Tree-ring Width Data Research Articles

Combination of Tree Rings and Other Paleoclimate Proxies to Explore the East Asian Summer Monsoon and Solar Irradiance Signals: A Case Study on the North China Plain

Paleoclimate research, which involves the study of climate and environmental changes in historical and geological periods, is typically conducted using high-resolution paleoclimatic proxies, such as tree rings, historical documentations, stalagmite, and ice core. Although each paleoclimate proxy has its own merits in paleoclimatic research, reconstructions based on a single proxy may suffer from shortcomings, including insufficient reliability and low coverage of the representative area. It may be possible to overcome these shortcomings by combining multi-paleoclimatic proxies to understand paleoclimatic changes. In this study, we attempt to combine tree-ring stable oxygen isotope ratio (δ18O), tree-ring width, and stalagmite thickness data as well as historical records to establish a 320-year (1675–1994) time series using principal component analysis in the water-scarce North China Plain (NCP). The results show that the first principal component (PC1) series is closely related to regional precipitation and the maximum temperature in summer. The spatial correlation pattern indicates that the PC1 series can represent the regional hydroclimate variation not only in the NCP but also in all of northern China. The significant (p < 0.001) correlations between the PC1 series and several East Asian summer monsoon (EASM) indices prove that the PC1 reflects the intensity of the EASM. The PC1 series is consistent with the interannual variations of two reconstructed solar activity correlation indexes (r = 0.48 and 0.46, n = 320, and p < 0.001). The results indicate that the hydroclimate variation in the NCP is affected by large-scale atmospheric circulations, such as EASM and solar activity, and shows the potential of combining multiple paleoclimate proxies for analyzing regional climate change.

Temperature sensitivity of blue intensity, maximum latewood density, and ring width data of living black spruce trees in the eastern Canadian taiga

The blue intensity (BI) technique provides opportunities to obtain surrogates to tree-ring density for reconstructing summer temperatures in high-latitude regions. In this study, we compare latewood BI (LBI) and delta BI (DBI), with the conventional X-ray maximum latewood density (MXD) and tree-ring width (TRW) data using 178 living trees of black spruce (Picea mariana (Mill.) B.S.P.), one of the most dominant species of conifers in the Northern Hemisphere, from 17 sites across the eastern Canadian taiga. The regional LBI and DBI chronologies are highly correlated to that of MXD (Pearson’s r = 0.97 and 0.92, respectively), while DBI is also similar to TRW (Pearson’s r = 0.67). Both LBI and DBI exhibit stronger responses to the May–August temperatures than TRW over larger time and spatial scales. However, only DBI is comparable to MXD data from inter-annual to decadal timescales. Low-frequency components of LBI data are likely distorted by color biases even if no obvious discoloration is present, as well as by the potentially low measurement resolution, leading to an overall weaker temperature sensitivity compared to the MXD data. Resampling experiments suggest that a minimum replication of 10 trees is needed to retain ≥90 % of the optimal temperature signal for MXD, LBI, and DBI data, and a minimum of 20 trees is required for TRW data.

A Unifying Concept for Growth Trends of Trees and Forests – The “Potential Natural Forest”

Changes in the environment will alter the growth rate of trees and forests. Different disciplines assess such growth rates differently, for example with, tree-ring width data, forest inventories or with carbon-flux data from eddy covariance towers. Such data is used to quantify forests biomass increment, forest's carbon sequestration or to reconstruct environmental variables before instrumental records. However, raw measurement data is typically not considered to be representative for the average growth rate of trees or forests. Depending on the research question, the effects of certain environmental variables or effects of tree and forest structure have to be removed first. It can be challenging to define and quantify a growth trend that can answer a specific research question because trees and forests grow and respond to environmental change in multiple ways simultaneously, for example with altered radial increment, height growth and stand density. Further challenges pose time-lagged feedback loops, for example between height and radial increment or between stand density and radial increment. Generally, different environments will lead to different tree and forest structures, but because of tree’s longevity this change will take decades or even centuries. Consequently, there can be an offset between the present forest structure and what we term the potential natural forest (PNF): Similar to the potential natural vegetation (PNV), the potential natural forest represents that forest that would develop under the current environmental conditions in the absence of human intervention. Because growth rates are affected by the tree and forest structure, growth-trend estimates will differ between the present and the potential forest. Consequently, if the legacy effects of the past are not of interest, the potential natural forest is the theoretical baseline to correct and estimate growth trends.

