To place recent hydroclimate changes, including drought occurrences, in a long-term historical context, tree-ring records serve as an important natural archive. Here, we evaluate 46 millennium-long ...tree-ring based hydroclimate reconstructions for their Data Homogeneity, Sample Replication, Growth Coherence, Chronology Development, and Climate Signal based on criteria published by Esper et al. (2016) to assess tree-ring based temperature reconstructions. The compilation of 46 individually calibrated site reconstructions includes 37 different tree species and stem from North America (n = 29), Asia (n = 10); Europe (n = 5), northern Africa (n = 1) and southern South America (n = 1). For each criterion, the individual reconstructions were ranked in four groups, and results showed that no reconstruction scores highest or lowest for all analyzed parameters. We find no geographical differences in the overall ranking, but reconstructions from arid and semi-arid environments tend to score highest. A strong and stable hydroclimate signal is found to be of greater importance than a long calibration period. The most challenging trade-off identified is between high continuous sample replications, as well as a well-mixed age class distribution over time, and a good internal growth coherence. Unlike temperature reconstructions, a high proportion of the hydroclimate reconstructions are produced using individual series detrending methods removing centennial-scale variability. By providing a quantitative and objective evaluation of all available tree-ring based hydroclimate reconstructions we hope to boost future improvements in the development of such records and provide practical guidance to secondary users of these reconstructions.
•Evaluating 46 millennium-long tree-ring based hydroclimate reconstructions.•Ranking the individual reconstructions into four groups using five parameters.•Providing objective evaluation criteria of tree-ring hydroclimate reconstructions.
We introduce in this paper the dendroTools R package for studying the statistical relationships between tree-ring parameters and daily environmental data. The core function of the package is ...daily_response(), which works by sliding a moving window through daily environmental data and calculating statistical metrics with one or more tree ring proxies. Possible metrics are correlation coefficient, coefficient of determination and adjusted coefficient of determination. In addition to linear regression, it is possible to use a nonlinear artificial neural network with the Bayesian regularization training algorithm (brnn). dendroTools provides the opportunity to use daily climate data and robust nonlinear functions for the analysis of climate-growth relationships. Models should thus be better adapted to the real (continuous) growth of trees and should gain in predictive capabilities. The dendroTools R package is freely available in the CRAN repository. The functionality of the package is demonstrated on two examples, one using a mean vessel area (MVA) chronology and one a traditional tree-ring width (TRW).
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•Trees near springs have higher absolute and relative growth than those away from springs.•Trees away from springs are more sensitive to climate change.•Differences in tree response ...are persistent and may facilitate survival under warming climate.
Tree rings have been widely used to reconstruct environmental history, especially water availability, because historical records of streamflow are often limited. In the semiarid southwestern USA, springs provide critical water resources and support biodiversity hotspots, but spring flows are poorly documented and spring effects on tree-ring growth are not well studied. Our project was designed to measure the effect of spring adjacency on ponderosa pine tree growth and drought response. We sampled trees adjacent to springs (“near”) and farther away (“away”) that were similar in latitude, slope, soil characteristics, height and stem diameter, so we inferred that differences in ring width were due to the springś influences. We gathered cores from a total of 50 ponderosa pine trees at ten different springs around Flagstaff, Arizona. We crossdated and measured the tree rings and developed chronologies of near and away trees. We compared absolute growth of trees in each category using basal area increment (BAI; mm2/year), which ranged from 806 to 2511 mm2 tree−1 year−1 near springs and between 503 and 2125 mm2 tree−1 year−1 away from springs. Near trees had consistently higher BAI growth over the past 66 years, the common period of analysis, although the difference was not statistically significant. Mean tree-ring sensitivity from the chronology near springs was 0.323, while the chronology away from springs was significantly higher, 0.366. Drought sensitivity index was significantly higher for away trees, indicating that years of severe drought had a greater negative impact for away than for near trees. Drought recovery index, however, showed inconsistent results. The findings indicate that ponderosa pine growth is responsive to spring settings, even in severe drought. Given that small springs are abundant in semiarid regions, they may provide valuable ecological buffers for warming climate. Further investigation to quantify springs perenniality and variability is needed.
Aim
Climate change is expected to modify growth trends of forests around the world. However, this modification may vary in strength and intensity across a species' biogeographical range. Here, we ...study European populations of silver fir (Abies alba) across its southern distribution limits in Spain, Italy and Romania. We hypothesized that growth trends of silver fir will differ across its distribution range, with a marked decline in growth in drought‐prone regions near the species' southernmost biogeographical limits.
