Treering samples of Picea crassifolia were collected from the upper treeline in the eastern mountainous area of Qaidam Basin in Qinghai Province. The tree-ring width and the cell number and size of the tree-ring were measured, and the standard chronologies for the early-wood cell number, late-wood cell number, total cell number of tree-rings, maximum cell size, and minimum cell size were constructed. By using correlation analysis and the response functions between cell characteristic indices and 1970-2000 climate factors at Chaka meteorological station which was close to the sampling site, the relationships between P. crassifolia growth at cell scale and climate factors were discussed. The results showed that the earlywood cell number was positively correlated to the wintertime temperature from previous October to current March, while the late-wood cell number was positively correlated to the minimum temperature in previous November and December and to the mean temperature in current July and August. Both the early-wood and the latewood cell numbers were negatively correlated to the precipitation in July, and the early-wood cell number was positively correlated to the precipitation in May. The chronology of maximum cell size of earlywood was positively related to the precipitation in February, while that of minimum cell size of late-wood was positivelyrelated to the precipitation in August. It was concluded that the cell number and cell size could not only reveal the information of temperature change, which was recorded by tree ring width as well, but also provide additional information of precipitation. Since different types of tree-ring indices contained different climate information, multiple aspects of climate change information could be extracted from different treering indices of the same species at the same site, and the cell level tree ring characteristics had great potential to supply the information regarding past climate.

This paper determined the δ¹³C annual series of three Cryptomeria fortunei tree rings at West Tianmu Mountain,and analyzed their similarities and differences.In the period of 1837～1982,the correlations among the three δ¹³C series were significant,with r₁₂=0.47,r₁₃=0.65 and r₂₃=0.52 (P<0.001,n=146),respectively.After removing the high-frequencies from the original δ¹³C series by using polynomial function model,a significant correlation was observed among three low-frequencies,with the correlation coefficient varied from 0.95 to 0.998.A significant correlation was also observed between original low-frequencies and simulated high-frequencies,with the correlation coefficient being 0.79～0.84.The three δ¹³C annual series had similar high-frequency and low-frequency variations.High-frequency variation recorded similar climate variation information,while low-frequency reflected the information of atmospheric CO₂ changes.It was the common case for different individuals of trees that in the three δ¹³C annual series,climatic factors caused highfrequency change,while atmospheric CO₂ concentration caused low-frequency variation.The differences among the three δ¹³C annual series were mainly caused by the local environmental conditions at the growth sites of trees,while the individual difference among the three δ¹³C series caused by local environmental conditions had very small effects on the changes of the three δ¹³C series.It could be concluded that the differences among the three δ¹³C series did not affect the suitability of using tree ring’s δ¹³C annual series as the indirect evidence in climatic variation study,and the reliability and coherence of reconstructing historical climate changes.

Picea schrenkiana is the dominant tree species in Ili River Basin located in the western Tianshan Mountains of Xinjiang. We investigated the growth decline characteristics of P. schrenkiana at different altitudes (1800, 2300 and 2800 m) based on tree-ring index (TRI) and percentage growth change (GC), aiming to understand the growth response of P. schrenkiana to drought events at different altitudes and the impacts of altitude on tree growth decline in this region. The results showed that P. schrenkiana experienced multiple decline events at low-altitude (1800 m). TRI and GC identified inconsistent occurrence time of the decline events. The variations of TRI indicated that P. schrenkiana at low-altitude experienced two large-scale declines during 1927-1933 and 2017-2014, respectively. The variations of GC identified four decline events, including 1891-1893, 1924-1926, 1973-1975, and 2004-2009. The radial growth of P. schrenkiana across altitudes from low to high was significantly affected by the Palmer drought severity index (PDSI) of the previous growing season. The impact of current PDSI on P. schrenkiana during the growing season initially enhanced but later decreased with increasing altitude. In the extreme drought year 1917, the magnitude of growth decline increased with altitude. At low-altitude (1800 m), the TRI was 0.65, which was 35% lower than the normal level. At mid-altitude (2300 m) and high-altitude (2800 m), it was 0.56 and 0.54, respectively, being 40% lower than the average level. The drought event in 1917 had a 2-year legacy effect on the growth of P. schrenkiana at all the altitudes, with the TRI in 1920 recovered to exceeding 0.9, being close to the normal level. The impact of altitude on drought-induced forest decline was significant. Tree growth in low-altitude areas was more vulnerable to drought events due to the relatively poorer water and temperature conditions at low-altitude, which could lead to multiple large-scale decline events. In mid- and high-altitude areas, where hydrothermal conditions were more favorable, trees could experience even more severe decline during extreme droughts.