Climate sensitive single tree growth modeling using a hierarchical Bayes approach and integrated nested Laplace approximations (INLA) for a distributed lag model

A novel methodological framework is presented for climate-sensitive modeling of annual radial stem increments using tree-ring width time series. The approach is based on a hierarchical Bayes model together with a distributed time lag model that take into account the effects of a series of monthly temperature and precipitation values, as well as their interactions. By using a set of random walk priors, the hierarchical Bayes model allows both the detrending of the individual time series and the regression modeling to be performed simultaneously in a single model step. The approach was applied to comprehensive tree-ring width data from Austria collected on sample plots arranged in triplets representing different mixture types. Bayesian predictions revealed that European larch (Larix decidua Mill.), Norway spruce (Picea abies (L.) H. Karst.), and Scots pine (Pinus sylvestris L.) show positive climate-related growth trends throughout higher elevation sites in Tyrol, and these trends remain unchanged under a mixed-stand scenario. At the lower Austrian sites, Norway spruce was found to show a severely negative growth trend under both the pure- and mixed-stand scenario. The increment rates of European beech (Fagus sylvatica L.) were found to have a negative climate-related trend in pure stands, and the trend diminished through an admixture of spruce or larch. The trends of European larch and sessile oak (Quercus petraea (Matt.) Liebl.) showed stationary behavior, irrespective of the mixture scenario. Scots pine data showed a positive trend at the lower elevation sites under both the pure- and mixed-stand scenario. These findings indicate that species mixing does not lower the climate-related increment fluctuations of beech, oak, pine, and spruce at lower elevation sites.

Tree ring and water deficit indices as indicators of drought impact on black truffle production in Spain

Black truffle is a highly-prized fungus that constitutes an important economic resource in many Mediterranean forests of southern Europe. Black truffle production in these forests and in cultivated truffle orchards is subject to important interannual variations linked to climatic factors, among which summer water shortage is particularly relevant in dry regions such as Mediterranean Spain. Thus, in recent years irrigation has become widespread in Spanish black truffle orchards, although no long-term proxies of black truffle production exist and scientific guidelines for the irrigation of these orchards are lacking. In this study, we explore the possibilities and limitations of pine tree-ring width data (seasonal wood production) and agroclimatic indices to predict black truffle production in Spain, while gaining more in-depth knowledge on water requirements of truffle production. For this purpose, we used the national annual estimates of black truffle production and compared these values with several tree-ring width series, monthly climatic factors, and water balance-based indices. We found a strong linkage between summer water availability, black truffle production and Mediterranean pine latewood formation, with summer drought intensity reducing both black truffle and Pinus pinaster latewood production. The adjusted latewood index for P. pinaster and the accumulated water deficit from April to September were robust predictors of black truffle production. The predictive skills of these two variables were further confirmed with a calibration-verification technique. These variables can be used as climatic proxies of black truffle production in agronomic or silvicultural studies, in a sector where no large-scale network for monitoring soil water content exists, and many truffle orchards are small and have low possibilities for modernisation.

Tree-ring reconstruction of June-July mean temperatures in the northern Daxing’an Mountains, China

Abstract In this study, the mean temperature of June to July was reconstructed for the period of 1880 to 2014 by using the Larix gmelinii tree-ring width data for the Mangui region in the northern Daxing’an Mountains, China. The reconstruction accounts for 43.6% of the variance in the temperature observed from AD 1959–2014. During the last 134 years, there were 17 warm years and 17 cold years, which accounted for 12.7% of the total reconstruction years, respectively. Cold episodes occurred throughout 1887–1898 (average value is 14.2°C), while warm episodes occurred during 1994–2014 (15.9°C). Based on this regional study, the warmer events coincided with dry periods and the colder events were consistent with wet conditions. The spatial correlation analyses between the reconstructed series and gridded temperature data revealed that the regional climatic variations were well captured by this study and the reconstruction represented a regional temperature signal for the northern Daxing’an Mountains. In addition, Multi-taper method spectral analysis revealed the existence of significant periodicities in our reconstruction. Significant spectral peaks were found at 29.7, 10.9, 2.5, and 2.2 years. The significant spatial correlations between our temperature reconstruction and the El Niño–Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO) and Solar activity suggested that the temperature in the Daxing’an Mountains area indicated both local-regional climate signals and global-scale climate changes.

