The Earth's sedimentary successions are an archive of past tectonic and climate events(1,2). The physical characteristics of the sediment record are controlled by three main factors: the sediment supply from the eroding source region, the grain size distribution of that sediment supply, and the area available for sediment accumulation in the downstream regions(3,4). The interplay of these factors can make the interpretation of a climatic or tectonic signal complex, particularly as these processes are nonlinear. Here we assess the evolution of a tectonically active landscape undergoing erosional and depositional processes, using a numerical model that incorporates variations in grain size and the volumetric sediment budget. Our simulations indicate that changes in precipitation and tectonic uplift both generate characteristic patterns of grain size and stratigraphic geometry. An increase in catchment precipitation results in the deposition of a laterally extensive sheet of coarse gravel. The responses to a changing tectonic regime are more diverse: a large increase in uplift rate results first in the deposition of sediments of larger grain size at proximal sites, followed by a reduction in grain size at distal locations. We conclude that the stratigraphic record is strongly controlled by the grain size of sediments released from catchments undergoing tectonic or climatic change.
Twenty ice cores drilled in medium to high accumulation areas of the Greenland ice sheet have been used to extract seasonally resolved stable isotope records. Relationships between the seasonal stable isotope data and Greenland and Icelandic temperatures as well as atmospheric flow are investigated for the past 150–200 years. The winter season stable isotope data are found to be influenced by the North Atlantic Oscillation (NAO) and very closely related to SW Greenland temperatures. The linear correlation between the first principal component of the winter season stable isotope data and Greenland winter temperatures is 0.71 for seasonally resolved data and 0.83 for decadally filtered data. The summer season stable isotope data display higher correlations with Stykkisholmur summer temperatures and North Atlantic SST conditions than with SW Greenland temperatures. The linear correlation between Stykkisholmur summer temperatures and the first principal component of the summer season stable isotope data is 0.56, increasing to 0.66 for decadally filtered data. Winter season stable isotope data from ice core records that reach more than 1400 years back in time suggest that the warm period that began in the 1920s raised southern Greenland temperatures to the same level as those that prevailed during the warmest intervals of the Medieval Warm Period some 900–1300 years ago. This observation is supported by a southern Greenland ice core borehole temperature inversion. As Greenland borehole temperature inversions are found to correspond better with winter stable isotope data than with summer or annual average stable isotope data it is suggested that a strong local Greenland temperature signal can be extracted from the winter stable isotope data even on centennial to millennial time scales.
Increasing access to extensively replicated and broadly distributed tree-ring collections has led to a greater use of these large data sets to investigate climate forcing on tree growth. However, the number of chronologies added to large accessible databases is declining and few are updated, while chronologies are often sparsely distributed and are more representative of marginal growing environments. On the other hand, National Forest Inventories (NFI), although poorly replicated at the plot level as compared to classic dendrochronological sampling, contain a large amount of tree-ring data with high spatial density designed to be spatially representative of the forest cover. We propose an a posteriori approach to validating tree-ring measurements and dating, selecting individual tree-ring width time series, and building average chronologies at various spatial scales based on an extensive collection of ring width measurements of nearly 94,000 black spruce trees distributed over a wide area and collected as part of the NFI in the province of Quebec, Canada. Our results show that reliable signals may be derived at various spatial scales (from 37 to 583,000 km(2)) from NFI increment core samples. Signals from independently built chronologies are spatially coherent with each other and well-correlated with independent reference chronologies built at the stand level. We thus conclude that tree-ring data from NFIs provide an extraordinary opportunity to strengthen the spatial and temporal coverage of tree-ring data and to improve coordination with other contemporary measurements of forest growth to provide a better understanding of tree growth-climate relationships over broad spatial scales.
Mangroves occur along the coastlines throughout the tropics and sub-tropics, supporting a wide variety of resources and services. In order to understand the responses of future climate change on this ecosystem, we need to know how mangrove species have responded to climate changes in the recent past. This study aims at exploring the climatic influences on the radial growth of Heritiera fomes from a local to global scale. A total of 40 stem discs were collected at breast height position from two different zones with contrasting salinity in the Sundarbans, Bangladesh. All specimens showed distinct tree rings and most of the trees (70%) could be visually and statistically crossdated. Successful crossdating enabled the development of two zone-specific chronologies. The mean radial increment was significantly higher at low salinity (eastern) zone compared to higher salinity (western) zone. The two zone-specific chronologies synchronized significantly, allowing for the construction of a regional chronology. The annual and monsoon precipitation mainly influence the tree growth of H. fomes. The growth response to local precipitation is similar in both zones except June and November in the western zone, while the significant influence is lacking. The large-scale climatic drivers such as sea surface temperature (SST) of equatorial Pacific and Indian Ocean as well as the El Nio-Southern Oscillation (ENSO) revealed no teleconnection with tree growth. The tree rings of this species are thus an indicator for monsoon precipitation variations in Bangladesh. The wider distribution of this species from the South to South East Asian coast presents an outstanding opportunity for developing a large-scale tree-ring network of mangroves.
