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    15 October 2021, Volume 32 Issue 10
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    Spatial and temporal variations of the responses of radial growth of Larix gmelinii to climate in the Daxing'anling Mountains of Northeast China
    HAN Yan-gang, GAI Xue-rui, QIU Si-yu, ZHANG Yue, WANG Shou-le, ZHOU Li, YU Da-pao
    2021, 32(10):  3397-3404.  doi:10.13287/j.1001-9332.202110.021
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    Following the distribution characteristics of Larix gmelinii in Daxing'anling Mountains, nine sampling sites along a latitude gradient were set up to analyze the spatial difference and temporal dynamic in the responses of radial growth of L. gmelinii to climate. Overall, the radial growth of L. gmelinii was positively correlated with the standardized precipitation evapotranspiration index (SPEI) in summer (June to August), summer precipitation, February SPEI, and February preci-pitation, but was negatively correlated with the March temperature. Spatially, in the southern area of the region with higher annual average temperature, the radial growth of L. gmelinii had a significant positive correlation with February SPEI. In the northern area with lower annual average tempera-ture, the radial growth of L. gmelinii was negatively correlated with the temperature in March. Temporally, the growth-climate relationship for L. gmelinii was unstable. In the area with higher annual average temperature, the positive effects of SPEI and precipitation, as well as the negative effects of temperature in summer on growth significantly enhanced with climate warming. In the area with lower annual average temperature, the negative response of growth to March temperature enhanced more obviously. Such a result indicated that climate change would alter growth-climate relationship, with great spatial variations. Our results suggested that radial growth of L. gmelinii would be limited in the future climate of warm and dry in the Daxing'anling Mountains. The growth of L. gmelinii might obviously decline in south due to summer water deficit and winter drought, and might be inhibited in north because of warm and dry winter.
    Responses of radial growth of Pinus sylvestris var. mongolica and Larix gmelinii to climate change
    GUO Xue-mei, WANG Zhao-peng, ZHANG Nan, ZHANG Dong-you
    2021, 32(10):  3405-3414.  doi:10.13287/j.1001-9332.202110.042
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    In the context of global warming, the increases of temperature may affect tree growth and thus disturb ecosystem balance. In this study, we explored the main limiting factors for radial growth of Pinus sylvestris var. mongolica and Larix gmelinii in the Mohe area of Greater Khingan Mountains by using growth-climate response function analysis and moving correlation analysis, as well as the interspecific difference of the responses of radial growth to rapid warming. The results showed that the radial growth of P. sylvestris var. mongolica and L. gmelinii was affected by both temperature and precipitation. P. sylvestris var. mongolica was more sensitive to climate change than L. gmelinii, and its sensitivity to climate factors was more stable than L. gmelinii. The radial growth of P. sylvestris var. mongolica was significantly positively correlated with the monthly mean temperature and the monthly mean minimum temperature of the growing season, while that of L. gmelinii was significantly positively correlated with the monthly mean temperature and the monthly mean maximum temperature of winter. Precipitation in winter promoted the growth of P. sylvestris var. mongolica, whereas precipitation in the late growing season of the previous year inhibited the radial growth of L. gmelinii. After the rapid warming in 1990, the limiting effect of precipitation on P. sylvestris var. mongolica changed from negative to significantly positive, with the inhibition effect of high temperature being greater than the promotion effect. The inhibitory effect of high temperature on L. gmelinii was enhanced, and the limiting effect of precipitation on L. gmelinii was also enhanced after heating up. The growth rate decreased significantly, with obvious difference being observed in the correlations between the growth rate of two species with temperature and precipitation. Our results could provide scientific basis for forest ecosystem management and protection in Greater Khingan Mountains.
    Response differences of radial growth of Larix gmelinii and Pinus sylvestris var. mongolica to climate change in Daxing'an Mountains, Northeast China
    YANG Jing-wen, ZHANG Qiu-liang, SONG Wen-qi, ZHANG Xu, LI Zong-shan, ZHANG Yuan-dong, WANG Xiao-chun
    2021, 32(10):  3415-3427.  doi:10.13287/j.1001-9332.202110.005
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    Daxing'an Mountains is one of regions in China with the most significant climate change. Larix gmelinii and Pinus sylvestris var. mongolica are the most important species in this area. The study of their radial growth response to climate change would provide a scientific basis for predicting the dynamics of boreal forests under climate change. A total of 451 tree-ring cores of L. gmelinii and P. sylvestris var. mongolica were collected from six sites in the Daxing'an region, and 12 standard chronologies were established. We compared the tree growth trend since 1900, and analyzed their response to the climate factor in each site using Pearson correlation analysis. Effects of temperature and precipitation on the annual radial growth of L. gmelinii and P. sylvestris var. mongolica were investigated by linear mixed models. The time stability of the relationship between two species growth-climate was compared by moving correlation. The results showed that the radial growth of L. gmelinii was negatively correlated with mean temperature in March and positively correlated with precipitation in the previous winter and July of current year. The radial growth of P. sylvestris var. mongolica was positively correlated with temperature in August and precipitation in the growing season (from May to September) of current year. Snow in winter played an important role in promoting the radial growth of L. gmelinii, whereas precipitation in summer limited the radial growth of P. sylvestris var. mongolica. The responses of L. gmelinii and P. sylvestris var. mongolica to climate change were significantly different, which affected tree growth, species composition, and spatial distribution in the boreal forests.
    Xylem anatomical characteristics of Fraxinus mandshurica and relationship with climate in different slope positions
    ZHENG Qin-ying, ZHANG Guo-shuai, ZHAO Bin-qing, WANG Xiao-chun
    2021, 32(10):  3428-3436.  doi:10.13287/j.1001-9332.202110.012
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    With global climate warming, warming and drying in Northeast China are becoming more and more serious. To understand the effects of drought on the radial growth of Fraxinus mandshurica at different slope positions in Xiaoxing'an Mountains, we analyzed the responses of xylem anatomical characteristics of F. mandshurica to moisture change at different slope positions by wood anatomi-cal method. The results showed that F. mandshurica on the upper and lower slope positions were the same in the changes of xylem anatomical parameters. The abundance of vessels showed a linear distribution, the maximum vessel area and total vessel area showed a logarithmic distribution, while the average vessel area showed a partial normal distribution. There were significant differences in many anatomical parameters among different slope positions. The abundance and area of vessels on the lower slope positions were larger than those on the upper slope positions. Most of the anatomical parameters were significantly positively correlated with daily accumulated temperature, though there were some differences between them. The total vessel area of F. mandshurica on the upper slope positions was positively correlated with the daily mean temperature, while the number and total area of vessels were positively correlated with the relative humidity. The correlation on the upper slope positions was stronger than that on the lower slope positions. The minimum vessel area was negatively correlated with daily accumulated temperature and relative humidity on the upper slope positions, while the total vessel area was positively correlated with relative humidity on lower slope positions. The warming and drying climate would reduce the area and number of vessels in F. mandshurica, but would not affect the distribution of vessels, while the distribution of vessels on the upper and lower slope positions was generally the same. The current climate warming and drying do not limit but promote the radial growth of F. mandshurica.
