June Of Current Year Research Articles

Responses of tree growth and intrinsic water-use efficiency of Robinia pseudoacacia to climate factors

We investigated tree growth in Robinia pseudoacacia plantations at Ansai in Shaanxi Province and at Ji-xian in Shanxi Province by comparing the tree-ring width, basal area increase (BAI), δ13C value, intrinsic water-use efficiency (iWUE), and stomatal regulation. We quantified the responses of tree growth and iWUE to climatic factors at each site. The tree-ring width at Ansai and Jixian decreased with stand age, whereas the BAI at Ansai increased, and that at Jixian decreased after the BAI peaked. The δ13C value and iWUE of trees at Jixian were higher than those at Ansai. The iWUE of trees at both sites was similar to the constant intercellular CO2 concentration/atmospheric CO2 concentration (Ci/Ca) scenario, indicating that the Ci of trees was elevated with increasing Ca, while the stomata remained open. The BAI at Ansai was significantly positively correlated with highest temperature in May, relative humidity in June, precipitation in August, relative humidity in September, and standardized precipitation evapotranspiration index (SPEI) in September and October of current year, but negatively correlated with temperature in June. The BAI at Jixian was significantly positively correlated with SPEI in June and July, and lowest temperature in October of current year. The iWUE of trees at Ansai was significantly positively correlated with relative humidity and precipitation in June of the current year, but negatively correlated with minimum temperature in May, relative humidity in June, and temperature and maximum temperature in July of current year. A significant positive correlation between iWUE of trees at Jixian and lowest temperature in June of current year was detected. At the annual scale, the BAI of trees at Ansai was positively correlated with precipitation and SPEI, but no significant relationship was observed for trees at Jixian. However, the iWUE of trees at both sites was significantly affected by precipitation. Path analysis showed that SPEI and minimum temperature had a direct effect on BAI and iWUE of trees at Ansai, whereas precipitation and average temperature indirectly affected BAI and iWUE through SPEI. The highest temperature had a direct effect on tree growth at Jixian, whereas precipitation, minimum temperature, and average temperature had direct effects on iWUE. These results suggested that SPEI was the main climatic factor that affected the growth of R. pseudoacacia, while Ci was an important physiological factor. Our results could provide reference for the protection and management of R. pseudoacacia plantations under climate change.

Precipitation variation reconstructed based on tree-ring width data for the past 399 years in the eastern Yinshan Mountains, China

Based on the tree-ring increment cores of Pinus tabuliformis collected from the eastern Yinshan Mountains, the tree-ring width chronology was developed. The correlation coefficients were calculated between the chronology and monthly mean temperature and monthly precipitation during the instrumental period of AD 1952-2007. The results showed that the highest correlation was found between the total precipitation from September of previous year to June of current year and the chronology (r=0.73, n=56, P<0.01). Based on the correlation, the September of previous year to June of current year total precipitation variation was reconstructed in the eastern Yin-shan Mountains during the past 399 years (AD 1619-2017). The reconstruction explained 54.9% of the variation in the total precipitation from September of previous year to June of current year for the calibration period (AD 1952-2007). Both the 'leave-one-out' cross validation and split-period validation showed that the model was relatively robust, with sufficient skills of estimation and high reliability. At the decadal scale, there were four wet periods (AD 1619-1663, AD 1705-1711, AD 1945-1963, and AD 1979-2017)) and four dry periods (AD 1734-1767, AD 1786-1814, AD 1839-1867, and AD 1888-1942) in the past 399 years. Among those periods, the AD 1979-2017 was the wettest period, and AD 1888-1942 was the longest dry duration with the driest period at the late 1920s. Results of power spectral analysis revealed cyclic fluctuations of precipitation series on 2-7 years and 125 years. In addition, the comparison with other reconstructions and spatial correlation analysis indicated that the reconstructed precipitation series well represented regional scale precipitation variation.

Radial growth of dominant coniferous species and their responses to climate changes in the Altay Mountains, China

Based on the standard method of dendrochronology, we examined the tree-ring width index of two dominant tree species in the Altay Mountains, China, including Picea obovata and Larix sibirica. We analyzed the basal area increments (BAI) of those two species and the relationships between their radial growth and the climatic factors, which were compared in similar habitats. The results showed that the BAI of P. obovata was greater than L. sibirica, but the radial growth rate of L. sibirica was greater. In recent 60 years, the radial growth of P. obovata negatively correlated with high temperature in the fast growing stage of previous year, while the high temperature in June of current year promoted the radial growth of L. sibirica. There was a significantly negative correlation between radial growth of L. sibirica with temperature in January of current year. The sensitivity of tree growth to climate showed an obvious increase after an abrupt climate change under the background of recent warming and wetting trend in mid-1980s. Results of the moving correlation analysis showed that the response of the radial growth of P. obovata and L. sibirica to temperature and precipitation were enhanced under the background of climate change in the study area.

