Growth trends clustering: A novel method for detecting forest disturbances and extracting climate signals in tree rings.

Tree-ring widths contain valuable historical information related to both forest disturbances and climate variability and changes within forests. However, current methods are still unable to accurately distinguish between disturbances and climate signals in tree rings, especially in the case of climate anomalies. To address this issue, we developed a novel method, called Growth Trends Clustering (GTC) that uses the distribution characteristics of tree-ring widths within a stand to distinguish the effects of climate and other forest disturbances. GTC employed a Gaussian mixture model to fit the probability density distribution of annual ring-width index (RWI) in a stand. Discriminative criteria were established to cluster diverse sub-distributions from the Gaussian mixture model into categories of growth release, suppression, or normal trends. This approach allowed us to identify the occurrence, duration, and severity of forest disturbances based on percentage changes in the growth release or suppression categories of trees. And the effect of climate on tree growth was assessed according to the mean statistics of the growth normal categories. Using common forest disturbances such as defoliating insects and thinning as examples, we validated our method using tree-ring collections from six sites in British Columbia and Quebec, Canada. We found that the GTC method was superior to traditional time-series analysis methods (e.g., Radial Growth Averaging, Boundary Line, Absolute Increase, and Curve Intervention Detection) for detecting past forest disturbances and was able to significantly enhance climate signals. In summary, the GTC method presented in this study introduces a novel statistical approach for accurately distinguishing between forest disturbances and climate signals in tree rings. This is particularly important for understanding forest disturbance regimes under climate change and for developing future disturbance mitigation strategies.

Recent warming and increasing CO2 stimulate growth of dominant trees under no water limitation in South Korea.

Increases in temperatures and atmospheric CO2 concentration influence the growth performance of trees worldwide. The direction and intensity of tree growth and physiological responses to changing climate do, however, vary according to environmental conditions. Here we present complex, long-term, tree-physiological responses to unprecedented temperature increase in East Asia. For this purpose, we studied radial growth and isotopic (δ13C and δ18O) variations using tree-ring data for the past 100 yr of dominant Quercus mongolica trees from the cool-temperate forests from Hallasan, South Korea. Overall, we found that tree stem basal area increment, intercellular CO2 concentration and intrinsic water-use efficiency significantly increased over the last century. We observed, however, short-term variability in the trends of these variables among four periods identified by change point analysis. In comparison, δ18O did not show significant changes over time, suggesting no major hydrological changes in this precipitation-rich area. The strength and direction of growth-climate relationships also varied during the past 100 yr. Basal area increment (BAI) did not show significant relationships with the climate over the 1924-1949 and 1975-1999 periods. However, over 1950-1974, BAI was negatively affected by both temperature and precipitation, while after 2000, a temperature stimulus was observed. Finally, over the past two decades, the increase in Q. mongolica tree growth accelerated and was associated with high spring-summer temperatures and atmospheric CO2 concentrations and decreasing intrinsic water-use efficiency, δ18O and vapour pressure deficit, suggesting that the photosynthetic rate continued increasing under no water limitations. Our results indicate that the performance of dominant trees of one of the most widely distributed species in East Asia has benefited from recent global changes, mainly over the past two decades. Such findings are essential for projections of forest dynamics and carbon sequestration under climate change.

Hydrothermal environments lead to differences in the radial growth response of Pinus tabulaeformis to climate in the monsoon marginal zone, Northwestern China.

Regional climatic differences increase the complexity of tree radial growth responses to climate change in the monsoon marginal zones and may alter the carbon sequestration capacity of forests. In this study, we collected cores of Pinus tabulaeformis trees at nine sampling sites across different regions. We analysed the relationship between tree-ring width chronology and climatic factors at different sites using dendroecological methods. We used the tree-ring index to calculate resistance, recovery, and resilience as well as to explore the capacity of radial growth to cope with drought events. The results indicate that (1) Drought was the primary factor limiting tree growth, and tree-ring climate response patterns varied across three regions. Tree growth was sensitive to both temperature and precipitation in the eastern Qilian Mountains, while it was more sensitive to temperature in the Hassan Mountains and more sensitive to precipitation in the Helan Mountains. (2) The tree-ring climate response pattern remained unstable over time, and the relative influence of current climate on tree growth increased. (3) The ecological resilience of trees to extreme events varies across three regions, which could be attributed to regional moisture conditions and the duration of drought. In the context of the management and protection of trees in the study area in the future, more attention should be paid to the elasticity of tree growth after drought events.

