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Increasingly frequent severe drought events are pushing Mediterranean forests to unprecedented responses. Lack of management leads to dense forests that are highly susceptible to drought stress, potentially resulting in extensive dieback and increased vulnerability to other disturbances. Forest treatments like thinning and slash burning reduce competition for resources and have the potential to enhance tree growth and vigor and minimize tree vulnerability to drought. Here, we used tree rings to study the growth and physiological response of black pine (Pinus nigra) to drought in northeastern Spain under different treatments, including two thinning intensities (light and heavy, with 10% and 40% basal area reduction, respectively) followed by two understory treatments (clearing alone and in combination with slash burning), resulting in a research design of four treatments plus an untreated control with three replicates. Specifically, we studied basal area increment (BAI), resilience indices, and intrinsic water use efficiency (iWUE) using carbon and oxygen isotope composition (δ13C and δ18O in tree‐ring cellulose) before and after treatments. Our results showed that BAI and resistance to drought increased in the heavy‐thin (burned and unburned) and light‐thin burned units. Resilience increased in the burned units regardless of the thinning intensity, while recovery was not affected by treatment. Slash burning additionally increased BAI in the light‐thin and resistance and resilience in the heavy‐thin units compared with clearing alone. The stable isotope analysis revealed a minor effect of treatments on δ13C and δ18O. No change in iWUE among treatments was presumably linked to a proportional increase in both net CO2 assimilation and stomatal conductance, which particularly increased in the heavy‐thin (burned and unburned) and light‐thin burned units, indicating that these trees were the least affected by drought. This study shows that management approaches aimed at reducing wildfire hazard can also increase the vigor of dominant trees under drought stress. By reducing competition both from the overstory and the understory, thinning followed by clearing alone or in combination with slash burning promotes tree growth and vigor and increases its resistance and resilience to drought. [ABSTRACT FROM AUTHOR]

Tidal freshwater forests are usually located at or above the level of mean high water. Some Louisiana coastal forests are below mean high water, especially bald cypress (Taxodium distichum (L.) Rich.) forests because flooding has increased due to the combined effects of global sea level rise and local subsidence. In addition, constructed channels from the coast inland act as conduits for saltwater. As a result, saltwater intrusion affects the productivity of Louisiana's coastal bald cypress forests. To study the long-term effects of hydrology and salinity on the health of these systems, we fitted dendrometer bands on selected trees to record basal area increment as a measure of growth in permanent forest productivity plots established within six bald cypress stands. Three stands were in freshwater sites with low salinity rooting zone groundwater (0.1–1.3 ppt), while the other three had higher salinity rooting zone groundwater (0.2–4.9 ppt). Water level was logged continuously, and salinity was measured monthly to quarterly on the surface and in groundwater wells. Higher groundwater salinity levels were related to decreased bald cypress radial growth, while higher freshwater flooding increased radial growth. With these data, coastal managers can model rates of bald cypress forest change as a function of salinity and flooding. [ABSTRACT FROM AUTHOR]

The impact of climates on the radial growth of muti-species remains insufficiently understood in the climate-sensitive southeastern Tibetan Plateau, and this hampers an effective assessment of forest growth under the background of global warming. Here, we studied the growth–climate relationships of three major species (Abies georgei, Larix potaninii, and Picea likiangensis) on the Baima Snow Mountain (BSM) by using dendrochronology methods. We constructed basal area increment (BAI) residual chronologies based on the dated ring-width measurements and correlated the chronologies with four climate factors. We also calculated the contributions of each climate factor to species growth. We found that photothermal conditions played a more important role than moisture in modulating radial growth, and P. likiangensi presented the strongest sensitivity to climate change among the three species. The growing season (June and July) temperature positively affected the radial growth of three species. Winter (previous December and current January) SD negatively impacted the tree growth of A. georgei and P. likiangensis. Significant correlations between growth and precipitation were detected only in A. georgei (January and May). Warming since the beginning of the 1950s promoted the growth of A. georgei and P. likiangensis, while the same effect on L. potaninii growth was found in the recent 50 years. [ABSTRACT FROM AUTHOR]

Neighbourhood interactions drive tree growth and forest ecosystem functioning. The strength of interactions depends on the climate. However, it remains unclear how plant–plant interactions are modified by environmental conditions operating both spatially and temporally, which is crucial for predicting forest dynamics under climate change and for effective forest management.In this study, we used annual growth data for 4139 stems from 2010 to 2021 across 50 permanent forest plots located at six sites in eastern China. We quantified the effect of neighbourhood crowding on the annual basal area increment. We explored how interactions among neighbouring trees vary with water availability and temperature gradients in the spatial (across sites) and temporal (across time within sites) dimensions.Our findings revealed a negative impact of neighbourhood crowding on stem basal area growth, which is size‐ and trait‐dependent at some sites. The negative effects of light competition tended to be more intense at warmer sites, supporting the stress‐gradient hypothesis (SGH) in a spatial dimension. However, the patterns of crowding effects along interannual climate anomalies are inconsistent across sites, making it difficult to predict crowding effects under the SGH framework in a temporal dimension.Synthesis: Our study demonstrated that tree interactions depend on the climate context. The climate dependence of interactions may be inconsistent between the spatial and temporal dimensions. Light competition across sites supported the SGH in the spatial dimension but not in the temporal dimension. These results further highlight the complexity of biotic interactions and the need for caution when extrapolating findings from the spatial to the temporal dimension. [ABSTRACT FROM AUTHOR]

We evaluated shoot nonstructural carbohydrate (NSC) concentrations, stem wound closure, and radial growth of sugar maple (Acer saccharum Marsh.) and red maple (Acer rubrum L.) trees in a novel ice storm experiment in which five storm treatments (0, 6.4, 12.7, and 19.1 mm of radial ice accretion in 1 year and 12.7 mm of ice in two consecutive years) were applied within a mature northern hardwood forest. We tested for changes in physiology at two levels: (1) associated with plot-level ice treatments and (2) with crown damage classes of individual trees. Few differences in NSC or wound closure associated with treatment were found. Growth decreased for red maple in the medium and high treatments and sugar maple in the high treatment but no other treatments. Changes in physiology were more evident when assessed using crown damage classes. Two NSC components were elevated in sugar and red maples with high (≥50%) crown damage. Wound closure was less for red maples with high damage, and separation among damage classes was even greater for sugar maple. Red maples with moderate (<50%) and high crown damage showed gradually declining growth, whereas sugar maples with high damage showed ∼80% reduction in growth the first year after injury. [ABSTRACT FROM AUTHOR]

Global warming may lead to increased tree growth but also reduced tree performance due to increased moisture stress. Under what conditions these conflicting responses occur remains uncertain, especially when growth is controlled by different climatic factors throughout the year. Here, we investigate the growth response of Tsuga dumosa, a Himalayan endemic tree species, to global climate change in unique old-growth forests that persist at around 3000 m elevation near Kanchenjunga, Nepal. Specifically, we are examining various growth parameters, including earlywood, adjusted latewood, maximum latewood density, and total basal area increment, to determine how different climatic factors influence growth dynamics during the year. First, we found that the response to climate change varied by season. Climate warming had contrasting effects on different components of tree growth. Higher temperatures during previous October and previous December and warming-induced moisture stress in April reduce earlywood and total annual increment. On the other hand, higher rainfall during June and July limits total tree ring width and adjusted latewood width, respectively. Second, warming is changing the sensitivity of tree growth to various climatic factors. Growth in the past two decades became more dependent on autumn conditions than on spring and summer conditions. Warming alleviates the cold limitation during the cool monsoon summer but reinforces the water deficit during autumn, winter, and pre-monsoon dry spring. Third, analysis of basal area increments, an indicator of aboveground biomass production, showed that accelerated warming in summer contributes to increased annual productivity. However, the growth reduction observed during warming spring and autumn months counteracts this effect. In conclusion, this study highlights the contrasting responses of Tsuga dumosa to climate warming in Himalayan montane forests. While accelerated warming makes the trees less sensitive to summer temperature limitations, warm autumns, dry springs, and less snowy winters become the main limiting factors for their growth. Understanding these complex and contrasting responses, as well as the sensitivity of different growth parameters, is essential for predicting the long-term impacts of climate change on mountain ecosystems. [ABSTRACT FROM AUTHOR]