A network of 41 local tree-ring chronologies of oak (Quercus petraea and Quercus robur) in Austria, Hungary, Slovenia, Croatia and Serbia (latitudes 45.00–48.00N, longitudes 13.14–21.63E, altitudes 80–800 m a.s.l.) was constructed and used to establish common climatic signals in oak tree rings in the region. Co-variation of residual chronologies could be resumed in 11 significant principal components (PC), explaining 79 % of common variability. Three of them, PC1, PC2 and PC3, made it possible to identify similarities among the sites. PC1, significantly correlated with all 41 chronologies, indicated a common positive response to precipitation in spring and summer (March and June) and a negative response to temperature in spring and summer (April and June). PC2, significantly correlated with 12 chronologies, indicated a common positive response to precipitation especially in spring (May) and a negative one to high summer temperatures (especially in August) with a pronounced north to south gradient. PC3, significantly correlated with ten chronologies, indicated that a warm previous December and warm current September have a positive effect on tree growth, especially in the south-western part of the study area. The obtained climate–growth relationships will help to understand better the variability of oak growth, to fill palaeoclimatic gaps and to improve dendrochronological research in the region.
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 Pious 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.
Stable isotope ratios in tree rings are increasingly used as palaeoclimatic archive and ecophysiological indicator. We used cross-dated tree-ring series from different tree functional types, i.e. the evergreen conifer and the deciduous broadleaved . The samples were collected from Chaharbagh Gorgon forest in northern Iran, where oaks and junipers grow on north-facing and south-facing slopes, respectively. We extracted α-cellulose from the whole wood of annually separated tree rings and evaluated their potential for palaeoclimate reconstructions by examining the relationships between variations of δ C in tree-ring cellulose and climate parameters. Based on tree-ring δ C, we calculated intrinsic water use efficiency (iWUE) and evaluated changes in water availability at the study site over the past 50 years. We found significant negative relationships between tree-ring δ C values in oak and juniper and precipitation in April and spring (only in junipers), while no significant correlations of tree-ring δ C with temperature occurred. A strong negative relationship between tree-ring δ C and summer Palmer Drought Severity Index (PDSI) was found at the drier site, indicating that juniper growing on south-facing slopes is a better indicator of drought stress in semiarid environments. A continuous increase in iWUE in both species was observed. δ C variations in both species reflect the combined influence of climate and local site conditions. The interplay between climatic conditions and species behavior determines the inter-annual δ C patterns of oak and juniper trees. Due to its more enriched mean δ C (i.e., less negative average δ C) and its higher climatic sensitivity, juniper is a more suitable proxy for paleoclimatic reconstructions in northern Iran.
Aim To identify the dominant spatial patterns of Fagus sylvatica radial growth in the Eastern Alps, and to understand their relationships to climate variation and bioclimatic gradients. Location Fourteen beech stands in the Eastern Alps, growing between 200 and 1500 m a.s.l. in Italy, Slovenia and Austria. Methods At each site, trees were sampled using increment borers or by taking discs from felled trees. Cores and discs were processed by measuring and crossdating ring width. Ring width series were standardized, averaged, and prewhitened to obtain site chronologies. Hierarchical Cluster Analysis (HCA) and Principal Components Analysis of prewhitened site chronologies were used to identify spatial and altitudinal growth patterns, related to the bioclimatic position of each stand. Bootstrap correlation and response functions were computed between monthly climatic variables and either principal component scores or composite chronologies from stands associated by HCA. The stability of dendroclimatic signals was analyzed by moving correlation functions (MCF). Correlation analysis (teleconnections) based on a data base of 37 Italian and Slovenian beech tree-ring chronologies revealed the spatial extent of principal component scores. Results Sampled trees were 200-400 years old, representing the oldest beech trees that have been crossdated for the Alps to date. Maximum age was directly related to altitude and to the presence of historical forms of conservation. Treering parameters varied according to geographic patterns and the age of sampled trees. Stands were bioclimatically organized according to their location, and with reference to their elevation and distance from the Adriatic Sea. A direct response to winter temperature was found at all elevations. The altitudinal gradient ranged from low-elevation stands, characterized by a Mediterranean-type, late spring-summer drought signal, to mountain and high-elevation stands, characterized by a direct response to growing season temperature plus an inverse response to the previous year's July temperature. The mountain and high-elevation signal was evident in Austria, the Central Alps and Slovenia, while the low-elevation signal was confined to mountains adjacent to the Adriatic Sea. MCF revealed trends in the response to climatic factors affecting tree-ring formation in mountain and high-mountain stands linked to climatic warming. Main conclusions Dendroclimatic networks can be used for bioclimatic studies of tree populations. A biogeographical separation emerged between the Alps and the Apennines at the upper elevations, while different degrees of mediterraneity distinguished sites at lower elevations. This information will be useful in assessing any future climate-related bioclimatic shifts, especially for forests at ecotones and along altitudinal gradients.
The predominance of secondary forest‐species in Brazilian subtropical forests highlights the importance of understanding the ecology of these taxa, and dendrochronology provides valuable information about the growth and climate response of tree species. The wide distribution of Alchornea triplinervia (Spreng.) Mull. Arg. (Euphorbiaceae), and the presence of growth rings in its wood, leds to its selection for this study. Samples were collected from 34 trees growing in rainy dense forest fragments in the cities of Blumenau and Brusque, in southern Brazil, and subjected to standard dendrochronological techniques. The local chronology spanned from 1889 to 2013 and the age of the trees ranged from 32 to 125 years. The mean age was 73 years and annual increment was 1.13 mm year−1; the diameter and age showed a weak correlation. The results suggest that A. triplinervia growth responded negatively to hot summers and increased rainfall in the previous spring and winter. The high perdiodicity trend characteristic of ENSO activity was reflected in wavelet power spectra of A. triplinervia chronology, affecting positively its growth after strong ENSO events (1970–2009). Negative influences occurred before 1970 during normal ENSO events. Also, there is evidence of the existence of a connection between Pacific and Atlantic sea surface temperatures influencing on tree growth.
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.