Ring-width Chronologies Research Articles

Climate-Driven Differences in Growth Performance of Cohabitant Fir and Birch in a Subalpine Forest in Dhorpatan Nepal

Himalayan Silver Fir (Abies spectabilis) and Himalayan Birch (Betula utilis) are tree species often found coexisting in sub-alpine forests of the Nepal Himalayas. To assess species-specific growth performances of these species, tree-ring samples were collected from the subalpine forest in the Dhorpatan Hunting Reserve, Nepal. Standard ring width chronologies of both species were correlated with climatic variables in both static and running windows. Differential and contrasting temporal responses of radial growth of these species to climate were found. Warmer and drier springs appeared to limit birch radial growth. Whereas radial growth of fir showed weakened climate sensitivity. Moving correlation analyses revealed divergent influences of spring climate on both fir and birch. Significant warming that occurred in the 1970s coincided with growth declines in birch and an increase in fir, as indicated by basal area increment. In summary, recent warming has been unfavorable for birch, and favorable to fir radial growth.

Comparison of the Radial Growth Response of Picea crassifolia to Climate Change in Different Regions of the Central and Eastern Qilian Mountains

It is important to explore the responses of radial tree growth in different regions to understand growth patterns and to enhance forest management and protection with climate change. We constructed tree ring width chronologies of Picea crassifolia from different regions of the Qilian Mountains of northwest China. We used Pearson correlation and moving correlation to analyze the main climate factors limiting radial growth of trees and the temporal stability of the growth–climate relationship, while spatial correlation is the result of further testing the first two terms in space. The conclusions were as follows: (1) Radial growth had different trends, showing an increasing followed by a decreasing trend in the central region, a continuously increasing trend in the eastern region, and a gradually decreasing trend in the isolated mountain. (2) Radial tree growth in the central region and isolated mountains was constrained by drought stress, and tree growth in the central region was significantly negatively correlated with growing season temperature. Isolated mountains showed a significant negative correlation with mean minimum of growing season and a significant positive correlation with total precipitation. (3) Temporal dynamic responses of radial growth in the central region to the temperatures and SPEI (the standardized precipitation evapotranspiration index) in the growing season were unstable, the isolated mountains to total precipitation was unstable, and that to SPEI was stable. The results of this study suggest that scientific management and maintenance plans of the forest ecosystem should be developed according to the response and growth patterns of the Qinghai spruce to climate change in different regions of the Qilian Mountains.

Different Wood Anatomical and Growth Responses in European Beech (Fagus sylvatica L.) at Three Forest Sites in Slovenia.

European beech (Fagus sylvatica L.) adapts to local growing conditions to enhance its performance. In response to variations in climatic conditions, beech trees adjust leaf phenology, cambial phenology, and wood formation patterns, which result in different tree-ring widths (TRWs) and wood anatomy. Chronologies of tree ring width and vessel features [i.e., mean vessel area (MVA), vessel density (VD), and relative conductive area (RCTA)] were produced for the 1960–2016 period for three sites that differ in climatic regimes and spring leaf phenology (two early- and one late-flushing populations). These data were used to investigate long-term relationships between climatic conditions and anatomical features of four quarters of tree-rings at annual and intra-annual scales. In addition, we investigated how TRW and vessel features adjust in response to extreme weather events (i.e., summer drought). We found significant differences in TRW, VD, and RCTA among the selected sites. Precipitation and maximum temperature before and during the growing season were the most important climatic factors affecting TRW and vessel characteristics. We confirmed differences in climate-growth relationships between the selected sites, late flushing beech population at Idrija showing the least pronounced response to climate. MVA was the only vessel trait that showed no relationship with TRW or other vessel features. The relationship between MVA and climatic factors evaluated at intra-annual scale indicated that vessel area in the first quarter of tree-ring were mainly influenced by climatic conditions in the previous growing season, while vessel area in the second to fourth quarters of tree ring width was mainly influenced by maximum temperature and precipitation in the current growing season. When comparing wet and dry years, beech from all sites showed a similar response, with reduced TRW and changes in intra-annual variation in vessel area. Our findings suggest that changes in temperature and precipitation regimes as predicted by most climate change scenarios will affect tree-ring increments and wood structure in beech, yet the response between sites or populations may differ.

