Climate-growth Responses Research Articles

Reconstructed springtime (March–June) precipitation tracked by tree rings dating back to 1760 CE in the Qinling-Bashan mountainous area

In recent decades, considerable advances have been made in dendroclimatic reconstruction in the eastern monsoon region of China. However, understanding of long-term hydroclimatic changes has not been comprehensive due to the complexity of the regional geography in China's north-south transitional zone. Growth-climate response analysis indicated that springtime precipitation is the main factor limiting the radial growth of pine trees in the Qinling-Bashan mountainous area. Based on the three tree ring chronologies distributed in the southeast of Shaanxi Province, we developed a March–June precipitation reconstruction spanning 1760–2020 CE for the Qinling-Bashan mountainous area. Precipitation reconstruction accounts for 40.6% of the total precipitation variance during the instrumental period 1955–2016. Spatial correlation analysis indicated that the precipitation reconstruction recorded similar common precipitation signals for the eastern Qinling Mountains and the Yangtze-Huai River Basin. The results of the superposed epoch analysis (SEA) revealed that low precipitation was one of the main causes of severe drought and locust plague events. The preliminary synoptic climatology analysis showed that our reconstructed precipitation is closely linked to the El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) variability.

Accelerated warming in the late 20th century promoted tree radial growth in the Northern Hemisphere

AbstractAccelerated global warming in the late 20th century led to frequent forest-decline events in the Northern Hemisphere and increased the complexity of the relationships between tree growth and climate factors. However, few studies have explored the heterogeneity of responses of tree growth to climate factors in different regions of the Northern Hemisphere before and after accelerated warming. In this study, a total of 229 temperature-sensitive tree-ring width chronologies from nine regions on three continents in the Northern Hemisphere were used in the data analysis performed herein. A bootstrapped correlation analysis method was used to investigate whether the tree growth-climate response changed significantly in different regions between the periods before and after rapid warming. Probability density functions and piecewise linear fitting were used to study the fluctuation characteristics of the tree-ring width indices before and after rapid warming. At the end of the 20th century (from 1977 to 2000), rapid warming significantly promoted the radial growth of trees in different regions of the Northern Hemisphere, but tree radial growth was heterogeneous among the different regions from 1950 to 2000. After 1976, except in central North America and northern Europe, the correlation between tree growth and temperature increased significantly in the Northern Hemisphere, especially in Asia. From 1977 to 2000, tree-ring index and temperature divergences were observed in nine regions with a divergence of 2–5 years. From 1950 to 2000, tree growth tracked better average temperature variability in the Northern Hemisphere than regional temperature.

Local environment prevails over population variations in growth-climate relationships of Pinus pinaster provenances

In view of the projected decrease in precipitation and increase in temperature, a better understanding on growth-climate responses in different populations of tree species is needed to improve and enhance the conservation and management strategies for major forest tree species. In this study, we assessed differences in growth traits (i.e., stem diameter, tree height, and stem radial growth) and analysed climate-growth relationships in five provenances of maritime pine (Pinus pinaster Ait.) grown in four replicated common gardens in Sardinia (Italy). Stem radial growth increased under a positive water balance in late winter and early spring. Conversely, high temperature and low precipitation in summer had a negative impact on stem radial growth. At age 40, none of the considered provenances (Portugal, Corsica, Tuscany, Sardinia-Telti, Sardinia-Limbara) showed a substantial advantage in more than one common garden site for tree height and stem diameter. Nevertheless, differences were found among common garden sites in terms of dendrometric parameters, stem radial growth, and growth-climate responses (including sensitivity to summer drought), suggesting a greater site dependent over tree growth. Although in juvenile stages the Portuguese provenance (in particular) showed greater growth than the Sardinian ones, this study showed that, with tree age, the differences among the five provenances tends to narrow. Therefore, irrespective of the seed source, tree growth patterns and growth-climate responses were similar at age 40. This result can be important for implementing forest management strategies to balance adaptation and mitigation potential of maritime pine plantations in harsh environmental conditions.