Location
Europe (Spain, Italy, Romania).
Methods
We collected tree‐ring data from at least 1300 silver fir trees located in 111 sites. The dataset was used to assess and model growth trends, quantified as changes in basal area increment, and to determine how growth responds to climate.
Results
We found contrasting patterns of basal area increments among countries and sites. Populations of silver fir located outside the Mediterranean area (e.g. northern Italy, Romania) have shown a clear increase in growth over the last two decades, whereas most populations in Spain and southern Italy have displayed a marked decline in growth since the 1980s. The growth of silver fir forests at the south‐western distribution limit is severely constrained by low spring–summer water availability, whereas growth of silver fir forests in non‐Mediterranean areas is limited by cold conditions in late winter to early spring.
Main conclusions
Climate warming is distinctly modifying growth patterns and responses to climate in silver fir across most of the species' European distribution area. In south‐western Europe the reduction in growth of many populations is related to an observed increase in aridity, whereas in more temperate areas warming is enhancing growth. Our results confirm a decline in the growth of silver fir at its south‐western distribution limits as a consequence of climate warming.
Cross-dating is considered one of the most important principles of dendrochronology. The first known cross-dating attempts, conducted between the years 1737 and 1783 by independent researchers in ...France, Germany, and Sweden, were related to the identification of growth rings believed to have formed during the harsh winter of 1708-1709. In this paper, we present a novel perspective on the birth of dendrochronology and cross-dating in the 1700s. We focus on the ideas and experimental studies of one of the lesser known pioneers, Johan Leche (1704-1764), the Professor of Medicine at the Royal Academy (Turku, Finland). Instead of winter harshness, Leche was fascinated by the drought that killed and damaged several trees and tree species in the summer of 1757. Leche conducted several dendrochronological and field experiments described only in his unpublished manuscript filed in the National Archives in Sweden. Reviewing Leche's measurements of ring-width series of multiple radii and his comparisons between the radii, it seems only fair to include him in the long list of natural historians who made important contributions to the field ofdendrochronology. His manuscript was never published, which is why Leche's dendrochronological experiments and recommendations never reached a wider audience.
Climate variations influenced the agricultural productivity, health risk, and conflict level of preindustrial societies. Discrimination between environmental and anthropogenic impacts on past ...civilizations, however, remains difficult because of the paucity of high-resolution paleoclimatic evidence. We present tree ring—based reconstructions of central European summer precipitation and temperature variability over the past 2500 years. Recent warming is unprecedented, but modern hydroclimatic variations may have at times been exceeded in magnitude and duration. Wet and warm summers occurred during periods of Roman and medieval prosperity. Increased climate variability from ∼250 to 600 C.E. coincided with the demise of the western Roman Empire and the turmoil of the Migration Period. Such historical data may provide a basis for counteracting the recent political and fiscal reluctance to mitigate projected climate change.
Understanding boreal/hemi-boreal forest growth sensitivity to seasonal variations in temperature and water availability provides important basis for projecting the potential impacts of climate change ...on the productivity of these ecosystems. Our best available information currently comes from a limited number of field experiments and terrestrial biosphere model (TBM) simulations of varying predictive accuracy. Here, we assessed the sensitivity of annual boreal/hemi-boreal forest growth in Canada to yearly fluctuations in seasonal climate variables using a large tree-ring dataset and compared this to the climate sensitivity of annual net primary productivity (NPP) estimates obtained from fourteen TBMs. We found that boreal/hemi-boreal forest growth sensitivity to fluctuations in seasonal temperature and precipitation variables changed along a southwestern to northeastern gradient, with growth limited almost entirely by temperature in the northeast and west and by water availability in the southwest. We also found a lag in growth climate sensitivity, with growth largely determined by the climate during the summer prior to ring formation. Analyses of NPP sensitivity to the same climate variables produced a similar southwest to northeast gradient in growth climate sensitivity for NPP estimates from all but three TBMs. However, analyses of growth from tree-ring data and analyses of NPP from TBMs produced contrasting evidence concerning the key climate variables limiting growth. While analyses of NPP primarily indicated a positive relationship between growth and seasonal temperature, tree-ring analyses indicated negative growth relationships to temperature. Also, the positive effect of precipitation on NPP derived from most TBMs was weaker than the positive effect of precipitation on tree-ring based growth: temperature had a more important limiting effect on NPP than tree-ring data indicated. These mismatches regarding the key climate variables limiting growth suggested that characterization of tree growth in TBMs might need revision, particularly regarding the effects of stomatal conductance and carbohydrate reserve dynamics.
