Tree-ring Formation Research Articles

Prosopis L. woody growth in relation to hydrology in South America: A review

Arboreal species of the genus Prosopis L. have played an important role in the development of tree-ring research in arid and semi-arid ecoregions of South America. Given the distribution of Prosopis across a broad precipitation gradient from 0 to 2000 mm y−1 and its unique role as a phreatophyte, the relationship between Prosopis species growth and water has been a recurring theme over the past century. We conducted a systematic review of the literature addressing Prosopis and water research in South America, and combined site coordinates with GIS data of mean annual precipitation (MAP), elevation, biome, and soil moisture from online databases to understand the spatial distribution of research to date. We compiled 40 publications from 1931 to 2022, including results from 11 species of Prosopis among four countries, on the relationship between Prosopis spp and precipitation, groundwater levels, soil humidity, among other hydrological parameters. The spatial distribution of research sites spans tropical-subtropical and temperate latitudes from 4° to 35°S, excluding regions where the genus is present in Patagonia and northeastern South America. Studies covered a broad range of elevations from 30 to 3500 m a.s.l. but was limited to 1–730 mm y−1 MAP, excluding more humid climates where Prosopis occurs. Results obtained from 32 dendrochronological studies and eight studies relating to Prosopis and hydrology, were grouped into sub-disciplines of tree-ring formation and the hydrosystem, dendroclimatology, dendrohydrology, and dendroecology. The review highlights the unique affinities of Prosopis to arid conditions, and the use of tree rings as a proxy for historical droughts and variability in water tables. Nonetheless, there are opportunities to expand the geographical-climatological extent of Prosopis growth research to humid climates, as well as to incorporate novel techniques such as stable isotopes and vessel size chronologies to understand how this genus records hydrological change throughout South America.

Tree-ring distinctness, dating potential and climatic sensitivity of laurel forest tree species in Tenerife Island

Macaronesian laurel forests are the only remnants of a subtropical palaeoecosystem dominant during the Tertiary in Europe and northern Africa. These biodiverse ecosystems are restricted to cloudy and temperate insular environments in the North Atlantic Ocean. Due to their reduced distribution area, these forests are particularly vulnerable to anthropogenic disturbances and changes in climatic conditions. The assessment of laurel forest trees’ response to climate variation by dendrochronological methods is limited because it was assumed that the lack of marked seasonality would prevent the formation of distinct annual tree rings. The aims of this study were to identify the presence of annual growth rings and to assess the dendrochronological potential of the most representative tree species from laurel forests in Tenerife, Canary Islands. We sampled increment cores from 498 trees of 12 species in two well-preserved forests in Tenerife Island. We evaluated tree-ring boundary distinctness, dating potential, and sensitivity of tree-ring growth to climate and, particularly, to drought occurrence. Eight species showed clear tree-ring boundaries, but synchronic annual tree rings and robust tree-ring chronologies were only obtained for Laurus novocanariensis, Ilex perado subsp. platyphylla, Persea indica and Picconia excelsa, a third of the studied species. Tree-ring width depended on water balance and drought occurrence, showing sharp reductions in growth in the face of decreased water availability, a response that was consistent among species and sites. Inter-annual tree-ring width variation was directly dependent on rainfall input in the humid period, from previous October to current April. The four negative pointer years 1995, 1999, 2008 and 2012 corresponded to severe drought events in the study area. This study gives the first assessment of dendrochronological potential and tree-ring climate sensitivity of tree species from the Tenerife laurel forest, which opens new research avenues for dendroecological studies in Macaronesian laurel forests.