Effects of altitude and slope on the climate–radial growth relationships of Larix olgensis A. Henry in the southern Lesser Khingan Mountains, Northeast China

BackgroundThe relationship between climate and radial growth of trees exhibits spatial variation due to environmental changes. Therefore, elucidation of how the growth–climate responses of trees vary in space is essential for understanding forest growth dynamics to facilitate scientific management with the ongoing global climate warming. To explore the altitudinal and slope variations of these interactions, tree-ring width chronologies of Larix olgensis A. Henry were analyzed in the southern Lesser Khingan Mountains, Northeast China.ResultsThe radial growth of L. olgensis exhibited significant 5- to 10-year periodic changes at three altitudes and two slopes, and the frequency change occurred mainly during the early growth stage and after 2000. The radial growth of L. olgensis was significantly negatively correlated with September precipitation only at low altitudes, but also with the mean temperature in July–August and the mean maximum temperature in June–August at high altitudes. The radial growth of L. olgensis at low and middle altitudes as well as on the sunny slope led to a higher demand for moisture, while temperature was the key limiting factor at high altitudes and on the shady slope.ConclusionsThe climate–radial growth relationship of L. olgensis exhibits altitudinal and slope variability. This study quantitatively describes the spatially varying growth–climate responses of L. olgensis in the southern Lesser Khingan Mountains, which provides basic data for the management of L. olgensis forests and the prediction of future climate impacts on forest ecosystems.

Regional Drought Conditions Control Quercus brantii Lindl. Growth within Contrasting Forest Stands in the Central Zagros Mountains, Iran

The magnitude and duration of ongoing global warming affects tree growth, especially in semi-arid forest landscapes, which are typically dominated by a few adapted tree species. We investigated the effect of climatic control on the tree growth of Persian oak (Quercus brantii Lindl.), which is a dominant species in the Central Zagros Mountains of western Iran. A total of 48 stem discs was analyzed from trees at three sites, differing in local site and stand conditions (1326 to 1704 m a.s.l.), as well as the level and type of human impact (high human intervention for the silvopastoral site, moderate for the agroforestry site, and low for the forest site). We used principal component analysis (PCA) to investigate the common climatic signals of precipitation, air temperature, and drought (represented by SPEI 1 to 48 months) across the site chronologies. PC1 explains 83% of the total variance, indicating a dominant common growth response to regional climatic conditions that is independent of the local environmental conditions (i.e., forest stand density and land-use type). Growth–climate response analyses revealed that the radial growth of Q. brantii is positively affected by water availability during the growing season (r = 0.39, p < 0.01). Precipitation during April and May has played an ever-important role in oak growth in recent decades. Our study provides evidence that hydroclimatic conditions control tree-ring formation in this region, dominating the effects of topography and human impact. This finding highlights the great potential for combining historical oak samples and living trees from different forest stands in order to generate multi-centennial tree-ring-based hydroclimate reconstructions.

Growth-climate sensitivity of two pine species shows species-specific changes along temperature and moisture gradients in southwest China

A better understanding of tree growth-climate sensitivity across regions and species may reduce uncertainties in simulating forest carbon budgets. We studied the spatial heterogeneity of growth-climate sensitivity of Pinus yunnanensis and Pinus kesiya across temperature and moisture gradients in the complex mountain regions of Southwest China. We developed tree ring-width chronologies from 22 sites for P. yunnanensis and 20 sites for P. kesiya, totaling 903 trees (1684 cores). We applied generalized additive mixed models (GAMMs) on basal area increment (BAI) series to remove the age and size effects on tree growth, and correlated BAI residual chronologies with climate variables. Radial growth of P. yunnanensis and P. kesiya at most sites (> 75%) were positively correlated with precipitation and one-month Standardized Precipitation-Evapotranspiration Index (SPEI1) during the early growing season. In contrast, high precipitation and SPEI1 during the late growing season reduced tree growth of both pine species. The growth-climate sensitivity of both pine species varied along the temperature and moisture gradients, i.e., moisture sensitivity of tree growth decreased along a dry-to-humid moisture gradients for P. kesiya during early growing season, whereas temperature sensitivity of P. yunnanensis shifted from positive (beneficial) to negative (limitative) along cold-to-warm gradients. Our results indicate that the growth-climate sensitivity of both pine species varies with site-specific environmental conditions. These findings contribute to improve our understanding about the spatial patterns of tree growth-climate responses of these economically important conifer species in Southwest China.

