祁连山中部低海拔地区青海云杉径向生长的气候响应机制

利用生理模型开展树木径向生长的气候响应机制研究对理解树木生长的生理机制、预估气候变化情景下森林生态系统的变化、提供森林保护管理的建议有重要意义。以祁连山中部低海拔地区青海云杉树轮记录为依据,利用Vaganov-Shashkin模型模拟青海云杉(Picea crassifolia)的径向生长,探讨青海云杉径向生长的生理机制。结果表明:降水对祁连山中部低海拔地区青海云杉径向生长起着决定性作用,5—8月份的降水直接影响当年青海云杉的径向生长,9月份的降水量影响翌年青海云杉的径向生长。根据本研究结果,水分是限制青海云杉径向生长的主要因子,建议青海云杉人工林种植时,可在5—8月份对青海云杉增加灌溉量。     

昌岭山两个优势树种径向生长对气候变化的响应

在气候变暖背景下,树木径向生长对气候变化的响应存在不稳定性。利用采自祁连山东部余脉昌岭山两个优势树种油松和青海云杉的树轮样芯,建立树轮宽度标准年表,通过分析树轮宽度年表与气候要素的相关关系,探讨两个树种径向生长对气候变化的响应。结果表明：（1）油松年表比青海云杉年表包含更多的气候信息,其平均敏感度、标准差、信噪比和样本对总体的代表性等统计量均高于青海云杉标准年表。（2）气候要素对不同树种径向生长限制程度不同,油松径向生长主要与降水（前一年9月和当年3-8月）和气温（前一年9月）有关,但对降水的响应更为敏感,而青海云杉径向生长则受到气温（当年9月）和降水（前一年9月、当年3月和7月）的共同作用。（3）气温突变后,油松和青海云杉年表与各气温要素的相关性显著增强,而青海云杉年表与气温要素的相关性变化更明显,指示了青海云杉径向生长对气温的响应更不稳定。（4）生长季平均最低气温的升高诱导的干旱胁迫是油松和青海云杉树木径向生长-气温响应变化的主要原因。     

Changes in the radial growth of Picea crassifolia and its driving factors in the mid-western Qilian Mountains,Northwest China since 1851 C.E

Examining the growth of trees in response to environmental factors is essential for evaluating the stability of forest ecosystems. In this study, using tree ring data obtained from 18 sites and climate diagnostic methods. we investigated relationships between the radial growth of Picea crassifolia in the mid-western Qilian Mountains and local climate/sea surface temperatures (SSTs) since 1851 C.E. The results revealed that the radial growth of P. crassifolia showed significant upward trends during three time periods (1884–1906, 1929–1946, and 1964–1983) and significant downward trends in a further three periods (1907–1928, 1947–1963, and 1984–1995). Variations in the growth of P. crassifolia showed a significant negative correlation with temperature in June and a positive correlation with precipitation from July in the previous year to June in the current year as a response to climate change. We also found that large-scale anomalies could influence the radial growth of P. crassifolia, which was reflected in results showing that extremely high radial growth is related to El Niño patterns in the central-eastern equatorial Pacific, whereas extremely low growth is related to anomalously warmer SSTs in the southern Indian Ocean. Notably, we found that the extremely low growth of P. crassifolia in response to SST was more stable than that of extremely high growth. Furthermore, on the basis of qualitative methodology, we established that years characterized by extremely high/low growth were largely/little influenced by the time window and threshold values that were selected when determining the positive/negative pointer years. Our results confirm the validity of using the relationships between extremely low growth and SSTs to predict forest dynamics.     