    Construction of the additive model system for heartwood, sapwoodand bark taper of Pinus koraiensis plantation in different regions of Heilongjiang Province, China
    SUBATI Saidahemaiti, JIA Wei-wei
    2021, 32(10):  3437-3447.  doi:10.13287/j.1001-9332.202110.029
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    With the commonly used variable-exponent taper models developed by Kozak (1988), Muhairwe (1999), Lee (2003) and Kozak (2004), we aimed to develop taper functions of diameter outside bark (DOB), heartwood diameter (HD), sapwood width (SW), and bark thickness (BT) based on the data of 2977 discs from 103 sample trees of Pinus koraiensis plantations under different conditions in Mengjiagang Forest Farm, Dongjingcheng and Linkou Forestry Bureau in Heilongjiang Province. We selected the optimal basic model after comparison. By using seemingly unrelated regression (SUR) method in the PROC MODEL of SAS software, we established an additive model system for the taper equations of DOB, HD, SW and BT. By introducing the region as a dummy variable, the models were evaluated by coefficient determination (Radj2), root mean square error (RMSE), Akaike information criterion (AIC) and Bayesian information criterion (BIC). The results showed that the taper model developed by Kozak (2004) was the optimal one for the DOB, HD, SW and BT. When satisfying the additivity of each component and total amount, the additivity model system got better prediction effect, with a prediction precision of more than 98%. The additive model system with dummy variables improved the prediction ability to varying degrees, especially the prediction precision of HD and SW models. Minor differences existed in DOB and BT among different regions, while enormous differences in HD and SW. The additive model system with dummy variables not only had high prediction accuracy but also satisfied the additive logic of DOB, HD, SW and BT, which provided a basis for accurate estimation of heartwood, sapwood and bark volume of P. koraiensis.
    Simulation analysis of the radial growth characteristics of Pinus sylvestris var. mongolica in Hulunbuir Sandy Land by Vaganov-Shashkin Model
    BAO Guang, LIU Zhi-ye, LIU Na, WU Mai-li
    2021, 32(10):  3448-3458.  doi:10.13287/j.1001-9332.202110.038
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    The Vaganov-Shashkin model was used to simulate the standardized ring-width chrono-logy of Pinus sylvestris var. mongolica on the sandy land in Hulunbuir. The results showed that the fitting degree was better in the period before 2000 than that after 2000. Thus, the simulation results before 2000 were selected to analyze the radial growth. The results showed that the main growing season of P. sylvestris var. mongolica in Hulunbuir Sandy Land was from May to September each year. Temperature had a significant impact on the early and late growth of P. sylvestris var. mongo-lica. In the prosperous period of the growing season, insufficient soil moisture was the main factor restricting the radial growth. The radial growth rates of P. sylvestris var. mongolica in extremely narrow years were more limited by soil moisture than that in extremely wide years. The radial growth rates in the middle of the growing season (from July to August) showed a decreasing trend in wide and narrow years, indicating that the growth of P. sylvestris var. mongolica was affected by drought stress. Our results were consistent with the characteristics of tree-ring physiological models in semi-arid areas of China. The model was applicable to the radial growth simulation of P. sylvestris var. mongolica in Hulunbuir Sandy Land.
    Warming-drying climate intensifies the restriction of moisture on radial growth of Pinus tabuli-formis plantation in semi-arid area of Northeast China
    ZHAO Ying, CAI Li-xin, JIN Yu-ting, LI Jun-xia, CUI Di, CHEN Zhen-ju
    2021, 32(10):  3459-3467.  doi:10.13287/j.1001-9332.202110.034
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    Plantation ecosystems are more vulnerable than natural ones to global climate change. Using the dendrochronology method, we established tree-ring width chronologies of Pinus tabuliformis distributed in the semi-arid region of Northeast China. We examined its growth dynamics, analyzed the relationship between radical growth and climate factors, and explored the effects of global warming on the growth and distribution of P. tabuliformis. The results showed that tree-ring width chronologies of P. tabuliformis were negatively correlated with mean temperature of growing season (May-July), and positively correlated with precipitation and Palmer drought severity index (PDSI) in the early growing season (April) and in the growing season (May-July). Water availability was the main limiting factor for the radial growth of P. tabuliformis. Along the increasing precipitation gradient from southwest to northeast, tree growth became more sensitive to annual mean temperature, and the correlation with annual precipitation shifted from positive to negative, indicating that tree growth in the relative arid area (southwest of the study area) was more severely restricted by water availability. Drought stress caused by climate warming resulted in growth declines at some sites in the southwest area. With the continuous warming-drying climate, the distribution boundary of P. tabuliformis in the study area would shrink locally, with the suitable growth boundary moving northward.
    Effects of moisture and heat coupling on xylem growth of Pinus tabuliformis in Shenyang, China
    LIU Wei-tao, LI Jun-xia, ZHAO Ying, HAN Qing, HOU Sen, ZHANG Jing-yuan, LI Feng, CHEN Zhen-ju
    2021, 32(10):  3468-3476.  doi:10.13287/j.1001-9332.202110.036
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    Based on the micro-core technology, we can accurately examine the tree cambium phenology and the radial growth at the cellular scale, and reveal the relationship between tree growth and climate. Pinus tabuliformis is one of the constructive species in forests of northern China. We investigated the growth pattern of P. tabuliformis in Shenyang and the changes in cambium and xylem cells throughout the growing season (April to November) in 2020. Results showed that the dividing activity in cambium started in early April and ended at the end of September. Xylem began to grow from the appearance of enlargement cells (mid April) to the end of the disappearance of lignified cells (late October), with a growth trajectory of ‘S' shape curve. Approximately 53 xylem cells per row in radical direction were produced in 2020. The maximum growth rate (0.55 ind/row/day) occurred at the end of May, while the change of earlywood and latewood cells occurred at the end of July. When the minimum temperature above 0 ℃ in Shenyang, the cambium began to divide. The minimum critical temperature that affected the beginning and ending of xylem growth was 2-3 ℃. Precipitation promoted the growth in the growing season. The high temperature and insufficient water supply at the end of July were the main factors driving the differentiation of xylem cells to form earlywood and latewood.
    Responses of radial growth of Quercus mongolica to stand density and climatic factors in a mountainous area of eastern Liaoning Province, China
    MAO Yi-xin, ZHANG Hui-dong, WANG Rui-zhao, YAN Ting-wu, WEI Wen-jun, YUN Li-li, PAN Wen-li, YOU Wen-zhong
    2021, 32(10):  3477-3486.  doi:10.13287/j.1001-9332.202110.008
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    To explore the effects of stand density and climatic factors on radial growth of Quercus mongolica, we used tree ring chronology to examine the radial growth changes in a secondary Q. mongolica forest under different levels of stand density (thinning). The meteorological data combined with the driving factors of Q. mongolica growth were analyzed. The results showed that the radial growth of Q. mongolica was significantly affected by stand density. The mean annual radial growth of Q. mongolica was 3.12 mm in low-density virgin forest, 1.55 and 1.42 mm in the two medium-density secondary forests, respectively, and 0.96 mm in high-density secondary forest. The thinning intensity of 20% had a limited effect on promoting the radial growth recovery of high-density forest (1900 trees·hm-2), but had a significant effect on medium-density forest (1600 trees·hm-2). The radial growth of Q. mongolica was sensitive to the precipitation changes in January and February of the current year. Thinning reduced the sensitivity of Q. mongolica radial growth to climate. Under scenarios of climate warming and drying, density regulation could be beneficial in mitigating the adverse effects of climate change on the growth of Q. mongolica.