Contrasting Impacts of Climate Warming on Coastal Old-Growth Tree Species Reveal an Early Warning of Forest Decline

Old-growth forests in the Pacific Northwest are being fundamentally altered by climate change. A primary example of this is yellow-cedar (Callitropsis nootkatensis), a culturally and economically important species, which has suffered widespread decline across its range since the beginning of the twentieth century. We used tree rings to compare the climate-growth response of yellow-cedar to two co-occurring species; western hemlock (Tsuga heterophylla) and Sitka spruce (Picea sitchensis), in an old-growth forest on Haida Gwaii, Canada, to better understand the unique climatic drivers of a species that is declining across its range. We developed three species-specific chronologies spanning 560–770 years, reconstructing a long-term record of species growth and dynamics over time. The climate is strongly influenced by the Pacific Decadal Oscillation (PDO), a multi-decadal pattern of ocean-atmospheric climate variability. Climate varied across three time periods that have coincided with major shifts in the PDO during the twentieth century [1901–1945 (neutral/positive), 1946–1976 (negative) and 1977–2015 (positive)]. Conditions were significantly warmer and wetter during positive phases, with the greatest maximum temperatures in the most recent period. We used complimentary methods of comparison, including Morlet wavelet analysis, Pearson correlations, and linear-mixed effects modeling to investigate the relations between climate and species growth. All three species exhibited multi-decadal frequency variation, strongest for yellow-cedar, suggesting the influence of the PDO. Consistent with this, the strength and direction of climate-growth correlations varied among PDO phases. Growing season temperature in the year of ring formation was strongly positively correlated to yellow-cedar and western hemlock growth, most significantly in the latter two time periods, representing a release from a temperature limitation. Sitka spruce growth was only weakly associated with climate. Yellow-cedar responded negatively to winter temperature from 1977 to 2015, consistent with the decline mechanism. Increased yellow-cedar mortality has been linked to warmer winters and snow loss. This study provides new insights into yellow-cedar decline, finding the first evidence of decline-related growth patterns in an apparently healthy, productive coastal temperate rainforest.

Altitudinal difference of growth-climate response models in the north subtropical forests of China

Altitudinal difference increases the complexity of the response of tree growth to climate change in the mountainous areas, and may change the carbon sequestration capacity of forests under the ongoing warming climate. In this work, four tree-ring width chronologies from Pinus henryi Mast. growing at different altitudes of Shiyan, the northern subtropical China were developed. Results of Pearson correlation analysis, factor analysis and redundancy analysis indicate that tree growth-climate response models can be divided into two types according to the altitudinal gradient: the high-altitude model, represented by SWDH and WDSH above 1330 m a.s.l., and the low-altitude model, represented by WDSL and DDZL less than 1070 m a.s.l. The biggest difference between the two models is that tree growth at the low altitudes shows significantly negative response to temperature in the previous September–December and current April–May, and positive response to moisture conditions from the previous September to current May, April–May in particular; while the high-altitude ones show consistently positive responses to temperature in current February–April, but no significant response to seasonal moisture condition. The existence of a temperature-related altitudinal threshold between 1070 m a.s.l. to 1330 m a.s.l. may change the hydro-thermal combination models above and below the threshold, thus lead to the change of climatic response models along altitude gradient. 30-yr moving correlation analysis reveals that the relationships between tree growth and the limiting climatic factors present evident altitudinal difference: gradually strengthened at the high altitudes but weakened at the low altitudes. It is distinct that water availability and demand are critical for the growth of low-altitude trees, and high-altitude trees show a stronger positive response to climate warming, therefore could be an important carbon sink in the future. In addition, future forest management should focus on the low altitudes and formulate effective protection strategies.