Growth and response patterns of Picea crassifolia and Pinus tabuliformis to climate factors in the Qilian Mountains,northwest China

Different tree species exhibit different phenological and physiological characteristics, leading to complexity in inter-species comparison of stem radial growth response to climate change. This study explored the climate-growth responses of Qinghai spruce (Picea crassifolia) and Chinese pine (Pinus tabulaeformis) in the Qilian Mountains, Northwest China. Meanwhile, Vaganov-Shashkin model (VS-oscilloscope) was used to simulate the relationships between radial growth rates and phenology. The results showed that 1) in their radial growth patterns, Qinghai spruce showed a significant increasing trend, while Chinese pine showed a decreasing trend, and Qinghai spruce has a longer growing season than Chinese pine. 2) For the radial growth-climate dynamic response, Qinghai spruce was influenced in an unstable manner by the mean temperature in the mid-growing season of the current year and the late growing season of the previous year and by the mean minimum temperature in the mid-growing season of the current year, while Chinese pine was influenced in a stable manner by the mean temperature and mean maximum temperature during the growing season of the current year. 3) The radial growth rates of the two conifer species were limited by temperature at the initiation and cessation of growth and by soil moisture at the peak of growth. But Chinese pine was more severely affected by soil moisture than Qinghai spruce in the middle of growth. Therefore, different management and restoration measures should be taken based on the differences in ecological responses and physical and physiological properties of the two conifer species to climate change in the subalpine forest ecosystems in the semiarid and arid regions of Northwest China.     

Effects of canopy position on climate-growth relationships of Qinghai spruce in the central Qilian mountains,northwestern China

Northwestern China has experienced dramatic climate change characterized by rapid warming since the 1980s with the warming trend substantially slowing after 2000. Qinghai spruce (Picea crassifolia Kom.), a key tree species in northwest China, has been predicted to be strongly coupled with climate change. However, how the trends in biomass growth change at different canopy positions under climate change and whether climate–growth responses vary with canopy position remain unclear. A total of 222 trees were sampled by a stand-total sampling strategy in the central Qilian Mountains. Trees were assigned to four canopy positions according to height and distance from neighbors: dominant, codominant, intermediate, and suppressed. Our results indicate that trees in dominant and codominant canopy positions dominate the decreasing trend in stand-level biomass from 1980 to 2000 and the increasing trend from 2000–2013, contributing 81.3 % and 86 %, respectively, whereas trees in the intermediate and suppressed canopy positions contributed less. This result was attributed to a more sensitive response of biomass growth in trees in dominant and codominant canopy positions to climate change. From 1980 to 2000, the stronger decreasing trend in biomass growth at dominant and codominant canopy positions is mostly accounted for by increasing temperature. A more pronounced water deficit might have restricted biomass growth more than that at the intermediate and suppressed canopy positions. However, from 2000 to 2013, drought stress was relieved and summer standardized precipitation evapotranspiration index became a leading factor, which promoted the recovery in biomass at dominant and codominant canopy positions. In a word, compared with intermediate and suppressed canopy trees, those in dominant and codominant positions are less resistant to drought, but dominant and codominant canopy position's biomass can recover more when drought stress is relieved. A more robust understanding of canopy-level growth response and resilience to climate change is crucial to fully understand forest growth dynamics under fluctuating climate conditions.     

Inconsistent response times to precipitation and soil moisture in Picea crassifolia growth

Quantifying the effects of environmental variables on radial growth has real significance for reasonably predicting the impacts of environmental changes on tree dynamics. This study used Picea crassifolia, a widely distributed dominant evergreen coniferous tree species found on the north-eastern fringe of the Tibetan Plateau, as a case study to analyse the associations of radial growth with environmental variables during 1960–2018 using a correlation analysis and sliding correlation analysis. The responses of radial growth to different moisture conditions were further quantitatively evaluated through the generalised linear model and relative dominance analysis. The results show that the radial growth of P. crassifolia is mainly influenced by moisture conditions in the study area. Specifically, the response times of P. crassifolia radial growth to soil moisture and precipitation differ, as radial growth has a significant positive correlation with precipitation in the early growth period. Notably, radial growth has a remarkable and stable correlation with soil moisture in the autumn and winter seasons of the previous year. This study provides a theoretical foundation and scientific grounds for analysing the response of Tibetan Plateau forests to climate change and can act as a reference for future research on the response of radial growth to soil moisture in alpine regions.     