Contrasting Signals of the Westerly Index and North Atlantic Oscillation over the Drought Sensitivity of Tree-Ring Chronologies from the Mediterranean Basin

Extreme drought events are becoming increasingly frequent and extended, particularly in Mediterranean drought-prone regions. In this sense, atmospheric oscillations patterns, such as those represented by the North Atlantic Oscillation (NAO) index and the Westerly Index (WI) have been widely proven as reliable proxies of drought trends. Here, we used the Standardized Precipitation–Evapotranspiration Index (SPEI), as a reliable indicator of drought, to investigate the drought sensitivity of tree-ring width data (TRW) from several long-lived tree species (Abies borisii-regis, Abies cilicica, Abies pinsapo, Cedrus atlantica, Cedrus libanii, Pinus nigra, Pinus heldreichii). NAO and WI relations with TRW were also investigated in order to identify potential non-stationary responses among those drought proxies. Our temporal and spatial analyses support contrasting Mediterranean dipole patterns regarding the drought sensitivity of tree growth for each tree species. The spatial assessment of NAO and WI relationships regarding SPEI and TRW showed on average stronger correlations westward with non-stationary correlations between annual WI index and TRW in all species. The results indicate that the drought variability and the inferred drought-sensitive trees species (e.g., C. atlantica) are related to the NAO and the WI, showing that TRW is a feasible proxy to long-term reconstructions of Westerly Index (WI) variability in the Western Mediterranean region. Spatial variability of drought severity suggests a complex association between NAO and WI, likely modulated by an east–west Mediterranean climate dipole.

Radial growth response of major conifers to climate change on Haba Snow Mountain, Southwestern China

Climate change has an inevitable impact on forest ecosystems, to better understand the influence of climate change on forest growth, we analyzed the growth response of four major conifers to climate on Haba Snow Mountain in central Hengduan Mountains. Tree ring samples were taken from four species at their upper distributional limits, and residual chronologies were developed by using tree ring width data. Response function and redundancy analysis were taken to reveal the key climatic factors affecting tree growth and moving interval analysis was applied to detect the stability of growth-climate relationships. The results showed that previous November temperature, precipitation in current February, current May and current June were common factors affecting the radial growth of the studied species. Abies georgei was mainly influenced by the temperature in previous November. The photothermal condition in May and June controlled the growth of Larix potaninii. Moisture condition in previous August and current May was the key factor affecting Pinus densata growth. As for Pinus yunnanensis, the drought in current May was the limiting factor influencing its growth. The dynamic relationship between tree growth and climatic factors varied among species, and the results were consistent with response function analysis. A forecast in future forest growth on Haba Snow Mountain was complex, since future climate change had both positive and negative effects on the radial growth of four major conifers.

Assessing non-linearity in European temperature-sensitive tree-ring data

We test the application of parametric, non-parametric, and semi-parametric calibration models for reconstructing summer (June–August) temperature from a set of tree-ring width and density data on the same dendro samples from 40 sites across Europe. By comparing the performance of the three calibration models on pairs” of tree-ring width (TRW) and maximum density (MXD) or maximum blue intensity (MXBI), we test whether a non-linear temperature response is more prevalent in TRW or MXD (MXBI) data, and whether it is associated with the temperature sensitivity and/or autocorrelation structure of the dendro parameters. We note that MXD (MXBI) data have a significantly stronger temperature response than TRW data as well as a lower autocorrelation that is more similar to that of the instrumental temperature data, whereas TRW exhibits a redder” variability continuum. This study shows that the use of non-parametric calibration models is more suitable for TRW data, while parametric calibration is sufficient for both MXD and MXBI data – that is, we show that TRW is by far the more non-linear proxy.