    Differences of drought tolerance of the main tree species in Dongling Mountain, Beijing, China as indicated by tree rings
    XIAO Jian-yu, ZHANG Wen-yan, MOU Yu-mei, LYU li-xin
    2021, 32(10):  3487-3496.  doi:10.13287/j.1001-9332.202110.001
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    Forests in Beijing exhibit vulnerability to increasing stress of extreme drought in recent years. To investigate the drought tolerance of different tree species, we chose three tree species (Larix principis-rupprechtii, Pinus tabuliformis, and Quercus wutaishanica) from the forest of Dongling Mountain in Beijing and used dendroecological method to analyze the relationship between radial growth and climate, as well as their resistance and resilience to extreme drought events. Our results showed that the radial growth of L. principis-rupprechtii and P. tabuliformis was significantly negatively correlated with monthly mean temperature from May to June, but that of Q. wutaishanica was significantly negatively correlated with monthly mean temperature only in May. The radial growth of L. principis-rupprechtii was significantly positively correlated with monthly mean precipitation in June, monthly mean relative humidity from May to June and August to September. The radial growth of P. tabuliformis was significantly positively correlated with monthly mean precipitation and monthly mean relative humidity from June to August. The radial growth of Q. wutaishanica was significantly positively correlated with monthly mean precipitation in February and May, and monthly mean relative humidity in May. The radial growth of all the three species was significantly positively correlated with monthly mean SPEI (standardized precipitation evapotranspiration index) from May to July. L. principis-rupprechtii was least drought tolerant, as indicated by the greatest growth reduction (46.6%-69.6%), lowest resistance (0.534, 0.304, 0.530) and resilience (0.686, 0.570, 0.753) during the three extreme drought events occurred in the 1994, 2001-2002, and 2007. In contrast, tree growth of Q. wutaishanica showed the highest drought resistance in 2007, whereas no significant differences were observed between other two species. Extreme drought events caused by continuous high temperature and reduced precipitation during the growing season accounted for the reduction in tree radial growth. The various physiological and ecological strategies of tree species were the possible reasons for the difference in drought tolerance. Our results could provide a basis for the selection of suitable afforestation tree species and the formulation of forest protection mea-sures to maintain forest ecosystem functions and services under the background of undergoing climate change.
    Responses of tree-ring width of Pinus tabuliformis plantation to climatic factors in Songshan Mountains, central China
    CUI Jia-yue, PENG Jian-feng, LI Jing-ru, LI Xuan, PENG Meng, YANG Liu
    2021, 32(10):  3497-3504.  doi:10.13287/j.1001-9332.202110.002
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    Taking Pinus tabuliformis plantations at different slopes in Songshan Mountains, Henan Province, China as subjects, we established different residual chronologies of P. tabuliformis in Paomaling (PML) and Junjifeng (JJF) and whole region (RC). The results showed that the chro-nological quality of PML was higher than that of JJF. Chronologies of PML and JJF had more climate information, which had significant positive relationship with mean temperature in current February, mean temperature and mean maximum temperature at the end of growing season (September-October), and significant negative relationship with mean maximum temperature in current May. The response of radial growth of P. tabuliformis to climate differed in PML and JJF. Radial growth of P. tabuliformis in PML was positively correlated with mean minimum temperature in March and precipitation in September, while that in JJF was positively correlated with precipitation in May and mean minimum temperature in September. Residual chronologies of P. tabuliformis in whole region contained more climate information. The multiple regression analysis method was used to simulate that the main limiting factors of tree-ring width growth of P. tabuliformis, which was a range of temperature indicators, especially current mean temperature in September. The result was consistent with that of correlation analysis. This study could provide basic services for forest protection and ecological construction in Songshan Mountains region.
    Response of intra-annual stem radial growth to drought events: A case study of Pinus tabuliformis in the Helan Mountains, China
    GAO Jia-ni, YANG Bao, QIN Chun
    2021, 32(10):  3505-3511.  doi:10.13287/j.1001-9332.202110.015
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    The stem radius growth of Pinus tabuliformis was monitored by dendrometer during the growing season in 2017 and 2018 at two altitudes (2010 and 2330 m) in the Helan Mountains. We investigated the responses of tree radial growth to drought events. The results showed that drought event in June 2018 reduced stem growth rate of P. tabuliformis. The precipitation in July and August reactivated the stem radius growth. The main growing season of P. tabuliformis stem was June-August in 2018, which was a month longer than that in 2017. The response patterns between stem radial growth of P. tabuliformis and climatic factors were consistent across forest stands in different altitudes. Drought in the early growing season suppressed the radial growth of trees, while precipitation in the mid- and late growing seasons played an important role in promoting the radial growth of trees. The effects of climatic factors in August on tree-ring width should be considered during climate reconstruction in this region.
    Responses of radial growth of two coniferous species to climate factors in western Sichuan Plateau, China
    LI Jing-ru, PENG Jian-feng, YANG Liu, CUI Jia-yue, LI Xuan, PENG Meng
    2021, 32(10):  3512-3520.  doi:10.13287/j.1001-9332.202110.032
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    Based on the method of tree-ring chronology, we established ring-width standard chrono-logies of Abies faxoniana and Sabina saltuaria in Liangtaigou, Lixian County, western Sichuan Province, and their regional composite chronology (RC) to study the responses of radial growth of those two coniferous species to climate change, which provided a basis for the protection and mana-gement of forest ecosystems in this region under the background of global warming. The results showed that the RC contained the common climatic information of two individual chronologies, which had higher signal-to-noise ratio and expressed population signal. The correlation analysis showed that three chronologies had a good consistency in the response to climate factors. All chronologies were significantly correlated with temperature, with S. saltuaria being more sensitive to temperature changes. Relative humidity had stronger limiting effect on both species than precipitation in May and October. After the abrupt warming in 1994, the correlation between ring-width chrono-logy of A. faxoniana and monthly mean temperature shifted obviously from negative to positive in some months, which indicated the radial growth of A. faxoniana showed unstable in response to temperature. However, the radial growth of both species showed different broadening trend and the sensitivity to temperature response was weakened.
    Radial growth dynamics of Chinese fir and its response to seasonal drought
    MENG Sheng-wang, YANG Feng-ting, DAI Xiao-qin, WANG Hui-min
    2021, 32(10):  3521-3530.  doi:10.13287/j.1001-9332.202110.031
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    We explored the seasonal dynamics and climate responses of radial variation of Chinese fir, we continuously monitored intra-annual stem radial size changes with the automated dendrometers in central Jiangxi Province in 2016 and 2017. We analyzed daily and seasonal dynamics of radial variations, and their Spearman correlations with climatic factors. We found that the diurnal radial variations had a pattern of contraction during the day and expansion at night. The growth onset in 2017 was one month earlier than that in 2016, whereas the continuous tree water deficit in the dry season caused the cessation one month early. During the main growing season (from April to September), the radial increment was significantly positively correlated with precipitation and relative humidity but negatively correlated with photosynthetically active radiation and vapor pressure deficit in both wet and dry seasons. However, the correlation for tree water deficit was opposite to stem radial increment. Severe water deficit significantly enhanced the impacts of soil water content on stem radial variation in the dry season. Moisture condition was always the key factor affecting stem radial variation of Chinese fir. Appropriate measures such as increasing soil water content could promote stem radial growth during summer drought.