Different trends and divergent responses to climate factors in the radial growth of Abies georgei along elevations in the central Hengduan Mountains

Climate change has been unprecedented in the last half-century. Tree growth dynamics and responses to climate warming at different elevations vary by study area due to regional diversity in site-specific climatic conditions in the central Hengduan Mountains. A. georgei is the dominant species in high-elevation montane forests in the central Hengduan Mountains. To study the response of A. georgei radial growth to climate and identify tree growth trends at different elevations, tree-ring width chronologies at four elevations across the subalpine A. georgei forest belt were built and growth-climate relationships were analyzed. The primary findings of this study were as follows: (1) radial growth rates of A. georgei decreased with elevation; (2) warming alleviated the limitation of low temperatures and abundant precipitation on tree radial growth at the highest sampling site; and (3) unlike at other elevations, the trend of trees basal area increment (BAI) at the lowest sampling site showed a significant decline over the past 20 years. This suggests the presence of an elevational inflection point, likely between 3800 m and 4000 m, where tree growth trends diverge. These results confirmed that A. georgei at higher elevation in the central Hengduan Mountains currently benefits from higher temperatures. However, the effects of drought on A. georgei at lower elevations would cause radial growth to decrease with climate warming. Therefore, it is critical to establish effective management strategies based on how A. georgei responds to climate change at various elevations.     

Stable carbon isotope analysis reveals widespread drought stress in boreal black spruce forests

Unprecedented rates of climate warming over the past century have resulted in increased forest stress and mortality worldwide. Decreased tree growth in association with increasing temperatures is generally accepted as a signal of temperature‐induced drought stress. However, variations in tree growth alone do not reveal the physiological mechanisms behind recent changes in tree growth. Examining stable carbon isotope composition of tree rings in addition to tree growth can provide a secondary line of evidence for physiological drought stress. In this study, we examined patterns of black spruce growth and carbon isotopic composition in tree rings in response to climate warming and drying in the boreal forest of interior Alaska. We examined trees at three nested scales: landscape, toposequence, and a subsample of trees within the toposequence. At each scale, we studied the potential effects of differences in microclimate and moisture availability by sampling on northern and southern aspects. We found that black spruce radial growth responded negatively to monthly metrics of temperature at all examined scales, and we examined ?¹³C responses on a subsample of trees as representative of the wider region. The negative ?¹³C responses to temperature reveal that black spruce trees are experiencing moisture stress on both northern and southern aspects. Contrary to our expectations, ?¹³C from trees on the northern aspect exhibited the strongest drought signal. Our results highlight the prominence of drought stress in the boreal forest of interior Alaska. We conclude that if temperatures continue to warm, we can expect drought‐induced productivity declines across large regions of the boreal forest, even for trees located in cool and moist landscape positions.     

Dynamic relationships between Picea crassifolia growth and climate at upper treeline in the Qilian Mts., Northeast Tibetan Plateau, China

Knowledge of the spatial pattern and temporal relationships between tree-growth and climatic factors are important not only for the projection of forest growth under varying climate but for dendroclimatology in general. Here, we systematically investigated tree-growth climate relationships of Picea crassifolia at upper treeline in the Qilian Mts., northwestern China. 297 trees from eleven sites, covering a large part of the natural range of this species, show increasing and partly divergent correlations with temperature in the most recent decades. The dominant signal at all sites was a strengthening of negative correlations of annual radial growth with summer temperature. In a subset of trees at six sites, a strengthening positive correlation with summer temperatures existed as well. Wetter and high altitude sites tended to show a higher percentage of trees that are positively correlated with warming temperatures, indicating that some individuals there may take advantage of warmer conditions. Divergent responses between the two sub-populations clustered by their response to climate factor were significantly stronger in the last 30 years compared to earlier time slices. In the same time frame, hydrothermal conditions of the investigation area changed to a drier and warmer combination. Drought conditions, most likely affecting the radial growth of most P. crassifolia, have been intensifying over time and expanding spatially from the middle Qilian Mts. to most of our study area during the last half century. While explanations such as methodological effects due to trend removal or human disturbance at the sampling sites might be able to explain the result at single sites, the spatial and temporal co-occurrence of large scale changes in climate and tree growth suggests a causal link between them.     

