Whether and how the timing of extreme events affects the direction and magnitude of legacy effects on tree growth is poorly understood. In this study, we use a global database of Ring‐Width Index ...(RWI) from 2,500 sites to examine the impact and legacy effects (the departure of observed RWI from expected RWI) of extreme drought events during 1948–2008, with a particular focus on the influence of drought timing. We assessed the recovery of stem radial growth in the years following severe drought events with separate groupings designed to characterize the timing of the drought. We found that legacies from extreme droughts during the dry season (DS droughts) lasted longer and had larger impacts in each of the 3 years post drought than those from extreme droughts during the wet season (WS droughts). At the global scale, the average integrated legacy from DS droughts (0.18) was about nine times that from WS droughts (0.02). Site‐level comparisons also suggest stronger negative impacts or weaker positive impacts of DS droughts on tree growth than WS droughts. Our results, therefore, highlight that the timing of drought is a crucial factor determining drought impacts on tree recovery. Further increases in baseline aridity could therefore exacerbate the impact of punctuated droughts on terrestrial ecosystems.
We examined whether and how legacy effects on tree growth after drought differs according to drought timing. Our results show that legacies from extreme droughts induced by anomalously low precipitation during the dry season lasted longer and were larger in magnitude in each of the 3 years post drought than those from extreme droughts characterized by an anomalously dry wet season, suggesting that the timing of drought is a crucial factor determining its impacts on tree recovery after severe drought.
Extreme climate events (ECEs) such as severe droughts, heat waves, and late spring frosts are rare but exert a paramount role in shaping tree species distributions. The frequency of such ECEs is ...expected to increase with climate warming, threatening the sustainability of temperate forests. Here, we analyzed 2,844 tree‐ring width series of five dominant European tree species from 104 Swiss sites ranging from 400 to 2,200 m a.s.l. for the period 1930–2016. We found that (a) the broadleaved oak and beech are sensitive to late frosts that strongly reduce current year growth; however, tree growth is highly resilient and fully recovers within 2 years; (b) radial growth of the conifers larch and spruce is strongly and enduringly reduced by spring droughts—these species are the least resistant and resilient to droughts; (c) oak, silver fir, and to a lower extent beech, show higher resistance and resilience to spring droughts and seem therefore better adapted to the future climate. Our results allow a robust comparison of the tree growth responses to drought and spring frost across large climatic gradients and provide striking evidence that the growth of some of the most abundant and economically important European tree species will be increasingly limited by climate warming. These results could serve for supporting species selection to maintain the sustainability of forest ecosystem services under the expected increase in ECEs.
There is an urgent need to assess the specific responses of trees to both drought and spring frost to provide solid bases for decision‐making regarding the selection of tree species matching the ongoing environmental change. Using tree‐ring width series from 2,844 trees from 104 Swiss sites ranging from 400 to 2,200 m a.s.l. for the period 1930–2016, we found strong disparities in the species resistance and resilience to extreme droughts and spring frosts. Oak, fir, and to a lower extent beech could moderately cope with severe droughts whereas spruce and larch only poorly resist and recover after such events.
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.
Using 2947 tree‐ring width residual chronologies of 32 species spanned from 1901 to 2018 at 2493 sample sites across the Northern Hemisphere, here we comprehensively analyzed the effects of daytime and nighttime temperatures on tree radial growth. We found that the growth decline due to drought stress was primarily triggered by daytime warming, but not nighttime warming. In addition, tree growth suffered a greater drought stress in warm region than in cold region, especially for angiosperms.