Global tree-ring response and inferred climate variation following the mid-thirteenth century Samalas eruption

The largest explosive volcanic eruption of the Common Era in terms of estimated sulphur yield to the stratosphere was identified in glaciochemical records 40 years ago, and dates to the mid-thirteenth century. Despite eventual attribution to the Samalas (Rinjani) volcano in Indonesia, the eruption date remains uncertain, and the climate response only partially understood. Seeking a more global perspective on summer surface temperature and hydroclimate change following the eruption, we present an analysis of 249 tree-ring chronologies spanning the thirteenth century and representing all continents except Antarctica. Of the 170 predominantly temperature sensitive high-frequency chronologies, the earliest hints of boreal summer cooling are the growth depressions found at sites in the western US and Canada in 1257 CE. If this response is a result of Samalas, it would be consistent with an eruption window of circa May–July 1257 CE. More widespread summer cooling across the mid-latitudes of North America and Eurasia is pronounced in 1258, while records from Scandinavia and Siberia reveal peak cooling in 1259. In contrast to the marked post-Samalas temperature response at high-elevation sites in the Northern Hemisphere, no strong hydroclimatic anomalies emerge from the 79 precipitation-sensitive chronologies. Although our findings remain spatially biased towards the western US and central Europe, and growth-climate response patterns are not always dominated by a single meteorological factor, this study offers a global proxy framework for the evaluation of paleoclimate model simulations.

Altered climate memory characterizes tree growth during forest dieback

Warming temperatures and droughts are driving widespread forest dieback and growth decline worldwide. In forests experiencing dieback, declining trees may exhibit altered climate memory of growth, indicative of physiological impairment. Thus, we evaluated climate-growth responses of trees in four drought-disturbed forests dominated either by gymnosperms (Abies alba, Pinus sylvestris) or angiosperms (Fagus sylvatica, Quercus humilis) in Northern Spain, where we compared responses of declining (heavily defoliated) and non-declining (slightly or not defoliated) trees. To disentangle the effects of forest dieback and past climate on tree growth, we applied the stochastic antecedent modeling (SAM) framework to annual tree-ring widths to quantify climatic memory. Declining trees had lower recent growth than non-declining conspecifics. All species responded positively to precipitation and temperature, independent of their vigor class, except for declining silver fir (A. alba) and European beech (F. sylvatica) individuals, which showed a negative effect of warmer temperatures on growth. Declining trees of these two species were also more sensitive to recent temperature and precipitation conditions, whilst climatic conditions further into the past were more important for non-declining trees. Silver fir and European beech from both vigor classes were also coupled to climate conditions during markedly different seasons, with dry summer conditions particularly affecting declining trees. Declining and non-declining Scots pine (P. sylvetris) and pubescent oak (Q. humilis) trees did not show different responses to past climate. While drought-triggered dieback differentially impacted silver fir and European beech individuals, Scots pine and pubescent oak trees suffered from a chronic process of loss in tree growth and vigor. Our results highlight the differences in climate sensitivity and climate memory of tree growth in forests experiencing ongoing dieback.

Recent changes in the climate-growth response of European larch (Larix decidua Mill.) in the Polish Sudetes

