Refine
Document Type
- Article (3)
Language
- English (3)
Has Fulltext
- yes (3)
Keywords
- - (2)
- Asian summer monsoon (1)
- conifers (1)
- dendroclimatology (1)
- forest ecosystems (1)
- growing season (1)
- growth (1)
- past millennium (1)
- precipitation variation (1)
- solar activity (1)
A tree ring-width record spanning from AD 1377—1998 was developed from Tibetan juniper (Cupressus gigantea) growing at sites north of the deep gorge of the Yarlung Tsangbo River of southeast Tibet. A linear regression model between ring width and mean January—June temperature accounts for 35% of January—June temperature variance for the period 1961—1998. Based on this model, we reconstructed January—June temperature variation history for the study region during the past 622 years. Warm conditions occurred during AD 1385—1418, 1443—1466, 1482—1501, 1523—1548, 1570s, 1705—1759, 1770—1790, 1851—1888, 1910s, and 1938—1965, and periods of relatively cold years are identified for AD 1419—1442, 1470s, 1502—1522, 1550—1569, 1610—1640, 1680—1700, 1760s, 1791—1850, 1900s and 1965—1995. Spatial correlation between tree rings and observed temperatures indicates that the reconstruction is representative of temperature change for southeast Tibet. Regional cold conditions during AD 1625, 1685, 1760, 1800—1850, 1890—1930 and 1965—1995, and warm conditions during 1710, 1730—1750, 1850—1890 and 1930—1960 can be identified in the eastern Tibetan Plateau. Our reconstruction shows good agreement with modelled regional temperatures derived from an ECHO-G model simulation. Common cold periods around 1470, 1685 and 1845 corresponding to the Spörer Minimum, the Maunder Minimum and the Dalton Minimum periods of low solar activity and increased volcanic activity were identified, indicating that solar and volcanic activity played an important role in temperature change of this region. The discrepancy between modelled and reconstructed temperatures was noted around 1965, reflecting that temperature decrease in the late 20th century (1965—1995) is anomalous.
Knowledge of Asian monsoon variability remains limited because of sparse instrumental data available only for short time series. Here, an updated tree-ring width record covering the period ad 1037–2009 was developed for the south-central Tibetan Plateau (TP). Correlation analysis revealed a significant relationship (r = 0.71) between the tree-ring index and annual (previous July to current June) precipitation series for the instrumental period 1963–2008, which accounts for 50.41% of the rainfall variability. Based on a linear regression model, the longest available regional precipitation history was reconstructed. Spatial correlation between tree ring width and annual precipitation data from previous July to current June indicates that the reconstruction is representative of precipitation changes on the south-central TP. Regional wet conditions occurred during ad 1095–1161, 1376–1403, 1414–1446, 1518–1537, 1549–1572, 1702–1757, 1848–1878 and 1891–1913, while dry periods were identified during ad1189–1242, 1256–1314, 1329–1357, 1470–1491, 1573–1623, 1636–1686, 1761–1821, 1823–1847, 1879–1890 and 1931–1985. The negative correlation between our reconstructed precipitation and India monsoon rainfall series indicates the seesaw pattern over northern and southern monsoon Asia. It is suggested that solar radiation-induced sea surface temperature (SST) anomalies over the tropical Pacific influence regional rainfall patterns. The degree of this influence has been stable at the multidecadal scale during the past 1000 years.
Relationships between Wood Formation and Cambium Phenology on the Tibetan Plateau during 1960−2014
(2018)
The variability of tree stem phenology plays a critical role in determining the productivity of forest ecosystems. Therefore, we aim to identify the relationships between the timings of cambium phenology, and forest growth in terms of tree-ring width over a long-term scale. A meta-analysis was performed that combined the timings of xylem formation, which were calculated by a tree-ring formation model of the VS (Vaganov-Shashkin)-oscilloscope during the period 1960–2014, and a tree-ring width series at 20 composite sites on the Tibetan Plateau. Both the start and length of the growing season significantly affected the formation of wood at 70% of the 20 composite sites within the study region. A wider tree ring probably resulted from an earlier start and a longer duration of the growing season. The influence of ending dates on tree-ring width was less evident, and more site-dependent. Weak relationships were identified between the start and end of the growing season at 85% of the composite sites. Compared to the monitoring results, which could only detect the relationships between cambium phenology and xylem cell production from a limited number of trees and years, our long-term relationships deepened such connections, and therefore should be used to improve mechanism models for the accurate evaluating and predicting of wood production and carbon sequestration in forest ecosystems under current and future climate change.