Multispecies forests have received increased scientific attention, driven by the hypothesis that biodiversity improves ecological resilience. However, a greater species diversity presents challenges for forest management and research. Our study aims to develop basal area growth models for tree species cohorts. The analysis is based on a dataset of 423 permanent plots (2,500 m2) located in temperate forests in Durango, Mexico. First, we define tree species cohorts based on individual and neighborhood-based variables using a combination of principal component and cluster analyses. Then, we estimate the basal area increment of each cohort through the generalized additive model to describe the effect of tree size, competition, stand density and site quality. The principal component and cluster analyses assign a total of 37 tree species to eight cohorts that differed primarily with regard to the distribution of tree size and vertical position within the community. The generalized additive models provide satisfactory estimates of tree growth for the species cohorts, explaining between 19 and 53 percent of the total variation of basal area increment, and highlight the following results: i) most cohorts show a "rise-and-fall" effect of tree size on tree growth; ii) surprisingly, the competition index "basal area of larger trees" had showed a positive effect in four of the eight cohorts; iii) stand density had a negative effect on basal area increment, though the effect was minor in medium- and high-density stands, and iv) basal area growth was positively correlated with site quality except for an oak cohort. The developed species cohorts and growth models provide insight into their particular ecological features and growth patterns that may support the development of sustainable management strategies for temperate multispecies forests. [ABSTRACT FROM AUTHOR]

Warming and persistent droughts may exacerbate drought stress in water-scarce areas, thereby negatively affecting tree growth. When riparian plants in arid regions experience severe drought stress, they sacrifice non-dominant branches with less competitive sap flow to improve the sap flow of dominant branches and thus ensure strong plant growth. Populus euphratica is one of the most dominant tree species in the riparian forest ecosystems of inland river basins in arid zones and is a reliable indicator of ecological change because of its diversity in growth and environment. To understand the adaptability of P. euphratica to the environment, the relationship between radial growth and meteorological factors, the growth decline and resistance of different heights and components of P. euphratica, as well as the resilience and resilience after recession were investigated. The results indicated that tree-ring width decreased gradually with increasing height and branching class of P. euphratica. Growth decreased at the bottom of the stem earlier than at the middle and top. Temperature, precipitation, and the Palmer drought index contributed to the growth at the bottom of P. euphratica, while precipitation contributed to growth at the top. The decline in the P. euphratica growth change rate was highly synchronized across heights and parts, with relatively high declines at the bottom and top. There were no significant differences in the recovery values for different heights and parts of P. euphratica, but the resistance, resilience, and relative resilience for the bottom and top were significantly lower than those for the other components, indicating vulnerability in the bottom and top of P. euphratica to drought. The relative resilience gradually decreased with the increase in branching class, and that of the secondary lateral branches at different heights was the lowest. In conclusion, the sensitivity of the top and lateral branches of P. euphratica to drought would cause the phenomenon of "breaking its arm" under drought disturbance in the future. [ABSTRACT FROM AUTHOR]

Increasingly severe and prolonged droughts are contributing to tree stress and forest mortality across western North America. However, in many cases, we currently have poor information concerning how drought responses in forests vary in relation to competition, climate, and site and tree characteristics. We used annual tree ring evidence of 13C discrimination (Δ13C) and growth metrics to assess drought resistance and resilience for six conifer species at the intersection of several bioregions in northern California. Within each species' range in northern California, we collected competition and tree characteristics from 270 focal trees across sites that varied from wetter to drier habitat conditions (54 sites). Across sites, all six conifer species weathered the severe 2013–2015 drought with reasonably high resistance and post‐drought resilience. However, we found important differences in drought responses between coastal and montane species based on annual growth and Δ13C metrics. Broadly, the two coastal species showed consistent declines in drought resistance across successive drought years, whereas the four montane species maintained high drought resistance across drought years. More specifically, we found lower Δ13C and growth during drought years in coastal species, suggesting stomatal closure during drought with the potential for vulnerability to carbon depletion during long‐term drought. Conversely, Δ13C and growth were stable in montane species throughout the drought, which may contribute to hydraulic failure under increased drought frequency and/or severity. We also evaluated environmental factors that affect Δ13C using data from before and during the drought. These physiological models were consistent for the two coastal species, with a positive relationship between annual precipitation and Δ13C and a negative relationship between tree density and Δ13C. Conversely, the four montane models illustrated a greater importance of site conditions on drought responses for these species. Our findings show differential risk for drought stress across diverse conifers during severe drought. This work highlights the importance of site and tree characteristics in determining drought responses across cool, annually humid coastal habitats to seasonally dry montane habitats. [ABSTRACT FROM AUTHOR]

Climate warming at high latitudes has contributed to the growing interest in shrub tree-ring analysis. Shrub architecture presents new challenges for dendrochronology, such as the seemingly lower and inconsistent climatic sensitivity of stems vs. root collars. Shrub stems may thus be considered as sub-optimal to study climate–growth relationships. In this paper, we propose that the lower climatic sensitivity of stems could be caused by the use of unsuitable detrending methods for chronologies spanning decades rather than centuries. We hypothesize that the conversion of the ring width (RW) to basal area increment (BAI) is better suited than traditional detrending methods to removing age/size-related trends without removing multi-decadal climate signals. Using stem and root collar samples collected from three sites in the forest–tundra ecotone of eastern Canada, we compared the climate–growth relationships of these two approaches for stems and root collars using mixed-effects models. The climate sensitivity was, on average, 4.9 and 2.7 times higher with BAI than with detrended (mean-centered) RW chronologies for stems and root collars, respectively. The climatic drivers of radial growth were identical for stems and root collars when using BAI (July temperature and March precipitation), but were inconsistent when using detrended RW series (root collars: July temperature and March precipitation at all sites; stems: April and June temperature, depending on the site). Although the use of BAI showed promising results for studying long-term climate signals in shrub growth chronologies, further studies focusing on different species and locations are needed before the use of BAI can become broadly used in shrub dendrochronology. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Increased winter and early spring temperatures due to climate change can enhance forest productivity due to earlier growth onset in temperate regions. However, drought‐prone forests can be highly vulnerable to the combined effect of high summer temperatures and water stress. Understanding how water stress and rising temperatures along the growing season control tree growth in co‐occurring species with contrasting drought tolerances is key to project climate change effects on forest dynamics. Here, we evaluated the interactive effect of seasonal temperature and water availability on annual radial growth and climate–growth instability over six decades (1951–2015) in three pine species with contrasting drought tolerances (Pinus pinaster, Pinus nigra, and Pinus sylvestris). For this, we retrospectively observed radial tree growth using dendroecological methods and evaluated seasonal temperature and water availability effects by using linear mixed models. Early growing season temperature and water availability had a positive effect on tree growth, but the positive effect of late season temperature was modulated by water availability. Moving time‐window analyses revealed temporal instability in climate–growth relationships. Since the 1980s, pine species showed a higher growth sensitivity to both seasonal temperatures and annual water availability. Furthermore, growth reductions were more pronounced due to increased summer temperatures and reduced precipitation. Our results were similar for the three studied pine species despite their contrasting tolerance to drought. Overall, climate warming effects on pine growth are contingent upon water availability in Mediterranean continental forests. Synchronization among species, climate–growth instability, and negative growth trends suggests an increased vulnerability to drought of Mediterranean pine species in response to ongoing climate change. [ABSTRACT FROM AUTHOR]

This article attempts an unusual interpretation of the observations characteristic of experiments that compare different tree species' provenances. The focus falls on larch (Larix decidua subsp. polonica). The data came from the experiment established in 1967 at the Siemianice forest experimental station, where 21 Polish larch provenances were compared. The study's main objective was to compare the basic estimates of growth dynamics, the maximum growth rate and acceleration, and the point in time when these values were achieved. A four-parameter sigmoid growth function was used to model the average stand basal area increments and its first and second derivatives to calculate the indicators of the growth dynamic. The models explained 98% of the observed variations resulting from the 21 inventories. Only one growth parameter showed a statistically significant difference among the compared provenances. The Góra Chełmowa provenance achieved the highest value of the maximum growth acceleration, but it was statistically significantly different only from the three underperformed provenances. However, when the average values for all the experimental plots (n = 86) were compared with those of the deterministic model (the stand volume and yield tables), the maximum growth rate and acceleration values were higher for the former. We discuss the potential factors responsible for this overperformance and point out the potential risks that arise from growth and quality metrics only when deciding on the best-performing provenances. The sigmoid growth model employed in this study might be an excellent alternative for comparing the growth dynamics among different stands or replications in experimental studies. Considering only the early results, the sigmoid growth model proves its limitations, and the conclusions reached should be treated with caution. [ABSTRACT FROM AUTHOR]