Spatial patterns of precipitation-induced moisture availability and their effects on the divergence of conifer stem growth in the western and eastern parts of China’s semi-arid region

Conifer forests in semi-arid regions are fragile and sensitive to climate change. As the climate changes, more frequent drought and higher temperatures may reduce conifer stem growth in these regions, but moistening and lengthening of the growing season may improve tree growth conditions. The relative influences of specific climate parameters on conifer stem growth, however, remain poorly quantified in Asian regions. We analyzed conifer stem growth responses to climate in the semi-arid region of China. Our analyses show a wetting trend since 1960 in the western part of this region, versus a drying trend in the east. We used tree-ring width data from a network of 33 forests as inputs for the process-based Vaganov–Shashkin-Lite growth model to assess how moisture patterns have affected tree growth in this region, and then used the resulting model to predict changes in tree growth during the 21st century. Tree-ring growth in our study region is mainly controlled by precipitation and soil moisture, and shows significant impacts of antecedent moisture conditions (the “water memory effect”). However, the contribution of soil moisture to tree growth was stronger in the eastern vs. western sub-regions (77% vs. 69%). Pointer-year analysis showed significantly stronger growth responses to soil moisture in the early growing season (April to June) in positive pointer years in the eastern sub-region, but showed no difference in the western sub-region. These results indicate that tree-ring growth in the eastern sub-region is more vulnerable to moisture availability. Our simulations suggest that tree growth will increase slightly under the RCP 4.5 and RCP 8.5 scenarios in both sub-regions, possibly due to the prolongation of the growing season caused by climate warming.

A multi-proxy reconstruction of moisture dynamics in a peatland ecosystem: A case study from Čepkeliai, Lithuania

In this study, six approaches were used to characterize hydrological changes in the Cepkeliai wetland complex (southeast Lithuania), namely (i) local water-table measurements (WTM), (ii) testate amoebae analysis, (iii) tree-ring width (TRW) series, (iv) peat stratigraphic data, (v) (hydro-) meteorological data (precipitation and river runoff), and (vi) a diachronic analysis of aerial photographs as well as historical maps. This multi-proxy framework provides complementary information on the hydrological evolution of the peatland and offers a unique opportunity to discuss the pros and cons of each approach. Local water-table measurements, for example, generated monthly resolved and precise (±0.01 m) hydrological information, but were limited to a 16-year period. On the other hand, the TRW data generated annually-resolved information linked to hydrological shifts over the period 1848–2018, but did not allow reconstruction of the amplitude of hydrological variations. Amongst the proxy records, the testate amoebae distribution is the only approach that gives a direct measurement of changes in water-table depths. At the same time, the approach is limited by chronological inaccuracies and weaker resolutions, similar to peat stratigraphic records. The meteorological data are theoretically representing the most highly resolved records. However, due to hydrological lags and feedbacks in peatlands, it was difficult to link regional changes observed in meteorological records to local changes in the peatland. The aerial photographs and historical maps offered an opportunity to document large-scale vegetation changes, which is useful for upscaling local results, but they may not capture rapid changes. Despite all these limitations, at Cepkeliai, most of the proxy records are in agreement with each other and suggest relatively moist conditions with water levels close to the peat surface during the late 1800s and early 1900s, followed by more detailed information towards the present showing shifts towards drier peat surface conditions during the 1930s and 1940s. The 1960s were dry, followed by a short, moist episode during the 1970s, and returning to drier conditions during the 1980s. A gradual change towards moister conditions was recorded over the 1990s and 2000s. The last decade in our records started with relatively wet conditions to end with lower water levels over the most recent years.

Abrupt regime shifts in post-fire resilience of Mediterranean mountain pinewoods are fuelled by land use

Post-fire forest resilience must be quantified in a long-term perspective considering changes in land-use related to fire dynamics. Historical land-use changes leading to increased wildfire severity may produce no analogue regime shifts including a loss in post-fire growth recovery. Here we reconstruct the historical fire dynamics by combining paleoecological proxies, historical fire records and tree-ring width data of relict Pinus nigra subsp. salzmannii forests in the Sierra de Gredos (central Spain). A high incidence of historical fires was recorded in the 1890s, coinciding with a peak in charcoal accumulation rates and a sharp decrease in pollen of P. nigra/Pinus sylvestris with a rapid increase of pollen of more flammable Pinus pinaster and shrubs. The shift observed in pollen assemblages, coupled with a peak in charcoal influx, support the occurrence of high-severity fires during the 1890s, when abrupt growth suppressions were observed. Trees took 2 years to recover to their pre-fire growth rates. Lasting growth-recovery periods or no growth suppression were observed in the 1920s and 1980s, when fire frequency was also high but the study sites were fragmented or protected. We documented an abrupt regime shift in the fire record during the 1890s affecting pine forests, which rapidly recovered pre-fire growth rates.