[Radial growth response of Populus euphratica to climate change in the Cele desert oasis ecotone, China]. / ç­–å‹’æ²™æ¼ ç»¿æ´²è¿‡æ¸¡å¸¦èƒ¡æ¨å¾„å‘ç”Ÿé•¿å¯¹æ°”å€™å˜åŒ–çš„å“åº”.

Populus euphratica is an important tree species in the arid regions of Northwest China, which is sensitive to climate changes. Climate of the Northwest China is changing to be "warm and humid", but how it would affect the regional forest growth is not clear. In this study, the radial growth response of P. euphratica to major climatic factors and their temporal changes during 1984-2021 were analyzed by using dendrochronology method in the desert oasis ecotone of Cele in the southern Tarim basin. The results showed that tree-ring width index of P. euphratica had a significant negative correlation with temperature in September of the previous year, and in February and May of current year, had significant positive correlation with precipitation in September of previous year and March and May of current year, and had significant positive correlations with SPEI in February and May of current year. The relationships between tree-ring width index and combined month climatic factors were more obvious. The results of moving correlation analysis showed that the correlation between tree-ring width index and temperature in the growing season tended to be strengthened in recent years, while the correlation between tree-ring width index and precipitation, SPEI tended to be declined or remain stable. The variations of the relationships between tree-ring width index and combined month climatic factors were more obvious compared that with single month. Current regional climate is conducive to the growth and development, as well as the improvement of ecological shelter function of P. euphratica forest in the desert oasis ecotone of Cele.

Non-linear response of Norway spruce to climate variation along elevational and age gradients in the Carpathians.

Climate change, namely increased warming coupled with a rise in extreme events (e.g., droughts, storms, heatwaves), is negatively affecting forest ecosystems worldwide. In these ecosystems, growth dynamics and biomass accumulation are driven mainly by environmental constraints, inter-tree competition, and disturbance regimes. Usually, climate-growth relationships are assessed by linear correlation due to the simplicity and straightforwardness of modeling. However, applying this method may bias results, since the ecological and physiological responses of trees to environmental factors are non-linear, and usually bell-shaped. In the Eastern Carpathian, Norway spruce is at the southeasternmost edge of its natural occurrence; this region is thus potentially vulnerable to climate change. A non-linear assessment of climate-growth relationships using machine-learning techniques for Norway spruce in this area had not been conducted prior to this study. To address this knowledge gap, we analyzed a large tree-ring network from 158 stands, with over 3000 trees of varying age distributed along an elevational gradient. Our results showed that non-linearity in the growth-climate response of spruce was season-specific: temperatures from the previous autumn and current growing season, along with water availability during winter, induced a bell-shaped response. Moreover, we found that at low elevations, spruce growth was mainly limited by water availability in the growing season, while winter temperatures are likely to have had a slight influence along the entire elevational gradient. Furthermore, at elevations lower than 1400 m, spruce trees were also found to be sensitive to previous autumn water availability. Overall, our results shed new light on the response of Norway spruce to climate in the Carpathians, which may aid in management decisions.

Reversal in the drought stress response of the Scots pine forest ecosystem: Local soil water regime as a key to improving climate change resilience.

In a changing climate, forest ecosystems have become increasingly vulnerable to continuously exacerbating heat and associated drought conditions. Climate stress resilience is governed by a complex interplay of global, regional, and local factors, with hydrological conditions being among the key players. We studied a Scots pine (Pinus sylvestris L.) forest ecosystem located near the southern edge of the boreal ecotone, which is particularly subjected to frequent and prolonged droughts. By comparing the dendrochronological series of pines growing in apparently contrasting hydrological conditions ranging from the waterlogged peat bog area to the dry soil at the surrounding elevations, we investigated how the soil water regime affects the climate response and drought stress resilience of the forest ecosystem. We found that in the dry land area, a significant fraction of the trees were replaced after two major climate extremes: prolonged drought and extremely low winter temperatures. The latter has also been followed by a three- to ten-fold growth reduction of the trees that survived in the next year, whereas no similar effect has been observed in the peat bog area. Multi-scale detrended partial cross-correlation analysis (DPCCA) indicated that tree-ring width (TRW) was negatively correlated with spring and summer temperatures and positively correlated with the Palmer drought severity index (PDSI) for the same year. For the elevated dry land area, the above effect extends to interannual scales, indicating that prolonged heatwaves and associated droughts are among the factors that limit tree growth. In marked contrast, in the waterlogged peat bog area, a reversed tendency was observed, with prolonged dry periods as well as warmer springs and summers over several consecutive years, leading to increasing tree growth with a one- to three-year time lag. Altogether, our results indicate that the pessimal conditions of a warming climate could become favorable through the preservation of the soil water regime.