Response of radial growth of Pinus koraiensis and Picea jezoensis to climate change in Xiao-xing'anling Mountains, Northeast China

Based on dendrochronological methods, we established residual chronologies of Pinus koraiensis and Picea jezoensis, with the dominant species of broadleaved Korean pine mixed forest at low altitudes chosen as the research object, to identify the key climatic factors affecting the radial growth of the two species in Xiaoxing'anling Mountains, Northeast China. The results showed that the responses of the two species to climate factors were different, and P. koraiensis was more sensitive, and hence more suitable for dendroclimatological analysis. Response function coefficients indicated that the radial growth of P. koraiensis negatively correlated with June mean temperature of current year, while positively correlated with precipitation in June of current year. There was no significant correlation between P. jezoensis and all climate variables. Spatial correlation analysis revealed that variations in chronology of P. koraiensis contained strong regional signals, and the highest correlation occurred in the vicinity of the study area. Warming caused drought stress, which was the main factor that limited the growth of P. koraiensis, and it might have adverse effects on the Korean pine if global temperature continues to increase. The coupling effects of large-scale atmospheric-oceanic variability may affect the radial growth of P. koraiensis in Xiaoxing'anling Mountains.

Tree-ring based February–April relative humidity reconstruction since A.D. 1695 in the Gaoligong Mountains, southeastern Tibetan Plateau

ABSTRACTHigh-resolution proxy data are limited in the southeastern Tibetan Plateau, which inhibits our understanding of long-term climate variability in historical periods. In this study, we developed one tree-ring-width chronology of Tsuga dumosa (D. Don Eichler) in the Gaoligong Mountains, southeastern Tibetan Plateau. Tree-ring-width chronology showed negative correlations with monthly temperatures in most months, especially for current year, whereas correlations with precipitation and relative humidity were mostly positive. Significant positive correlations were found between tree rings and relative humidity in February, April and June of current year and May of previous year. February–April relative humidity was reconstructed for the past 321 years (A.D. 1695–2016) in the Gaoligong Mountains, which explained 26% of the actual variance during the calibration period 1962–2004. In this reconstruction, dry periods occurred in 1808–1820, 1831–1842, 1914–1921, 1958–1964 and 1980–1988. Wet periods were found in 1700–1727, 1821–1830, 1843–1859, 1944–1957 and 1965–1979. The dry and wet episodes of our relative humidity reconstruction match well other studies in the nearby regions, which demonstrate that the new record is reliable and captures large-scale climate signals.

Response of radial growth of Pinus koraiensis in broad-leaved Korean pine forests with different latitudes to climatical factors.

To reveal the radial growth trends of Pinus koraiensis and the differences in their responses to climate factors among different latitudes, and to assess the dynamic characteristics, adaptabi-lity and sensitivity of P. koraiensis under the influence of climate change, dendrochronological techniques were used to study the relationships between the climatic variables and the radial growth of P. koraiensis in broad-leaved Korean pine forests with different latitudes. The results showed that there were differences in the responses of the radial growth of P. koraiensis in four different latitudes to local climatic factors. In Baishilazi Nature Reserve, the southernmost sample plot, the radial growth of P. koraiensis was significantly positively correlated to the average relative humidity but significantly negatively correlated to the average maximum temperature of growing season. In low altitude of Changbai Mountain Nature Reserve, the intermediate sample plot, it was significantly positively correlated with precipitation, average relative humidity and PDSI, and significantly negatively correlated with the average maximum temperature in growing season. In Liangshui Nature Reserve, the intermediate sample plot, significantly positive correlations occurred for average relative humidity and PDSI in growing season, while significantly negative correlations occurred for the average temperature and the average maximum temperature in growing season. Nevertheless, in Shengshan Nature Reserve, the northernmost sample plot, it was positively correlated to the tempe-rature factors of most months. The climatic variables in June of current year were the main factors limiting the radial growth of P. koraiensis in all latitudes, and the average maximum temperature in June of current year was highly negatively correlated with radial growth for P. koraiensis measured at all sites. In recent four decades, with the rising of temperature, the radial growth of P. koraiensis decreased significantly in the southernmost point, increased significantly in the northernmost point, and did not change significantly in middle latitudes. The distribution area of P. koraiensis would be reduced if the temperature increased and precipitation remained unchanged in the future.

Growth responses of broad-leaf and Korean pine mixed forests at different successional stages to climate change in the Shengshan Nature Reserve of Heilongjiang Province, China

Aims This research examined the different response of tree growth to climate change at the early, middle, late and matured successional stages of Korean pine (Pinus koraiensis) and broadleaf mixed forest. Methods This research used dendroecological methods to analyze radial growth at different successional stages of Korean pine forests in response to climatic change in the Shengshan Nature Reserve of Heilongjiang. Important findings Chronology statistics indicated that the sensitivity of radial growth to inter-annual climate variability decreased from early to later successional stage. Meanwhile, the influence of some climate indices to radial growth also changed during the successional process. Radial growth of matured forest was positively re- lated to mean monthly temperature in June and December of previous year, revealing an obvious lag of temperature. The ring-width of matured forest had a negative correlation with mean monthly temperature but a positive correlation with monthly precipitation in June of current year, reflecting the limiting role of growing sea- son water availability. However, these limiting effects gradually disappeared towards the earlier stages of forest succession. On the contrary, the growth of early successional forest was negatively correlated to precipitation in June of previous year, and this effect disappeared towards the later successional stages. These differences revealed increased demand of water by dominant species from early to later successional stages. A moving correlation analysis showed that the increased warming and drying climate in the research area had both positive and negative influences on radial growth of each forest type. Earlier successional forests did not show clear long-term growth