Variation in Climate Signals in Teak Tree-Ring Chronologies in Two Different Growth Areas

We developed two tree-ring chronologies of teak (Tectona grandis L.f.) from Mae Tuen (462-year, 1555–2016) and Umphang (165-year, 1852–2016) in Tak province, northwestern Thailand. The chronologies were based on 67 and 71 living teak trees, respectively. We used crossdating methods to check and verify the tree-ring width data and tree-ring chronology construction using the ARSTAN program. In this study, the two teak tree-ring chronologies from two different growth areas could not be crossdated. The relationship among these chronologies is, thus, relatively low (r = 0.33, n = 165, p < 0.01). This result shows that the growth of tree-ring structure from two sites can be affected by a variety of non-climatic patterns due to site variation, such as topography, nutrient, light, and internal factors. However, these chronologies have a significant positive correlation with rainfall, during the pre-monsoon season (April to May). As demonstrated by the spatial correlation patterns, these chronologies represent April to May rainfall, which was a limiting factor of teak growth from northwestern Thailand. While the difference in surface temperatures of the Indian Ocean Dipole (IOD) might not be affected by rainfall, its unstable relationship with the El Niño-Southern Oscillation (ENSO) was noted to have occurred.

Increasing intrinsic water-use efficiency over the past 160 years does not stimulate tree growth in southeastern China

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 76:115-130 (2018) - DOI: https://doi.org/10.3354/cr01526 Increasing intrinsic water-use efficiency over the past 160 years does not stimulate tree growth in southeastern China Guoyang Guo1, Keyan Fang1,2,*, Jinbao Li3, Hans W. Linderholm2, Dawen Li1, Feifei Zhou1, Zhipeng Dong1, Yingjun Li1, Lei Wang1 1Institute of Geography, Key Laboratory of Humid Subtropical Eco-geographical Process (Ministry of Education), College of Geographical Sciences, Fujian Normal University, Fuzhou 350007, PR China 2Regional Climate Group, Department of Earth Sciences, University of Gothenburg, Box 460, 405 30 Gothenburg, Sweden 3Department of Geography, University of Hong Kong, Pokfulam, Hong Kong SAR *Corresponding author: kfang@fjnu.edu.cn ABSTRACT: Understanding the responses of tree growth and intrinsic water-use efficiency (iWUE) to anthropogenic CO2 increase and climate warming provides important benchmarks for evaluating future forest dynamics under different scenarios of warming and CO2 changes. Relative to the short period of instrumental data of the past few decades, long-term tree-ring width and stable carbon isotopic (δ13C) data are invaluable in fully comprehending their interactions during the entire industrial era, since ~1850. Here, we present a tree-ring width chronology (1856 to 2015) and δ13C series (1876-2015) of Pinus massoniana for Yongtai county of Fujian province, in humid subtropical China, a ‘green island’ relative to other dry subtropical areas of the world. Tree growth was limited by precipitation of the hydrological year (previous November to current October) (r = 0.568, p < 0.001), and the stable carbon isotope discrimination (Δ13C) was strongly correlated with relative humidity in September-October (r = -0.677, p < 0.001) of the current growing season. We found that the iWUE increased by 40.9% since 1876. Specifically, we found that the ci:ca ratio decreased during the study period whereas intercellular CO2 concentration (ci) increased. The negative relationship between basal area increment (BAI) and iWUE indicated that increasing iWUE may not lead to long-term enhancement of tree growth. Our results indicated a drought-induced limitation to tree growth in response to rising CO2, and that trees may mitigate the negative effects of a decrease in water availability through a reduction in stomatal conductance. KEY WORDS: Tree-ring · Stable carbon isotope · Intrinsic water-use efficiency · Pinus massoniana · Humid subtropical China Full text in pdf format PreviousNextCite this article as: Guo G, Fang K, Li J, Linderholm HW and others (2018) Increasing intrinsic water-use efficiency over the past 160 years does not stimulate tree growth in southeastern China. Clim Res 76:115-130. https://doi.org/10.3354/cr01526 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 76, No. 2. Online publication date: October 10, 2018 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2018 Inter-Research.