Factors Limiting Radial Growth of Conifers on Their Semiarid Borders across Kazakhstan.

The forests of Central Asia are biodiversity hotspots at risk from rapid climate change, but they are understudied in terms of the climate-growth relationships of trees. This classical dendroclimatic case study was performed for six conifer forest stands near their semiarid boundaries across Kazakhstan: (1-3) Pinus sylvestris L., temperate forest steppes; (4-5) Picea schrenkiana Fisch. & C.A. Mey, foothills, the Western Tien Shan, southeast; (6) Juniperus seravschanica Kom., montane zone, the Western Tien Shan, southern subtropics. Due to large distances, correlations between local tree-ring width (TRW) chronologies are significant only within species (pine, 0.19-0.50; spruce, 0.55). The most stable climatic response is negative correlations of TRW with maximum temperatures of the previous (from -0.37 to -0.50) and current (from -0.17 to -0.44) growing season. The strength of the positive response to annual precipitation (0.10-0.48) and Standardized Precipitation Evapotranspiration Index (0.15-0.49) depends on local aridity. The timeframe of climatic responses shifts to earlier months north-to-south. For years with maximum and minimum TRW, differences in seasonal maximal temperatures (by ~1-3 °C) and precipitation (by ~12-83%) were also found. Heat stress being the primary factor limiting conifer growth across Kazakhstan, we suggest experiments there on heat protection measures in plantations and for urban trees, alongside broadening the coverage of the dendroclimatic net with accents on the impact of habitat conditions and climate-induced long-term growth dynamics.

Sap flow and growth response of Norway spruce under long-term partial rainfall exclusion at low altitude.

Introduction: Under ongoing climate change, more frequent and severe drought periods accompanied by heat waves are expected in the future. Under these conditions, the tree's survival is conditioned by fast recovery of functions after drought release. Therefore, in the presented study, we evaluated the effect of long-term water reduction in soil on tree water use and growth dynamics of Norway spruce. Methods: The experiment was conducted in two young Norway spruce plots located on suboptimal sites at a low altitude of 440 m a.s.l. In the first plot (PE), 25% of precipitation throughfall was excluded since 2007, and the second one represented the control treatment with ambient conditions (PC). Tree sap flow, stem radial increment, and tree water deficit were monitored in two consecutive growing seasons: 2015-2016, with contrasting hydro-climatic conditions. Results: Trees in both treatments showed relatively isohydric behavior reflected in a strong reduction of sap flow under the exceptional drought of 2015. Nevertheless, trees from PE treatment reduced sap flow faster than PC under decreasing soil water potential, exhibiting faster stomatal response. This led to a significantly lower sap flow of PE, compared to PC in 2015. The maximal sap flow rates were also lower for PE treatment, compared to PC. Both treatments experienced minimal radial growth during the 2015 drought and subsequent recovery of radial growth under the more the humid year of 2016. However, treatments did not differ significantly in stem radial increments within respective years. Discussion: Precipitation exclusion treatment, therefore, led to water loss adjustment, but did not affect growth response to intense drought and growth recovery in the year after drought.

Tree-ring-based seasonal temperature reconstructions and ecological implications of recent warming on oak forest health in the Zagros Mountains, Iran.

Abrupt changes in temperature have especially strong impacts on fragile ecosystems located in semi-arid regions. In this study, we analyzed tree-ring widths (TRW) of Mediterranean cypress (Cupressus sempervirens var. horizontalis) in the Zagros Mountains, Iran. Furthermore, we separately measured earlywood width (EWW) and latewood width (LWW) of Persian oak (Quercus brantii Lindl.) to examine if intra-annual resolution of tree-ring parameters of Q. brantii tree rings can be used as high-resolution paleoclimate proxies. Climate-growth relationships revealed that mean monthly maximum temperatures (Tmax) are a dominant factor determining radial tree growth and negatively affect both oak and cypress in the Zagros Mountains. Accordingly, we reconstructed two different seasonal windows of past Tmax variability, namely, January-March and June-August over the periods 1860-2015 and 1560-2015, respectively. Regime shift detection identified twelve warm and nine cold significant regime shifts in our summer Tmax reconstructions. The longest hot summer period occurred in the twentieth century, and two warm regime shifts occurred in 1999 and 2008. The highest values of the warm summer regime shift index occurred in 2008, which coincided with fungal pathogen attacks and insect outbreak of the oak leaf roller moth (Tortrix viridana L.) in the Zagros oak woodlands. Interestingly, we found common warm and cold periods in historic climate variability between the summer and winter Tmax reconstructions. Warm and cold regime shifts occurred simultaneously from 1955 to 2015, and significant regional warm summer and winter regime shifts have occurred between 2008 and 2015. The winter and summer Tmax reconstructions show high spatial correlations with large areas in West Asia, North Africa, and the eastern Mediterranean region. Our results strengthen initial studies on past climate variability in Iran and contribute to an enhanced understanding of past temperature variability in West Asia.