Key messageRecently observed temporal changes in the climate-growth relationship of larch in the Polish Sudetes suggest growth limitations in the future.Larches in the Sudetes are very sensitive to the currently changing climatic factors, and an extreme negative response to drought is observed. In this study, temporal changes in the climate-growth relationship of European larch were analyzed using moving-window correlation. Change-point detection analysis was performed to determine whether there is a temporal connection between tree-ring growth responses and changes in climatic factors trends. The Random Forest predictor importance determination method was used to establish the set of climatic factors that influence larch tree-ring growth the most and to show how this set changes over time. Additionally, cluster analysis was applied to find spatial growth patterns and to generalize the growth response of larch. The results indicate that the main clustering factor is altitude. Nevertheless, an increasing unification of the larch’s response to dominant climatic factors is observable throughout the whole study area. This unification is expressed in the increasingly positive and recently dominant effect of May temperature. A progressively negative influence of the temperature in the summer and late autumn of the year preceding growth was observed, as was an increasing influence of water availability in the summer months. The study indicates that there is a connection between the observed changes and the recent rapid rise in temperature, which has consequently had a negative influence on water availability. The growth of this tree species in the Sudetes is expected to be very limited in the future due to its sensitivity to drought, the predicted increase in temperatures and thermal extremes, and the decrease of the share of summer precipitation in the annual total.

Climate-growth relations of congeneric tree species vary across a tropical vegetation gradient in Brazil

Seasonally dry tropical forests are an important global climatic regulator, a main driver of the global carbon sink dynamics and are predicted to suffer future reductions in their productivity due to climate change. Yet, little is known about how interannual climate variability affects tree growth and how climate-growth responses vary across rainfall gradients in these forests. Here we evaluate changes in climate sensitivity of tree growth along an environmental gradient of seasonally dry tropical vegetation types (evergreen forest – savannah – dry forest) in Northeastern Brazil, using congeneric species of two common neotropical genera: Aspidosperma and Handroanthus. We built tree-ring width chronologies for each species × forest type combinations and explored how growth variability correlated with local (precipitation, temperature) and global (the El Niño Southern Oscillation - ENSO) climatic factors. We also assessed how growth sensitivity to climate and the presence of growth deviations varied along the gradient. Precipitation stimulates tree growth and was the main growth-influencing factor across vegetation types. Trees in the dry forest site showed highest growth sensitivity to interannual variation in precipitation. Temperature and ENSO phenomena correlated negatively with growth and sensitivity to both climatic factors were similar across sites. Negative growth deviations were present and found mostly in the dry-forest species. Our results reveal a dominant effect of precipitation on tree growth in seasonally dry tropical forests and suggest that along the gradient, dry forests are the most sensitivity to drought. These forests may therefore be the most vulnerable to the deleterious effects of future climatic changes. These results highlight the importance of understanding the climatic sensitivity of different tropical forests. This understanding is key to predict the carbon dynamics in tropical regions, and sensitivity differences should be considered when prioritizing conservation measures of seasonally dry topical forests.

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.

Intra-Annual Wood Formation of Cryptomeria fortunei and Cunninghamia lanceolata in Humid Subtropical China

Monitoring cambial activity is important for a better understanding of the mechanisms governing xylem growth responses to climate change, providing a scientific basis for tree-ring-based climate reconstructions and projections about tree growth under future climate scenarios. It plays an even more important role in investigating evergreen tree growth in regions with less distinct seasonal cycles. Subtropical evergreen forests have been studied in recent years for their sensitivity to climate change, but it remains unclear how xylem growth is driven by subtropical climates. To further understand the climate-growth response strategies of subtropical conifers, we micro-cored Cryptomeria fortunei and Cunninghamia lanceolata weekly in 2016 and 2017 at the humid subtropical Gushan Mountain in southeastern China. Our weekly growth monitoring showed that the vegetation periods of these two species were both approximately 2–3 months longer than trees in temperate and boreal forests. The growth of C. fortunei in 2016 and 2017 and C. lanceolata in 2017 showed a bimodal pattern of xylogenesis, which was induced by summer drought. The results also indicated that the earlier end of the xylem formation was related to the yearly drought stress. These findings provide more specific information about tree growth and evidence of how climate influences wood production at the cellular level in subtropical regions.

Non-linear Response to Cell Number Revealed and Eliminated From Long-Term Tracheid Measurements of Scots Pine in Southern Siberia.