    Differences in the ecological resilience of planted and natural Pinus massoniana and Cunninghamia lanceolata forests in response to drought in subtropical China
    CAO Xin-guang, HU Hong-bing, LI Ying-jun, DONG Zhi-peng, LU Xiao-rong, BAI Mao-wei, ZHENG Zhuang-peng, FANG Ke-yan
    2021, 32(10):  3531-3538.  doi:10.13287/j.1001-9332.202110.035
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    We sampled Pinus massoniana and Cunninghamia lanceolata in both plantation and natural forests in central and western Fujian Province, China. Using tree-ring width, tree-ring width index, and basal area increment, we reconstructed the annual growth of 109 conifer individuals from four sites for the 20-year period from 1993 to 2012. We then calculated resistance, recovery, and resilience indices of those trees in response to two consecutive extreme droughts (2003-2004 and 2011) and analyzed the differences in resistance and resilience between plantations and natural fore-sts. The results showed that there were temporal differences in moisture requirements between P. massoniana and C. lanceolata, which accounted for their inconsistent responses to drought in 2003-2004. For both species, drought induced a marked growth reduction, without any clear lag effect. The growth responses during and following the 2003-2004 drought were significantly stronger than that for the 2011 drought. Those results indicated that P. massoniana was more resilient to drought stress than C. lanceolata, and the natural forests were more sensitive than plantations, but with stronger capacity to recover. C. lanceolata plantations were more susceptible to frequent extreme drought events. To mitigate the vulnerability of plantation trees to more frequent droughts in the future, we suggested select trees from genetic provenances with strong drought resistance.
    Ecological resilience of ancient Pinus massoniana trees to climate change and insect infestation in southeastern Fujian, China
    LI Ying-jun, FANG Ke-yan, BAI Mao-wei, CAO Xin-guang, DONG Zhi-peng, TANG Wan-ru, MEI Ze-peng
    2021, 32(10):  3539-3547.  doi:10.13287/j.1001-9332.202110.010
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    Pinus massoniana is a typical pioneer afforestation tree species widely distributed in southern China. It is crucial to study the ecological resilience of P. massoniana to disturbances under global warming, drying, and frequent pest infestation, which can shed lights on forest mana-gements. In this study, tree-ring samples collected from old-growth P. massoniana trees in Baisong Village, Xianyou County, Fujian Province, were used to develop the first standard chronology of P. massoniana ring width (1865-2014) in this region. The results showed that the low relative humidity from July to September and the extremely high temperature from May to September were the main limiting factors for tree growth. The extremely narrow years were identified in 1869, 1889, 1986, 1991 and 1993. These extremely narrow years were exacerbated after the persistently low values of the previously two years via the superposed epoch analysis (SEA). The insect infestations were more likely to happen in dry years. Insect outbreak exerted strongest effect on tree growth in 1889. The narrow tree-rings in 1986 and 1991 were affected by both insect infestation and drought. The other extremely narrow years were mainly affected by drought. The resistance of trees to insect infestation was weaker than that to drought event. The relative resilience of trees to insect infestation was higher than that to drought event, except for 1991. The relative resilience was the highest in 1889 and the lowest in 1991 under the influence of successive extreme events. Under the enhanced drying trend since 2000, more trees had died possibly due to the combined effects of insect infestation and drought.
    Radial growth responses of four coniferous species to climate change in the Potatso National Park, China
    ZHANG Ju-mei, FAN Ze-xin, FU Pei-li, SHANKAR Panthi, TANG Hua
    2021, 32(10):  3548-3556.  doi:10.13287/j.1001-9332.202110.033
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    Using the principles and methods of dendrochronology, we measured tree-ring width of four dominant coniferous species, i.e., Larix potaninii var. macrocarpa, Picea brachytyla, Pinus densata, and Abies georgei, in the Potatso National Park, and established the tree-ring width resi-dual chronologies. We analyzed the correlation of tree-ring width residual chronologies with daily and monthly climate data from the Shangrila meteorological station to analyze the response of radial growth to climate factors. The results showed that L. potaninii var. macrocarpa had the highest annual growth rate, and A. georgei had the lowest. Radial growth showed species-specific responses to climate changes, with the highest sensitivity of L. potaninii var. macrocarpa and the lowest sensitivity of P. brachytyla. Ring-width chronology of A. georgei correlated positively with mean temperature during previous winter (November and December) and current summer (July). Ring-width chronology of L. potaninii var. macrocarpa correlated positively with temperature during the early-growing season (June), but negatively with precipitation and relative humidity. Ring-width chronology of P. densata correlated positively with precipitation and humidity but negatively with maximum temperature during the early-growing season (May), indicating that its radial growth was primarily influenced by water availability during the early-growing season.
    Responses of radial growth of Pinus yunnanensis to climatic and hydrological factors at different altitudes in Western Yunnan, China
    WANG Shi-jie, CHEN You-ping, CHEN Feng, ZHANG He-li
    2021, 32(10):  3557-3566.  doi:10.13287/j.1001-9332.202110.016
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    A tree-ring width chronology (STD) was established using tree-ring cores of Pinus yunnanensis from two sites with different altitudes in Western Yunnan, to study the responses of radial growth to climatic and hydrological factors. The results showed that the radial growth of P. yunnanensis in Western Yunnan was mainly affected by precipitation, temperature and runoff. The radial growth of P. yunnanensis at high altitude (2413.3 m) was controlled primarily by high temperature in summer and runoff in the monsoon season. In contrast, the radial growth of P. yunnanensis at low altitude (1062.6 m) was mainly controlled by precipitation in the growing season and annual runoff. The responses of radial growth of P. yunnanensis at high altitude to temperature change was unstable due to the existence of the temperature threshold. Due to the weakening of the East Asian summer monsoon in the 1980s, the temporal stability of tree growth response at low altitude to precipitation and runoff fluctuated. The radial growth of P. yunnanensis at different altitudes in Western Yunnan was related to the Asian summer monsoon and El Nio-Southern Oscillation.
    Intra-annual radial growth of Garuga floribunda in tropical seasonal rain forest and its response to environmental factors in Xishuangbanna, Southwest China
    WEI Xiao-lian,FAN Ze-xin, KAEWMANO Arisa, LIN You-xing, CHEN Li-min, FU Pei-li
    2021, 32(10):  3567-3575.  doi:10.13287/j.1001-9332.202110.027
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    We examined the seasonal growth dynamics of a deciduous tree species Garuga floribunda in the tropical seasonal rain forest in Xishuangbanna and monitored the stem radial growth with both high resolution dendrometer and microcoring methods. Combining with the monitoring of non-structural carbohydrates (NSCs) in stem and environmental factors, we analyzed the eco-physiological drivers underlying the seasonal cambial activity and radial growth dynamics. The results of high reso-lution dendrometer method showed that the growth of G. floribunda began at the end of May (day of year, DOY: 149.3±7.2) and ended at the end of August (DOY: 241.0±14.7) in 2020, the annual total radial growth was 3.12 mm, and the maximum growth rate was 0.04 mm·d-1. Based on the microcoring methods, we found that xylem cell enlarging started from March 9th (69.2±6.2) and cell wall thickening ended on September 19th (DOY: 262.8±2.8). The cumulative xylem radial growth was 1.76 mm, and the maximum growth rate was 0.009 mm·d-1. The daily radial growth rate of G. floribunda was significantly and positively correlated with precipitation, relative humidity, daily minimum air temperature, soil moisture and temperature at the depth of 20 cm, and was negatively correlated with daily maximum air temperature, vapor pressure deficit, maximum wind speed, and water vapor pressure. The starch and soluble sugar contents in the sapwood of G. floribunda were relatively higher before the growing season. The starch content was lowest in the end of March, while the content of soluble sugars was lowest in middle of May. At the end of the growing season, the contents of starch and soluble sugar in G. floribunda peaked in the middle of October and the end of December, respectively.