Usporedna analiza utjecaja klimatskih čimbenika na radijalni rast autohtonih vrsta borova (Pinus spp.) u središnjoj Bosni i Hercegovini

In central Bosnia and Herzegovina, in the Zavidovići-Teslić area, the study of the radial growth of Austrian and Scots pine (autochthonous pine species) trees was conducted using the dendrochronological method in order to identify the differences between the species in terms of the influence of climatic variables on the tree ring formation. Trees were sampled in five experimental areas or five sites. The first site had a Scots pine stand, while the second had an Austrian pine stand, and the other three sites had mixed stands of Scots and Austrian pine. Cross-dating was conducted using visual on-screen techniques of CDendro software and statistical methods using Cofecha software. The tree ring series were standardized using the Arstan program and cubic smoothing spline. It produced Scots pine regional chronology, 145 years long (1870-2014), and Austrian pine regional chronology, 180 years long (1835-2014). Correlation analysis of the relationship between the index of tree-ring width and precipitation and temperature in the characteristic periods of the year showed a negative effect of temperature (except in winter months) and a positive effect of precipitation on the tree ring formation. The statistically significant dependence of the tree-ring width index on the SPEI indices indicates a significant impact of moisture deficiency on the tree ring formation in the period from June to August (r = 0.33 in June, r = 0.45 in July and r = 0.47 in August) for Scots pine and in the period from June to September (r = 0.36 in June, r = 0.43 in July, r = 0.47 in August and r = 0.30 in September) for Austrian pine. The analysis of the relationship between climatic parameters and the chronologies of Scots and Austrian pine shows similar relationships between radial growth and climate but the influence of climate is somewhat more pronounced in Austrian pine. In the study area, the radial growth of both tree species is significantly determined by climate conditions. In other words, the chronology of these species has a good climatic signal, especially the drought signal in the summer months.

Tracheidogram’s Classification as a New Potential Proxy in High-Resolution Dendroclimatic Reconstructions

Quantitative wood anatomy (QWA) is widely used to resolve a fundamental problem of tree responses to past, ongoing and forecasted climate changes. Potentially, QWA data can be considered as a new proxy source for long-term climate reconstruction with higher temporal resolution than traditional dendroclimatic data. In this paper, we considered a tracheidogram as a set of two interconnected variables describing the dynamics of seasonal variability in the radial cell size and cell wall thickness in conifer trees. We used 1386 cell profiles (tracheidograms) obtained for seven Scots pine (Pinus sylvestris) trees growing in the cold semiarid conditions of Southern Siberia over the years 1813–2018. We developed a “deviation tracheidogram” approach for adequately describing the traits of tree-ring formation in different climate conditions over a long-term time span. Based on the NbClust approach and K-means method, the deviation tracheidograms were reliably split into four clusters (classes) with clear bio-ecological interpretations (from the most favorable growth conditions to worse ones) over the years 1813–2018. It has been shown that the obtained classes of tracheidograms can be directly associated with different levels of water deficit, for both the current and previous growing seasons. The tracheidogram cluster reconstruction shows that the entire 19th century was characterized by considerable water deficit, which has not been revealed by the climate-sensitive tree-ring chronology of the study site. Therefore, the proposed research offers new perspectives for better understanding how tree radial growth responds to changing seasonal climate and a new independent proxy for developing long-term detailed climatic reconstructions through the detailed analysis of long-term archives of QWA data for different conifer species and various forest ecosystems in future research.

Variability in Growth Patterns and Tree-Ring Formation of East European Scots Pine (Pinus sylvestris L.) Provenances to Changing Climatic Conditions in Lithuania

An increase in the mean monthly temperature in July and a lack of precipitation during the vegetation period will cause an increase in the frequency and severity of droughts during the vegetation period in Lithuania. Thus, the aim of this study was to assess the growth response to climate change of East European pine provenances in Lithuania. The research was performed based on a long-term pine provenance experiment that was established in 1975 in Lithuania. The results showed that central populations demonstrated the same or better survival and growth results compared with western populations that also included local Lithuanian provenances. Even though southern populations were characterized by the same productivity, their low survival rate suggests a negative introduction effect. Analysis of temporal variation in climate sensitivity showed a higher resistance of central and southern Scots pine provenances to the negative climatic changes, compared to the western provenances. Provenances from the central, southern and especially western locations demonstrated an increasing statistically significant negative effect of monthly temperatures in July. Additionally, provenances from western locations were more sensitive to precipitation amounts, water balance and droughts in June and July. Considering that central and southern provenances demonstrated the consistent effect of growth tolerance, the incorporation of the genetic material from the southern part of European Russia and Ukraine into local breeding programs of Scots pine might amplify positive effects of the transfer. Moreover, knowledge gaps remain regarding the growth performance of Scots pine provenances that originated from central or western European regions. Thus, Scots pine origins from Poland and the northeastern part of Germany should be included in Lithuanian provenance experiments.

