Intra-annual Density Fluctuations Frequency Research Articles

Influence of monsoon anomalies on intra-annual density fluctuations of Chinese pine in the Loess Plateau

In the past few decades, the East Asian summer monsoon (EASM) has experienced an unprecedented weakening, exacerbating drought in northern China, especially in the monsoon margin area. Improving our understanding of monsoon variability will benefit agricultural production, ecological construction, and disaster management. Tree-ring is widely used as proxy data for extending the monsoon history. However, in the East Asian monsoon margin, the tree-ring width were mostly formed before the rainy season, thus may have limited ability to indicate the monsoon variability. Intra-annual density fluctuations (IADFs) can provide higher resolution information on tree growth as well as evidence of short-term climate events. Here, we used Chinese pine (Pinus tabuliformis Carr.) samples from the eastern edge of the Chinese Loess Plateau (CLP), where the climate is deeply affected by monsoon, to investigate the response of tree growth and IADFs frequency to climate variation. We show that tree-ring width and IADFs record significantly different climatic signals. The former was mainly affected by moisture conditions at the end of the previous growing season and the current spring. While the latter was common in years when severe droughts occurred in June and July, especially in June. This period coincides with the onset of the EASM, so we further analyzed the relationship between IADFs frequency and the rainy season. Both correlation analysis and the GAM model suggest that the frequent occurrence of IADFs may be related to the late start of the monsoon rainy season, meaning that we have found a new indicator in tree-ring records that can capture monsoon anomalies. Our results provide further insight into drought variation in the eastern CLP, which also implicates the Asian summer monsoon dynamic.

Intra-annual density fluctuations in silver fir are triggered by drought conditions

Key messageIn Abies alba Mill. (silver fir), the frequency of intra-annual density fluctuations (IADFs) increases along the latitudinal transect, from North to South, is higher in pure than in mixed stands, and their formation is linked to spring and/or summer drought conditions.Trees respond to climate, recording information in tree rings and their anatomical features, such as IADFs. The IADFs are regions within the tree ring where density changes in response to tree physiological processes and environmental conditions. The objective of this study was to assess the effect of different forest-stand structures and of climate on IADF formation and frequency in populations of silver fir along a latitudinal gradient in Italy (Trentino, Molise and Calabria regions). In doing so, we aimed to compare the frequency of IADFs in pure or mixed stands and to understand the ability of silver fir to cope with environmental fluctuations. Results showed higher frequency of IADFs in pure than mixed stands (in Trentino and Calabria) and in younger trees (namely in the pure stand in Calabria), because of the higher sensitivity to environmental variability. The formation of IADFs in silver fir emerged as a response to cope with drought. Summer precipitation (both pure and mixed stands in Trentino) and early spring/summer (both pure and mixed stands in Calabria) played a key role in the formation of IADF-type E+. The formation of IADF-type L+, on the other hand, was related to temperature/precipitation in late summer and early autumn (both pure and mixed stands in Molise) and to precipitation in summer (pure stand in Calabria). Our findings support the theory that IADFs are an important structural/functional mechanism for responding to climate fluctuations.

Xylem Plasticity in Pinus pinaster and Quercus ilex Growing at Sites with Different Water Availability in the Mediterranean Region: Relations between Intra-Annual Density Fluctuations and Environmental Conditions

Fluctuations in climatic conditions during the growing season are recorded in Mediterranean tree-rings and often result in intra-annual density fluctuations (IADFs). Dendroecology and quantitative wood anatomy analyses were used to characterize the relations between the variability of IADF traits and climatic drivers in Pinus pinaster Aiton and Quercus ilex L. growing at sites with different water availability on the Elba island in Central Italy. Our results showed that both species present high xylem plasticity resulting in the formation of L-type IADFs (L-IADFs), consisting of earlywood-like cells in latewood. The occurrence of such IADFs was linked to rain events following periods of summer drought. The formation of L-IADFs in both species increased the hydraulic conductivity late in the growing season, due to their larger lumen area in comparison to “true latewood”. The two species expressed greater similarity under arid conditions, as unfavorable climates constrained trait variation. Wood density, measured as the percentage of cell walls over total xylem area, IADF frequency, as well as conduit lumen area and vessel frequency, specifically in the hardwood species, proved to be efficient proxies to encode climate signals recorded in the xylem. The response of these anatomical traits to climatic variations was found to be species- and site-specific.