    Effects of warming on radial growth of Picea crassifolia in the eastern Qilian Mountains, China
    LIU Lan-ya, GOU Xiao-hua, ZHANG Fen, YIN Ding-cai, WANG Xue-jia, XIA Jing-qing, LI Qian, DU Miao-miao
    2021, 32(10):  3576-3584.  doi:10.13287/j.1001-9332.202110.019
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    Tree-rings of Picea crassifolia from high (3000 m), middle (2750 m) and low (2500 m) altitudes were collected from the Xiying River basin in the eastern Qilian Mountains, with the standard chronology being established using dendrochronological methods. Results of the correlation analysis between tree-ring width index and temperature and precipitation during different periods showed that radial growth of P. crassifolia at different altitudes responded differently to climate warming in the eastern Qilian Mountains. Water and heat availability were the main limiting factors for the radial growth of P. crassifolia in the eastern part of Qilian Mountains. The growth limiting factors at different altitudes were generally the same. Before the prominent warming (1961-1986), radial growth of P. crassifolia at the three sampling altitudes was significantly negatively correlated with mean maximum temperature in July-August of the previous year and August of the current year, and significantly positively correlated with the relative humidity in June of the current year. After the prominent warming period (1986-2014), tree growth at high, middle, and low altitudes remained significantly negatively correlated with air temperature, changed from non-significantly negative to significantly positive correlation with relative humidity in February of the current year, and changed from significantly positive to non-significantly negative correlation with precipitation and relative humidity in June. Warming caused a slowing growth of P. crassifolia tree-ring at all altitudes, with the highest altitude being the most sensitive. Drought stress caused by climate warming might be the main reason for the changes of radial growth of P. crassifolia.
    Stem radial growth of Picea crassifolia in response to climatic factors in the western Qilian Mountains, China
    XIA Jing-qing, GOU Xiao-hua, WANG Ling-ling, WANG Fang, ZHANG Jun-zhou, ZHANG Fen
    2021, 32(10):  3585-3593.  doi:10.13287/j.1001-9332.202110.020
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    The radial growth of eight individuals of Picea crassifolia and environmental factors were monitored by Dendrometer and automatic meteorological station in the western Qilian Mountains. The Gompertz function fitted results showed that the radial growth of P. crassifolia started on April 19, April 17, and April 10 in 2018, 2019 and 2020, respectively, and that the radial growth started when daily mean temperature exceeded 5.5 ℃. The radial growth of P. crassifolia ended on August 17, August 21, and July 19 in the three years, respectively. The ending time of radial growth was related to precipitation at the end of growing season. The radial growth of P. crassifolia was strongly inhibited by drought, and it had the strongest correlation with daily mean temperature (negative correlation) and daily precipitation (positive correlation) in July. The correlation of radial growth with the daily precipitation in the early growing season (May) showed significant inter-annual variation.
    Radial growth of dominant coniferous species and their responses to climate changes in the Altay Mountains, China
    GOU Xiao-xia, ZHANG Tong-wen, YUAN Yu-jiang, YU Shu-long, ZHANG Rui-bo, JIANG Sheng-xia, GUO Yu-lin
    2021, 32(10):  3594-3608.  doi:10.13287/j.1001-9332.202110.041
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    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.
    Responses of radial growth of Pinus sibirica to climate and hydrology in Altay, Xinjiang, China
    HU Mao, CHEN Feng, CHEN You-ping
    2021, 32(10):  3609-3617.  doi:10.13287/j.1001-9332.202110.017
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    Based on a standardized tree-ring width chronology established at Altay, Xinjiang, we examined the climatic and hydrological factors affecting the tree-ring width of Pinus sibirica. The results showed that the tree-ring width chronology of P. sibirica was negatively correlated with the average temperature and the average maximum temperature in May-June of current year and positively correlated with May-June PDSI and January-June precipitation. The tree-ring width chronology of P. sibirica was positively correlated with previous November runoff of the Irtysh River. The radial growth of P. sibirica was affected by temperature and precipitation, with precipitation in early stage of tree growth and temperature in summer being the key climatic factors. The study of the extreme years of chronology showed that the radial growth of P. sibirica was related to ENSO events and global large-scale circulations. By affecting the location of cyclones over Central Asia, ENSO affected water vapor transport to Altay, with consequences on the radial growth of P. sibirica.
    Reconstructing January-June precipitation in Southeastern Shanxi over the past 296 years inferred from tree-ring records of Pinus tabuliformis
    CAO Hong-hua, ZHAO Xiao-en, CHEN Feng, WANG Shi-jie, LIU Xing-hua
    2021, 32(10):  3618-3626.  doi:10.13287/j.1001-9332.202110.018
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    The study of regional historical climate change is limited by the availability of observational data, which is not conducive to understanding long-term climate change. In this study, we used the tree-ring cores of Pinus tabuliformis to establish a tree ring width chronology (RES) from the southeast Shanxi Province, and analyzed the relationship between precipitation and tree-ring width chronology. The results showed that the residual chronology had a good correlation (r=0.636, n=59, P<0.01) with January-June precipitation. A linear regression was used to reconstruct the January-June precipitation for the southeastern Shanxi Province, which accounts for 40.4% of the instrumental precipitation variation during 1724-2019. Dry conditions occurred during 1742-1771, 1830-1848, 1872-1894, 1917-1945, 1961-1981, and 1990-2019, while the periods of 1727-1741, 1772-1829, 1849-1871, 1895-1916 were relatively wet. There were 10 extremely dry years and six extremely wet years during the period from 1724 to 2019. The longest dry periods were 1742-1771 and 1990-2019, while the longest wet period was 1772-1829. Results of spatial climate correlation analyses with gridded land surface data showed that the precipitation reconstruction contained a strong regional precipitation signal for southeast Shanxi Province. Power spectrum analysis of the precipitation reconstruction showed remarkable 2.3, 3.2-3.3, 3.7-3.8, 6.3-6.7, 8.3-8.7 years cycles for the past 296 years, the 2.3 year cycle corresponds to the ‘quasi-two-year pulsation', and the 3.2-3.3, 3.7-3.8 and 6.3-6.7 year cycles might have a certain relationship with ENSO. Results of the spatial correlation analysis showed that the reconstructed precipitation series could better represent precipitation changes in the study area.
    Tree-ring reconstruction of March-August drought variability over the past 567 years in the Yajiang region of West Sichuan Plateau, China
    YUAN Qing-xue, YU Shu-long, JIANG Sheng-xia, QIN Ning-sheng, ZHANG Tong-wen
    2021, 32(10):  3627-3635.  doi:10.13287/j.1001-9332.202110.023
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    We constructed standard tree-ring-width chronology of Picea likiangensis var. rubescens for the Larima sampling site in the Ganzi Prefecture, Sichuan Province, by the single-free detren-ding method. The results showed that there was significant and positive correlation between the tree-ring chronology and March-August 1-month scale standardized precipitation and evapotranspiration index (SPEI1) of Yajiang region. The variation of the March-August SPEI1 sequence for 1942-2008 was reconstructed based on the current and last year sequences of the tree-ring chronology, with an explained variation of 42.8%. The newly reconstructed series mainly represented the variation of SPEI1 in the low-frequency domain over the historical period. Three wet periods were found in 1442-1465, 1516-1601 and 1836-2008, while the two intervals were dry periods for the March-August SPEI1 reconstruction in the Yajiang region of West Sichuan Plateau. There was a significant drying trend in 1456-1762 for the reconstructed sequence, a significant wetting trend in 1455-1762, while the wetting trend was the most significant in 1959-2008. Mutation test showed that the sudden changes from dry to wet for the March-August SPEI1 reconstructions occurred in 1512, 1733, 1767, 1831, 1941, 1957 and 1975, while that in 1684 and 1961 was the opposite. The comparison with surrounding region showed a good coherence of variations in the low-frequency domain among the SPEI1 reconstruction for the Yajiang region, the annual precipitation reconstruction for the northeastern Tibetan Plateau, and the SPEI05 reconstruction for the northern slope of the eastern Qilian Mountains. The reconstructed sequence well represented the variation of the March-August SPEI1 in the northeastern Tibetan Plateau and the southern Qinhai Province.