There is debate on which tree species can sustain forest ecosystem services in a drier and warmer future. In Europe, the use of non-native timber species, such as Douglas fir (Pseudotsuga menziesii [Mirb.] Franco), is suggested as a solution to mitigate climate change impacts because of their high growth resilience to drought. However, the biogeographical, climatic and ecological limits for widely planted timber species still need to be defined. Here, we study the growth response to climate variables and drought of four Douglas fir plantations in northern Spain subjected to contrasting climate conditions. Further, we measure wood density in one of the sites to obtain a better understanding of growth responses to climate. Correlative analyses and simulations based on the Vaganov–Shaskin process-based model confirm that growth of Douglas fir is constrained by warm and dry conditions during summer and early autumn, particularly in the driest study site. Minimum wood density increased in response to dry spring conditions. Therefore, planting Douglas fir in sites with a marked summer drought will result in reduced growth but a dense earlywood. Stands inhabiting dry sites are vulnerable to late-summer drought stress and can act as "sentinel plantations", delineating the tolerance climate limits of timber species. [ABSTRACT FROM AUTHOR]

Changing climate can strongly affect tree growth and forest productivity. The dendrochronological approach to assessing the impact of climate change on tree growth is possible through climate–growth correlation analysis. This study uses an individual tree-based approach to model Pinus wallichiana (P. wallichiana) radial growth response to climate across the physiographic gradients in the lower distributional range of Nepal. This study sampled six sites across the Makwanpur district of central Nepal that varied in elevation and aspect, obtaining 180 tree-ring series. Climate data series were obtained from Climate Research Unit (CRU 4.0). The pair correlation approach was used to assess P. wallichiana growth response to climate and site-level physiographic variables such as site-level environmental stress. The study also determined long-term growth trends across the elevation and aspect gradients. Trees at sites with higher elevation and northeast aspect (NEA) were more responsive to winter and spring precipitation, whereas trees with lower elevation and northwest aspect (NWA) were more responsive to winter and spring precipitation. Basal area increment (BAI) analysis showed the variation of growth at site-level environmental stress, suggesting that the sensitivity of forest ecosystems to changing climate will vary across the lower growth limit of P. wallichiana due to differences in local physiographic conditions. [ABSTRACT FROM AUTHOR]

Ethiopian mixed forests have multipurpose benefits and services. However, there is a gap of information in the entire Ethiopian highlands on forest growth needed for implementation of sustainable forest management and provision of ecosystem services. Therefore, main aim of this study was to identify main factors deriving tree growth in forest and woodland in Amhara Regional State of Ethiopia and to provide an individual tree basal area increment (BAI) model based on increment cores. The data came from 170 sampling plots in study area and cover 51 tree species. For each tree species, diameter at breast height (DBH), height, increment core measurement, tree location, and distance from subject tree measurements were recorded. Because of large number of trees species, it is difficult to develop growth functions for each individual tree species. Thus, classification of species groups provided a framework to organize information that differs between vegetation types. Our classification resulted in three groups. For each tree species group, an individual tree BAI model was calibrated. The tree species group of BAI differs by DBH class. The response to BAI depends on competitive condition of a tree. This growth model can be used to predict tree growth for Ethiopian mixed-species forests. [ABSTRACT FROM AUTHOR]

Opencast mining is currently one of the most destructive economic activities of natural ecosystems. Many restoration techniques have been developed to promote the recovery of terrestrial ecosystems degraded by mining, and afforestation and reforestation are among the most important methods to this purpose. In this study, we evaluated the combined effect of tree species mixture and thinning intervention on growth dynamics and responses to the climate of a target native planted oak (pedunculate oak, Quercus robur L.) about 40 years after reforestation of an opencast lignite mining area in Central Italy. The species used for reforestation were a native tree species (Q. robur L.), two valuable broadleaved trees (Fraxinus angustifolia Vahl. and Prunus avium L.) and a nitrogen-fixing tree (Alnus cordata Loisel.) to improve timber quality and restore the ecological and environmental value of the degraded land. Climate-growth relationships for precipitation, the Standardised Precipitation-Evaporation Index (SPEI), and temperature (on a monthly and seasonal scale) were tested together with indices based on tree-ring responses to drought. Thinning improved the stem quality and promoted a significant long-term increase in basal area increment (BAI, +31.0%) only in the mixture with alder. The thinning effect slightly mitigated radial growth reductions of oak trees during drought (resistance) and produced a general improvement in the magnitude of resilience and post-drought growth recovery (+37% and +27% on average, respectively). This effect was most evident when oak trees were mixed with only the N-fixing alder species, both after shorter- and longer-term drought or rainfall reduction. In conclusion, the mixture with alder combined with thinning practices resulted in the best management option to produce good-quality stems, improve growth performances, and mitigate drought effects in the recovery of opencast lignite mines through reforestation. [ABSTRACT FROM AUTHOR]

One of the most important proxy archives for past climate variation is tree rings. Tree-ring parameters offer valuable knowledge regarding how trees respond and adapt to environmental changes. Trees encode all environmental changes in different tree-ring parameters. In this study, we analyzed how air temperature is encoded in different Norway spruce tree-ring proxies along an altitude gradient in an intramountain valley of the Carpathians. The study area, in the Gheorgheni region, Romania (Eastern Carpathians), has a mountain climate with a frequent temperature inversion in winter. The climate–growth relationship was analyzed for two contrasting altitudes: low elevation, i.e., below 1000 m a.s.l., and high elevation, i.e., above 1500 m a.s.l. Two local weather stations, one in the valley and the other on the upper part of the mountains, provide daily temperatures (Joseni—750 m a.s.l. and Bucin—1282 m a.s.l.). The bootstrap Pearson correlation between cumulative daily temperature data and three tree-ring proxies (tree-ring width—TRW, basal area increment—BAI, and blue intensity—BI) was computed for each series. The results show that elevation modulates the climate response pattern in the case of BI, and remains relatively similar for TRW and BAI. The winter temperature's positive influence on spruce growth was observed in both TRW and BAI chronologies. Additionally, the BAI chronology highlights a positive relationship with summer temperature. The highest correlation coefficient (r = 0.551, p < 0.05, n = 41) was recorded between BI residual chronology from high elevation series and summer/autumn temperature from the upper-part weather station for a cumulative period of 59 days (the second half of August to the beginning of October). Our results show that, for this intramountain valley of the Eastern Carpathians, different tree-ring proxies capture different climate signals. [ABSTRACT FROM AUTHOR]

Key message: The growth of Shorea robusta is positively correlated with temperature, whereas the relation to moisture is weak. Tree-ring analyses provide a rich archive of information on environmental attributes affecting tree growth. Tree-ring studies conducted so far have mostly focused on temperate species, and research on tropical trees is limited. This study aims to develop a tree-ring chronology of Shorea robusta and understand the climatic sensitivity of its growth in the tropical region of Nepal. Tree-ring samples of S. robusta were analysed following the standard dendrochronological sample analysis procedure. A 134-year-long ring-width chronology of S. robusta was developed, extending from 1851 to 2018, which is the longest chronology reported for this species. The chronology statistics revealed its high dendroclimatic potential with moderate R-bar, high expressed population signal, and low autocorrelation. The mean annual radial growth was 2.87 mm per year, while the mean basal area increment (BAI) was 9.245 cm2 per year. The ring width, BAI chronology and size-based growth analysis revealed an increasing growth trend of the species, which is likely favoured by the ongoing climate change. The tree growth of the species was positively correlated to temperature throughout the year; however, the relation to moisture parameters was weak. The temperature sensitivity of the species is stable over time, though a slight temporal difference exists in the strength of association. [ABSTRACT FROM AUTHOR]

Studying the effect of surface ozone (O3) and water stress on tree growth is important for planning sustainable forest management and forest ecology. In the present study, a 22-year long time series (1998–2019) on basal area increment (BAI) and fructification severity of European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) H.Karst.) at five forest sites in Western Germany (Rhineland Palatinate) was investigated to evaluate how it correlates with drought and stomatal O3 fluxes (PODY) with an hourly threshold of uptake (Y) to represent the detoxification capacity of trees (POD1, with Y = 1 nmol O3 m−2 s−1). Between 1998 and 2019, POD1 declined over time by on average 0.31 mmol m−2 year−1. The BAI showed no significant trend at all sites, except in Leisel where a slight decline was observed over time (−0.37 cm2 per year, p < 0.05). A random forest analysis showed that the soil water content and daytime O3 mean concentration were the best predictors of BAI at all sites. The highest mean score of fructification was observed during the dry years, while low level or no fructification was observed in most humid years. Combined effects of drought and O3 pollution mostly influence tree growth decline for European beech and Norway spruce. [ABSTRACT FROM AUTHOR]

