New perspective on spring vegetation phenology and global climate change based on Tibetan Plateau tree-ring data

Abstract

Phenological responses of vegetation to climate, in particular to the ongoing warming trend, have received much attention. However, divergent results from the analyses of remote sensing data have been obtained for the Tibetan Plateau (TP), the world's largest highelevation region. This study provides a perspective on vegetation phenology shifts during 1960-2014, gained using an innovative approach based on a well-validated, process-based, tree-ring growth model that is independent of temporal changes in technical properties and image quality of remote sensing products. Twenty composite site chronologies were analyzed, comprising about 3,000 trees from forested areas across the TP. We found that the start of the growing season (SOS) has advanced, on average, by 0. April-June and August-September minimum temperatures are the main climatic drivers for SOS and EOS, respectively. An increase of 1°C in April-June minimum temperature shifted the dates of xylem phenology by 6 to 7 d, lengthening the period of tree-ring formation. This study extends the chronology of TP phenology farther back in time and reconciles the disparate views on SOS derived from remote sensing data. Scaling up this analysis may improve understanding of climate change effects and related phenological and plant productivity on a global scale.tree rings | cambial activity | plant phenology | climate change | Tibetan Plateau P henology has a profound impact on vegetation growth (1), carbon balances of terrestrial ecosystems (2), and climate change feedback mechanisms (3). The importance of phenology has prompted many studies, mainly using ground-based observations (4-7), which provide useful phenological information at the species level. However, such studies are also quite time-intensive and typically focus on a few individuals in restricted geographic areas, which often limits their applicability to larger spatiotemporal scales. Changes in plant phenology can be detected on larger spatial scales through near-surface remote sensing, using digital repeat photography (8), but this approach remains limited to the stand level. Another commonly used approach is satellite remote sensing, which can cover large areas (9-11); however, this method has yielded inconsistent results on the Tibetan Plateau (TP) (9, 12, 13).The TP, with an average altitude of over 4,000 m above sea level (a.s.l.), covers more than 2 million square kilometers and is strongly affected by ongoing climate change. Due to its vast area, and its position in subtropical latitudes with high incoming solar radiation, changes in vegetation period duration may have major consequences for regional climate and for carbon sequestration in SignificanceInconsistent results regarding the rate of change in spring phenology and its relation to climatic drivers on the Tibetan Plateau have been obtained in the past. We introduce and describe here an innovative approach based on tree-ring data, which converts daily weather data into indices of the start (and end) of the growing season. This method pro...

Relationships between Wood Formation and Cambium Phenology on the Tibetan Plateau during 1960–2014

“…Firstly, the significant correlations between the modeled results and actual tree-ring width chronologies (TRW) suggest that the model performance is robust (95% series reaches the significance level of p < 0.01, and the remaining 5% series is significant at the level of p < 0.03). Secondly, the derived phenological series are generally consistent with the available monitored results in the study region [18]. Thirdly, the regionally averaged phenological variability closely matches with the vegetation green-up series derived from remote sensing data over their common period 1982-2011, as conducted by Yang et al [18].…”

“…Secondly, the derived phenological series are generally consistent with the available monitored results in the study region [18]. Thirdly, the regionally averaged phenological variability closely matches with the vegetation green-up series derived from remote sensing data over their common period 1982-2011, as conducted by Yang et al [18]. Hence, in comparison to the monitoring results that could only detect connections from a limited number of trees and years [10][11][12], our analysis is thus able to deepen the understanding of the relationships between the stem radial growth of a tree and the start (SOS), the end (EOS), and the length (LOS) of cambial activity.…”

“…Tree-ring phenology data was available from Yang et al [18], which was derived from results of the VS-oscilloscope model [17]. This model defines the climatic drivers of tree-ring growth through control on the rate and duration of cell-based processes (cell division, enlargement, and maturation) in the developing xylem.…”

Strong evidence for changing fish reproductive phenology under climate warming on the Tibetan Plateau

“…One limitation of this study is that partitioning larval otolith growth due to temperature increase vs. growing season length was not based on the entire growing season of YOY (as larvae could not be collected from all sites at the end of the growing season). In addition, a very recent terrestrial study on the TP has also proposed comparable methods of using tree-ring microstructure chronology data to examine changes in spring vegetation phenology (Yang et al, 2017). Another potential limitation in this study is that we assumed that temperature was the key factor influencing otolith growth and we did not consider other factors such as food, which may be important in some circumstances (Hinrichsen, Voss, Huwer, & Clemmesen, 2010;Schismenou et al, 2014).…”

A Carbon Flux Assessment Driven by Environmental Factors Over the Tibetan Plateau and Various Permafrost Regions

“…In terms of seasonal mean GPP, we found that spring warming significantly promoted the GPP of alpine grassland. In fact, some studies reported that the start of the vegetation growing season in the Tibetan Plateau exhibited an advancing trend during the past few decades, which maybe the reason causing the increase of spring GPP (G. Zhang et al, ; Yang et al, ). Although increasing temperature in autumn may extend the growth season, there was no significant influence on GPP changes.…”