(I) Climate sensitivity index (Climateindex, the difference between temperature and precipitation importance) in the boreal and hemi-boreal forests estimated from basal area increments (BAI). Positive Climateindex indicates temperature (thermal limitation) has a greater influence of annual tree growth fluctuations than precipitation (water limitation), while negative values indicate the opposite. (II) Importance weighted means (IWM) of 12 seasonal climate variables estimated from analyses of basal area increments (BAI-Clim) compared with the responsiveness of net primary productivity (NPP) simulations by an ensemble of fourteen terrestrial biosphere models (TBMs). The seasons analysed range from the summer of the pre-growth year to the fall of the contemporary growth year. A positive IWM score indicates that the climate variable is beneficial to growth (or NPP); a negative IWM score denotes that the climate variable is detrimental. TBMs failed to reproduce growth sensitivities to key seasonal variables: they all overestimated the positive temperature sensitivity, and many underestimated the drought sensitivity. Display omitted
•Canadian boreal/hemi-boreal forests display a gradient in growth sensitivity to climate variability•Terrestrial Biosphere Models (TBMs) reproduced the same growth limitation gradient observed in tree rings•However, a strong mismatch was observed in the key seasonal climate variables underlying this gradient•TBMs overestimated the positive effect of temperature on growth, and underestimated the detrimental effect of drought•Improvement for TBMs could involve leaf conductance and rooting and carbohydrate reserve dynamics
The development of high-resolution terrestrial palaeoclimate records in Australia is hindered by the scarcity of tree species suitable for conventional dendrochronology. However, novel analytical ...techniques have made it possible to obtain climate information from tree species that do not reliably form annual growth rings. In this paper we assess the potential of stable carbon and oxygen isotopes in the xylem wood of grey mangroves (Avicennia marina (Forssk.) Vierh.) as hydroclimate proxies for eastern Australia. Bomb-pulse radiocarbon dating and simple age models were used to estimate the age of the growth layers in radial sequence in stems from four grey mangrove trees in two adjacent estuaries in New South Wales, Australia. Stable isotope data measured from the xylem wood of the four stems were composited to yield mean δ18O and δ13C series for the 1962–2016 period. Significant negative Spearman correlations were found between δ18O and rainfall, sea level, instrumental Palmer Drought Severity Index (scPDSI) and the El Niño Southern Oscillation (ENSO), while δ13C was positively correlated with temperature, vapour pressure and evapotranspiration. The results demonstrate that stable oxygen isotopes in grey mangroves have the potential to yield valuable information about pre-instrumental hydroclimate. Grey mangroves can survive with intact centres for an estimate of >250 years based on observed growth rates, are widespread along northern Australian and tropical coastlines and could provide important information regarding pre-instrumental climate in regions currently lacking high-resolution (i.e., near annual) centennial scale climate proxy records.
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•Masting creates distinct signals in male and female A. araucana tree-rings.•Sex-specific growth analysis may facilitate multi-century reconstructions of masting.•Accounting for sex-specific growth ...will improve dendroclimatic calibration.
Araucaria araucana is a dioecious evergreen conifer endemic from temperate forests of south Argentina and Chile. It is a long-lived species (maximum age > 1000 years), and it presents a high potential for tree-ring based climate reconstructions. However, the species’ dioecious habit can result in distinct sex-specific growth patterns, which introduce novel challenges in the interpretation of tree-ring chronology variations. We used a network of 10 tree-ring chronologies from northwest Patagonia (Argentina) to analyze sex-specific growth patterns in A. araucana and, for the first time, demonstrate that they result from the contrasting responses of ring width index of male (RWImale) and female (RWIfemale) trees to regional mast events (years with high seed production). During the year of seed maturation and seed dispersal, the growth of females was strongly and significantly reduced, while a growth response of similar magnitude was found in male trees in the previous year, corresponding to the year of pollination. We interpret these growth responses as representing contrasting allocation shifts between growth and reproduction in males and females. The sex-specific growth responses associated with mast events resulted in a particularly strong and distinct signal in a RWImale–RWIfemale chronology. Male and female tree-ring chronologies shared a strong common signal, and responded similarly (but not exactly) to broad-scale climatic conditions in the growing season. Our results indicate that sex-specific tree-ring chronologies can be used to isolate mast events in A. araucana chronologies, providing an opportunity to develop unique multi-century reconstructions of large mast events, and improve dendroclimatic calibration for this species.
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