Do Different Tree-Ring Proxies Contain Different Temperature Signals? A Case Study of Norway Spruce (Picea abies (L.) Karst) in the Eastern Carpathians.

One of the most important proxy archives for past climate variation is tree rings. Tree-ring parameters offer valuable knowledge regarding how trees respond and adapt to environmental changes. Trees encode all environmental changes in different tree-ring parameters. In this study, we analyzed how air temperature is encoded in different Norway spruce tree-ring proxies along an altitude gradient in an intramountain valley of the Carpathians. The study area, in the Gheorgheni region, Romania (Eastern Carpathians), has a mountain climate with a frequent temperature inversion in winter. The climate−growth relationship was analyzed for two contrasting altitudes: low elevation, i.e., below 1000 m a.s.l., and high elevation, i.e., above 1500 m a.s.l. Two local weather stations, one in the valley and the other on the upper part of the mountains, provide daily temperatures (Joseni­750 m a.s.l. and Bucin­1282 m a.s.l.). The bootstrap Pearson correlation between cumulative daily temperature data and three tree-ring proxies (tree-ring width­TRW, basal area increment­BAI, and blue intensity­BI) was computed for each series. The results show that elevation modulates the climate response pattern in the case of BI, and remains relatively similar for TRW and BAI. The winter temperature's positive influence on spruce growth was observed in both TRW and BAI chronologies. Additionally, the BAI chronology highlights a positive relationship with summer temperature. The highest correlation coefficient (r = 0.551, p < 0.05, n = 41) was recorded between BI residual chronology from high elevation series and summer/autumn temperature from the upper-part weather station for a cumulative period of 59 days (the second half of August to the beginning of October). Our results show that, for this intramountain valley of the Eastern Carpathians, different tree-ring proxies capture different climate signals.

Early Summer Temperature Variation Recorded by Earlywood Width in the Northern Boundary of Pinus taiwanensis Hayata in Central China and Its Linkages to the Indian and Pacific Oceans.

The Tongbai Mountains are an ecologically sensitive region to climate change, where there lies a climatic transitional zone from a subtropical to a warm−temperate monsoon climate. The northern boundary of Pinus taiwanensis Hayata is here; thus, climate information is well recorded in its tree rings. Based on developed earlywood width (EWW), latewood width (LWW) and total ring width (RW) chronologies (time period: 1887−2014 year) of Pinus taiwanensis Hayata in the Tongbai Mountains in central China, this paper analyzed characteristics of these chronologies and correlations between these chronologies and climate factors. The correlation results showed that earlywood width chronology contains more climate information than latewood width chronology and total ring width chronology, and mean temperature and mean maximum temperature in May−June were the main limiting factors for radial growth of Pinus taiwanensis Hayata. The highest significant value in all correlation analyses is −0.669 (p < 0.05) between earlywood width chronology and May−June mean temperature (TMJ) in the pre-mutation period (1958−2005) based on mutating in 2006. Thus, this paper reconstructed May−June mean temperature using earlywood width chronology from 1901 to 2005 (reliable period of earlywood width chronology is 1901−2014). The reconstructed May−June mean temperature experienced eight warmer periods and eight colder periods and also showed 2−3a cycle change over the past 105 years. The spatial correlation showed that the reconstructed series was representative of the May−June mean temperature variation in central and eastern China and significant positive/negative correlation with the sea surface temperature (SST) of the subtropical Pacific Ocean and the tropical Western Pacific Ocean and Indian Ocean from the previous October to the current June. This also indicated that May−June mean temperature periodic fluctuations might be related to the quasi-biennial oscillation (QBO) in the tropical Western Pacific Ocean and Indian Ocean. The results of this study have extended and supplemented the meteorological records of the Tongbai Mountains and have a guiding significance for forest tending and management in this area.