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

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

495-Year Wood Anatomical Record of Siberian Stone Pine (Pinus sibirica Du Tour) as Climatic Proxy on the Timberline

The application of quantitative wood anatomy (QWA) in dendroclimatic analysis offers deep insight into the climatic effect on tree-ring formation, which is crucial in understanding the forests’ response to climate change. However, interrelations between tree-ring traits should be accounted to separate climatic signals recorded during subsequent stages of cell differentiation. The study was conducted in the South Siberian alpine timberline on Pinus sibirica Du Tour, a species considered unpromising in dendroclimatology. Relationships between tree-ring width, cell number N, mean and maximum values of radial diameter D, and cell wall thickness (CWT) were quantified to obtain indexed anatomical chronologies. Exponential functions with saturation D(N) and CWT(N) were proposed, which explained 14–69% and 3–61% of their variability, respectively. Indexation unabated significance of the climatic signals but separated them within a season. Analysis of pointer years and climatic extremes revealed predominantly long-term climatogenic changes of P. sibirica radial growth and QWA and allowed to obtain QWA-based 11-year filtered reconstructions of vegetative season climatic characteristics (R2adj = 0.32–0.66). The revealed prevalence of low-frequency climatic reactions is probably explained by a strategy of slow accumulation and utilization of resources implemented by P. sibirica. It makes this species’ QWA a promising proxy for decadal climatic variations in various intra-seasonal timeframes.

TRANSPIRATION RATE OF SCOTS PINE TREES ON VERY OLIGOTROPHIC SOILS OF NORMAL MOISTURE IN RELATION TO DIFFERENT METEOROLOGICAL CONDITION

Continuous monitoring of the tree ring formation and transpiration throughout the year is crucial for understanding the tree reaction to changes in meteorology, and evaluating its adaptiveness to recent environmental changes. Data were collected from four Pinus sylvestris L. trees which sapflow was measured by the heat wave propagation method using SFM1 sensors (ICT International, Australia) and annual tree stem increment by electronic dendrometer DRL26. Investigation was performed in middle age pine stand on very oligotrophic soil. Meteorological data revealed that 2019 was the year of drought. In this year pine transpiration rate and volume increment were the lowest. However, water was used most efficiently, which means that pines needed less water to produce 1 cm3 of wood. 2020 was characterized as a year of recovery of moisture regime, when during vegetation precipitation increased up to long term value and the mean air temperature was the lowest. Annaul volume increment of pine trees in this year was the biggest, transpiration rate the highest, but WUE was the smallest, indicating that pine used more water to produce 1 cm3 of wood. Obtained data on WUE during different growing season revealed that Scots pine trees are well adapted to recent meteorological condition. Increase in tree diameter reduced values of Scots pine WUE, what means that bigger pine trees used significantly less water to produce 1 cm3 of wood

Teleconnections and edaphoclimatic effects on tree growth of Cedrela odorata L. in a seasonally dry tropical forest in Brazil