Intra-annual density fluctuations (IADFs) inPinus nigra(J. F. Arnold) at high-elevation in the central Apennines (Italy)

Although wood anatomical features can provide yearly resolved climatic information at sub-seasonal resolution, the occurrence of intra-annual density fluctuations (IADFs) might be triggered by several abiotic factors under different ecological settings. Here, we use information on cambial age and tree-ring width to standardize the frequency of IADFs in European black pines from three different mountain slopes in the central Apennines (Italy). At each site, we sampled isolated 15–30-year pioneer pines above the forest limit, as well as close-grown 40–60-year planted pines at the forest limit. Mainly restricted to the latewood of both pioneer and planted trees, the occurrence of IADFs reveals a significant positive relationship with cambial age and ring width. Although the standardized IADFs are well synchronized between the planted and pioneer pines, the frequency of IADFs in narrow rings was higher in the pioneer pines. Drought conditions in July and August are responsible for the highest IADFs frequency in planted and pioneer pines, respectively. Our study underlines the value of IADFs to obtain a more nuanced understanding of the climatic drivers of wood formation at the intra-annual scale.

Wood Growth in Pure and Mixed Quercus ilex L. Forests: Drought Influence Depends on Site Conditions.

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.

Effect of provenance and climate on intra-annual density fluctuations of Norway spruce Picea abies (L.) Karst. in Poland

Understanding the growth pattern of trees of various provenances in response to climatic conditions provides information on the adaptive potential of trees. Intra-annual density fluctuations (IADFs) are anatomical markers of variations in wood density within the annual wood increment. Latewood-like cells within earlywood, resulting from severe drought during spring and early summer, express the structural adaptation of the wood tissue to unfavorable climatic conditions. In this study, we used two 40-year old IUFRO provenance trials of Norway spruce located in the western and north-eastern Poland to i) determine the effect of provenance on the IADF frequency and ii) to define the climatic factors determining the formation of IADF. Three highly polymorphic nuclear microsatellites are used to determine the differentiation among provenances in particular between the northern and southern Polish distribution area.Our results demonstrate that the frequency of all types of IADFs is determined by the growing conditions, and only the IADFs in the transition zone are determined by provenance origin. The highest variability between provenances in response to climatic differences was observed for IADF in transition zone, where temperatures and rainfall of spring and early summer differentiated northern and southern provenances. Moreover, the IADF frequency was influenced by drought, thereby differentiating provenances in terms of their sensitivity to severe conditions. Furthermore, environmental differentiation of climate-growth reaction was expressed by a stronger impact of climatic conditions observed in the western than in the northeastern trial site.The results of this study confirm the dependency of climate related changes in wood characteristics on provenance origin. Therefore, density fluctuations seem to be an appropriate adaptive trait for selecting Norway spruce provenances with varying degree of drought sensitivity.

Wood-trait analysis to understand climatic factors triggering intra-annual density-fluctuations in co-occurring Mediterranean trees