We used tree rings of Pinus tabuliformis sampled in the Muwang National Forest Park to establish a standardized chronology (STD) and calculated the correlation coefficients between the standardized chronology and climatic factors of Zhen’an meteorological station. With linear regression analysis, we reconstructed the March-April mean maximum temperature of Zhen’an over 165 years from 1853 to 2017. The highest correlation coefficient was observed between the standardized chronology and the March-April mean maximum temperature (r=0.596, n=60, P<0.01). The variance interpretation of the March-April mean maximum temperature reconstruction function was 33.2%, and the reconstruction function and results were credible and reliable. Warm years occurred 25 times and cold years occurred 29 times in the reconstruction sequence. The warm years were more accompanied by flood events, while the cold years were accompanied by more drought events. Temperature fluctuated obviously in the reconstruction sequence, with two cold periods (1902-1917 and 1953-2000) and four warm periods (1868-1892, 1917-1937, 1941-1953 and 2001-2012). The obvious periodic variations of 2-7, 8-15, 18-28, 75-96, and 100-125 years were found in the reconstruction sequence, in which the quasi-113, 88 and 22 years were the first, second and third main periods, respectively. These variations might potentially be the fingerprints of some climate change forces such as solar activity, monsoon and EI Niño-Southern Oscillation (ENSO) activity.

With dendrochronology method, standard and residual chronologies of Pinus massoniana were established at low altitude (260 m), middle altitude (460 m), high altitude (690 m), sunny slope (270 m), and shady slope (265 m). Relationships between the tree-ring width and the climatic factors were quantified using correlation analysis and redundancy analysis (RDA). The optimal multiple regression models for the radial growth of P. massoniana and the climatic factors were established. We analyzed the change rule of radial growth and its relationship with the climatic factors along with the altitude and slope. The results showed that the radial growth of P. massoniana was significantly affected by precipitation and temperature across the altitude gradient and the slope level, respectively. Among the 120 climatic variables, precipitation in December of last year and the extreme minimum temperature in February of current year had the most significant negative effects on the radial growth at different altitudes and slopes, respectively. This study quantitatively described the impacts of climate change on the radial growth of P. massoniana in the subtropical region, and provided a scientific basis for the planting and management of P. massoniana forest in Jiangle Country under the climate warming background.

To understand the responses of radial growth of Fraxinus mandshurica from different provenances to climatic factors, we used the dendrochronological method to establish the standard chronologies of F. mandshurica from 20 provenances in Maoershan provenance test forest, and analyzed the differences in radial growth and their correlation with climate factors. The results showed that the overall trend of F. mandshurica chronologies from 20 provenances was generally similar. There were differences in growth amplitude, with the average radial growth of F. mandshurica from Dailing, Lushuihe and Sanchazi being the highest. The radial growth of F. mandshurica from 20 provenances was significantly positively correlated with the highest temperature in July and the average temperature in July except for Huinan. The radial growth of F. mandshurica from 14 provenances was significantly positively correlated with the precipitation in August. The radial growth of F. mandshurica was constrained by temperature and precipitation during the growing season. There was difference in radial growth among F. mandshurica from different provenances under drought stress. F. mandshurica from Wangqing, Dailing, and Hailin had stronger resistance to drought, while that from Wandianzi, Zhanhe, and Xinglong had better recovery ability after drought.

The Three-North Shelter Forest is an important ecological defense of Beijing-Tianjin-Hebei area. About four-fifths of poplar plantations declined and about a third of them were dying or already dead in the last ten years. The mortality of trees resulted in the decline of ecological function of poplar plantation. In this study, we investigated the differences of δ¹³C and intrinsic water-use efficiency (WUE_i) values in the tree-ring between dieback and non-dieback trees with stable carbon isotope method. The cause of poplar plantation degradation and mortality was retrospectively ana-lyzed. The results showed that the diameter of poplar trees of nearly the same age decreased with the increase of degradation degree. The δ¹³C value of rings from dieback trees varied between -25.26‰ and -22.97‰, whereas that of non-dieback ones was -26.15‰ to -23.50‰. The δ¹³C values of dieback trees were higher than that of non-dieback ones from 1997. There was a nonsignificant difference of the WUE_i between dieback and non-dieback tree-ring from 1997 to 2001. And the difference of WUE_i between dieback and non-dieback tree was significant since 2002. The continuous occurrence of positive ΔWUE_i(WUE_idieback-WUE_inon-dieback) values might be one of important factors for subsequent divergence of the dieback and non-dieback poplar trees. The WUE_i of both dieback and non-dieback trees had no significant relationship to precipitation, relative humidity and ET₀, while significantly related with air temperature and ground water depth. The retrospective ana-lysis results showed that extreme drought in 1997 was a threshold when poplar trees began to decline. The underground water was overused because of land use change, which increased the intensity and duration of the drought, thus accelerated the degradation and mortality of poplar trees.