The Seasonally Dry Tropical Forests (SDTF) present very high biodiversity and a number of tree species that are adapted to prolonged periods of water stress. Considering tree ring formation is mainly driven by seasonal variation in precipitation in tropical environments, tree-ring studies from STDF can provide important contributions to understanding how these forests are responding to climate variations. In the present study, we demonstrate the influence of edaphoclimatic variables (precipitation, air temperature and soil water deficit-SWD) and the ocean teleconnections (Tropical Southern Atlantic-TSA, Atlantic Multidecadal Oscillation-AMO, Western Hemisphere Warm Pool-WHWP and El Niño 3.4) on Cedrela odorata L. growth from a SDTF of northeastern Brazil. We used standard dendrochronological methods to develop an 89-year-long ring-width index chronology. The climate sensitivity of C. odorata was assessed through Pearson's correlation tests and linear regressions, which allowed to identify the determinant months (cause-effect) of each variable on the chronology. Tree growth was positively correlated with precipitation and negatively correlated with air temperature and SWD, particularly during the rainy season (March to August). In parallel, we identified that extremely dry years can contribute to missing rings, exposing the lack of growth in C. odorata caused by water stress. Among the oceanic variables, all of them showed a negative effect on radial growth of C. odorata, except for TSA, which had no significant effect. Tree growth is constrained in years with strong El Niño and high values of AMO index during the rainy months (May, June and October). However, the WHWP showed a more pronounced negative effect in the beginning of the dry season (September). Our findings add valuable information on C. odorata responses to hydrological seasonality from SDTF and the fluctuations in oceanic teleconnections, which in turn, influence the rainfall dynamics in northeastern Brazil.

Exploring wood anatomy, density and chemistry profiles to understand the tree-ring formation in Amazonian tree species

Long-term analysis of tree growth using annual tree rings is increasingly in demand for tropical tree species. The basis of these studies has traditionally been the anatomical identification of the annual ring boundary. However, the structure of these annual rings has been sparsely explored for complementary physical and chemical wood traits. Here, we explore the relationships among wood density features and chemical elements (S, K, Ca, Mn) involved in the annual tree ring formation of 12 tropical tree species from non-flooded forest in the southern Amazon basin. Transverse wood sections were used for each species to determine: 1) macroscopic distinction (radial growth and wood density), 2) microscopic analyse of vessels, axial and ray parenchyma (anatomy) and 3) X-ray densitometry (physical) and X-ray fluorescence (chemical). For some species, the profiles of wood density, and Ca and Mn content showed intra- and inter-annual patterns that allowed to define and characterize the growth boundary of tree rings. Ca, K and S were mainly distributed in axial parenchyma cells, and around vessels, whereas, Mn was mainly distributed in fibres. Our results showed significant species-specific correlations between tree-ring width, density and concentrations of Ca, K and Mn. The anatomical characterization and the complementary information provided by the density and chemical profiles in some Amazonian species can represent a valuable proxy to improve the definition of annual ring-boundaries and improve the understanding of long-term growth and physiological patterns.

The buffering effect of the Lake Baikal on climate impact on Pinus sylvestris L. radial growth

Large lakes and wetlands control local and regional climate conditions. Since climate controls tree-ring formation, it is expected that air-water-land interaction at Lake Baikal region (southern Siberia), the world's largest freshwater reservoir, could potentially impact tree growth in the surrounding areas. Therefore, we aimed to determine if Lake Baikal influences Pinus sylvestris L. tree-ring growth by modifying climate conditions and alleviating climate limiting factors of tree growth in its neighboring areas. Here we combine dendrochronological measurements with tree growth modeling to evaluate the variability in the climate response of Scots pine annual (tree-ring width) and intra-annual (earlywood and latewood widths) growth and phenology at four sites (two inland and two coastal sites) in the Baikal region for the 1960–2016 period. Tree growth was significantly higher, with longer growing seasons, at the inland sites than at coastal sites. However, an increasingly negative effect of summer temperature and a positive effect of relative humidity on tree-ring growth were observed with increasing distance to the lake. The results suggest that although Lake Baikal's thermal mass lessens the climate control on the tree growth by acting as a thermal and hydric buffer in the downwind coastal sites, other factors than climate might potentially control tree growth in the region. Our results also suggest that the high plasticity of P. sylvestris to thrive in different environmental conditions will probably allow a better adaptation to the projected warmer regional climate than non-drought tolerant species inhabiting the same region.