Assessing cross-datable distinct annual growth rings in non-native Pinus kesiya Royle ex Gordon in Zambia

The response of non-native forest plantation trees to climate change remains poorly understood.We hypothesized that precipitation and temperature modulate tree-ring width chronology at each site and that higher tree growth is exhibited at remote sites than sites near copper mines. This study investigates if the annual tree-ring boundaries in non-native Pinus kesiya Royle ex Gordon in Zambia are distinct, cross-datable, and coherent with climate signal. We collected increment cores from live trees and climate data near and further away from emission sources and developed site tree-ring width chronologies. Based on cross-dating and chronology building statistics (i.e., ESP > 0.85; Glk > 0.6 and series inter-correlation > 0.4), P. kesiya posses cross-datable distinct annual growth ring boundaries that exhibited a high climate signal at both sites. The tree-ring width chronology was positively modulated by precipitation and negatively by solar radiation and temperature. The dry season precipitation was the limiting factor for the growth of P. kesiya. The predicted decrease in dry season precipitation and increase in temperature and solar radiation may reduce tree growth of P. kesiya, reduce productivity, and extend the rotation age. The mean ring width in P. kesiya was not significantly (p = 0.296) different between sites. However, the mean basal area increment at the site near the emission source (Ichimpe) was significantly (p < 0.001) higher than at the remote site (Chati), suggesting site-specific influences that require investigation. We recommend evaluating the causes and consequences of tree growth variation between sites and their relation to environmental variation, including microclimate, soils, and pollution. In this regard, an assessment of site-specific ring-width chronology and tree growth variation in this study directly contributes to an improved understanding of non-native P. kesiya ecology, and it offers the potential to study trees' responses to edaphic and climatic factors. Knowing these responses deepens our understanding of non-native pine tree growth in the face of climate change, given the significant role of tropical forests in the global carbon cycle.

351-year tree ring reconstruction of the Gongga Mountains winter minimum temperature and its relationship with the Atlantic Multidecadal Oscillation

Scarcity of high-resolution proxy records has hindered our understanding of long-term climate variations and their mechanism in climate-sensitive regions such as the Tibetan Plateau (TP). In this study, we present a winter minimum temperature (Tmin) reconstruction for the past 351 years (1648–1998) based on a composite tree ring width chronology from three upper treeline sites in the Gongga Mountains, southeastern TP. Despite a loss of sensitivity to winter Tmin after the 1990s, tree growth agrees well with previous December to current March (pDec-cMar) Tmin during 1953–1998, and a regression model based on climate-tree growth relationship over this period explains 52% of the instrumental Tmin variance. The resulting reconstruction exhibits three major cold (1670–1745, 1805–1853, and 1877–1949) and four major warm (1648–1669, 1746–1804, 1854–1876, and 1950–1998) periods over the past four centuries. Long-term winter Tmin variations in the Gongga Mountains have high coherence with those represented by temperature reconstructions in the nearby regions. Together, they indicate close association of the reconstructed warm/cold periods with the positive/negative phases of the Atlantic Multidecadal Oscillation (AMO), suggesting that the AMO may have been a key driving force affecting regional climate over the past few centuries.

June–July Temperature Reconstruction of Kashmir Valley from Tree Rings of Himalayan Pindrow Fir

The Himalaya is one of the major mountain ecosystems that is most likely to be impacted by climate change. The main drawback in understanding climate change in the remote Himalayan ecosystems is the lack of long-term instrumental climate records. Reconstructing past climates from tree-rings offers a useful proxy for adding data to the instrumental climate records. In this study, climatically sensitive tree-rings of Himalayan fir (Abies pindrow) were used for reconstruction of mean June–July temperatures of Kashmir valley. Total ring-width chronology was built from 60 tree-ring cores growing near the higher altitudinal limits of the species. The radial growth showed a strong positive response to growing season temperature. The strong response of site chronology to mean June–July temperatures was used for reconstruction purposes. Mean June–July temperatures of Kashmir valley were reconstructed since 1773 from residual site chronology. Though the reconstruction did not show any strong long-term trend, on a centennial-scale, 20th-century summers were the warmest with a mean annual summer temperature of 22.99 °C. Seven of the warmest years and five of the warmest decades were seen in the 20th century. The reconstruction for 1773–2012 showed 23 extreme hot summers above the hot threshold of a 23.47 °C mean temperature and 19 extreme cold years below the cold threshold of a 22.46 °C mean summer temperature. The cold years in the reconstruction did not coincide with known volcanic eruptions. This reconstruction will help in providing a better understanding of regional climate change.

Dendrohydrological Reconstructions Based on Tree-Ring Width (TRW) Chronologies of Narrow-Leaved Ash in the Sava River Basin (Croatia)

Current flood risk management is based on statistical models and assessments of the risk of occurrence over a given time period, although with very short measurement periods, usually following catastrophic events. Ongoing monitoring of basic hydrological (river-water level and streamflow) and climate data are the basis for sustainable water management and long-term flood control planning. The lack of data has proven to be particularly negative during this period of global climate change, when non-seasonal flooding (during summer) is becoming increasingly frequent, and the resulting damage greater. The aim of this study was to analyse the possible use of tree ring width chronologies of trees growing in floodplain areas to reconstruct hydrodynamic variables (river-water level and streamflow). The study analysed the influence of climatic and hydrological variables on the growth of narrow-leaved ash (Fraxinus angustifolia Vahl) in the Sava River basin. The results indicate the significant potential of narrow-leaved ash tree-ring width chronologies to reconstruct the summer streamflows of the Sava River (R2 = 0.45). These results can serve to develop long-term data series on the summer streamflows of the river, thereby enabling better insight into its spatial and temporal dynamics with the goal of more successful, sustainable management of floodplain areas.