Drought variation recorded by growth rings of the shrub Sabina vulgaris in the middle Qilian Mountains,northwest China

The evergreen coniferous creeping shrub, Sabina vulgaris, is widely distributed in China, from high and cold mountain sites to low-elevation arid desert areas. This paper performed dendroclimatological analysis of the samples of S. vulgaris from three sampling sites (2700–2900 m a.s.l.) at sites in the northern border of the middle Qilian Mountains, Northwest China. We found that the radial growth of S. vulgaris was mainly limited by rainfall during the growing season, especially in May and June, but was also limited by low temperatures in the late growing season. It presents the regional differention of the climate response of the shrub radial growth from the other distributed areas, such as the sandland and mountains. We constructed a 274-year drought record by calibrating growth-ring data and relating this data to the regional monthly Palmer Drought Severity Index (PDSI₅₆), which represents regional moisture conditions. The PDSI₅₆ reconstruction accounted for 35.5 % of the variation of the actual May to June PDSI₅₆ during the period for which meteorological data was available (1950–2014). The most severe drought occurred during the 1920s, followed by the 1950s, 1740s, and the period from the 1870s to the 1880s; the wettest years were during the 1980s, followed by the 2010s, 1770s, and 1750. The changes between drought, normal, and wet periods were consistent with the reconstructed results from previous conifer ring series for Sabina przewalskii and Picea crassifolia in the study area. Our results demonstrate the value of S. vulgaris in dendrochronology.     

Impact of extreme drought on tree-ring width and vessel anatomical features of Chukrasia tabularis

Multiple sources of evidence suggest an increasing frequency of extreme climatic events during the past century. In Bangladesh, a country strongly influenced by the South Asian monsoon climate, the years 1999 and 2006 were the most severe droughts among the ten drought events identified over the last four decades. We investigated the impact of these two drought events on radial growth and xylem anatomical features of the brevi-deciduous tree species Chukrasia tabularis in a moist tropical forest in Bangladesh. Tree radial growth declined by 54% during the 1999 and 48.7% during the 2006 droughts, respectively. Among the wood anatomical features, the number of vessels (NV) showed the highest sensitivity to drought, with a 45% decrease in the 1999 drought year, followed by total vessel area (TVA) and mean vessel area (MVA). On the other hand, Vessel density (VD) increased by 13% during the 1999 drought but the increase in VD was very low in the drought year 2006. The decreasing vessel area and increasing vessel density indicate xylem hydraulic adaptation of C. tabularis to minimize drought induced cavitation risk and to avoid hydraulic failure. The significant correlations between the Standardized Precipitation Evapotranspiration Index (SPEI) and time series of tree-ring width and vessel variables imply that decline in radial growth and changes in vessel features in C. tabularis are likely to be caused by drought induced water stress. Our analyses suggest that radial growth and wood anatomical features of C. tabularis are highly sensitive to extreme drought events in South Asian moist tropical forests and can be used to reconstruct past droughts and to model tree response to drought stress under future climate conditions.     

Warming induced tree-growth decline of Toona ciliata in (sub-) tropical southwestern China

Tropical forests play an important role in the global carbon cycle and climate regulation. However, our understanding of how Asian tropical forest growth responds to climatic variations is still limited. We developed tree ring-width chronologies of Toona ciliata from 90 trees (139 cores) from two study regions in the tropical/subtropical forests in Yunnan, southwestern China. Bootstrapped correlation analysis revealed positive moisture sensitivity (precipitation, self-calibrated Palmer drought severity index, relative humidity, and soil moisture) and negative temperature sensitivity of T. ciliata, and the relationship was strongest during dry and/or dry-to-wet transition months, indicating that radial growth of T. ciliata is primarily limited by moisture availability during early growing season. Furthermore, radial growth of T. ciliata was significantly and negatively correlated with the vapor pressure deficit and potential evapotranspiration during dry and/or dry-to-wet transition months. We analyzed long-term growth trends of T. ciliata using ‘size class isolation' (SCI) and ‘generalized additive mixed models' (GAMM) approaches which remove the effects of tree size on tree growth. We detected decreasing growth trend for both approaches at both study regions, indicating that the growth decline of T. ciliata stands in southwestern China is likely due to global warming-induced moisture deficit. The growth of T. ciliata trees is likely to continually decline under projected warming and drying conditions. The observed growth declines of T. ciliata raised concerns about developing sustainable management and conservation programs for tropical/subtropical forests in China.     