ABSTRACTMediterranean trees and shrubs form intra-annual density fluctuations (IADFs) in tree rings as a sign of their plasticity in wood formation in response to intraseasonal variations of environmental conditions. Different species show a different aptitude to form IADFs, due to their diverse ability to cope with climate stressors, since the occurrence of IADFs may affect plant hydraulics. Dendroecology and quantitative wood anatomy were used to characterise IADFs in Pinus pinea and Arbutus unedo co-occurring at a Mediterranean site in Italy. The relations between climate parameters (i.e. temperature and precipitation) and intra-annual tree-ring traits (i. e. IADF frequency and conduit size) were analysed to highlight the main triggers for IADF formation and their functional role.Data showed that both species are characterised by a high plastic response to climate and formed a high frequency of L-IADFs (occurrence of earlywoodlike conduits in latewood). The two species, although forming the same type of IADFs, showed different sensitivity to environmental factors. Pinus pinea showed a high dependence of tracheid size on temperature, while Arbutus unedo was more sensitive to precipitation in spring and autumn. Arbutus unedo promptly developed more than one IADF per year in response to rainfall events following drought periods.The overall results were useful to compare the aptitude of the two species in forming IADFs and to highlight the factors priming their formation. This is useful to understand wood growth reactions to environmental drivers and to evaluate the adaptive capabilities in these two species, and thus to predict forest reactions after climate changes.

Linking fungal dynamics, tree growth and forest management in a Mediterranean pine ecosystem

Fungal dynamics are a key component of forest ecosystem functioning. Understanding the links between stand dynamics and mushroom productivity together with the impact of anthropogenic disturbance (i.e., forest management) is necessary to provide further insight into plant-soil interactions in forest ecosystems. The aim of this research was to shed light on the relationship between tree growth and mushroom yield of ectomycorrhizal (ECM) and saprobic fungi in a Mediterranean forest ecosystem. We hypothesized that: (i) increased tree growth is linked to higher ECM mushroom yield arising from increased carbohydrate allocation to ECM fungi; (ii) saprobic mushroom yield is less dependent on tree growth patterns; and (iii) mushroom yields can be predicted based on certain wood-anatomical features. The study area was a Mediterranean Pinus pinaster forest located in northeastern Spain. Mushroom yield data were measured from 2008 to 2014 in 27 permanent plots within a thinning experiment. Dendrochronological analyses were conducted in each plot to characterize and quantify seasonal radial growth (earlywood and latewood width) and the frequency of latewood intra-annual density fluctuations (IADFs). Spearman correlation and “Gleichläufigkeit” (GLK) analyses were conducted to detect significant correlations and to quantify the synchrony between tree-ring features and ECM and saprobic mushroom yield patterns, the latter being used as a benchmark to better assess the relationships between tree growth and ECM fungi. To further inspect tree growth-mushroom yield relationships, mixed-effects models using dendrochronological variables as predictors were fitted to annual ECM and saprobic mushroom occurrence and yield data. We observed that the latewood IADFs frequency was the best predictor of ECM mushroom yield, i.e., better than early- or latewood width. The analysis also revealed that not only the precipitation of late summer and early autumn, but also forest thinning effects, were mediating the relationship between tree growth and ECM mushroom production. We found 2-year lagged effects between the current saprobic mushroom production and latewood width, whereas ECM mushroom yield was more correlated with current latewood production. The models presented in this study may be used to reconstruct mushroom production along historical periods based on dendrochronological information, but also to predict future mushroom yield based on climate-sensitive tree and stand growth predictions.

Climatic Signals from Intra-annual Density Fluctuation Frequency in Mediterranean Pines at a Regional Scale.

Tree rings provide information about the climatic conditions during the growing season by recording them in different anatomical features, such as intra-annual density fluctuations (IADFs). IADFs are intra-annual changes of wood density appearing as latewood-like cells within earlywood, or earlywood-like cells within latewood. The occurrence of IADFs is dependent on the age and size of the tree, and it is triggered by climatic drivers. The variations of IADF frequency of different species and their dependence on climate across a wide geographical range have still to be explored. The objective of this study is to investigate the effect of age, tree-ring width and climate on IADF formation and frequency at a regional scale across the Mediterranean Basin in Pinus halepensis Mill., Pinus pinaster Ait., and Pinus pinea L. The analyzed tree-ring network was composed of P. pinea trees growing at 10 sites (2 in Italy, 4 in Spain, and 4 in Portugal), P. pinaster from 19 sites (2 in Italy, 13 in Spain, and 4 in Portugal), and P. halepensis from 38 sites in Spain. The correlations between IADF frequency and monthly minimum, mean and maximum temperatures, as well as between IADF frequency and total precipitation, were analyzed. A significant negative relationship between IADF frequency and tree-ring age was found for the three Mediterranean pines. Moreover, IADFs were more frequent in wider rings than in narrower ones, although the widest rings showed a reduced IADF frequency. Wet conditions during late summer/early autumn triggered the formation of IADFs in the three species. Our results suggest the existence of a common climatic driver for the formation of IADFs in Mediterranean pines, highlighting the potential use of IADF frequency as a proxy for climate reconstructions with geographical resolution.