Tree‐ring data has been widely used to inform about tree growth responses to drought at the individual scale, but less is known about how tree growth sensitivity to drought scales up driving changes in forest dynamics. Here, we related tree‐ring growth chronologies and stand‐level forest changes in basal area from two independent data sets to test if tree‐ring responses to drought match stand forest dynamics (stand basal area growth, ingrowth, and mortality). We assessed if tree growth and changes in forest basal area covary as a function of spatial scale and tree taxa (gymnosperm or angiosperm). To this end, we compared a tree‐ring network with stand data from the Spanish National Forest Inventory. We focused on the cumulative impact of drought on tree growth and demography in the period 1981–2005. Drought years were identified by the Standardized Precipitation Evapotranspiration Index, and their impacts on tree growth by quantifying tree‐ring width reductions. We hypothesized that forests with greater drought impacts on tree growth will also show reduced stand basal area growth and ingrowth and enhanced mortality. This is expected to occur in forests dominated by gymnosperms on drought‐prone regions. Cumulative growth reductions during dry years were higher in forests dominated by gymnosperms and presented a greater magnitude and spatial autocorrelation than for angiosperms. Cumulative drought‐induced tree growth reductions and changes in forest basal area were related, but initial stand density and basal area were the main factors driving changes in basal area. In drought‐prone gymnosperm forests, we observed that sites with greater growth reductions had lower stand basal area growth and greater mortality. Consequently, stand basal area, forest growth, and ingrowth in regions with large drought impacts was significantly lower than in regions less impacted by drought. Tree growth sensitivity to drought can be used as a predictor of gymnosperm demographic rates in terms of stand basal area growth and ingrowth at regional scales, but further studies may try to disentangle how initial stand density modulates such relationships. Drought‐induced growth reductions and their cumulative impacts have strong potential to be used as early‐warning indicators of regional forest vulnerability. [ABSTRACT FROM AUTHOR]

Riparian trees and their annual growth rings can be used to reconstruct drought histories related to streamflow. Because the death of individual trees reduces competition for survivors, however, tree‐ring chronologies based only on surviving trees may underestimate drought impacts. This problem can be addressed by calculating productivity at the stand scale to account for tree mortality and establishment. In the semi‐arid Great Basin in the western United States, we calculated riparian wood production from 1946 to 2016 along a stream where most flow has been removed by a diversion pipeline since 1961. The water table was found to be generally below the root zone of cottonwoods (Populus angustifolia and P. angustifolia × trichocarpa) in the pipeline‐dewatered reach but within it in reference reaches. To reconstruct forest productivity through time, we separately combined measurements of tree‐ring basal area increment with either changing forest area from aerial photos or a census of cross‐dated living and dead cottonwoods. Both approaches revealed productivity declines in the dewatered reach relative to adjacent reference reaches, and the decline accelerated in the 2000s. Tree‐ring narrowing resulted in divergence between the dewatered reach and one reference reach within 5 years after diversion. However, the dewatered reach did not diverge from the other reference reach until 40 years later, when an unprecedented early 2000s atmospheric drought coupled with diversion to cause extensive cottonwood mortality. We conclude that dendrochronological investigations of forest response to environmental stress should incorporate stand dynamics and that the full impacts of flow diversion can be delayed for decades. [ABSTRACT FROM AUTHOR]

The need to understand the carbon sequestration ability of trees under current and future climatic scenarios is fundamental to predict the role of forest in counterbalancing the global warming. In this study, we investigated the carbon sequestration ability of Pinus sylvestris L. in a setting of pure and mixed forests with Quercus petraea (Matt.) Liebl. in Central Poland. Beside the traditional growth measures, i.e., Ring Width, Basal Area Increment, and wood density, we utilized also a new Index called BAIden, which combines Basal Area Increment and mean ring wood density to depict the carbon sequestration ability of trees. Pinus sylvestris showed different sensitivity to climatic variability depending on tree admixture, while the Basal Area Increment and wood density presented few differences between pure and mixed forests. According to the BAIden index, carbon accumulation in P. sylvestris showed similar sensitivity to climatic variability in pure and mixed forests. The new index was also informative on the main climatic drivers of carbon sequestration. Considering future climatic scenarios, the carbon sequestration ability of P. sylvestris will be facilitated by rising temperatures in late winter-early spring and reduced by decreasing precipitation and rising temperatures during summer. Finally, we discussed the perspective and applicability of BAIden for further studies on carbon sequestration ability under climate change. [ABSTRACT FROM AUTHOR]

Recent temperature rise caused by human activities has led to profound changes in the forest ecosystem. Shrubs play an important role in the boreal forest. However, it is not clear how shrub growth responds to climate change, especially whether there is a difference in the response of shrub at different altitudes to climate change. Here, we developed three ring-width chronologies of Pinus pumila along an altitudinal gradient in the Aokelidui Mountains, northeast China, then analyzed the relationship between the growth of P. pumila and climate at different altitudes. The results showed that the radial growth of P. pumila at low altitude had more prominent climate signals than those at medium and high altitude and was more sensitive to climate change. The chronological similarity was the highest in low and middle altitudes (72.5%, p < 0.01). Summer temperature had a significant negative effect on the growth of shrubs, and summer precipitation was conducive to the formation of wider rings at medium altitude. The warmer winter of the previous year favored P. pumila growth at low and medium altitudes but just the opposite at high altitudes. After rapid warming, the negative correlation between temperature and P. pumila growth in the growing season changed to a positive correlation at high altitude. On the contrary, the relationship between precipitation and P. pumila growth in the growing season changed from a positive to a negative correlation. We also found that the sensitivity of the growth of P. pumila to the Standardized Precipitation Evapotranspiration Index (SPEI) has gradually increased at medium-altitude since the 1980s. Therefore, in recent decades, the effect of moisture on the radial growth of shrub has become more and more important at medium altitudes. At the same time, the temperature rise was beneficial to the growth of P. pumila at low altitude. Our results suggest that the treeline advancement in this area is unlikely to occur in the near future since the shrub at high altitudes is not sensitive to climate warming. [ABSTRACT FROM AUTHOR]

Spatial interactions between trees influence forest community succession. The objective of this study was to investigate how shifts in forest composition and proximity between tree species affect stand development over time in mixed forest systems. At six locations across the Fishlake National Forest, Utah, USA, in stands where facilitation has been documented previously, tree‐ring samples were collected from aspen and subalpine fir trees. Basal area increment was calculated to characterize the effects of the proximity of overstory trees on multidecadal growth responses of aspen and subalpine fir in aspen‐dominant and mixed aspen–conifer stands. Subalpine fir seedlings were established next to aspen (within 10 cm) when aspen was between 15 and 120 years old with a mean age of 60 years. Aspen and subalpine fir growth rates were reduced with increasing conifer abundance. Aspen trees growing next to a proximate subalpine fir tree had slower growth rates over time than aspen trees growing independently. Growth rates of subalpine fir in aspen‐dominated stands were similar when growing independently or near aspen trees. However, subalpine fir in conifer‐dominated stands maintained higher growth rates when growing next to an aspen tree than when growing independently. The data suggest that as stand competition increases with conifer abundance, the proximity of overstory trees increases competitive exclusion of aspen while having a beneficial growth effect on subalpine fir. These results underscore the importance of maintaining natural fire regimes in forest systems that keep competitive interactions in balance. [ABSTRACT FROM AUTHOR]

The current increase in deforestation rates of the Brazilian Amazon raises important questions about the resilience of trees in distinct vertical profiles in the world's largest tropical rainforest. Seeking to prove the existence of temporal differences in tree growth response after forest fragmentation and edge effects through a dendrochronological perspective, we revealed that Theobroma sylvestre Mart. (Malvaceae), a typically understory and midstory strata tree of the Amazon upland forest (terra firme), increased the basal area increment rates compared to the forest interior, mainly over the first 20 years after forest fragmentation and edge effects. This pattern could not be extrapolated to the entire vertical forest profile, considering previous dendrochronological evidences from trees located in the forest canopy that presented an opposite pattern, a negative increment rate after forest fragmentation and edge creation. These divergences suggest that trees under the canopy of Amazon terra firme forest can be more tolerant to environmental stress (i.e. more incidence of droughts) derived by microclimatic and structural changes in forest subjected to forest fragmentation and edge effects processes, however, future dendroclimatic studies may confirm these hypotheses. In this sense, we highlighted that the increase in basal area increment of trees in the understory and midstory exposed to edge effects may indicate an important component of above-ground biomass stock recovery after forest fragmentation. This fact should be considered in forest management and restoration practices, promoting a new perspective on forest resilience ability after forest fragmentation and its strong impact on plant productivity and capacities in long-term carbon storage. [ABSTRACT FROM AUTHOR]