In mountains, the reactions of trees to climatic fluctuations and changes depend on various factors, including ecological gradients and species. This study investigates the radial growth of Siberian ...stone pine (Pinus sibirica Du Tour), a widespread key conifer in the Siberian taiga, across its elevational range in the Western Sayan Mountains of Southern Siberia. Wood samples were gathered along three latitudinal-elevational transects spaced ca. 80–100 km apart from each other, spanning from west to east across the Western Sayan region. The midpoint of these transects coincided with a large reservoir on the Yenisei River. Each transect encompassed three distinct sites: the lower limit of species growth at 400–500 m a.s.l., a site located at 1700–2050 m a.s.l. near the upper forest line, and an intermediary site falling between these boundaries. A spectacular synchronicity was observed in TRW residual chronologies (R=0.56–0.78 over 1936–2010) and their climatic responses across all sites near the upper forest line and 200–300 m below it. In these areas, temperatures showed a predominantly positive impact from the previous July-August to the current August, except for the end of March–April. The negative influence of excess precipitation during these seasons decreased from west to east, whereas early spring precipitation exhibited a positive correlation with TRW. At the lower limit of growth, the TRW chronologies of species showed lower correlation values between each other (R=0.26–0.36). Here, the species exhibited a positive impact of annual precipitation and a negative influence of temperature, particularly in the previous August and current May-June, albeit of varying intensities. At the mid-montane site, located at 300–500 m above the lower limit of species growth, a mixed climatic influence was observed with a positive response to annual temperatures and June precipitation. Further, the pointer years of the maximum or minimum indexed TRW also occurred much more synchronously in highland forests. The observed shifts in climatic responses indicated that climate warming has advanced the onset of vegetation and delayed the dormancy in these regions. The majority of the Siberian stone pine stands under consideration showed a positive response to warming. Interestingly, an absence of steady growth decline, even in the foothills, indicated a non-climatic range border. The study approach allowed us to recognize with daily resolution annual and seasonal climatic variables impacting stone pine growth that can be probably reconstructed on a local (precipitation) or regional (temperature) scale. This study enhanced the understanding of climate–growth relationships in P. sibirica, offering insights into the species’ resilience and vulnerability across ecological gradients in response to changing climatic conditions.
•Pinus sibirica Du Tour growth in Western Sayan is more synchronized in highlands.•Heat impact is stable in highlands, but precipitation shows a longitudinal gradient.•Pinus sibirica growth and climatic signal are more diverse at lower elevations.•Climate warming lengthened vegetation period and increased impact of autumn rains.•Climate change in Western Sayan mostly benefited Pinus sibirica growth.
ABSTRACT
High mountains are some of the most vulnerable regions to climate change and therefore a matter of global concern. Here, the climatic growth factors of conifers and their course in time and ...space along an elevational gradient in the northwestern Himalayan part of India were studied. Increment cores of Juniperus semiglobosa and Cedrus deodara (xeric species), and Abies pindrow and Picea smithiana (mesic species) were collected from thirteen sites. Tree‐ring width and maximum latewood density were measured and cross‐dated. The time‐series were standardized and site‐ and species‐level chronologies were built. Static and moving bootstrap correlation and response functions between the tree‐ring chronologies and monthly climatic variables were computed. The largest climate changes in the region were increasing winter and early‐spring temperatures and decreasing monsoon precipitation. The growth of all species was negatively correlated with pre‐monsoon temperature, as the higher temperatures probably increased evapotranspiration and caused water deficit. The phenomenon was most pronounced in May, but also in June for the Juniperus at the northernmost, highest, and driest sites. The pre‐monsoon temperature signal of the drought‐prone Juniperus and Cedrus endured, while the signal of the climate‐susceptible Abies and Picea at the mesic sites was unstable. Namely, the May temperature signal of Picea became significant since the second half of the last century whereas the signal of Abies shifted from May to April. This apparently related to the earlier onset of spring due to the accelerated warming in the region. Besides, maximum latewood density of Picea and Abies negatively correlated with May and June temperature, respectively. Additionally, the Cedrus benefitted from winter precipitation and the Abies and Picea from pre‐monsoon rainfall. Counterintuitively, we detected no direct effect of monsoon precipitation decrease on the conifers because their growth was driven by pre‐monsoon conditions, which changed only slightly.