    Climatic signals recorded by Qinghai spruce tree-ring density in the western part of Qilian Mountains, China
    YANG Liu, QIN Chun, LI Gang
    2021, 32(10):  3636-3642.  doi:10.13287/j.1001-9332.202110.026
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    Dendroclimatology is one of the important methods for studying climate changes in the past. Previous studies showed that tree-ring density is an important proxy for temperature in the growing season. In this study, we established 132-135 years chronologies of tree-ring maximum density, the minimum density, the latewood and the earlywood average density of Picea crassifolia at the western Qilian Mountains. We compared the climatic signal and its seasonal best combination of different tree-ring density chronologies, and evaluated their potential values as climate proxies. The responses of tree-ring latewood average density and the earlywood average density to climate signals during the growing season were much lower than that of tree-ring maximum and the minimum den-sity. The tree-ring earlywood average density and the minimum density had a strong relationship with the Palmer drought index, indicating that the earlywood average density and the minimum tree-ring density had the potential as substitute indicators for drought.
    Changes of wet and dry climate in the past 205 years indicated by Pseudotsuga forrestii of river valley from southeastern Tibetan Plateau, China
    ZHAO Xiao-en, YUE Wei-peng, GAO Zhi-hong, CHEN Feng
    2021, 32(10):  3643-3652.  doi:10.13287/j.1001-9332.202110.007
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    The residual chronology of tree-ring width was constructed using Pseudotsuga forrestii collected from the low-altitude valley in the Chayu County, southeastern Tibetan Plateau of China. Pearson correlation analysis was carried out between the residual chronology of tree-ring width and climatic factors. The changes of Palmer drought severity index (PDSI) from April to May between 1812 and 2016 in the southeastern Tibetan Plateau were reconstructed by linear regression method (the variance interpretation was 47%). There was a significantly positive correlation between the PDSI index and tree-ring width index (r=0.69, P<0.01). The PDSI reconstructed sequence had four wet periods (1831-1844, 1853-1863, 1938-1948 and 1988-2002) and three dry periods (1864-1876, 1908-1926 and 2003-2016). Compared with other reconstructed sequences and historical records, our reconstructed sequence could better express dry and wet changes in the study area. The spatial analysis showed that the reconstructed sequence was consistent with the variation trend of PDSI index in southeastern Tibetan Plateau, with a strong spatial representation. Multiple tapers spectral analysis demonstrated that the PDSI reconstructed sequence had remarkable 19-20, 3.9, 3.2, 2.4 and 2.1 years quasi-periodic changes for the past 205 years, probably related to Asian summer monsoon and ENSO activities.
    Impacts of human activity on Bayin River runoff as revealed by tree rings in Qaidam Basin, China
    ZHU Xiao-long, CHEN Qing-mei, LYU Ai-feng, HUANG Ru, SHAO Xue-mei, LIANG Er-yuan, ZHU Hai-feng
    2021, 32(10):  3653-3660.  doi:10.13287/j.1001-9332.202110.040
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    Evaluating the impacts of human activity on river runoff has important implications for regional water resource management. Here, we used seven tree-ring width chronologies to establish a regional mean tree-ring width chronology from the northern mountain of Delingha, Qaidam Basin. We conducted the correlation, moving correlation and regression analysis of regional mean tree-ring width chronology with runoff data from Bayin River gauge station. Then, we stimulated the June runoff of Bayin River from 1956 to 2002. The results showed that the highest correlation coefficient was found for June runoff (r=0.63, P<0.01), and their moving correlation coefficient decreased after 1986. Based on the stable relationship between tree-ring width chronology and the June runoff during 1956-1986, we built the reconstruction function, which was explained 50.8% of observed runoff. The stimulated runoff during 1987 to 2002 was significantly higher than the observed runoff (3.01 m3·s-1, P<0.001). These results indicated that human activity from the upper river had significant impacts on Bayin River runoff. Human activity should be considered as an important factor to protect security of sustainable water resource utilization for future water resource development and utilization in Bayin River region.
    May-July NDVI variation for the middle Qinling Mountains over the past 194 years indicated by tree rings of Pinus tabuliformis
    RAN Yi-lin, CHEN You-ping, CHEN Feng, ZHANG He-li, JIA Xiao-bo
    2021, 32(10):  3661-3670.  doi:10.13287/j.1001-9332.202110.028
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    Due to the short-term observation record of the normalized difference vegetation index (NDVI), the research on long-term NDVI changes is scarce, which limits our understanding of the impacts of NDVI changes in the context of global warming. In this study, a regional tree-ring chronology was developed based on the tree-ring samples of Pinus tabuliformis in the middle Qinling Mountains. The results showed that tree-ring width of P. tabuliformis was significantly positively correlated with May-July NDVI (r=0.624, P<0.01, n=34). The Sig-Free tree-ring width chronology was used to reconstruct May-July NDVI during the period 1825—2018, which explained 38.9% of the total NDVI variance. Results of spatial analysis showed that the reconstructed series could better represent the NDVI changes in the study area. There were six high NDVI periods and five low NDVI periods in the past 194 years. The vegetation grew best in 2006-2018, indicating vegetation cove-rage in the middle of Qinling Mountains had been improved during the warming hiatus. Low NDVI periods in the reconstruction series were consistent with drought over much of study area. Results of wavelet analysis indicated the existence of 2-4 years and 12-16 years cycles in the reconstruction series. SEA analysis showed that the reconstruction series decreased significantly in the El Nino year, while increased significantly in the first to third years after the La Nina event. The growth of P. tabuliformis was predicted to increase slightly under the SSP2-4.5, SSP3-7.0 and SSP5-8.5 scenarios.
    Reconstruction of summer NDVI over the past 339 years based on the tree-ring width of Picea schrenkiana in Bayinbuluke, Central Tianshan, China
    ZHANG Quan, LIU Yu, LI Qiang, SUN Chang-feng, LI Teng, LI Pei, YE Yuan-da
    2021, 32(10):  3671-3679.  doi:10.13287/j.1001-9332.202110.025
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    The normalized difference vegetation index (NDVI) is widely used in various fields of vegetation research. Due to the short observation time, however, it is difficult to meet the research needs at long time scale. Here, we established a tree-ring width chronology (STD) based on Picea schrenkiana in Bayinbuluke, and calculated the correlation coefficient of chronology and NDVI with meteorological data. The results showed that both tree-ring width index and NDVI were significantly correlated with meteorological data. Combined with the significant positive correlation between width chronology and NDVI in June-August (r=0.7, P<0.01, n=38), summer NDVI (from June to August) was reconstructed over the past 339 years using a regression model. During 1680-2018, the reconstruction series had four dense vegetation periods (1738-1765, 1786-1798, 1964-1973 and 2000-2018) and five sparse vegetation periods (1690-1714, 1825-1834, 1850-1880, 1895-1920 and 1945-1955). The reconstruction reflected the hydrological signals in the central Tianshan Mountains. The comparison with the surrounding reconstructions revealed that when the runoff of Kaidu River increased and the local environment was humid, the vegetation coverage was high; otherwise the vegetation coverage was low. The extreme value of the reconstruction series also captured a series of natural disasters recorded in historical documents. Results of HYSPLT (Hybrid Single-Particle Lagrangian Integrated Trajectory Model) backward trajectory model and wind field analysis showed that NDVI anomalies were affected by the precipitation from Westerlies.