A major foundation of trait‐based ecology is that traits have an impact on individual performance. However, trait–growth relationships have not been extensively assessed in trees, especially outside tropical ecosystems. In addition, measuring traits directly related to physiological processes remains difficult and the differences between inter‐ and intraspecific relationships are seldom explored.Here, we use individual‐level data on a set of hydraulic, leaf and stem traits to assess their ability to predict basal area increment (BAI) and growth efficiency (BAI per unit of tree leaf area, GE) among and within species for six dominant tree species along a water availability gradient under Mediterranean climate (Catalonia, NE Spain). Measured traits include: leaf mass per area (LMA), leaf nitrogen concentration (N), leaf C isotopic composition (δ13C), the leaf water potential at turgor loss (Ptlp), stem wood density (WD) and branch‐level estimates of the Huber value (Hv), sapwood‐ and leaf‐specific hydraulic conductivity (KS and KL) and resistance to xylem embolism (P50).Trait–growth associations were generally weak, particularly for BAI and within species. High values of both growth metrics were associated with 'conservative' leaf and hydraulic traits. In particular, BAI was negatively associated with KL (and wood density), while GE increased with LMA, allocation to sapwood relative to leaves (Hv) and resistance to xylem embolism (P50). Climate effects on BAI and GE were indirectly mediated by changes in traits, stand structure and tree basal area. Overall, these results suggest that maintaining functionality over extended periods of time may be more important than maximum gas exchange or hydraulic capacity to achieve high radial growth under Mediterranean climates.Our study reveals that widely used 'functional traits' may be poor predictors of tree growth variability along environmental gradients. Moreover, trait effects (when present) do not necessarily conform to simple hypotheses based on our understanding of organ‐level processes. An improved understanding of trait coordination along common axes of variation together with a revaluation of the variables that better reflect whole‐tree performance can greatly improve our understanding of trait–growth relationships. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

Forest site (FS) and meteorological conditions are recognized as the main factors affecting tree growth and whole-stand sustainability. This study aims to detect the combined effects of FS and meteorological conditions on tree ring formation of Scots pine (Pinus sylvestris L.), the most common tree species in Lithuania and hemi-boreal forests of northeastern Europe. We used data on stand structure and productivity from the Lithuanian National Forest Inventory (NFI) and stem radial increment series of dominating trees during the period 1993-2012 collected since 2013. Pine stem basal area increment (BAI) was chosen as the response variable, while temperature in March (°C) and precipitation in June (mm) were used as predictor variables, as they best express the effect of climate change on Lithuanian forests. We simulated the effects on dominating pine annual increment of deciduous tree species, mainly Betula sp. and the level of soil moisture and fertility, accounting in addition for the random effects of NFI network tract, plot direction, and tree number. A nonlinear mixed-effects model explained up to 68% of the variation in the BAI of pine trees. The annual pine trees BAI increased with the increase in the proportion of deciduous trees in pine stands. Increases in temperature and precipitation in considered months reinforced this positive effect on pine BAI, especially in mature pine stands in temporarily waterlogged meso-eutrophic FSs on mineral soils. A negative effect of deciduous trees on pine stem increment was observed only in nutrient-rich eutrophic and drained peatland FSs. Forestry treatments directed towards the increase in deciduous tree proportion in the most common normal or temporarily waterlogged meso-eutrophic and oligotrophic pine stands might increase the biodiversity and productivity of pine stands, and their sustainability in future climate change scenarios. [ABSTRACT FROM AUTHOR]

Key message: Large sugar pine mortality was associated with recent growth and defense measures. Many old-growth pine forests across the western United States have encountered widespread and concerning increases in tree mortality attributed to increased competition and reduced vigor associated with prolonged fire exclusion that can make trees more vulnerable to bark beetles. We investigated the importance of growth and resin duct defense on recent mortality of large sugar pine (Pinus lambertiana) in a fire-excluded, mixed-conifer forest of the Sierra Nevada, in California, USA. Growth and defense were measured from tree rings for 33 pairs of live and dead sugar pine. The 10-year trend in basal area increment prior to sampling declined by 1.78 cm2 year− 1 in sugar pine that died and increased by 0.34 cm2 year− 1 in paired live sugar pine. The 10-year trend in resin duct total area showed declines of 0.0154 mm2 year− 1 in trees that died and increases of 0.0068 mm2 year− 1 in trees that survived. The most informative models of large sugar pine mortality included measures of both growth and defense. The top model included the trends of basal area increment and resin duct total area 10 years before mortality, and growth variability 5 years before mortality. In general, trends and variability in growth and defense over shorter time windows (< 10 years) were more informative than average measures or longer time windows. The results from our study suggest treatments that result in neutral to positive trends in allocation to growth and defense may contribute to conditions that reduce probability of mortality in the future. [ABSTRACT FROM AUTHOR]

Key message: Although an increased intrinsic water-use efficiency has been observed, drought stress played a leading role in controlling Chinese pine growth in semi-arid region of northern China. Climate change, which is acknowledged as the most important factor in affecting plant performance, could be modulated by increasing atmospheric CO2 concentration. In this study, a total of 141 Chinese pine (Pinus tabuliformis) trees were studied to estimate tree-ring width. Based on tree-ring δ13C records, we measured the fluctuations in leaf intercellular CO2 (Ci) and intrinsic water-use efficiency (iWUE) since industrialization period on Hasi mountain, Gansu province. We found that the long-term variation of iWUE has been increasing since 1850. On average, 73% of the total variance in iWUE was explained by temperature, Standardized Precipitation-Evapotranspiration Index (SPEI) and CO2 concentration. Over 19 and 23% of the variance was attributed solely to drought stress and CO2 concentration, respectively. For BAI (basal area increment), nearly 50% of the variance was explained by temperature, SPEI and CO2, with 40% of the variance in tree growth attributed to drought stress. In addition, our results show that the positive relationship between tree growth and drought stress did not change over time. When there was a wetter condition, a larger proportion of higher tree growth occurred, otherwise more trees had lower tree growth. We therefore, conclude that despite the clear increase of iWUE, its beneficial effect of this higher iWUE on tree growth was overcome by drought stress at our study area. [ABSTRACT FROM AUTHOR]

Understanding the forest response to ongoing climate change is crucial in forest management strategies under anticipated climate adversity. To understand the retrospective growth dynamics of Jeffrey pine (Pinus jeffreyi Grev. & Balf.), tree-ring chronology from the subalpine forest in the Lake Tahoe Basin, California was correlated with air temperature, precipitation, and Palmar Drought Severity Index (PDSI). The years 1757, 1782, 1886, 1859, 1876, 1920, 1929-30, 1977, 1988-89, 2001-02, 2008, and 2014 were some of the years with noticeable low growth. There was robust growth in 1747-49, 1792, 1828, 1866-68, 1913, 1969, 1984, 1998, and 2011. Ring width index (RWI) and basal area increment showed a recent growth increase. Climate-growth response analysis revealed the growth-inhibiting influence of the hot and dry summer. More pronouncedly, warm and wet winter was found to be conducive to tree growth in the following year. A significant growth correlation with the previous year climate (stronger with PDSI) and its absence in current spring may be suggestive of potential growth stimulation by predicted warmer and longer growing season in the future. However, since the RWI chronology consisted mostly of mature trees and because the old cambial age tends to have signal divergence, further studies incorporating younger trees and cohabitant species would provide deeper insights into the growth-climate response. [ABSTRACT FROM AUTHOR]

In many regions, such as the Mediterranean, anticipated climate change is seen as a serious threat to tree vitality and forest productivity. Recent studies show that wood and bark structure as well as the number of dormant cambial cells bear valuable information about the growth condition and vitality of trees and thus could function as indicators to help manage forests in the future. Microcores and tree cores were sampled from stems of adult Cedrus libani trees growing at different altitudes in SW-Turkey. Trees were divided into two groups based on basal area increments: vital trees (positive growth trend), and trees of diminishing vitality (negative growth trend). Histological cross-sections were investigated for their number of dormant cambial cells as well as their xylem and phloem characteristics. We measured the widths of the conducting phloem, most recent xylem ring, earlywood, and latewood. We further calculated the ratio between the width of xylem ring and conducting phloem (XR:CPH ratio), and earlywood to latewood ratio. Vital trees had a significantly higher number of dormant cambial cells (on average 32%), higher xylem (67%), and conducting phloem (36%) widths, and a higher XR:CPH ratio (47%). The XR:CPH ratio ranged between 1.8:1 and 21.4:1. The number of dormant cambial cells was closely related to xylem and conducting phloem widths and showed a significant decrease with tree age. Altitude showed no direct effect on the measured and calculated parameters. Our results indicate the potential of dormant cambium, xylem, and phloem characteristics to assess the vitality and growth conditions of C. libani trees. [ABSTRACT FROM AUTHOR]

