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Tree-ring width (TRW) and stable carbon isotope (δC) in tree-ring cellulose of subalpine fir ( Abies fabri) were used to develop high-resolution climate proxy data to indicate snow-depth variations in the Gongga Mountain, west China. Tree radial growth- and δC-climate response analyses demonstrated that the TRW and δC at the timberline (3,400 m.a.s.l.) are mainly influenced by temperature and precipitation of previous growth seasons and current summer (June to August) under cold and humid conditions. Considering the analogous control factors on both tree growth and carbon isotope discrimination (ΔC) and snow accumulation, the negative and significant relationships between tree-ring parameters (TRW and ΔC) and mean monthly snowpack depth were found. Herein, by combining two tree-ring parameters, a primary snow-depth reconstruction (previous October to current May) over the reliable period A.D. 1880-2004 was estimated. The reconstruction explains 58.0% of the variance in the instrumental record, and in particular captures the longer-term fluctuations successfully. Except the period with extreme higher snowpack depth around 1990, the snowpack depth seems to fluctuate in a normal way. The reconstruction agrees with the nearby snowpack depth record in Kangding and the mean observed snowpack-depth variations of the stations on the Tibetan Plateau, particularly at long-term scales. The snowpack depth in low-frequency fluctuations, during the past century, agrees quite well with the Eastern India precipitation covering the period of previous October-current May. Our results suggest that combing tree-ring width and δC in certain subalpine tree species growing on the Tibetan Plateau may be an effective way for reconstructing regional snowpack variations. [ABSTRACT FROM AUTHOR]

The article presents a study which investigates the effect of climate change on terrestrial ecosystem in China. The study employs various data and methods which include the 1961-2100 projected climatic data to lessen data noise and the atmospheric-vegetation interaction model (AVIM2) to simulate terrestrial ecosystem. Moreover, the study reveals that the net primary productivity (NPP) decreases when the projected temperature increases.

Little is known about the spatial variability in tree growth and its responses to climate on the Tibetan Plateau; however, such information is essential for improving predictions of forest ecosystem response to climatic change. A network of 16 ring width chronologies was developed along a latitudinal transect in the Qilian Mountains, northeastern Tibetan Plateau. A principal components analysis revealed that the residual chronologies had a positive loading on the first unrotated principal component (PC1). After rotation, PC1 yielded the highest loadings on the driest sites in the northwest and decreased to the south and to the east. PC2 was negatively correlated with altitude. Moisture availability was a dominant limiting factor for tree growth, and this dominance increased northwards and westwards along the precipitation gradient. Loadings of the first two rotated principal components separated the 16 forest sites into three major groups corresponding to the three regions affected by the East Asian Monsoon, Westerlies, and their interaction. Thus, spatial variability in tree growth is an excellent bioindicator of regional climate. [ABSTRACT FROM AUTHOR]

Midlatitude regions experienced frequent droughts during the twentieth century, but their impacts on terrestrial carbon balance are unclear. This paper presents a century-scale study of drought effects on the carbon balance of terrestrial ecosystems in China. The authors first characterized the severe extended droughts over the period 1901–2002 using the Palmer drought severity index and then examined how these droughts affected the terrestrial carbon dynamics using tree-ring width chronologies and a process-based biogeochemistry model, the Terrestrial Ecosystem Model (TEM). It is found that China suffered from a series of severe extended droughts during the twentieth century. The major drought periods included 1920–30, 1939–47, 1956–58, 1960–63, 1965–68, 1978–80, and 1999–2002. Most droughts generally reduced net primary productivity (NPP) and net ecosystem productivity (NEP) in large parts of drought-affected areas. Moreover, some of the droughts substantially reduced the countrywide annual NPP and NEP. Out of the seven droughts, three (1920–30, 1965–68, and 1978–80) caused the countrywide terrestrial ecosystems to switch from a carbon sink to a source, and one (1960–63) substantially reduced the magnitude of the countrywide terrestrial carbon sink. Strong decreases in NPP were mainly responsible for the anomalies in annual NEP during these drought periods. Changes in heterotrophic respiration happened in the same direction, but mostly with smaller magnitude. The results show that severe extended droughts had significant effects on terrestrial carbon cycling in China, although future studies should consider other important processes such as drought-induced mortality and regrowth, land-use change, disturbances (e.g., fire), human management (e.g., fertilization and irrigation), and environmental pollution (e.g., ozone pollution, nitrogen deposition). These drought effects are of particular importance in light of projected widespread summer drying in midlatitude regions during the twenty-first century. Future droughts could lead to a reduced terrestrial carbon sink or even a source and exert a positive feedback to the global climate system. [ABSTRACT FROM AUTHOR]