Climate signal shift under the influence of prevailing climate warming – Evidence from Quercus liaotungensis on Dongling Mountain,Beijing, China

Increasing climate warming is inducing drought stress and resulting in forest growth decline in many places around the world. The recent climate of northern China has shown trends of both warming and drying. In this study, we obtained tree ring width chronology of Quercus liaotungensis Koidz. from Dongling Mountain, Beijing, China. We divided the temperature series of the study area into cooling (1940–1969) and warming intervals (1970–2016). The climate–tree growth response analysis showed that temperature exerted a limiting impact on the annual radial growth of Q. liaotungensis during the cooling period, whereas the influence of temperature was lower during the warming period. The moving correlation analysis showed that the influence of summer temperature decreased with the warming climate since the 1970s, and that the influence of winter and spring temperatures decreased since the 2000s. The correlation values between the chronology and precipitation decreased during the cooling period, whereas spring and early summer precipitation correlations began to increase in the 1970s and reached significance (p < 0.05) in the 1990s. Our results show that the positive influence of temperature on radial growth of Q. liaotungensis in the study area has weakened, whereas precipitation has become the dominant regulator with climate warming. These findings suggest that forest growth on Dongling Mountain will decline if climate warming continues in the future.     

Diverging growth and resilience of Pinus tabulaeformis and Pinus massoniana to droughts in north-south transition zone,central China

Climate transition zone is a sensitive area of climate change and ecological transition where forests are vulnerable to climate extremes. Extreme droughts are increasing in frequency and magnitude under climate change, resulting in structure and function changes of forest ecosystems. Here, to analyze climate-growth relationships and quantify tree resilience to extreme droughts, we developed six tree-ring-width chronologies from P. tabulaeformis and P. massoniana sampling sites in Mt. Jigong region, Central China. The results indicated that all chronologies from the two species had good consistency, precipitation in current April and mean temperature in current August or mean minimum temperature from current August to October were the main limiting factors of the two tree species growth, but the responses of P. massoniana ring-width to climatic factors was more complex than that of P. tabulaeformis. The results also showed that tree growth of 1999–2005 was the lowest growing period during 1979–2018, and P. massoniana grew better than P. tabulaeformis before 2005 and vice versa after 2005. Comparing low growth years of trees, we identified to study tree growth resilience. The calculations from 1988, 1999–2005 and 2011 drought years indicated that P. tabulaeformis had more increased resilience to extreme droughts than that of P. massoniana, and the two species had stronger ecological recovery and resilience under global warming and non-extreme drought conditions in the recent 40 years. These results have implications for predicting tree resilience and identifying tree species in heterogeneous forest landscapes vulnerable to future climate change in climatic transition zone.     

秦岭中西部油松径向生长对气候因子的响应差异研究

在气候变暖背景下,树木径向生长对气候因子的响应会随区域干湿变化而有所差异。秦岭属于气候敏感区和生态脆弱区,南北气候特征差异明显,分析气候变化背景下树木径向生长对气候因子及干旱事件的响应,对准确预测未来气候变化对树木生长的影响至关重要。为探究该地区不同干湿环境下油松对气候因子及干旱事件响应的特点及差异,共采集秦岭中西部南北坡共4个样点的油松树轮样芯,利用树木年轮生态学的方法,分析各地油松年表与气候因子之间的关系,通过计算抵抗力、恢复力、恢复弹力等指标探究树木径向生长对干旱事件的应对能力,结果表明：1)在西部和北坡的3个样点,油松径向生长主要与前一年7—9月、当年5—7月的气温呈显著负相关,与当年5月降水呈显著正相关,在中部南坡油松径向生长主要与当年2—4月、9月气温呈显著正相关,与当年4月降水呈显著负相关;2)生长季气温升高所引发的水分亏缺,是研究区西部和北坡油松径向生长受限制的主要原因,且中部南坡油松生长受气温和干旱因子的制约要明显弱于其它3个样点;3)西部北坡油松对干旱的抵抗能力、恢复能力及恢复弹力均弱于西部南坡及中部北坡油松。在未来对研究区树木的管理与保护工作中,应更加关注西部北坡...     