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.
The relationship between white spruce growth and temperature showed a stronger negative correlation in warmer regions and a stronger positive correlation in warmer periods, which means the growth response changes caused by spatial versus temporal climate variations showed opposite trends. The projected growth‐climate correlation coefficients using the SFTS were significantly lower than the observed values. Applying SFTS to project the growth response of white spruce may lead to an overestimation 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.
•RWI is negatively impacted by drought and high temperatures.•EVI data can only capture drought/heat stress when physical canopy damage is caused.•EVI based trend analysis has the potential to assess ...areas suitable for beech.
Climate change is predicted to affect tree growth due to increased frequency and intensity of extreme events such as ice storms, droughts and heatwaves. Yet, there is still a lot of uncertainty on how trees respond to an increase in frequency of extreme events. Use of both ground-based wood increment (i.e. ring width) and remotely sensed data (i.e. vegetation indices) can be used to scale-up ground measurements, where there is a link between the two, but this has only been demonstrated in a few studies. We used tree-ring data together with crown features derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) to assess the effect of extreme climate events on the growth of beech (Fagus sylvatica L.) in Slovenia. We found evidence that years with climate extremes during the growing season (drought, high temperatures) had a lower ring width index (RWI) but we could not find such evidence for the remotely sensed EVI (Enhanced Vegetation Index). However, when assessing specific events where leaf burning or wilting has been reported (e.g. August 2011) we did see large EVI anomalies. This implies that the impact of drought or heatwave events cannot be captured by EVI anomalies until physical damage on the canopy is caused. This also means that upscaling the effect of climate extremes on RWI by using EVI anomalies is not straightforward. An exception is the 2014 ice storm that caused a large decline in both RWI and EVI. Extreme climatic parameters explained just a small part of the variation in both RWI and EVI by, which could indicate an effect of other climate variables (e.g. late frost) or biotic stressors such as insect outbreaks. Furthermore, we found that RWI was lower in the year after a climate extreme occurred in the late summer. Most likely due to the gradual increase in temperature and more frequent drought we found negative trends in RWI and EVI. EVI maps could indicate where beech is sensitive to climate changes and could be used for planning mitigation interventions. Logical next steps should focus on a tree-based understanding of the short -and long-term effects of climate extremes on tree growth and survival, taking into account differential carbon allocation to the crown (EVI) and to wood-based variables. This research highlights the value of an integrated approach for upscaling tree-based knowledge to the forest level.
Tree growth at northern treelines is generally temperature‐limited due to cold and short growing seasons. However, temperature‐induced drought stress was repeatedly reported for certain regions of ...the boreal forest in northwestern North America, provoked by a significant increase in temperature and possibly reinforced by a regime shift of the pacific decadal oscillation (PDO). The aim of this study is to better understand physiological growth reactions of white spruce, a dominant species of the North American boreal forest, to PDO regime shifts using quantitative wood anatomy and traditional tree‐ring width (TRW) analysis. We investigated white spruce growth at latitudinal treeline across a >1,000 km gradient in northwestern North America. Functionally important xylem anatomical traits (lumen area, cell‐wall thickness, cell number) and TRW were correlated with the drought‐sensitive standardized precipitation–evapotranspiration index of the growing season. Correlations were computed separately for complete phases of the PDO in the 20th century, representing alternating warm/dry (1925–1946), cool/wet (1947–1976) and again warm/dry (1977–1998) climate regimes. Xylem anatomical traits revealed water‐limiting conditions in both warm/dry PDO regimes, while no or spatially contrasting associations were found for the cool/wet regime, indicating a moisture‐driven shift in growth‐limiting factors between PDO periods. TRW reflected only the last shift of 1976/1977, suggesting different climate thresholds and a higher sensitivity to moisture availability of xylem anatomical traits compared to TRW. This high sensitivity of xylem anatomical traits permits to identify first signs of moisture‐driven growth in treeline white spruce at an early stage, suggesting quantitative wood anatomy being a powerful tool to study climate change effects in the northwestern North American treeline ecotone. Projected temperature increase might challenge growth performance of white spruce as a key component of the North American boreal forest biome in the future, when drier conditions are likely to occur with higher frequency and intensity.