Growth of Pinus cembroides Zucc. in Response to Hydroclimatic Variability in Four Sites Forming the Species Latitudinal and Longitudinal Distribution Limits

Climate change modifies the distribution and dominance of forest tree species, particularly near their distribution limits. This study used tree-ring width data for Pinus cembroides Zucc. at its distribution limits in Mexico and the SW USA to assess how tree populations responded to hydroclimatic variability. Indexed ring-width chronologies were built and correlated with climate and drought records at four marginal stands. We found that P. cembroides responds differently to climatic conditions depending on the bioclimatic and biogeographic conditions, with the forests situated in the driest area (Nuevo León) presenting the highest growth association to maximum temperatures and drought, while the forest situated in the wettest area (Puebla) was the least correlated to these hydroclimatic factors. In particular, dry and hot conditions, during the prior autumn and winter, reduced radial growth. Drought conditions could result in more vulnerable forests at the driest sites. These results advance our understanding of the radial growth responses of P. cembroides and similar widely distributed trees to climatic change near their biogeographical limits.

Long-term changes in the tree radial growth and intrinsic water-use efficiency of Chuanxi spruce (Picea likiangensis var. balfouriana) in southwestern China

Elevated CO2 level in the atmosphere is expected to improve the tree growth rates and intrinsic water-use efficiency (iWUE). Although current results inferring from tree rings found the tree growth decline in water-limited area, it is still unclear whether spruce trees in humid southwestern China benefit from the increasing CO2. In this study, tree-ring width data were used to investigate the tree radial growth rate of Chuanxi spruce (Picea likiangensis var. balfouriana). Moreover, combining with the tree-ring carbon isotope date, we analyzed the physiological responses of Chuanxi spruce to rising CO2 concentrations in the atmosphere (Ca) associated with climatic change in southwestern China. From 1851 to 2009, iWUE of Chuanxi spruce rose by approximately 30.4%, and the ratio of atmospheric CO2 to leaf intercellular CO2 concentration (Ci/Ca) showed no significant trend in the study area. The result suggested that Chuanxi spruce used an active response strategy when Ca was significantly increased. iWUE showed a significant increasing trend in parallel with tree radial growth, indicating that the increasing iWUE resulted in an increase in radial growth. These results suggest that spruce forests in southwestern China have not shown declining trends under increasing Ca and climate change scenarios, in contrast to trees growing in water-limited areas. Therefore, spruce forests benefit from the increasing CO2 in the atmosphere in the humid areas of southwestern China.

Forest resilience to drought varies across biomes.

Forecasted increase drought frequency and severity may drive worldwide declines in forest productivity. Species-level responses to a drier world are likely to be influenced by their functional traits. Here, we analyse forest resilience to drought using an extensive network of tree-ring width data and satellite imagery. We compiled proxies of forest growth and productivity (TRWi, absolutely dated ring-width indices; NDVI, Normalized Difference Vegetation Index) for 11 tree species and 502 forests in Spain corresponding to Mediterranean, temperate, and continental biomes. Four different components of forest resilience to drought were calculated based on TRWi and NDVI data before, during, and after four major droughts (1986, 1994-1995, 1999, and 2005), and pointed out that TRWi data were more sensitive metrics of forest resilience to drought than NDVI data. Resilience was related to both drought severity and forest composition. Evergreen gymnosperms dominating semi-arid Mediterranean forests showed the lowest resistance to drought, but higher recovery than deciduous angiosperms dominating humid temperate forests. Moreover, semi-arid gymnosperm forests presented a negative temporal trend in the resistance to drought, but this pattern was absent in continental and temperate forests. Although gymnosperms in dry Mediterranean forests showed a faster recovery after drought, their recovery potential could be constrained if droughts become more frequent. Conversely, angiosperms and gymnosperms inhabiting temperate and continental sites might have problems to recover after more intense droughts since they resist drought but are less able to recover afterwards.