Species-specific growth-climate responses of Dahurian larch (Larix gmelinii) and Mongolian pine (Pinus sylvestris var. mongolica) in the Greater Khingan Range,northeast China

Responses of tree growth to climate are usually spatially heterogeneous. Besides regionally varying external environments, species specificity is a crucial factor in determining said spatial heterogeneity. A better understanding of this species specificity would improve our estimations of the warming effects on forests. In this study, we selected two widely-distributed boreal conifers, Dahurian larch (Larix gmelinii) and Mongolian pine (Pinus sylvestris var. mongolica), to compare their growth-climate responses, including long-term growth-climate correlations and short-term growth resilience to drought. We sampled 160 trees and 481 tree-ring cores from the two species in two pure and two mixed forests, located in the Greater Khingan Range, northeast China. We found that Dahurian larch was generally positively correlated with spring temperature and negatively correlated with summer temperature. In contrast, Mongolian pine was more sensitive to summer moisture. Our results suggest that the main climatic limitations were low spring temperatures for Dahurian larch and summer moisture deficits for Mongolian pine. Dahurian larch represented higher growth resistance to drought, while Mongolia pine represented higher recovery. Based on this, we inferred that Dahurian larch was more vulnerable to extreme droughts, while Mongolian pine was more vulnerable to frequent droughts. We also demonstrated the effects of forest type on growth-climate responses. The negative effects of summer temperatures on Mongolian pine seemed to be more significant in mixed forests. As warming continued, Mongolian pine in this area would suffer severer moisture deficits, especially when coexisting with Dahurian larch. Our results suggest that Dahurian larch gained an advantage in the competition with Mongolian pine during high moisture stress. Driven by the warming trends, the species specificity in growth response would ultimately promote the separation of the two species in distribution. This study will help improve our estimations of the warming effects on forests and develop more species-targeted forest management practices.     

Forward modeling analyses of Qilian Juniper <Emphasis Type="Italic">(Sabina przewalskii)</Emphasis> growth in response to climate factors in different regions of the Qilian Mountains,northwestern China

Key message

The process-based Vaganov–Shashkin model simulations accurately represent the nonlinear process of Qilian Juniper growth–climate relationship over different regions of the Qilian Mountains.

Abstract

The Qilian Mountains (QM), northeastern edge of the Tibetan Plateau (TP), is one of the most studied areas in China for tree-ring research; considerable dendroclimatic reconstructions have been carried out and a series of important achievements made over this region. However, most reconstructions were primarily based on empirical relationships between tree growth and climate factors identified through statistical analysis. Reliable information on the physiological processes of tree responses to climate change in different regions is still scarce. Here, the process-based Vaganov–Shashkin (VS) model was used to simulate regional patterns of climate–tree growth relationships using observed temperature and precipitation over the different regions of the QM. Results showed that the sequences of simulated growth curves were broadly consistent with the actual tree-ring chronologies in all three regions of the QM. VS model simulations accurately represented the effect of climatic controls on the growth of Qilian Juniper (Sabina przewalskii). VS model outputs closely corresponded to statistical relationships between tree-ring width and climate factors as well as observational physiological behavior; i.e., available water in May and June had the largest contribution to ring formation in Qilian Juniper over the QM. The simulated and actual data analyses revealed that the radial growth of trees in the western QM was more sensitive to moisture conditions in May and June, compared with growth in the central and eastern QM. Tree growth in this region is representative of large areas in northwestern China with drought conditions.