Are wood fibres as sensitive to environmental conditions as vessels in tree rings with intra-annual density fluctuations (IADFs) in Mediterranean species?

Wood fibres are as sensitive to environmental conditions as vessels in tree rings with intra-annual density fluctuations (IADFs) in Mediterranean species. Forecasted environmental changes are likely to increase the frequency of intra-annual density fluctuations (IADFs) in Mediterranean tree rings. The interpretation of intra-annual anatomical variability of tree rings with IADFs can be useful to understand plant-growth response to environmental changes with seasonal resolution. We analysed the intra-annual variability of quantitative traits of both vessels and fibres in the woods of Arbutus unedo L. and Erica arborea L. to compare the sensitivity of different cell types to environmental variations. We applied digital image analysis on microphotographs of semi-thin sections of tree rings formed at sites with different soil water availability. Wood of both species showed good adaptability that allows anatomical traits of vessels and fibres to be harmonised by changing the water transport capacity and wood strength, promoting the efficiency or safety of water transport according to water availability during wood formation. The size of fibres showed trends of variation similar to vessels. Not all parameters of vessels were accurate indicators of the IADF presence. In conclusion, parameters of fibres, which offer advantages during automatic measurement, showed the same sensitivity to environmental fluctuations as vessels. Thus, they could be good indicators of summer drought to describe and interpret the ecological meaning of IADFs in tree rings.

Climatic signals of tree-ring width and intra-annual density fluctuations in Pinus pinaster and Pinus pinea along a latitudinal gradient in Portugal

Tree-ring width integrates the prevailing environmental conditions during the whole growing season (annual resolution). Other wood anatomical traits, like intra-annual density fluctuations (IADFs), imprint environmental conditions within the growing season (sub-annual resolution). IADFs are anatomically characterized by latewood-like cells within earlywood or earlywood-like cells within latewood. Under climate change scenarios, it is increasingly important to understand which traits are more relevant in the adjustment of long-lived species. We established a latitudinal transect along Portugal and compared tree-ring width and the frequency of IADFs in Pinus pinaster growing under temperate and Mediterranean climate, and of P. pinaster and P. pinea growing under Mediterranean climate. Pinus pinaster growing under temperate and Mediterranean climate showed similar correlations between climate and tree-ring width, whereas P. pinaster and P. pinea under Mediterranean climate presented a different pattern of climate–growth correlations. We therefore suggest that the climate–growth response is species dependent. However, the climate–IADFs correlation was driven by site conditions and less related to the species. We propose that the correlations between climate and growth are conserved within the distribution range of a species, whereas IADFs function as a finer morphological adjustment to the environmental conditions during the growing season.

Age, climate and intra-annual density fluctuations in Pinus halepensis in Spain

Intra-annual density fluctuations (IADFs) in tree rings of Aleppo pine (Pinus halepensis) are considered to be among the most promising wood anatomical features in dendrochronological studies. They provide environmental information in addition to those obtained from tree-ring widths. We used a network of 35 sites in Spain, ranging from nearly desert to temperate climate. We analysed tree-ring series of 529 trees to study IADF frequencies, and their dependence on climatic factors and cambial age. The results showed that IADF frequency is age dependent, with its maximum at the cambial age of 27 years (evaluated at breast height). The frequencies varied across the network and at different sites we recorded that 0.3% to 33% of the analysed tree rings contained IADFs. They were more frequent where and when the temperatures were higher, summer drought was intense and autumn was the main precipitation season. IADF formation was particularly related to high minimum temperatures and wet conditions in late summer and autumn. These results suggest that IADF formation is not related to stressful conditions during summer but to favourable conditions during autumn. These conditions promote cambial reactivation and consequently formation of wider tree rings.