Some studies suggest that tapping sugar maple (Acer saccharum Marshall) trees can cause their growth to decline, particularly on poor and acidic soils. We tested this hypothesis in seven sugar bushes located in the Quebec Appalachians by comparing the growth of tapped trees with nearby untapped trees. The sites represented a range of soil fertility, from very good for sugar maple to strongly deficient in calcium. Trees were cored, and individual dendrochronology series were used to analyze trends in basal area growth, from a period of 10 years before, to 8–10 years after tapping began. Basal area growth of sugar maples did not appear to be influenced by tapping (p ≥ 0.134), except at one site (p < 0.001), where the growth of tapped trees decreased by 33% over 10 years. This decline could not be explained only by the poor soil fertility observed at the site. Although a tree biomass distribution budget indicated that maple syrup production represented only 4–6% of the carbon allocated annually to net primary production, the long-term relationship between maple syrup production and tree growth requires further study. [ABSTRACT FROM AUTHOR]

Old-growth forests have an important role in maintaining animal and plant diversity, are important carbon (C) reservoirs and are privileged sites to study long-term plant physiological responses, long-term forest dynamics and climate change impact on forest ecosystems. Several studies have highlighted how old-living trees undergo age-related declines with hydraulic limitations and reduction in photosynthesis, though some recent works have suggested that such a decline is not always observed. Our study aims at understanding the role of atmospheric CO2 increase on tree C uptake and stomatal conductance (gs) in old-living trees by analysing the long-term patterns of tree growth and intrinsic water use efficiency (iWUE) in three old-growth forests in the Balkans (Bosnia-Herzegovina and Montenegro), using dendrochronology and isotopic analysis. We hypothesised a long-term increase in iWUE in the studied old-growth forests, mostly related to enhanced photosynthesis rather than reduced stomatal conductance. Tree cores were sampled from dominant silver fir (Abies alba Mill.) trees in each forest. Tree-ring widths were measured and basal area increments (BAI) were assessed for each sampled tree and, from the six longest chronologies, five decades were chosen for cellulose extraction, its isotopic analysis (δ13C, δ18O), iWUE and leaf water 18O evaporative enrichment above the source water (Δ18OL) determination. We observed a continuous and significant increase in iWUE from 1800 to 2010 in the sampled dominant trees at all the three old-growth forests. Our BAI data and our estimates of Δ18OL across the study period support the idea that enhanced photosynthesis rather than reduced stomatal conductance is the major driver of the measured iWUE increase. Thus, our results support some recent findings challenging the hypothesis that iWUE in forests is primarily the result of a CO2-induced reduction in stomatal conductance as well as the so called hydraulic limitation hypothesis. [ABSTRACT FROM AUTHOR]

Purpose: It has been well reported in many studies globally that the increased atmospheric carbon dioxide (CO2) concentration has positively influenced plant growth in the past century. However, it is crucial to understand how long the tree growth trend will remain alongside the rising CO2 concentration before it is tipped over. Methods: In this study, we focused on studying the long-term tree growth responses to the rising CO2 concentration, in combination with other environmental factors, and its feedback to the changing climate. This study has reported two tree species, Pseudolarix amabilis (P. amabilis) and Cryptomeria japonica (C. japonica), sampled from a subtropical monsoon forest located in eastern China, and established the long-term tree ring chronologies by applying tree ring width measurement and cross dating, and then, basal area increment (BAI) was calculated. Meanwhile, intrinsic water-use efficiency (iWUE) was calculated through the measurement of carbon isotope composition (δ13C) in tree ring samples, and its relationships with BAI and atmospheric CO2 concentration were also quantified. Results: BAI values continuously increased in both P. amabilis and C. japonica with the rising of CO2 concentration until the atmospheric CO2 concentration tipping points were reached, after which tree growth started to decline with the rising CO2, while iWUE exerted a continuous increase trend with the increasing CO2 concentration. Conclusions: Tree growth of both species was more photosynthesis driven before reaching the maximum BAI points, once the tipping points of atmospheric CO2 were passed, leading to the positive feed of forest carbon cycling to climate change and global warming. Therefore, tree growth was more water limitation driven in the last 20 years. [ABSTRACT FROM AUTHOR]

The influence of climate on the vitality and growth of European beech (Fagus sylvatica L.) has become a focus of forest research over the last decade. Beech locally reaches its continental xeric limit in Hungary within its European distribution area, giving a unique opportunity to study the climatic sensitivity of the species, based on tree-ring analysis. A comparison of four geographically and climatically different sites is presented from Hungary, combining data collected on stand level with systematic forest inventory plots. Tree-ring width chronologies covering the past 90-100 years of the lifetime of mature and middle-aged trees and different climatic variables were used to evaluate the growth-climate relationships and recent growth trends of the selected beech stands by multivariate regression analysis. Strong relationships were found between annual radial growth and (mainly water availability related) meteorological variables of the vegetation season, exceeding previous results from elsewhere in Europe. A clear spatiotemporal variability of the growth sensitivity was also revealed, following a (climatic) gradient from the northern to the southwestern parts of the country. In the northern sites, climatic sensitivity was found to be more fluctuating, while southwestern sites facing more continuous effects of changing climatic conditions seem to show weakening correlation over time. Trends of relative basal area increments and climatic sensitivity of growth over the past decades may be due to unfavorable climatic changes, though extreme and recurrent drought events superimposed on the long-term trends seem to have a decisive impact on growth patterns and associated resilience of beech. [ABSTRACT FROM AUTHOR]

Atlantic white cedar (AWC) stands form peat substrates in association with a seasonally flooded, saturated hydrologic regime. Less than 2% of the AWC swamp land area present during the pre-colonial era remains, and most of the current area now exhibits a temporarily flooded hydrologic regime. The purpose of this study was to quantify radial AWC growth at time scales that were cumulative (throughout ~60-year lifespans) and annual to clarify the relationship with hydrologic regime and climate in drained and undrained stands. Two 60-year-old stands having either drained or undrained conditions were selected in national wildlife refuges in Virginia and North Carolina, USA. Shallow groundwater wells fitted with continuous recorders measured depth-to-water-table during the 1999 calendar year to verify hydrologic regimes, and tree ring widths were evaluated from 54 trees per site. Cumulative time scale growth of individual tree stems was strongly suppressed by high water tables in the undrained stand. Annual growth rates among climate variables also diverged such that wetter months were positively correlated with tree ring width in the drained stand. Results suggest that AWC tree ring growth patterns can provide natural resource managers with insights into historic hydrologic conditions that influence ecosystem services and biodiversity. [ABSTRACT FROM AUTHOR]

Key message: While radial growth patterns at different stem heights were similar, tree-ring samples collected at breast height showed diminishing chronology strength for detecting climatic signals because of differences in climate responses. In this study, basal area increments (BAI) and tree-ring chronologies for different heights of Schrenk spruce (Picea schrenkiana) in the western Tianshan Mountains were calculated and used to assess the radial growth pattern along the stem. The mean BAI for different stem heights gradually decreased with increasing stem height (1.3 m > 5 m > 10 m > 15 m > 20 m). The five mean BAI series all showed a significant increasing trend since 1961. The mean BAI for the 10 m height showed the fastest increase among the five series. The significant correlations in the original, high-, and low-frequency domains, and the high Gleichläufigkeit index, indicate coherence among the radial growth patterns for different heights along the stem. A correlation analysis revealed that for three periods (July–September of the previous year, November–December of the previous year, and May–October of the current year) the mean minimum temperature mainly affected the radial growth at the upper positions of the bole, while the relationship between the ring width at breast height and climatic values was clearly weak. The results support the hypothesis that traditional tree-ring sampling at breast height may diminish the strength of tree-ring width chronologies in detecting climatic signals to some extent. [ABSTRACT FROM AUTHOR]