Applying space-for-time substitution to infer the growth response to climate may lead to overestimation of tree maladaptation: Evidence from the North American White Spruce Network.

Under climate change circumstances, increasing studies have reported the temporal instability of tree growth responses to climate, which poses a major challenge to linearly extrapolating past climate and future growth dynamics using tree-ring data. Space-for-time substitution (SFTS) is a potential solution to this problem that is widely used in the dendrochronology field to project past or future temporal growth response trajectories from contemporary spatial patterns. However, the projected accuracy of the SFTS in the climate effects on tree growth remains uncertain. Here, we empirically test the SFTS method by comparing the effect of spatial and temporal climate variations on climate responses of white spruce (Picea glauca), which has a transcontinental range in North America. We first applied a response surface regression model to capture the variations in growth responses along the spatial climate gradients. The results showed that the relationships between growth and June temperature varied along spatial climate gradients in a predictable way. And their relationships varied mainly along with local temperate condition. Then, the projected correlation coefficients between growth and climate using SFTS were compared against the observed. We found that the growth response changes caused by spatial versus temporal climate variations showed opposite trends. Moreover, the projected correlation coefficients using the SFTS were significantly lower than the observed. This finding suggests that applying the SFTS to project the growth response of white spruce might lead to an overestimation of the degree of tree maladaptation in future climate scenarios. And the overestimation is likely to get weaker from Alaska and Yukon Territory in the west to Quebec in the east. Although this is only a case study of the SFTS method for projecting tree growth response, our findings suggest that direct application of the SFTS method may not be applicable to all regions and all tree species.

Non-linear modelling reveals a predominant moisture limit on juniper growth across the southern Tibetan Plateau.

BACKGROUND AND AIMS: Tree growth in plateau forests is critically limited by harsh climatic conditions. Many mathematical statistical methods have been used to identify the relationships between tree growth and climatic factors, but there is still uncertainty regarding the relative importance of these factors across different regions. We tested major climatic limits at 30 sites to provide insights into the main climatic limits for juniper trees (Juniperus tibetica Kom.) across the southern Tibetan Plateau. METHODS: We analysed the linear and non-linear relationships between tree growth and climatic factors using Pearson correlation statistics and a process-based forward Vaganov-Shashkin-Lite (VS-Lite) model, respectively. These relationships were used to identify the strength of the influence of different climatic factors throughout the species' growing season and to identify the main climatic factors limiting tree growth. KEY RESULTS: Growth of juniper trees began in April and ended in October in the study area. The radial growth of juniper trees was limited by soil moisture throughout the summer (June-August) of the current year at 24 sampling sites and was limited by temperature at the other six sites on the southern Tibetan Plateau. CONCLUSIONS: Soil moisture limited juniper growth at the majority of sites. Temperature in the current summer limited the growth of juniper trees at a few sampling sites in the western part of the study area. Local climate conditions may contribute to different limiting factors in the growth response of trees on the southern Tibetan Plateau. These findings may contribute to our understanding of divergent forest dynamics and to sustainable forest management under future climate scenarios.

Daytime warming triggers tree growth decline in the Northern Hemisphere.

Global warming has been linked to declines in tree growth. However, it is unclear how the asymmetry in daytime and nighttime warming influences this response. Here, we use 2947 residual tree-ring width chronologies covering 32 species at 2493 sites, between 1901 and 2018, across the Northern Hemisphere, to analyze the effects of daytime and nighttime temperatures, precipitation, and drought stress on the radial growth of trees. We show that drought stress was primarily triggered by daytime rather than nighttime warming. The radial growth of trees was more sensitive to drought stress in warm regions than in cold regions, especially for angiosperms. Our study provides robust evidence that daytime warming is the primary driver of the observed declines in forest productivity related to drought stress and that daytime and nighttime warming should be considered separately when modelling forest-climate interactions and feedbacks in a future, warmer world.

Competition and disturbance affect elevational distribution of two congeneric conifers.