Tree-ring growth and intra-annual density fluctuations of Pinus pinaster responses to climate: does size matter?

Dendroclimatology generally assumes that climate–growth relationships are age and size independent. However, there is evidence that climate response can be unstable across different age/size classes. In addition, the occurrence of some anatomical features, such as intra-annual density fluctuations (IADFs), is age dependent. The present study investigates whether the climate–growth responses and the occurrence of IADFs in an even-aged stand of Pinus pinaster Ait., growing under Mediterranean climate, are also size-dependent. We randomly selected 60 P. pinaster trees falling within two stem diameter classes: small ( 35 cm). Tree rings were crossdated, measured and IADFs identified according to their position within the ring. The residual chronologies of both size classes were strongly correlated, suggesting a common signal. In fact, similar growth–climate relationships were observed in large and small trees. The frequency of IADFs was higher in large than in small trees, suggesting that IADFs were more likely to occur in wider rings of fast-growing trees. In both size classes, most of the IADFs were found in latewood. Latewood IADFs were triggered by the combination of dry June, wet September, and warm December, whereas IADFs located at the end of earlywood were triggered by previous winter precipitation and favorable conditions before summer (high precipitation for large trees and lower temperature for small trees). Our results suggest that IADFs can be a mechanism used at the individual level for adaptation to drought in P. pinaster. The climatic signal of IADFs between earlywood and latewood was mediated by stem size suggesting that future tree-ring studies should include trees stratified by size to better estimate the sensitivity of IADFs to climate.

Climatic control of intra-annual wood density fluctuations of Pinus pinaster in NW Spain

Tree rings of Pinus pinaster often contain intra-annual density fluctuations (IADFs), which have been attributed to the succession of dry and rainy periods typical of Mediterranean climate, but their formation has not been studied yet under Atlantic climate. We analyzed the occurrence and climatic significance of replicated IADFs in ten monospecific stands in NW Spain. The frequency of IADFs was higher than previously reported for this species under Mediterranean conditions and consistently decreased with increasing elevation. The formation of bands of latewood-like tracheids within the earlywood was favored by dry previous August, cold previous winter and dry April. Bands of earlywood-like tracheids within the early latewood were also favored by low winter temperatures. However, their occurrence was geographically heterogeneous, with two groups of stands being defined by their distances to the shoreline. In coastal stands, cold May–August triggered IADFs formation, while in inland stands their formation was favored by dry May–July. Regional winter temperatures and April water balance were strongly related to the East Atlantic (EA) pattern, which greatly conditioned the occurrence of IADFs in the earlywood and the early latewood. By contrast, the presence of bands of earlywood-like tracheids in the late latewood was independent of the EA pattern, being strongly related to warm conditions in spring and especially to a wet October. The link between regional climate and the EA pattern strongly controlled the physiological processes that determine intra-annual growth dynamics and short-term cell enlargement of P. pinaster in NW Spain.

Intra-annual density fluctuations of Pinus pinaster are a record of climatic changes in the western Mediterranean region

Climate projections for the Mediterranean area estimate a decline in total precipitation, warmer temperatures, and a higher frequency of extreme drought events. It is important to understand how trees respond to these climatic changes and which wood anatomical structures best document the trees’ response to those changes. The present work investigates the climatic signal of tree-ring width, latewood width, and the frequency of intra-annual density fluctuations (IADFs) during the last 100 years for Pinus pinaster Aiton growing in the western Mediterranean region. Based on meteorological data, it was observed that since the 1950s, average annual temperature and autumn and winter precipitation increased. Tree-ring width and latewood width of P. pinaster were positively correlated with winter and summer precipitation and negatively correlated with spring and summer temperatures. The frequency of latewood IADFs showed a positive and time-stable correlation with September and October precipitation. However, after the 1970s, the frequency of IADFs also became correlated with climatic conditions later in the year, specifically with the temperatures of November and December, probably because of the recent climate changes. IADFs chronologies, besides being very useful to reconstruct autumn precipitation, can add new climatic information to ring-width chronologies.