Aims: Pinus yunnanesis is commercially, culturally and economically important, but there is a lack of ecological data on its role in stand dynamics. Our aims are to clarify the structure, composition, regeneration and growth trends of primary mature P. yunnanensis forests. Study area: The Tianchi National Nature Reserve in the Xuepan Mountains, Yunlong County, northwestern Yunnan, China. Methods: We investigated forests containing P. yunnanensis, measured tree ages and analyzed the data. Results: Six forest types were identified: (1) coniferous forest: Pinus yunnanensis (Type 1); (2) mixed coniferous and evergreen broad-leaved forest: P. yunnanensis-Lithocarpus variolosus (Type 2); (3) mixed coniferous and deciduous broad-leaved forest: P. yunnanensis-Quercus griffithii (Type 3); (4) mixed evergreen broad-leaved and coniferous forest: Castanopsis orthacantha-P. yunnanensis-Schima argentea (Type 4); (5) mixed coniferous, evergreen and deciduous broad-leaved forest: Pinus yunnanensis-Schima argentea-Quercus griffithii (Type 5); (6) mixed coniferous and evergreen broad-leaved forest: Pinus armandii-Quercus rehderiana-Pinus yunnanensis (Type 6). The size- and age-structure and regeneration patterns of P. yunnanensis were highly variable within these six forest types. P. yunnanensis regeneration was well balanced in forest Type 1 as compared to the other five types. All six forest types were identified as rare and old-growth with P. yunnaensis trees reaching ages of more than 105 years (a maximum age of 165 years with a diameter 116 cm at breast height) except for the Type 4 forest (a 90-year-old stand). Growth rates of P. yunnanensis, based upon ring width measurements, were high for the first 10 years, then declined after the 10th year. In contrast, basal area increment (BAI) increased for the first 25 years, plateaued, and only declined as trees became older. Trees in the older age classes grew more quickly than younger trees at the same age, a consequence of either site quality or competitive differences. The BAI of P. yunnanensis in all age classes in the Tianchi National Nature Reserve was much higher than those of the secondary and degraded natural P. yunnanensis forests of other areas. Conclusions: The P. yunnanensis forests of the Tianchi area appear to be some of the last remnants of primeval and old-growth forests of this species. These forests are structurally diverse and contain a rich diversity of overstory, mid-story, and understory species. [ABSTRACT FROM AUTHOR]

Edge effects are a major cause of natural dynamics of fragmented forests; however, studies that evaluate edge effects during the lifetime of trees are relatively rare. Through a long-term perspective of tree growth, dendroecology can contribute to a better understanding of the influence of edge effects. In order to frame our interpretation, we raised the following hypotheses: (1) trees located close to a forest edge have lower growth rates compared to trees growing far from edges, and (2) climate sensitivity of trees naturally growing on the forest edge is different from the trees in the interior. This study was conducted in Southern Brazil, where 21 Araucaria angustifolia located 50mfrom the edge and 19 individuals located 4000 m from the forest edge were sampled. Dendrochronological study followed the usual procedures and growth patterns were evaluated using basal area increment, specific threshold value of fast and slow growth, and principal components analysis. During the 54 years analyzed, results indicated that the edge effect reduced growth by 30% in diameter increment and wood production of A. angustifolia trees. Regarding the influence of climatic variability on tree growth, we observed that edge effects may exert strong pressure on growth responses to climate in A. angustifolia located on forest edges, making individuals in those environments potentially more sensitive to variations in temperature and rainfall, mainly at warmer times of year. We therefore emphasize the importance of considering edge trees as potential bioindicators of historical environmental changes and forest fragmentation. Future studies should be carried out in other forest types and with different tree species (e.g. pioneer vs. shade-tolerant, trees vs. shrubs) to test the reliability of our results and provide more robust conclusions about this phenomenon. [ABSTRACT FROM AUTHOR]

Several important environmental influences of tree growth and carbon sequestration have changed over the past several decades in eastern North America, specifically, more frequent pluvial conditions, increased carbon dioxide (CO2) concentrations, and decreased acidic deposition. These factors could lead to changes in the relationship between tree growth and water availability, and perhaps even decouple the two, having large implications on how future climate change will impact forest productivity and carbon sequestration. Here, we examine the concurrent influence of the climatic water balance (precipitation minus potential evapotranspiration), CO2 concentrations, and sulfate and nitrogen deposition on radial tree growth, carbon isotopes, and intrinsic water‐use efficiency (iWUE) for several hardwood tree species in the Midwestern United States. We found that when considering the simultaneous influence of these factors, the climatic water balance is the dominant influence on annual growth. Therefore, the recent pluvial period is the primary cause of the weakening relationship between radial growth and water availability. Even during pluvial periods, water availability is the primary control on growth, with increasing CO2 concentrations and decreased SO4 deposition being secondary factors. Importantly, the weakening in the climate‐growth relationship is species specific, with Acer species having stable relationships with the climatic water balance, Liriodendron tulipifera showing a strengthening relationship, and Quercus species and Populus grandidentata exhibiting weakening. Thus, interannual variations in soil moisture unevenly impact tree growth and carbon sequestration. Our findings suggest that, despite recent pluvial conditions, increasing CO2 concentrations and decreasing acidic deposition have not buffered the impact of water availability on tree growth and carbon sequestration. Plain Language Summary: In recent decades, many factors that influence tree growth have changed across the Midwestern United States, including more precipitation, higher carbon dioxide concentrations in the atmosphere, and fewer pollutants. Changes in these environmental factors could result in tree growth being less sensitive to water availability. While a weakening relationship between water availability and tree growth is present, it is difficult to determine the cause. Here, we examine the simultaneous influence of a wetter climate, higher carbon dioxide concentrations, and a decrease in pollutants deposition on tree growth and how efficiently trees use water. We found that when considering all three variables, increased moisture was the leading influence on tree growth. Therefore, the recent wet period is behind trees being less sensitive to soil moisture, not increases in carbon dioxide or decreases in pollutants. It is important to note that some species such as oak and aspen did become less sensitive to soil moisture, other species such as maple and tuliptree did not. This is important because when drought conditions return to the region, trees will still be sensitive despite higher carbon dioxide concentrations or decreases in sulfate and nitrate deposition. Key Points: Recent weakening of the relationship between climatic water balance and radial growth and C isotopes was species specificWater availability is the dominant factor influencing long‐term radial growth even when considering the simultaneous influence of other factors such as increasing atmospheric CO2 and decreasing acidic depositionIncreasing atmospheric CO2 concentrations increased water‐use efficiency but not growth of most tree species [ABSTRACT FROM AUTHOR]

Key message: This work studied the response of tree growth to the increased drought and carbon dioxide in semi-arid areas of northwestern China. Forests ecosystems play a key role in the global carbon cycle. However, effects of increased drought and rising atmospheric carbon dioxide (Ca) on it are complex and there are many uncertainties. In this study, we evaluated this issue through dendroecology in semi-arid regions of northwest China. Results found the basal area increment of trees decreased by 28% (from 7.59 to 5.43 cm2 year−1) as the intrinsic water use efficiency increased 32% (from 98.61 to 130.28 µmol mol−1). Despite both Ca and drought positively affected intrinsic water use efficiency, they did not promote tree growth. Meanwhile, values of intercellular [CO2] increased 14% (from 158.83 to 180.89 ppm) while the ratio of intercellular [CO2] to Ca decreased 7% (from 0.50 to 0.46). Our study advances understanding of the variability of the global carbon cycle under climate change. [ABSTRACT FROM AUTHOR]

A large variability of water use efficiency (assessed from the carbon isotopic discrimination in leaves and leaf soluble sugars) has been detected among poplar genotypes. Checking whether such differences detected in young trees (1-2 years old) remain stable with tree age is a prerequisite to use this trait with confidence for breeding purposes. In this study, a synchronic approach was used to test the age-related stability of the genotypic ranking of carbon isotopic discrimination in wood (Δ13C) until tree maturity. We sampled 376 trees between 4 and 20 years from three Populus deltoides × P. nigra genotypes growing in 41 common-garden trials across France. Carbon and nitrogen percentages along with δ13C was measured in the bulk wood of the year 2009 and used to compute the Δ13C. Basal area increment between 2008 and 2009 was also measured. Results showed that Δ13C increased (i.e., water use efficiency decreased) between ages 4 to 6 and remained stable later on. Significant differences among genotypes were found but the ranking among genotypes remained stable with age during the assessed life span. Furthermore, basal area increment and Δ13C were positively correlated interannually. This large-scale survey shows that despite crossing over in the temporal trend, water use efficiency remained stable with age across 3 poplar genotypes. However, further studies with a large number of genotypes are required to confirm whether this trait can be used to maintain or even improve productivity of poplar plantations, while lowering water consumption. [ABSTRACT FROM AUTHOR]