     

北京东灵山辽东栎林树木生长对气候要素的响应特征

根据北京东灵山辽东栎(Quercus wutaishanica)的年轮宽度资料,分析了该地区树木生长在1951—2010年时段对气候要素的响应特征。相关分析表明,夏季干旱胁迫是限制东灵山辽东栎树木生长的最为重要的气候要素,主要体现在与夏季(7—9月)温度的负相关关系和夏季降雨(7月)的正相关关系,另外春季(5月)温度对树木生长也有一定的限制性影响;年表与生长季节干旱指数普遍呈正相关关系,进一步证实了干旱胁迫对树木生长的限制性作用。滑动相关分析表明,年表与夏季温度负相关关系及与夏季降雨的正相关关系在近期趋于增强,这表明夏季干旱胁迫对树木生长影响作用有不断加强的趋势。辽东栎林是北京东灵山温带落叶阔叶林的优势群落,在暖干化气候不断发展背景下,辽东栎林生长的干旱胁迫效应将更加突出,对北京东灵山地区森林的生产力及固碳能力产生负面影响。     

Large old trees increase growth under shifting climatic constraints: Aligning tree longevity and individual growth dynamics in primary mountain spruce forests

In a world of accelerating changes in environmental conditions driving tree growth, tradeoffs between tree growth rate and longevity could curtail the abundance of large old trees (LOTs), with potentially dire consequences for biodiversity and carbon storage. However, the influence of tree-level tradeoffs on forest structure at landscape scales will also depend on disturbances, which shape tree size and age distribution, and on whether LOTs can benefit from improved growing conditions due to climate warming. We analyzed temporal and spatial variation in radial growth patterns from ~5000 Norway spruce (Picea abies [L.] H. Karst) live and dead trees from the Western Carpathian primary spruce forest stands. We applied mixed-linear modeling to quantify the importance of LOT growth histories and stand dynamics (i.e., competition and disturbance factors) on lifespan. Finally, we assessed regional synchronization in radial growth variability over the 20th century, and modeled the effects of stand dynamics and climate on LOTs recent growth trends. Tree age varied considerably among forest stands, implying an important role of disturbance as an age constraint. Slow juvenile growth and longer period of suppressed growth prolonged tree lifespan, while increasing disturbance severity and shorter time since last disturbance decreased it. The highest age was not achieved only by trees with continuous slow growth, but those with slow juvenile growth followed by subsequent growth releases. Growth trend analysis demonstrated an increase in absolute growth rates in response to climate warming, with late summer temperatures driving the recent growth trend. Contrary to our expectation that LOTs would eventually exhibit declining growth rates, the oldest LOTs (>400 years) continuously increase growth throughout their lives, indicating a high phenotypic plasticity of LOTs for increasing biomass, and a strong carbon sink role of primary spruce forests under rising temperatures, intensifying droughts, and increasing bark beetle outbreaks.     

Observed and projected impacts of climate on radial growth of three endangered conifers in northern Mexico indicate high vulnerability of drought-sensitive species from mesic habitats

A decline in productivity and radial growth in conifer forests from mesic areas has been associated with increased drought stress induced by climate warming. Nevertheless, studies showing how vulnerable tree species will be in response to forecasted warming conditions are scarce in such mesic habitats. Here we address this issue by analyzing how growth responds to drought and to observed and projected climate conditions in a conifer forest from northern Mexico, which is a hotspot of conifer diversity. We quantify the trends in radial growth (quantified as basal area increment, BAI) of three species (Abies durangensis, Picea chihuahuana, Cupressus lusitanica) using dendrochronology and a process-based model of tree growth. Growth decreased in A. durangensis and P. chihuahuana from the late 1980s onwards in response to warmer and drier conditions, whereas C. lusitanica growth showed very low sensitivity to precipitation and increased as temperature did. Winter-spring dry conditions adversely affected the growth of A. durangensis and P. chihuahuana. Our modeling approach anticipates growth reductions and an increase in the vulnerability of A. durangensis and the endangered P. chihuahuana against the warmer and more arid conditions predicted after the 2050s. Future warmer and drier climatic conditions could reduce the productivity and lead to growth decline of these mesic conifer forests triggering dieback episodes in highly drought-sensitive species as A. durangensis and P. chihuahuana.