Climate and intraannual density fluctuations in Pinus pinaster subsp. mesogeensis in Spanish woodlands

Intraannual features or anomalies in the tree rings of woody species may provided useful information for ecological and climatological studies. The frequency of intraannual density fluctuations (IADFs), differences in IADFs according to the cambial age, changes in IADFs in the last century, and relationships of IADFs to radial growth and climate were analyzed in five stands of Pinus pinaster subsp. mesogeensis (Fieschi & Gaussen) Silba in east-central Spain. Standard dendrochronological techniques were used. Two cores were extracted 1.30 m above ground level from 15 dominant and codominant trees at each sampling site. The data were analyzed by analysis of variance, Pearson’s correlation, and logistic regression. Results showed that (i) the mean frequency of IADFs was higher in younger than older trees; (ii) the frequency of IADFs increased from the 1940s to the present; (iii) radial growth was negatively correlated with the presence of IADFs; and (iv) density fluctuations may be predicted by using a logistic model, with monthly rainfall and temperature as independent variables. Studies of intraannual features or anomalies in radial growth may be useful for ecological and climatological applications under forecasted climate change scenarios.

Age-dependent responses of tree-ring growth and intra-annual density fluctuations of Pinus pinaster to Mediterranean climate

Dendrochronology generally assumes that climate–growth relationships are age independent once the biological growth trend has been removed. However, tree physiology, namely, photosynthetic capacity and hydraulic conductivity changes with age. We tested whether the radial-growth response to climate and the intra-annual density fluctuations (IADFs) of Pinus pinaster Ait. varied with age. Trees were sampled in Pinhal de Leiria (Portugal), and were divided in two age classes: young ( 115 years old). Earlywood and tree-ring width of young P. pinaster trees were more sensitive to climate influence while the response of latewood width to climate was stronger in old trees. Young trees start the growing season earlier, thus a time window delay occurs between young and old trees during which wood cells of young trees integrate environmental signals. Young trees usually have a longer growing season and respond faster to climate conditions, thus young P. pinaster trees presented a higher frequency of IADFs compared with old trees. Most of the IADFs were located in latewood and were positively correlated to autumn precipitation. The radial-growth response of P. pinaster to climate and the IADFs frequency were age dependent. The use of trees with different age to create a tree-ring chronology for climate studies can increase the resolution of climatic signals. Age-dependent responses to climate can also give important clues to predict how young and old trees react to climate change.

Ecological interpretation of tree-ring width and intraannual density fluctuations inPinus sylvestrison dry sites in the central Alps and Siberia

The radial growth of Pinus sylvestris L. from nine sites at the semiarid lower forest border of the central Alps (Switzerland) and central Siberia (Russia) has been investigated using dendroecological methods. Tree growth differed according to soil substrate, with trees on dune sites showing lower mean ring widths, lower mean sensitivities, and higher autocorrelation. The relationships between climate and tree-ring width were studied using response function analysis. Independent of the climatic zone and the soil substrate, precipitation just before and at the beginning of the growing season is positively correlated with radial growth. The climatic response of dune sites is low, possibly because of the poor water-holding capacity and the high permeability of the sandy soils. Intraannual density fluctuations (IADFs) were observed at all the sites. Most IADFs were found in latewood. On dunes, fewer cores contain IADFs, and their frequency is lower. All stands showed significant relationships between IADF frequency and tree-ring width (positive) and ring age (negative). For Swiss sites, moist-cool conditions in the middle of the growing season are demonstrated as the triggering factor for IADFs. For the Russian sites, inadequate climatic data made it impossible to demonstrate any climate dependence of IADFs.