We examined how the observed phases of 20th century PDO (pacific decadal oscillation) variability influenced the temporal relationships between tree growth (assessed using wood anatomical traits and tree‐ring width) and water availability in a dominant conifer species (white spruce) of the North American treeline ecotone along a longitudinal gradient. We found xylem anatomical traits being significantly associated with water availability during positive (dry/warm) phases of the PDO, while there were no or spatially contrasting associations during the cool/wet phase. Our findings indicate temporally and spatially adapted growth of white spruce and provide insights on its physiological functioning under climate change.
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•Ring width samples were collected from Norway spruce and European beech in Central Europe.•Climate–growth interactions were assessed along an altitudinal gradient.•Species-specific ...responses to temperature and water availability depended on altitude.•The climatic sensitivity of the growth of both species showed significant temporal shifts.•Spring temperature and summer drought were the main factors limiting tree growth.
Norway spruce has experienced unprecedented forest declines in recent decades, leading to extensive salvage logging. Currently, because of the conversion of conifer forests into more natural mixed forests in Central Europe, spruce has begun to be replaced, mainly by European beech. The frequently discussed changing climate has a crucial effect on the vitality of both species. To improve our understanding of spruce and beech responses to climate change, including more frequent temperature and drought extremes, we investigated the impact of temporal climate variability on the growth of these species along an elevation gradient. In total, 79 spruce and 90 beech trees were used to build species-specific tree-ring width chronologies representing the altitudinal range in which both species grow (450, 650, 800, and 950m asl) under the conditions of the Czech Republic. The climate–growth relationship indicates strong dependence of spruce and beech tree-ring growth on spring temperature (Mar–May) at all sites and summer (Jun–Aug) water availability at lower altitudes. Significant temporal shifts in the climate–growth relationships of both species indicate an increasing negative effect of summer temperature and positive effect of water availability in summer. The increasing drought and temperature sensitivity of both species suggest a significant impact of the predicted climate change on such forest ecosystems. Discussion emphasizes the current importance of adaptive forest management strategies.
Global change, characterized by elevated atmospheric CO2 concentrations and warming, is profoundly affecting terrestrial forests. However, whether the increasing atmospheric CO2 concentration has a ...fertilizer effect on tree growth and whether intrinsic water use efficiency (iWUE) promotes tree growth in semi‐arid regions is not entirely clear. In this study, we evaluated the relationships between tree‐ring widths, δ13C values and iWUE of Qinghai Spruce (Picea crassifolia Kom.) in the eastern Qilian Mountains, northwestern China. We found that the iWUE is significantly consistent with the δ13C of rings in the high‐frequency signal, and the relationship between iWUE and tree‐ring width is unstable. The first‐order difference correlation analysis with meteorological data showed that both the iWUE and tree‐ring width were drought‐limited. The radial growth was mainly regulated by water availability in current April and July, while annual variation of iWUE was primarily controlled by that in current July. In the early stage of trees growth, there was a positive relationship between iWUE and radial growth due to the CO2 fertilization. During the 1970s–2000s, the effect of water availability in July on radial growth increases because of the decreased precipitation in July. This has decreased stomatal conductance, intercellular CO2 concentration, carbon uptake and growth, contributing to the negatively significant correlation between tree‐ring widths and iWUE (p < .05). Since the year of 2010, the relationship between the radial growth and iWUE shifted because of the increased precipitation in July. This study provided new insights for whether increased water‐use efficiency enhances tree growth under semixeric conditions.
There is no direct connection between the intrinsic water‐use efficiency and radial growth of trees. Variations of July precipitation affected the relationship between iWUE and tree radial growth.
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