Dendroclimatic research offers insight into tree growth–climate response as a solution to the forward problem and provides reconstructions of climatic variables as products of the reverse problem. Methodological developments in dendroclimatology have led to the inclusion of a variety of tree growth parameters in this field. Tree-ring traits developed during short time intervals of a growing season can potentially provide a finer temporal scale of both dendroclimatic applications and offer a better understanding of the mechanisms of tree growth reaction to climatic variations. Furthermore, the transition from classical dendroclimatic studies based on a single integral variable (tree-ring width) to the modern multitude of quantitative variables (e.g., wood anatomical structure) adds a lot of complexity, which mainly arises from intrinsic feedbacks between wood traits and muddles seasonality of registered climatic signal. This study utilized life-long wood anatomical measurements of 150- to 280-year-old trees of Pinus sylvestris L. growing in a moisture-sensitive habitat of the forest-steppe of Southern Siberia (Russia) to investigate and eliminate legacy effect from cell production in tracheid traits. Anatomical parameters were calculated to describe the results of the three main subsequent stages of conifer xylem tracheid development, namely, cell number per radial file in the ring, mean and maximum cell radial diameter, and mean and maximum cell-wall thickness. Although tree-ring width was almost directly proportional to cell number, non-linear relationships with cell number were revealed in tracheid measurements. They exhibited a stronger relationship in the areas of narrow rings and stable anatomical structure in wider rings. The exponential models proposed in this study demonstrated these relationships in numerical terms with morphometric meaning. The ratio of anatomical measurements to their modeled values was used to develop long-term anatomical chronologies, which proved to retain information about climatic fluctuations independent of tree-ring width (cell number), despite decreased common signal.

Responses of radial growth of Pinus sylvestris var. mongolica and Larix gmelinii to climate change

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.

Climate-growth pattern of Pinus tabulaeformis plantations and their resilience to drought events in the Loess Plateau

Large-scale plantations were established under the Grain for Green project to improve the ecological environment of the Loess Plateau (LP) of China. However, there are increasing concerns regarding the sustainability of plantation ecosystems under climate change. In this study, we developed tree-ring width chronologies of Pinus tabulaeformis at seven sites along a precipitation gradient from south to north in the LP. Correlation analysis was performed to investigate the climate (temperature, precipitation, self-calibrating Palmer Drought Severity Index)-growth relationship. Moreover, the tree resilience components were computed to study the adaptability of trees to extreme drought during the growth periods. The results showed that the differences in radial growth to climate change along the precipitation gradient and the cluster analysis of the tree ring width index (RWI)-scPDSI correlation coefficient illustrated that the climate-growth response pattern along the LP was divided into southern and northern regions. Tree growth in the southern region is limited by humid environment conditions, while tree growth in the early and middle growing seasons of the northern region is limited by warming-induced drought. As the temperature rising over the past fifty years, the growth was found to be negatively correlated with temperature, especially in the spring and autumn seasons of the northern region. In contrast, the effect of precipitation on tree growth became more negative in the southern region, but more positive in the middle and late growing seasons of the northern region. Moreover, tree resilience analysis showed that the high resistance of Pinus tabulaeformis in the southern region, whereas high recovery in the northern region. It was difficult for the growth of Pinus tabulaeformis to recover from drought in the southern region, but stronger adaptability to extreme drought events in the northern region. Our study illustrated that there are different climate response patterns and limiting factors of Pinus tabulaeformis along the precipitation gradient in the LP; thus, different ecological restoration and regional forestry management strategies should be initiated in the LP.