    GIS-based measurement of Haloxylon ammodendron tree ring
    SUN Tian-tian, CAI Xi-xi, SUN Yang, CHENG Yong-xiang, HUANG Jing-feng
    2021, 32(10):  3680-3686.  doi:10.13287/j.1001-9332.202110.030
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    Tree ring data is of significance for reconstructing climate and predicting environmental dynamics. In order to accurately measure spacing and other parameters of Haloxylon ammodendron tree ring, we first assigned coordinate system to the scanned H. ammodendron disc PS images based on GIS, and then completed the H. ammodendron tree ring spacing measurement by using ENVI image classification software and GIS measuring tool. The measurement accuracy was proved by WinDENDRO tree ring analysis system. The results showed that there was no significant difference between those two methods (P=0.63), and that the difference of paired mean value was 0.87 μm, indicating that the measured results were accurate and reliable. The constructed method in this study could be used to measure the spacing of H. ammodendron tree ring, which lay the foundation for the automatic measurement of tree ring parameters such as area and perimeter. Our method could replace the current professional tree ring analysis system for some ring parameter measurement. The study would contribute to the dendroclimatology analysis and the investigation on age structure of H. ammodendron population.
    Tree species identification of wooden funeral utensil from Qing Dynasty's tombs and its potential of ecological and environmental indicator in Shenyang, Northeast China
    LI Jun-xia, MA Xin-bo, FU Yong-ping, YUN Rui-xin, JIN Yu-ting, CHEN Zhen-ju
    2021, 32(10):  3687-3698.  doi:10.13287/j.1001-9332.202110.039
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    The wood used for funeral utensil in ancient tomb is a kind of valuable materials and important for understanding vegetation, climate and society conditions in the history. Here, we identified the tree species and dated the time of wooden utensils for funeral excavated from tombs in Shuijia Village, Shenyang, using wood anatomy methods and dendrochronological techniques. The results showed that 7 out of the 16 wood samples were identified as Pinus tabuliformis from Pinaceae, 8 were Larix sp. from Pinaceae and most likely Larix olgensis, and the rest one was Acer sp. from Aceraceae. Currently, these tree species are still widely distributed in Liaoning Province, indicating that forest structure (tree species composition) is relatively stable and that the climate at that time was quite similar to that at present. The timbers used for wooden utensils of funeral for civilian tombs had regional biogeographic characteristics and reflected regional social productivity development level in Mukden (now Shenyang) in Qing Dynasty: most of them were native tree species with low cost and high availability; the main timber trees were conifer species, and a few of them were broadleaved trees. These timbers were likely from the forest in Shenyang or mountainous areas in Eastern Liaoning, with Hunhe River waterway being an important transport way for timbers to Shenyang. Some P. tabuliformis and Larix sp. timbers could be cross-dated well, and the growth period of the trees was determined to be 1680s-1770s (early to mid-Qing Dynasty). The variations of tree-ring width of these timbers had good consistency and high climate sensitivity, reflecting the consistency of regional climate and environment. These timbers have the potential to indicate the climate condition of the early to mid-Qing Dynasty.
    Age estimation of ancient trees based on dendrochronology: A case study of Pyrus ussuriensis in Dunhuang City, China
    QIN Chun, XIA Sheng-fu, QIN Zhan-yi, WANG Xiao-feng, YANG Liu, YANG Bao
    2021, 32(10):  3699-3706.  doi:10.13287/j.1001-9332.202110.014
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    Age is the sole criterion for identifying ancient trees. Dendrochronology was used to examine the age of the old trees of Pyrus ussuriensis in the Fourth group of Doujiadun Village (formerly Yangjiayuanzi), Mogao Town, Dunhuang City. As all the old pear trees had been decayed and hollow, we collected cores of P. ussuriensis of different ages to establish the age-related curve of tree radial growth, and estimated the number of tree rings in the missing segment. Combined with accurate count on tree rings, the age of P. ussuriensis was restored. The results showed that the average age of the 13 old pear trees in the orchard was (280±35) years, presenting further evidence for the record about old pear trees in Dunhuang Zhi. These old trees could be classified as the third-class ancient tree according to tree age, and should be properly protected and preserved. This study provided a detailed scientific basis to resolve the dispute over the conservation of ancient P. ussuriensis in Dunhuang City.
    Reviews
    Evaluating the growth status and threatened factors for old trees in China
    DONG Jin-yi, HU Jun-he, JIN Chen-zhong, LIU Yong-bo
    2021, 32(10):  3707-3714.  doi:10.13287/j.1001-9332.202110.037
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    Old trees are critical components of ecosystems, with important ecological function and high genetic diversity. To strengthen the protection and management of old trees, we analyzed the distribution, survival and protection status of old trees and their threatened factors in China. The results showed there were a total of 10.66 million old trees in China. The Inner Mongolia Autonomous Region and Yunnan Province had more than one million trees, respectively. For 440000 old trees in 102 counties, 94.3% grew normally, 5.5% in a weak or endangered status, and 0.2% had been dead. The main factors threatened to old trees included natural disasters (e.g., elevated temperature, drought, fire), urbanization, land use, pests and diseases, and cutting and stealing. Among those factors, damage from pests and diseases was the most serious, which was found in 83 counties (81.4%). The second important threatened factor was natural disasters, which occurred in 68 regions (66.7%). In addition, most of the old trees (around 89%) grew in remote countryside, lacking of enough protection. Modern technologies should be used to protect old trees, such as using unmanned aerial vehicles to monitor the growth status of old trees, strengthening pest and disease control, and avoiding natural disasters. Establishing a database of old tree resources is important to update and share information timely to avoid stealing and felling old trees.
    Growth response of coniferous trees to climate change in the Qinling Mountains, China
    BAI Yao-yu, HAN Yi-jie, WANG Ke-ke, LIU Bo
    2021, 32(10):  3715-3723.  doi:10.13287/j.1001-9332.202110.013
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    As an important geographical boundary, the subalpine coniferous forests in the Qinling Mountains have critical effects on water conservation, biodiversity conservation and climate regulation at the regional and even larger scale. In recent decades, temperature significantly increased in the Qinling Mountains, with significant spatial heterogeneity. An understanding of the responses of the Qinling coniferous trees to climate change is important for the protection and management of mountain forests under climate change. In this study, we synthesized the relationships between the radial growth of coniferous trees and climate at different altitudes in the western, central, and eas-tern Qinling Mountains. The effects of climate change on coniferous trees were investigated from the aspects of radial growth, NDVI, phenology, and species distribution range. Furthermore, know-ledge gaps in the responses of tree growth to climate change and possible future directions in this field were discussed.