Mean sensitivity (MS) of tree ring is a key index representing the sensitivity of tree rings to climate. Understanding the variation of MS and its influencing factors at a large area is helpful to understand the interaction between tree growth and climate. We used 573 tree-ring width chronologies in Asia from the International Tree Ring Date Bank (ITRDB) to examine the variation of tree-ring sensitivity and potential influencing factors. The results showed that the MS of trees was high in the arid regions and cold regions. Precipitation was more important than temperature in diriving MS. Consistent with the pattern of up-down-up for precipitation, MS showed a down-up-down fluctuation with increasing altitude, indicating that precipitation affected by altitude was a key climate factor for the MS. MS had great difference due to different physiological traits among tree species. Light-adapted species, such as Juniperus przewalskii and Pinus gerardiana, had high MS due to drought tole-rance. Shade-adapted species, such as Picea and Abies, had low MS. Old trees may have high MS.

Taking windfall woods of Picea schrenkiana in the southern mountainous area of the Ili Prefecture as the research object, tree-ring density chronologies were developed from the discs for maximum density (MXD), minimum density (MID), mean earlywood density (EWD), and mean latewood density (LWD) at five different stem heights (1.3, 5, 10, 15 and 20 m) to examine the climatic responses of tree-ring density by correlation analysis with local meteorological data. The results showed that there was a good coherence among the four types of tree-ring density chronologies for the same stem height, which was relatively significant for the data from 10, 15 and 20 m. The LWD had good coherence among different stem heights, while the climatic responses of tree-ring density at different stem heights varied. The MXD and LWD at 15 m were sensitive to mean tempera-ture from July to September in the previous year and from May to September in the current year. It might underestimate the response of P. schrenkiana to temperature if we sample tree-ring at 1.3 m.

Water use efficiency (WUE) is different among species and regions. Few literatures have been reviewed related to long-term WUE of Platycladus orientalis in mountainous areas of Beijing, China. Tree-ring δ¹³C of P. orientalis was used to determine the long-term variation of annual intrinsic water use efficiency (WUE_i) and its response to environmental change. Combining with quantification of tree-ring width, the relationship between net carbon sequestration and WUE_i of P. orientalis was eventually explored. The results showed that mean annual temperature increased with the increase of time from 1918 to 2013, whereas annual precipitation fiercely fluctuated. Tree-ring δ¹³C decreased and WUE_i increased over time. WUE_i was positively related and more sensitive to air temperature increasing than temperature decreasing. Correlation between WUE_i and fluctuated annualprecipitation was ambiguous, which indicated the precipitation was not the main factor affecting WUE_i. The de-trend tree-ring width of P. orientalis increased initially and then decreased, especially in recent 20 years. According to the correlation between WUE_i and environmental factors, temperature resulted in stomatal conductance (g_s) decreasing, which caused a reduction in evapotranspiration and an increase in respiratory loss, leading to the increase of WUE_i and a down trend in net carbon sequestration and tree growth.

We used the correlation analysis of Larix chinensis tree-ring width chronologies, meteorological data as well as regional NDVI data to reconstruct the NDVI sequence variation of the north and south aspects of Taibai Mountain Nature Reserve in the recent 172 years. The results showed that the NDVI variation of Taibai Mountain Nature Reserve was consistent with plant growth dyna-mics. Hydrothermal condition in growing season was the dominant factor controlling NDVI changes. Tree-ring width was significantly positively correlated with NDVI in growing season. The strongest correlation occurred in July. Thus, we used the long time series of tree ring width index in July to reconstruct the regional historical period variation of NDVI sequence. The results demonstrated that historical changes of July NDVI sequence existed five dense periods and five sparse periods. Further analysis indicated that these periods corresponded with the climate change trends and drought events. The reconstructed July NDVI sequence of both northern and southern slopes of Taibai Mountain Nature Reserve highlighted the existence of quasi periodic variation of 60 years.

We established 340-year chronologies of total ring width, early wood width, and late wood width with tree-ring samples of Pinus taiwanensis at high altitude collected from the western Tianmu Mountain in northern Zhejiang Province. According to the criterion that subsample signal strength (SSS) should be larger than 0.8, the reliable period was from 1810 to 2019. Through the correlation analysis between chronologies and climatic factors, we examined the responses of tree ring growth to climate. The results showed that radial growth of P. taiwanensis was more sensitive to temperature than to precipitation. Comprehensively considering the correlation analysis results for the raw and first-order difference series, early wood width was significantly correlated with the early growing season mean and maximum temperatures of the prior year, while late wood width with prior May and current September mean and maximum temperatures. The correlation pattern of total ring width was similar to that of early wood width, although at a low level. The optimal correlation was between early wood width and prior April-July mean temperature. Based on this relationship, April-July mean temperature of the Tianmu Mountain, East China was reconstructed for the period of 1809-2018 with an explained variance of 61.5%. Both the raw and first-order difference series passed the split sample calibration-verification test. The warm periods were 1809-1833 and 1965-2018, with a cold period in 1834-1964. Temperature had risen rapidly since the 1960s. From the standpoint of low frequency, it reached an unprecedented level since the 1980s over the past 210 years. Spatial correlation analysis showed that the reconstructed temperature series could represent temperature variations of East China, which had a good agreement with a reconstructed regional temperature series from East China. Our results showed that P. taiwanensis had a great potential for paleoclimate reconstruction in East China.