Changes in the Tree-Ring Width-Derived Cumulative Normalized Difference Vegetation Index over Northeast China during 1825 to 2013 CE

Vegetation coverage is very important in terrestrial ecosystems and climate systems. However, the observational record of the normalized difference vegetation index (NDVI), which started in the 1980s when satellites became widely used, is too short to investigate the history of variation in vegetation coverage beyond the modern observation period. Here, we present a 189 y vegetation coverage series based on a total of 349 Mongolian pine (Pinus sylvestris var. mongolica Litv) cores from seven locations from the central–western Da Hinggan Mountains (CW–DHM), northeastern China. We found a significant relationship between tree-ring width and the regional cumulative normalized difference vegetation index (CNDVI). The correlation between the ring-width chronology and the regional June–July CNDVI (CNDVIJJ) was significant, with r = 0.68 (n = 32, p &lt; 0.001) and an explained variance of 45.8% (44.0% after the adjustment for the loss of the degree of freedom). On this basis, we designed a transfer function to reconstruct the CNDVIJJ for the CW–DHM region from 1825 to 2013 CE (Common Era). During the last 189 years, there were 28 years with high CNDVIJJ values, and another 28 years with low values. We also observed CNDVIJJ fluctuations at the inter-annual and decadal time scales, including eight low value periods and nine high value periods. Based on our analysis, the variation in CNDVI is associated with climatic factors, such as temperature, precipitation and the Palmer Drought Severity Index (PDSI), which combines both temperature and precipitation. From 1950 to 2002 CE, the CNDVI showed a noticeable decreasing trend in the CW–DHM region, whereas after 2003 CE, the CNDVI exhibited an apparent increase, which has also been observed in southern Central Siberia, eastern Mongolia and northeastern and eastern China, indicating that the CNDVI change in the CW–DHM is related to climate change in the local region and in some parts of Asia.

Multi-centennial reconstruction of drought events in South-Western Iran using tree rings of Mediterranean cypress (Cupressus sempervirens L.)

Semi-arid regions are among the most vulnerable areas prone to the negative impacts of climate change. Long-term high-resolution proxy climate data will enable us to put the recent climate trends into a long-term context of natural climate variability. We developed the hitherto first regional ring-width chronology (1450–2015C.E.) from Cupressus sempervirens L. in the Zagros Mountains, western Iran and reconstructed precipitation variability for the semi-arid region during the period 1560–2015C.E. Climate-growth relationships revealed that precipitation and minimum temperatures are positively correlated with radial growth, whereas maximum temperatures reveal negative impacts. Spatial correlations with gridded precipitation data, Palmer drought severity index (PDSI), and standardized precipitation-evapotranspiration index (SPEI 01) further indicate that the climate signals contained in tree-ring width variations capture the precipitation variability in the Near East and other eastern Mediterranean regions. The southern Zagros Mts. experienced multiple megadroughts during the reconstructed period. The longest dry period occurred from 1956 to 1971 and the highest frequency of dry events occurred in the 20th century. In addition, documented famines in Iran occurred within prolonged droughts. The southern Zagros Mts. has experienced high frequency of extreme/severe dry events and long dry phases during the Little Ice Age (1560–1850C.E.). The reconstructed dry and wet events occurred irregularly, and one-year and two-year drought/wet events showed the highest frequency during the reconstructed period, highlighting the importance of sustainable water management strategies for the semi-arid southern Zagros region.

Multi-century tree-ring anatomical evidence reveals increasing frequency and magnitude of spring discharge and floods in eastern boreal Canada