    Effects of biotic interactions on ecological processes of treeline ecotone under climate change
    WANG Ya-feng, WANG Ya-lei, HUANG Ru, LIANG Er-yuan
    2021, 32(10):  3724-3732.  doi:10.13287/j.1001-9332.202110.006
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    Treeline ecotone is an alpine ecological transition zone characterized by strong biotic interactions, which are closely related to treeline ecological processes. Herein, we reviewed the research progress regarding the impacts of plant-plant, plant-animal, and plant-microbe interactions on the ecological processes of treeline ecotone under climate change. Both facilitation and competition among individual plants are important factors mediating dynamics of treeline processes under climate change. However, there is a dearth of dendroecological evidence. Impacts of higher-order interactions on the ecological processes of treeline ecotone remain to be tested. Herbivory and microbe-plant interactions could enhance or reduce the couplings of treeline and climate through affecting soil conditions or altering dynamics of ecological processes such as tree growth and recruitment. How the linkages between aboveground and belowground processes affect treeline responses to climate change remain unclear. In addition, biotic interactions across trophic levels might regulate the responses of ecological processes of treeline ecotone to climate change. Tibetan Plateau provides an excellent opportunity to explore the effects of biotic interactions on the changes of ecological process of treeline ecotone.
    Mercury in tree rings: Advances, problems and prospects
    KANG Hu-hu, LIU Xiao-hong, ZHANG Xin-yu, GUO Jun-ming, WU Guo-ju, XU Guo-bao, KANG Shi-chang
    2021, 32(10):  3733-3742.  doi:10.13287/j.1001-9332.202110.003
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    As a highly biotoxic element, mercury (Hg) can be enriched by the food chain and has negative effect on ecosystems. Changes of Hg flux and reserves in forest have important effects on its biogeochemical cycle in forest ecosystem. Due to limitation of temporal and spatial monitoring, there is not comprehensive understanding on Hg distribution. Widely distributed trees can be used as effective bio-monitors and Hg records in tree rings can be used to study Hg temporal and spatial distribution. Hg accumulated by root, leaf, bark, and other tissues can be detained in bole and record environmental Hg variations. Therefore, historical Hg trends can be restructured by analyzing Hg concentration in tree rings and the biogeochemical characteristics can be understood with Hg isotope ratio. We reviewed the method of measurement of Hg concentration and isotope ratio and application of reconstruction using Hg concentration in tree ring. We suggested the great application potential of Hg isotope ratio in atmospheric Hg construction and biogeochemistry cycle and raised concerns in further studies.
    Intra-annual high resolution stable isotope records of tree ring: Methods, progress and prospects
    LI Yao, ZENG Xiao-min, NI Ping, WANG Wen-chao, LIU Xiao-hong
    2021, 32(10):  3743-3752.  doi:10.13287/j.1001-9332.202110.024
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    Stable isotope ratios of tree ring can effectively record climate and environmental changes during tree growth and the physiological responses of trees to such changes. Intra-annual high resolution stable isotope ratios of tree ring can provide more detailed climatic and environmental information, reveal the physiological and ecological response mechanism of trees to seasonal climatic variation, and thus with great potential in the study of paleoclimate and global change ecology. Based on the intra-annual high resolution stable isotope ratios related literature since 1990, we reviewed the research progress of intra-annual high resolution tree ring stable isotope records in the aspects of sample stripping method, chemical extraction method of α-cellulose and application, and further proposed the potential and future development direction of intra-annual high resolution tree ring stable isotope records.
    Measurement and research status of stable hydrogen isotopes in tree-ring lignin methoxyl groups
    WANG Ya-bo, LIU Xiao-hong, LU Qiang-qiang, ZENG Xiao-min, ZHANG Ling-nan, WANG Zi-yi
    2021, 32(10):  3753-3760.  doi:10.13287/j.1001-9332.202110.004
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    The primary hydrogen (H) source for all organic compounds in the biosphere is from water, and then participates in biogeochemical cycles through photosynthesis and plant physiological metabolism. As a new proxy of paleoclimate and paleoenvironment, stable hydrogen isotope ratios in wood lignin methoxyl groups (δ2HLM) show great advantages in the studies of paleoclimatic change and have been used to reconstruct precipitation stable hydrogen isotope ratios and paleoclimate signals in many regions. Based on the lignin application mechanism and analysis method of δ2HLM, we evaluated the stability and effectiveness of δ2HLM-measurement method from lignin content and lignin monomer composition, and expounded the tree lignin methoxyl groups' stable isotope proxies of current research outcomes. In the middle latitudes, the tree-ring δ2HLM had great potential in recording temperature signals and precipitation stable hydrogen isotope ratios. However, the study of tree-ring δ2HLM was still in its infancy as evidenced by following reasons: 1) The study area was limited to the middle latitude of the northern hemisphere, and the study subjects were limited to conifer species; 2) To compensate for the limitation of hydrogen isotopic records of nitrocellulose, high resolution tree-ring δ2HLM would be studied; 3) The potential of tree-ring δ2HLM utilization in plant physiology and forest ecology remained to be exploited.
    Research progress on cambial activity of trees and the influencing factors
    WANG Ling-ling, GOU Xiao-hua, XIA Jing-qing, WANG Fang, ZHANG Fen, ZHANG Jun-zhou
    2021, 32(10):  3761-3770.  doi:10.13287/j.1001-9332.202110.022
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    Tree growth is the main way of carbon sequestration in forest ecosystems, which is influenced by climatic and non-climatic factors. The long-term location monitoring of cambial phenology and wood formation dynamics (xylogenesis) is an important method to clarify the responses of radial growth to climate change. Here, we reviewed studies on cambial phenology and xylogenesis by microcoring method. Firstly, we reviewed the effects of climatic factors on cambial phenology. The onset and cessation of xylogenesis were determined by temperature in cold and humid conditions. Temperature and water availability collectively modulated the onset of xylogenesis under dry conditions, and the later determined the end of xylogenesis. The radial increment was regulated by rate and duration of cell production, with the maximum of growth rate occurring around the summer solstice. Short-term N addition did not affect wood formation dynamics. Secondly, we reviewed the roles of biological factors in regulating xylogenesis. The onset of xylogenesis differred among species, ages, and inter-specific competition. Seasonal dynamics of non-structural carbohydrates were coupled with wood formation. Finally, we reviewed the response mechanisms of xylogenesis to the interaction of climatic and biological factors. In conclusion, we put forward problems in current studies and prospected future development to provide reference for further scientific research.
    Influence of large volcanic eruptions on climate as revealed by tree-ring data on the Tibetan Plateau, China
    NIE Wen-zheng, LI Ming-qi
    2021, 32(10):  3771-3780.  doi:10.13287/j.1001-9332.202110.009
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    Large volcanic eruption is an important factor affecting global climate change. In the past few decades, many researchers reconstructed a number of climate series based on tree rings on the Tibetan Plateau, and examined the impacts of large volcanic eruptions on the climate. The results showed that these tree-ring sites used to examined the influences of large volcanic eruptions on climate change were primarily located in the eastern Tibetan Plateau. In addition, the series comparison and the superposed epoch analysis were main methods for studying the climate effects of large volcanic eruptions. Based on the results analyzed using two methods, we suggested that the large volcanic eruptions in low-mid latitudes had a significant impact on temperature and dry/wet variation. Cooling or drought occurred after large volcanic eruptions in the subsequent 1-2 years. How-ever, the large volcanic eruptions in high latitudes had minor impacts on climate change. Furthermore, consecutive multiple volcanic eruptions could result in cooling at the decades scale. The factors influencing the climate effects of large volcanic eruptions included the location of the volcanic eruptions, intensity of the volcanic eruptions, atmospheric circulation, etc. Finally, we proposed research projects that need to be carried out in the future.