The Impact of Local Climate Change on Radial Picea abies Growth: A Case Study in Natural Mountain Spruce Stand and Low-Lying Spruce Monoculture

Picea abies L. Karst is undeniably one of the most important tree species growing in Slovakia. In addition to natural mountain spruce forests, monocultures planted in lower areas are also quite common. In this article, we analyze the climate–growth response differences between these two types of spruce stands in the context of local climate change consequences. The study area representing natural mountain spruce forests is located under Osobitá Mt. (Tatra Mountains, Slovakia), while the analyzed low-lying planted monoculture is situated near Biely kríž (Malé Karpaty Mountains, Slovakia). Temporal variation of the dendroclimatological relationships was expressed by the running Spearman correlation coefficient during the observed period 1961–2018. The results showed crucial differences in the dendroclimatological relationships between the selected study areas. For the natural mountain spruce stand, consistent, weak, and positive correlations to the temperature variables were typical, with negative relationships to precipitation during the growing season. In this case, the negative impact of a recent temperature rise was limited. In contrast, the monoculture reacted to the temperature variation during the growing season with fluctuations, while in the case of precipitation, almost no dependence was found. Such incoherency may be a consequence of worsened health conditions, as well as insufficient resiliency to climate-driven stress. The importance of this paper is in its wide applicability, mainly in forestry.

Contrasting growth response of evergreen and deciduous arctic‐alpine shrub species to climate variability

AbstractBroad‐scale changes in arctic‐alpine vegetation and their global effects have long been recognized and labeled one of the clearest examples of the terrestrial impacts of climate change. Arctic‐alpine dwarf shrubs are a key factor in those processes, responding to accelerated warming in complex and still poorly understood ways. Here, we look closely into such responses of deciduous and evergreen species, and for the first time, we make use of high‐precision dendrometers to monitor the radial growth of dwarf shrubs at unprecedented temporal resolution, bridging the gap between classical dendroecology and the underlying growth physiology of a species. Using statistical methods on a five‐year dataset, including a relative importance analysis based on partial least squares regression, linear mixed modeling, and correlation analysis, we identified distinct growth mechanisms for both evergreen (Empetrum nigrum ssp. hermaphroditum) and deciduous (Betula nana) species. We found those mechanisms in accordance with the species respective physiological requirements and the exclusive micro‐environmental conditions, suggesting high phenotypical plasticity in both focal species. Additionally, growth in both species was negatively affected by unusually warm conditions during summer and both responded to low winter temperatures with radial stem shrinking, which we interpreted as an active mechanism of frost protection related to changes in water availability. However, our analysis revealed contrasting and inter‐annually nuanced response patterns. While B. nana benefited from winter warming and a prolonged growing season, E. hermaphroditum showed high negative sensitivity to spring cold spells after an earlier growth start, relying on additional photosynthetic opportunities during snow‐free winter periods. Thus, we conclude that climate–growth responses of dwarf shrubs in arctic‐alpine environments are highly seasonal and heterogenic, and that deciduous species are overall likely to show a positive growth response to predicted future climate change, possibly dominating over evergreen competitors at the same sites, contributing to the ongoing greening trend.

Stationarity of climate-growth response is only marginally influenced by the soil moisture regime in Western Siberia

Stationary (time-stable) relationships between a tree-ring proxy and climatic drivers are a prerequisite for using tree rings as paleo-climatological archives, but non-stationarity has been detected worldwide. Here we use a classical, temperature-sensitive treeline site in Western Siberia to specifically test the influence of micro-site conditions (wet versus dry) on the stationarity of climate-growth relationships in three co-existing conifer species: Larix sibirica Ledeb., Picea obovata Ledeb., and Pinus sibirica DuTour. We test two commonly used tree-ring proxies, annual tree-ring width (TRW) and maximum latewood density (MXD), using moving windows and the bootstrapped transfer function stability test (BTFS). Summer temperature is the main driver of tree growth in all three species, but non-stationarities exist in all species and both tree-ring proxies. For TRW, we found stationarity only for larch from both micro-sites, while for MXD, we found stationarity for spruce from both micro-sites, and for pine from the wet micro-site. Micro-site variability did not seem to affect stationarity in any systematic way. We highlight the necessity to systematically test the influence of different methods of stationarity tests, since BTFS was more sensitive than moving-window analysis. Taken together, our results underscore the importance of testing the assumption of stationarity for diverse micro-sites, different species and proxies at all sites prior to any tree-ring based temperature reconstruction, since even within one site results can be drastically different.