Past growth suppressions as proxies of fire incidence in relict Mediterranean black pine forests

Abstract Global warming and land use changes, contributing to landscape level fuel increments, could threaten Mediterranean pine forest resilience to wildfire disturbances. Reconstructions of historical fire regimes allow for the disentanglement of these two drivers by comparing the influence of climatic and anthropogenic variables on fire. Here we combine three sources of historical data: charcoal accumulation rates from a peat bog, detailed historical records of fire incidence and tree-ring width data from five relict black pine (Pinus nigra) forests with fire-scarred trees located in Sierra de Gredos (central Spain). We found growth suppression in 1893 and 1894 in all the sites which coincided with a peak of fire incidence in historical records and an increase in charcoal accumulation rates. The occurrence of these three synchronous events suggests increased wildfire incidence in the area which shaped the current stand structure of relict black pine forests. These late 19th century developments, we argue, can be mainly attributed to anthropogenic factors and contributing climatic drivers. We argue that the dissolution of the “Mesta”, the biggest transhumance livestock organization in Europe lasting from the 13th to the 19th centuries, led to more extensive grazing and uncontrolled use of forests and grasslands which likely contributed to increased wildfire incidence. Additionally, 1893 was characterized by anomalously warm spring temperatures which may have facilitated vegetation flammability. Our approach couples human and climate systems as drivers of historical fire incidence in Mediterranean pine forests.

Recent growth trends of black pine ( Pinus nigra J.F. Arnold) in the eastern mediterranean

Abstract Past and present environmental changes cause significant changes in tree growth in many parts of the world, where both decreasing and increasing growth trends have been detected over the last decades. The Mediterranean basin is especially sensitive to climate change and subsequent tree growth declines. In this article, we present the first study on recent tree growth trends in Turkey. Pinus nigra is a drought-sensitive species and one of the most common and economically important native conifers to Turkey. Tree-ring cores were taken from 61 Pinus nigra plots spread over the entire Lakes District (Southwest Turkey), near the species’ southern range limit. The samples cover the 1839–2013 time period. We apply the Regional Curve Standardization technique and statistical modeling to the tree ring width data to investigate long-term growth trends. Both methods show remarkably similar results: a slowly increasing growth trend until the 1970s, followed by a decreasing trend. This recent negative trend is highly correlated with increased temperature and drought in summer, which suggests that it is likely caused by climate change.

Scots pine (Pinus sylvestris L.) based reconstruction of 130 years of water table fluctuations in a peatland and its relevance for moisture variability assessments

Continuous water-table (WT) measurements from peatlands are scarce and – if existing at all –very short. Consequently, proxy indicators are critically needed to simulate hydrological changes in peatlands over longer time periods. In this study, we demonstrate that tree-ring width (TRW) records of Scots pine (Pinus sylvestris L.) growing in the Čepkeliai peatland (southern Lithuania) can be used as a proxy to reconstruct hydrological variability in a raised bog environment. A two-step modelling procedure was applied to extend existing measurements and to develop a new and longer peatland WT time series. To this end, we used instrumental WT measurements extending back to 2002, meteorological records, a P-PET (difference between precipitation and potential evapotranspiration) series covering the period 1935–2014, so as to construct a tree-ring based time series of WT fluctuations at the site for the period 1870–2014. Strongest correlations were obtained between average annual WT measured at the bog margin and total P-PET over 7 years (r = 0.923, p < 0.00001), as well as between modelled WT and standardized TRW data with a two years lag (r = −0.602, p < 0.001) for those periods where WT fluctuated at the level of pine roots which is typically at <50 cm depth below the peat surface. Our results suggest that moisture is a limiting factor for tree growth at peatlands, but below a certain WT level (<50 cm under the soil surface), drought becomes a limiting factor instead. To validate the WT reconstruction from the Čepkeliai bog, results were compared to Nemunas river runoff since CE 1812 (r = 0.39, p < 0.00001, 1870–2014). We conclude that peatlands can act both as sinks and sources of greenhouse gases in case that hydrological conditions change, but that hydrological lags and complex feedbacks still hamper our understanding of several processes affecting the hydrology and carbon budget in peatlands. We therefore call for the development of further proxy records of water-table variability in peatlands to improve our understanding of peatland responses to climatic changes.