Intra- and Inter-Annual Growth Patterns of a Mixed Pine-Oak Forest under Mediterranean Climate

Temperature and precipitation variability throughout the year control the intra-annual dynamics of tree-ring formation. Physiological adaptation of trees to climate change is among the key issues to better understand and predict future forest performance and composition. In this study, we investigated the species’ coexistence and performance of Scots pine and pubescent oak growing in a mixed sub-Mediterranean forest in the northeast of the Iberian Peninsula. We assessed intra-annual cumulative growth patterns derived from band dendrometers during four consecutive growing seasons and long-term changes in basal area increment for the period 1950–2014. Our results revealed that Scots pine followed an intra-annual bimodal growth pattern. Scots pine growth was mainly limited by water availability at intra-annual, interannual and decadal time scales, which resulted in a negative long-term growth trend. Conversely, oak displayed a unimodal growth pattern, which was less climatically constrained. A significant increase in basal area of oak denotes an overall better potential acclimation to prevailing climatic conditions at the expenses of a higher risk of physiological failure during extreme climate events.

Hillslope Processes Affect Vessel Lumen Area and Tree Dimensions.

The height growth of the trees depends on sufficient mechanical support given by the stem and an effective hydraulic system. On unstable slopes, tree growth is affected by soil pressure from above and potential soil erosion from below the position of tree. The necessary stabilization is then provided by the production of mechanically stronger wood of reduced hydraulic conductivity. Unfortunately, the interaction between tree growth (both radial and axial) and stabilization in the soil is still insufficiently understood. Therefore, in this study, we aimed to quantify the impact of hillslope dynamics on the degree of tree growth and hydraulic limitation, and the potential effect on tree height growth and growth plasticity. To evaluate this effect, we took four cores from 80 individuals of Quercus robur and Fraxinus excelsior and measured tree-ring widths (TRWs) and vessel lumen areas (VLAs). The tree heights were evaluated using a terrestrial laser scanner, and local soil depth was measured by a soil auger. Our data showed a significant limitation of the tree hydraulic system related with the formation of eccentric tree-rings. The stem eccentricity decreased with increasing stem diameter, but at the same time, the negative effect of stem eccentricity on conduit size increased with the increasing stem diameter. Even though this anatomical adaptation associated with the effect of stem eccentricity differed between the tree species (mainly in the different degree of limitations in conduit size), the trees showed an increase in the proportion of hydraulically inactive wood elements and a lowered effectiveness of their hydraulic system. In addition, we observed a larger negative effect of stem eccentricity on VLA in Quercus. We conclude that the stabilization of a tree in unstable soil is accompanied by an inability to create sufficiently effective hydraulic system, resulting in severe height-growth limitation. This affects the accumulation of aboveground biomass and carbon sequestration.

Scots pine’s capacity to adapt to climate change in hemi-boreal forests in relation to dominating tree increment and site condition

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.

Wood anatomy and tree growth covary in riparian ash forests along climatic and ecological gradients

Riparian ash forests subjected to seasonal drought are among the most endangered ecosystems in Europe. They are threatened by climate warming causing aridification and by land-use changes modifying river flow. To assess the impacts of these two stress factors on riparian forests, we studied radial growth and xylem anatomical traits in five narrow-leaved ash (Fraxinus angustifolia) stands across wide climatic and ecological gradients from northern Italy to southern Portugal. Radial growth rates and earlywood hydraulic diameter (Dh) were directly correlated, whilst earlywood vessel density and growth rates were inversely associated. Ash growth positively responded to precipitation. Higher and lower rates of growth increase in response to precipitation were found in dry (annual precipitation 357–750 mm, annual water balance −39 to −48 mm) and wet (annual precipitation 1030 mm, annual water balance 27 mm) sites, respectively. Wet conditions in autumn and winter of the year prior to tree-ring formation lead to larger Dh values, except in the wet site where warmer conditions from prior autumn to current spring were positively associated to wider vessels. Growth was also enhanced by a higher river flow, reflecting higher soil moisture due to elevated groundwater table levels. Peaks in river flow from late winter to early spring increased Dh in dry-continental sites. Growth and potential hydraulic conductivity in drought-prone riparian ash forests are differently impacted by climate variability and river flow depending on site and hydrological conditions. Nevertheless, covariation between radial growth and the earlywood vessel diameter was found, regardless of site specific differences. Wood production and hydraulic conductivity are coordinated through the production of large earlywood vessels which may allow reaching higher growth rates.