Climatic change will affect elevational vegetation distribution because vegetation distribution is related to thermal conditions. However, how elevational species distributions are determined by biotic and abiotic factors is not clear. The long-term plot census along an elevational gradient is indispensable to clarify mechanisms of elevational distribution of tree species. Two congeneric conifers, the less shade-tolerant Abies veitchii and shade-tolerant A. mariesii, dominate at low and high elevations, respectively, in the subalpine zone in Japan. This study investigated the population dynamics of the two species at three elevations (low, middle, high) for 13 years to examine why the two species dominated the different elevations from the viewpoints of competition and disturbance. This study showed that growth and survival rates were not highest at the most dominant elevations for each species. At the high elevation where A. mariesii dominated and small disturbances frequently occurred, the recruitment rate of A. mariesii was highest among the three elevations and that of A. veitchii was largely decreased by tree competition. However, A. veitchii was dominant earlier than A. mariesii at the low elevation after large disturbances by the high growth rate of individual trees. Therefore, A. mariesii was superior to A. veitchii at the high elevation because of its high recruitment rate and large reduction of recruitment of A. veitchii due to competition, while A. veitchii was superior to A. mariesii at the low elevation after large disturbances because of higher growth rate than A. mariesii. It is suggested that the elevational distributions of the two species were determined by elevational changes in population dynamics in relation to competition and disturbance. Long-term observational studies of forest dynamics among various elevations are indispensable to predict the effects of climatic change on vegetation distribution.

Assessing the influence of local environment, regional climate and tree species on radial growth in the Hexi area of arid northwest China.

Radial growth is influenced by the local environment, regional climate, and tree species. Assessing the influence of these variables on radial growth can help to reveal the relationships between tree growth and the environment. Here, we used standard dendrochronological approach to explore the response of radial growth to climate factors. We reported ring-width (TRW) residual chronologies from five sites along a longitudinal gradient in the Hexi area, arid northwestern China, based on a total of 249 Qinghai spruce (Picea crassifolia) ring-width records. We found that Qinghai spruce in the west of the Hexi area is more sensitive to climate change than in the east, and that drought condition in the previous growing season and the early growing season (March to June) limits spruce growth. Comparison between the regional standard chronologies of Qinghai spruce and Qilian juniper (Juniperus przewalskii) in the Hexi area during 1813-2001 showed that both chronologies were more consistent in the high-frequency domain than in the low-frequency domain. The findings emphasize the impacts of local environment, regional climate and tree species on radial growth, suggesting that accounting for these variables could improve large-scale and multi-species dendrochronological studies.

Tunneling-induced groundwater depletion limits long-term growth dynamics of forest trees.

Human interventions such as tunnel construction have caused groundwater depletion, which substantially affected the functions of forest tree species and their communities. However, the extent to which tunneling-induced groundwater depletion (TIGD) degrades their function levels at various spatial-temporal scales under varying climate conditions remains still unclear. Researchers used stand-scale dendrological records to track and extract the effects of TIGD associated with a single or series of tunneling events (three tunneling events during 1999-2001, 2006-2008, and 2010-2013) on short- and long-term growth levels of two dominant drought-tolerant tree species across (karst and non-karst) landscapes affected by tunnel construction and landscapes not subjected to tunnel construction in a mountainous forest ecosystem located in the southwest of China. The results showed that growth responses of both trees stand to TIGD, and the TIGD-linked water losses of other available water sources were negative and widespread across tunnel-affected landscapes, particularly in the karst landscapes known as delicate landscapes. Tree stands with faster (more vigorous) growth rates showed more significant adverse growth levels in response to either tunneling-induced or drought-induced water stresses. Also, they showed the highest recovered growth levels in response to favorable climatic conditions. Moreover, the growth level in the tunnel-affected forest never fully recovered during six years of very wet weather (2012-2018) after the construction of the final (third) tunnel in 2010-2013. Current research shows that tunnel construction has a cumulatively detrimental impact on the long-term survival of the forest. Even with the mediation of long-term very wet circumstances, it can substantially restrict the development dynamics of the forest compared to drought.

[Responses of tree-ring width of Pinus tabuliformis plantation to climatic factors in Songshan Mountains, central China]. / åµ©å±±åœ°åŒºæ²¹æ¾äººå·¥æž—æ ‘è½®å®½åº¦å¯¹æ°”å€™å› å­çš„å“åº”.

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.

[Radial growth responses of four coniferous species to climate change in the Potatso National Park, China]. / æ™®è¾¾æŽªå›½å®¶å ¬å›­å››ç§é’ˆå¶æ ‘å¾„å‘ç”Ÿé•¿å¯¹æ°”å€™å› å­çš„å“åº”.

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.

[Changes of wet and dry climate in the past 205 years indicated by Pseudotsuga forrestii of river valley from southeastern Tibetan Plateau, China]. / 河谷澜沧黄杉指示的青藏高原东南地区过去205年干湿变化.

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.