The article discusses about the effects of temperature and precipitation changes in time on the tree growth of Qilian junipers (Sabina przewalskii Kom.), found along the Qinghai-Tibetan Plateau. According to the article, studies before had shown that water usage stress is the most restraining factor for the growth of trees in the Qaidam Basin region. A water balance modelling using a 1955-2002 meteorological data was used to evaluate the impacts of changes in temperature and precipitation. From the experiment conducted, it was concluded that the climate variability at the interannual and interdecadal scales are reflected by moisture conditions reconstructed from tree-ring widths.

Qilian juniper ( Sabina przewalskii Kom.) and Qinghai spruce ( Picea crassifolia Kom.) represent different tree functional types, which can be found extensively in northwestern China. The former is drought-tolerant, whereas the latter is hygrophilous and shade-tolerant. We compared their intrinsic water-use efficiency (iWUE, inferred from carbon isotopic discrimination, δ13C, in their wood) as a function of atmospheric CO2 concentration, [CO2], and climate. δ13C of spruce was consistently about $${1.23\permille}$$ higher than that of juniper in semi-arid areas but was lower in arid areas. This difference was stable over time and demonstrated strong cross-correlations between species, although some subtle high-frequency (2 or 3 years) variations existed in both species, suggesting that regional climate may control carbon isotope discrimination. The $${{C_{\rm i}/C_{\rm a}}}$$ ratio (the [CO2] values in leaf intercellular and the atmosphere, respectively) of the juniper increased steadily over time, whereas that of the spruce showed a long-term downward trend. IWUE increased at all sites over the 150-year study period, mainly caused by increasing [CO2]. The relationship between iWUE and [CO2] reveals that the spruce was more sensitive than the juniper to increasing [CO2], suggesting a species-specific adaptation to long-term environmental changes. Correlations between the high-frequency variations in stable carbon discrimination (Δ) and climate indicate similar intra-site responses to climate in both species, but different response strengths. Overall, complex interactions of temperature and moisture on stable carbon discrimination during current growth seasons of both species were environmental-determined. Regulation of gas exchange and reduced transpiration may influence water and energy budgets directly; therefore species-dependent responses of trees to elevated CO2 should be considered in future research on global plant physiological ecology. [ABSTRACT FROM AUTHOR]

Using long-lived Qilian juniper (Sabina przewalskii Kom.) in the middle Qilian Mountains, the temperature variations in the last 1000 yr were reconstructed. We find that the annual growth ring width and δ13C series mainly reflect variations in regional temperature. Except in May, warmer temperatures indicate greater growth over the period from December to April, and δ13C values in tree-rings are higher for years with higher temperature. The notable features in the temperature reconstruction are the occurrence of the Little Ice Age from A.D. 1600 to 1880 and the abrupt warming over the end of past millennia. The comparison of our chronology to a Northern Hemispheric temperature proxy shows that our tree-ring data will facilitate intercontinental differentiation of large-scale synoptic climate variability. [ABSTRACT FROM AUTHOR]

Using a network of tree-ring data, we show that there had been significant growth decline in the 1920s and early 1930s throughout a wide area of northern China. This growth depression is indicative of a severe and sustained drought in the 1920s and early 1930s, which was then confirmed with a variety of historical and instrumental records including hydrological, meteorological, and documentary evidence. The 1920s drought had a devastating effect not only on agricultural productivity, hydrological resources and society in the affected areas, but also on natural vegetation, as inferred from the tree-ring network and historical records. This research offers a picture of the drought calamity during the 1920s and early 1930s in northern China, and demonstrates the potential to identify spatial anomalies of large-scale drought using tree-ring networks in the semi-arid and arid areas of northern China. [ABSTRACT FROM AUTHOR]