A novel tight cylindrical mold for epoxy resin embedding allows enhanced microscopic analysis of microcores extracted from woody plants

A novel mold was devised to embed microcores extracted from stems of trees in epoxy resin, which has been widely used for optical and electron microscopic analysis of xylem formation. The embedding mold of a tight cylindrical shaped tube was designed to avoid displacement of microcores from the right position during the process of resin embedding. Microcores of a ring-porous hardwood species, Quercus crispula, with higher wood density and much larger differentiating vessel elements laid down on the boundary between the current xylem and the previous one, which generally cause difficulty in thin sectioning and breaks in sections, respectively, were embedded in the cylindrical molds full of epoxy resin. Locations of the three principal planes of wood anatomy could be determined in cylindrical resin-embedded microcores as follows: the transverse plane could be found on their side of cylinder, the radial one was vertical to the transverse, and the tangential ones were their circular ends of cylinder. The present embedding mold, therefore, can provide all three principal sections for microscopic wood anatomy from the side or ends of the same cylindrical microcore in principle. To confirm the usefulness of the resin-embedded microcores, we examined the differentiation of vessel elements during the period of earlywood formation on their transverse sections under microscopes, consequently could observe cell division in the cambial zone and sequential stages of vessel element differentiation, including cell expansion and deposition of the secondary cell wall. The present embedding mold for epoxy resin is simple but highly useful and innovative for a wide range of applications of microcores in microscopy for studies on tree-ring formation.

Intra-Annual Variation of Stem Circumference of Tree Species Prevailing in Hemi-Boreal Forest on Hourly Scale in Relation to Meteorology, Solar Radiation and Surface Ozone Fluxes

(1) Background: Continuous monitoring of the tree stem increment throughout the year is crucial for the understanding of trees’ reactions to changes in meteorology, solar radiation and surface ozone and evaluating the adaptive capacity of prevailing tree species to recent environmental global changes; (2) Methods: Data on tree intra-annual sequences based on electronic dendrometer data of Picea abies (L.) Karst, Pinus sylvestris L., Betula pendula, and Betula pubescens, growing under different nutritional and humidity conditions in the north-eastern part of Lithuania, together with their stem sap flow intensity, common meteorology and O3 fluxes, were used to meet the objectives of the study; (3) Results: Stem shrinking/contraction during the day, due to transpiration, and the swelling/expansion during the night was significantly related to meteorology, sun activity and O3 flux intensity. These variations were negatively related to current time and temperature, but positively to precipitation and relative humidity. O3 fluxed through the stomata stimulated the shrinking process more intensively than it inhibited the swelling process, but only for pine and birch trees. Spruce trees demonstrated the highest sensitivity to O3 impact due to its significant effect on the stem swelling process. Pine trees were less sensitive to O3 damages and birch trees were the least sensitive. An over-moisture regime at measoeutrophic organic soil forest site increased the significance of the effect of O3 on the tree increment of the considered tree species; (4) Conclusion: The most intensive tree ring formation of Scots pine trees in relation to recent environmental changes indicated their high resiliencies and adaptations to a local specific condition. Reduced tree growth intensity and weak relationships between the birch tree radios increment and main meteorological parameters indicated the lowest adaptive capacity of this tree species to recent environmental changes.