Climate response of tree-species growth may be influenced by intra- and inter-specific interactions. The different physiological strategies of stress response and resource use among species may lead to different levels of competition and/or complementarity, likely changing in space and time according to climatic conditions. Investigating the drivers of inter- and intra-specific interactions under a changing climate is important when managing mixed and pure stands, especially in a climate change hot spot such as the Mediterranean basin. Mediterranean tree rings show intra-annual density fluctuations (IADFs): the links among their occurrence, anatomical traits, wood growth and stable isotope ratios can help understanding tree physiological responses to drought. In this study, we compared wood production and tree-ring traits in Quercus ilex L. dominant trees growing in two pure and two mixed stands with Pinus pinea at two sites in Southern Italy, on the basis of the temporal variation of cumulative basal area, intrinsic water use efficiency (WUEi), δ18O and IADF frequency in long tree-ring chronologies. The general aim was to assess whether Q. ilex trees growing in pure or mixed stands have a different wood production through time, depending on climatic conditions and stand structure. The occurrence of dry climatic conditions triggered opposite complementarity interactions for Q. ilex growing with P. pinea trees at the two sites. Competitive reduction was experienced at the T site characterized by higher soil water holding capacity (WHC), lower stand density and less steep slope than the S site; on the opposite, high competition occurred at S site. The observed difference in wood growth was accompanied by a higher WUEi due to a higher photosynthetic rate at the T site, while by a tighter stomatal control in mixed stand of S site. IADF frequency in Q. ilex tree rings was linked to higher WUEi, thus to stressful conditions and could be interpreted as strategy to cope with dry periods, independently from the different wood growth. Considering the forecasted water shortage, inter-specific competition should be reduced in denser stands of Q. ilex mixed with P. pinea. Such findings have important implications for forest management of mixed and pure Q. ilex forests. [ABSTRACT FROM AUTHOR]

Forecasting the growth of tree species to future environmental changes requires a better understanding of its determinants. Tree growth is known to respond to global‐change drivers such as climate change or atmospheric deposition, as well as to local land‐use drivers such as forest management. Yet, large geographical scale studies examining interactive growth responses to multiple global‐change drivers are relatively scarce and rarely consider management effects. Here, we assessed the interactive effects of three global‐change drivers (temperature, precipitation and nitrogen deposition) on individual tree growth of three study species (Quercus robur/petraea, Fagus sylvatica and Fraxinus excelsior). We sampled trees along spatial environmental gradients across Europe and accounted for the effects of management for Quercus. We collected increment cores from 267 trees distributed over 151 plots in 19 forest regions and characterized their neighbouring environment to take into account potentially confounding factors such as tree size, competition, soil conditions and elevation. We demonstrate that growth responds interactively to global‐change drivers, with species‐specific sensitivities to the combined factors. Simultaneously high levels of precipitation and deposition benefited Fraxinus, but negatively affected Quercus' growth, highlighting species‐specific interactive tree growth responses to combined drivers. For Fagus, a stronger growth response to higher temperatures was found when precipitation was also higher, illustrating the potential negative effects of drought stress under warming for this species. Furthermore, we show that past forest management can modulate the effects of changing temperatures on Quercus' growth; individuals in plots with a coppicing history showed stronger growth responses to higher temperatures. Overall, our findings highlight how tree growth can be interactively determined by global‐change drivers, and how these growth responses might be modulated by past forest management. By showing future growth changes for scenarios of environmental change, we stress the importance of considering multiple drivers, including past management and their interactions, when predicting tree growth. Tree growth responds to global‐change drivers such as climate change or atmospheric deposition and to local land‐use drivers such as forest management. Yet, large geographical‐scale studies examining interactive growth responses to multiple global‐change drivers are relatively scarce and rarely consider management effects. We assessed interactive effects of three global‐change drivers (temperature, precipitation and nitrogen deposition) on tree growth of three study species across Europe (Quercus robur/petraea, Fagus sylvatica, Fraxinus excelsior) and accounted for management effects for Quercus. We demonstrate that growth responds interactively to these drivers, with species‐specific sensitivities. Furthermore, past management modulated the effects of changing temperatures on Quercus' growth. [ABSTRACT FROM AUTHOR]

Defoliation caused annually by Cameraria ohridella has a considerable impact on the general condition of horse chestnut trees. We investigated the consequences of tree endotherapy against this insect. Wood samples, leaves and insect specimens were collected ten years after the treatment (injection) with pesticides. Insect invasion was manifested in all investigated trees by distinct radial growth depression. Treatment resulted in a growth upturn, while non-treated trees maintained decreased growth. The overall foliage infestation level was lower in treated trees, but pupal mass and potential fecundity of insect females were not affected. Our study revealed a long-lasting, positive effect of endotherapy on trees' appearance and growth. [ABSTRACT FROM AUTHOR]

Abstract: Forests sequester large amounts of carbon annually and are integral in buffering against effects of global change. Increasing atmospheric CO2 may enhance photosynthesis and/or decrease stomatal conductance (gs) thereby enhancing intrinsic water‐use efficiency (iWUE), having potential indirect and direct benefits to tree growth. While increasing iWUE has been observed in most trees globally, enhanced growth is not ubiquitous, possibly due to concurrent climatic constraints on growth. To investigate our incomplete understanding of interactions between climate and CO2 and their impacts on tree physiology and growth, we used an environmental gradient approach. We combined dendrochronology with carbon isotope analysis (δ13C) to assess the covariation of basal area increment (BAI) and iWUE over time in lodgepole pine. Trees were sampled at 18 sites spanning two climatically distinct elevation transects on the lee and windward sides of the Continental Divide, encompassing the majority of lodgepole pine's northern Rocky Mountain elevational range. We analyzed BAI and iWUE from 1950 to 2015, and explored correlations with monthly climate variables. As expected, iWUE increased at all sites. However, concurrent growth trends depended on site climatic water deficit (CWD). Significant growth increases occurred only at the driest sites, where increases in iWUE were strongest, while growth decreases were greatest at sites where CWD has been historically lowest. Late summer drought of the previous year negatively affected growth across sites. These results suggest that increasing iWUE, if strong enough, may indirectly benefit growth at drier sites by effectively extending the growing season via reductions in gs. Strong growth decreases at high elevation windward sites may reflect increasing water stress as a result of decreasing snowpack, which was not offset by greater iWUE. Our results imply that increasing iWUE driven by decreasing gs may benefit tree growth in limited scenarios, having implications for future carbon uptake potential of semiarid ecosystems. [ABSTRACT FROM AUTHOR]

The aim of this study was to estimate a basal area growth model for individual trees in uneven-aged Caspian forests. A survey was conducted in order to find a natural forest without any harvesting activities, a so called ‘untouched forest’ and an area was selected from the Iranian Caspian forest. Three sample plots in the same aspect and of the same forest type were selected. In each plot, total tree height, diameter at breast height, distance of neighbor trees and azimuth were measured. Thirty trees were selected and drilled with increment borer to determine the increment model. Regression analysis was used to estimate the growth model. Results show that, for individual trees, there is a significant nonlinear relationship between the annual basal area increment, as the dependent variable, and the basal area. The results also show that the basal area of competing trees has a positive influence on growth. That the increment is higher with more competing neighboring trees is possibly because plots with higher volume per hectare and more competition, most likely also have higher site index or better soil or better site productivity than the plot with lower volume per hectare. [ABSTRACT FROM AUTHOR]

The Three-North Shelter Forest (TNSF) is a critical ecological barrier against sandstorms in northern China, but has shown extensive decline and death in Populus simonii Carr. in the last decade. We investigated the characteristics--tree-ring width, basal area increment (BAI), carbon isotope signature (13Ccor), and intrinsic water-use efficiency (iWUE)--of now-dead, dieback, and non-dieback trees in TNSF shelterbelts of Zhangbei County. Results from the three groups were compared to understand the long-term process of preceding drought-induced death and to identify potential early-warning proxies of drought-triggered damage. The diameter at breast height (DBH) was found to decrease with the severity of dieback, showing an inverse relationship. In all three groups, both tree-ring width and BAI showed quadratic relationships with age, and peaks earlier in the now-dead and dieback groups than in the non-dieback group. The tree-ring width and BAI became significantly lower in the now-dead and dieback groups than in the non-dieback group from 17 to 26 years before death, thus, these parameters can serve as early-warning signals for future drought-induced death. The now-dead and dieback groups had significantly higher δ13Ccor and iWUEs than the non-dieback group at 7-16 years prior to the mortality, indicating a more conservative water-use strategy under drought stress compared with non-dieback trees, possibly at the cost of canopy defoliation and long-term shoot dieback. The iWUE became significantly higher in the now-dead group than in the dieback group at 0-7 years before death, about 10 years later than the divergence of BAI. After the iWUE became significantly different among the groups, the now-dead trees showed lower growth and died over the next few years. This indicates that, for the TNSF shelterbelts studied, an abrupt iWUE increase can be used as a warning signal for acceleration of impending drought-induced tree death. In general, we found that long-term drought decreased growth and increased iWUE of poplar tree. Successive droughts could drive dieback and now-dead trees to their physiological limits of drought tolerance, potentially leading to decline and mortality episodes. [ABSTRACT FROM AUTHOR]