree-ring chronologies show no significant correlation with increasing elevation. All the sampled tree growth was controlled by a common climatic signal (local precipitation) across the investigated altitudinal gradient (520 m). During the common reliable period, covering the past 450 years, the four chronologies have exhibited coherent growth patterns in both the high- and low-frequency domains. These results contradict the notion of contrasting climate growth controls at higher and lower elevations, and specifically the assumption that inter-annual tree-growth variability is controlled by temperature at the upper treeline. It should be stressed that these results relate to the relatively arid conditions at the sampling sites in the Qilian Mountains.

A 3,500-year tree-ring record of annual precipitation on the northeastern Tibetan Plateau

“…The interpretation of a dominant moisture control on tree growth in this region is supported by a number of previous studies (16,(19)(20)(21)(22). Interpreting local tree growth for this species as a predominant response to interannual variability of prior July to current-year June precipitation is consistent with the results of refs.…”

Differential response of Qilian juniper radial growth to climate variations in the middle of Qilian Mountains and the northeastern Qaidam Basin

“…In contrast, the present study found consistent patterns of Qilian juniper growth at the high-and low-elevation sites. Consistent growth at high-and low-elevation sites has been reported in other parts of the Qinghai-Tibetan Plateau (Gao et al 2013;Yang et al 2013). Water stress was the main climatic factor that caused homogeneous tree growth across an altitudinal gradient in the western of the Qilian Mountains .…”

Growth–climate relationships along an elevation gradient on a southeast-facing mountain slope in the semi-arid eastern Qaidam Basin, northeastern Tibetan Plateau

“…Another recent study examined samples of Qilian junipers also in the Qilan Mountains of the northeastern Tibetan Plateau (Gao et al 2013). Instead of sampling sites with broad elevation ranges as in He et al (2013) and Yang et al (2013), they sampled in four narrow elevation zones of 20-40 m on a single slope ranging from 3200 to 3600 m. Their results did not show general trends of decreased sensitivity of tree growth to precipitation and increased sensitivity to temperature as elevation increases.…”

“…They concluded that elevation has no significant effects on tree growth. Similarly, Yang et al (2013) sampled Qilian junipers (Sabina przewalskii Kom.) at four sites on a mountain slope, from the lower-to upper-treeline in the semi-arid Qilian Mountains area, and found that precipitation remained the major limiting factor of tree growth for all sites within the elevation range from 3000 to 3520 m a.s.l.…”