An Analysis of Atlantic White Cedar (Chamaecyparis thyoides (L.) B.S.P.) Tree Rings as Indicators of Ghost Forest Development in a Globally Threatened Ecosystem

Atlantic White Cedar (AWC) swamps are a globally threatened type of wetland ecosystem and are a new form of ghost forest in the mid-Atlantic region of the US. Hydrogeomorphic regimes foster peat formation, resulting in unique biodiversity and carbon sequestration services. Our sites include regimes that are exposed to sea-level rise and storm-driven seawater intrusion, yet other sites are protected by higher elevations. In this study, we evaluated climatic variables to discern differences in tree ring formation as an indicator of growth among nine stands including micro-tidal, oligohaline sites as well as other protected areas which served as a control. Standard dendrochronological techniques were used, and series were divided into two sub-chronologies, 1895 to 1971 (early) and 1972 to 2018 (recent). AWC growth in response to precipitation parameters, e.g., Palmer Drought Severity Index (PDSI), were largely non-significant but were somewhat reversed among sub-chronologies. Early correlations were primarily negatively correlated with PDSI, while recent correlations were mostly positive, which suggests that even though inundation may reduce photosynthate availability for growth, precipitation has begun to increase growth by alleviating osmotic and toxic stresses associated with seawater. Analysis of climatic variables and tree growth at the reference site found that other anthropogenic stressors associated with ditching exert a greater influence. Hurricane impacts on tree growth exhibited no lasting negative effects; however, an AWC ghost forest report from New Jersey connected mortality to a hurricane. Hydrogeomorphic regimes may delay rather than eliminate risks associated with sea-level rise and storm-driven seawater.

Tree-rings, genetics and the environment: Complex interactions at the rear edge of species distribution range

Under climate change, modifications on plants’ growth are expected to be the strongest at species margins. Therein, tree acclimation could play a key role as migration is predicted to be too slow to track shifts of bioclimatic envelops. A requirement is, however, that intra-population genetic diversity be high enough for allowing such adaptation of tree populations to climate change. In this study, we tested for the existence of relationships between genetic diversity, site environmental conditions, and the response of annual tree growth to climate of Pinus cembra at its southern limit in the Alps. Site-specific climatic and environmental factors predominantly determined the response of trees along the precipitation gradient. The growth-climate interactions were chiefly linked to mean annual precipitation and temperature, slope and tree-size, and less to genetic diversity. We show that genetic background of Pinus cembra has exclusively indirect modulating power with limited effects on tree-ring formation, and within the southern limit in the Alps, genetic variability is not necessarily well expressed in the patterns of annual tree growth. Our results may imply little adaptive capacity of these populations to future changes in the water balance.

The greening effect characterized by the Normalized Difference Vegetation Index was not coupled with phenological trends and tree growth rates in eight protected mountains of central Mexico

In temperature-limited ecosystems such as high-elevation forests, rising temperatures and increasing carbon dioxide can result in a greening effect and changes in the phenology of the forests. Up to now, phenological metrics of subtropical high-elevation forests remain primarily unquantified, which strongly limits a global comprehension of climate change impacts. We assessed the long-term trend dynamics (greenness and land surface phenology) using the Normalized Difference Vegetation Index (NDVI) and compared them with data from an existing dendrochronological network that came from eight protected mountains in the Trans-Mexican Volcanic Belt in central Mexico during the last 20 yr (2000–2019). We found three main NDVI clusters reflecting a longitudinal geographical pattern (Pacific, Center, and the Gulf of Mexico). A notable greening effect at the canopy level was seen for all mountains (up to 23.8% increase concerning the year 2000). Nevertheless, the NDVI trends were not uniform, and they differed along an elevation gradient with the highest increases at the bottom. Minimum temperature and soil moisture positively impacted the NDVI time series and explained up to 87% of the variance, while maximum temperature negatively affected. Regarding phenological metrics, the start, and end of the growing season were the day of the year 148 ± 20 (late-May) and 9 ± 12 (early-January), respectively, with an average length of 226 ± 33 d, differing from previous studies related to annual tree-ring formation. We did not see a later or earlier start of either the spring or the fall, which partially refutes the hypothesis that the growing season extended despite the increase in temperature. Finally, our investigation revealed that the common greening effect was not parallel with radial growth trends, except for the wettest site from the Gulf of Mexico cluster, and partially related to the forest management strategies. Further modelling of regional phenology coupled with more intensive tree-ring monitoring is needed to explain the factors that mediate the processes of photosynthesis (NDVI) and storage of carbon (tree-ring formation) under a global warming outlook.