Abstract In eastern boreal Canada, variability in river discharge is poorly understood at the multi-century scale due to short instrumental records. In recent decades, increased magnitude and frequency of spring floods have raised concerns about the potential effects of climate change on flood risk. Unlike tree-ring width, flood rings have a demonstrated dendrochronological utility for reconstructing high discharge in boreal environments. In this study, twelve chronologies of earlywood vessel cross-sectional area (a new hydrological proxy) and ring width were developed from riparian Fraxinus nigra trees periodically flooded in spring. These chronologies were used as predictors of Harricana River spring discharge, which was reconstructed for the period 1771–2016. The reconstruction captured 69% of the variance over a 102-year calibration period. The reconstruction indicates that the magnitude and frequency of spring high discharge has increased since the end of the Little Ice Age (1850–1870 CE) and since 1950. The change from a multi-decadal frequency in the late 19th century to a decadal and then interannual frequency in the late 20th century is associated with an increase in snow cover over much of central-eastern Canada. The association between the reconstructed spring discharge and spring atmospheric circulation indices NINO3.4, AMO, NAO may also have changed in these periods and further work is needed to assess the stability of these associations. The correlation between reconstructed and instrumental spring discharge at the regional scale, as well as the shared features in reconstructed discharge and other paleorecords from subarctic Quebec suggest a common hydrological signal across the study area and for the early 20th to 21st centuries. The unprecedently low and high spring discharge in recent decades compared to the historical natural variability of the last 250 years also suggests that the increase in flood frequency and magnitude originates from climate change.

Prospects of Using Tree-Ring Earlywood and Latewood Width for Reconstruction of Crops Yield on Example of South Siberia

Improvement of dendrochronological crops yield reconstruction by separate application of earlywood and latewood width chronologies succeeded in rain-fed semiarid region. (1) Background: Tree-ring width chronologies have been successfully applied for crops yield reconstruction models. We propose application of separated earlywood and latewood width chronologies as possible predictors improving the fitness of reconstruction models. (2) Methods: The generalized yield series of main crops (spring wheat, spring barley, oats) were investigated in rain-fed and irrigated areas in semiarid steppes of South Siberia. Chronologies of earlywood, latewood, and total ring width of Siberian larch (Larix sibirica Ledeb.) growing in forest-steppe in the middle of the study area were tested as predictors of yield reconstruction models. (3) Results: In the rain-fed territory, separation of earlywood and latewood allowed increasing variation of yield explained by reconstruction model from 17.4 to 20.5%, whereas total climatic-driven component of variation was 41.5%. However, both tree-ring based models explained only 7.7% of yield variation in the irrigated territory (climate inclusion increased it to 34.8%). Low temperature sensitivity of larch growth was the main limitation of the model. A 240-year (1780–2019) history of crop failures and yield variation dynamics were estimated from the actual data and the best reconstruction model. (4) Conclusions: Presently in the study region, breeding of the environment-resistant crops varieties compensates the increase of temperature in the yield dynamics, preventing severe harvest losses. Tree-ring based reconstructions may help to understand and forecast response of the crops to the climatic variability, and also the probability of crop failures, particularly in the rain-fed territories.

244-year long tree-ring based drought records from Uttarakhand, western Himalaya, India

Droughts in the orography dominated mid-to-high elevation Himalaya have serious impact on the agrarian economy and biodiversity of the region. Temporally and spatially limited weather records from the Himalaya restrict our understanding on the socioeconomic impact of droughts in long-term perspective. In view of this, high-resolution proxies are required to develop long-term drought records from the data scarce Himalayan region. To fill this void, we developed February–May (FMAM) 4-month standardized precipitation-evapotranspiration index (SPEI4-May), a metric of drought, extending back to AD 1773 using ring-width chronology of Himalayan cedar (Cedrus deodara (Roxb.) G. Don) from Chakrata region of Garhwal, Uttarakhand, western Himalaya. The calibration model (1969–2016) captured 43% of the variance in the observed SPEI series. The SPEI reconstruction revealed high year-to-year and inter-decadal variation with 1774 (SPEI -3.11) and 1787 (SPEI +2.13) being the driest and the wettest years, respectively. The five year mean of reconstructed SPEI revealed droughts in 1818–1822, 1798–1802, 1813–1817, 1793–1797, 1958–1962 and pluvials in 1783–1787, 1838–1842, 1788–1792, 1933–1937, 1808–1812. A comparison of present SPEI reconstruction with other available tree-ring based precipitation and drought records from the western Himalayan region revealed synoptic scale features represented in our data. The findings underscore that a wide network of such large tree-ring based drought records from the data scarce Himalayan region should be very useful to understand the spatial distribution of droughts.

Impact of Channel Dredging and Straightening in an Atlantic White Cedar (Chamaecyparis thyoides L. (B.S.P.)) Freshwater Tidal Wetland

Stotts, S.; Callahan, J., and Gulledge, O., 2021. Impact of channel dredging and straightening in an Atlantic white cedar (Chamaecyparis thyoides L. (B.S.P.)) freshwater tidal wetland. Journal of Coastal Research, 37(5), 973–986. Coconut Creek (Florida), ISSN 0749-0208. Once prominent up the eastern coast of the United States, freshwater wetlands with Atlantic white cedar (AWC; Chamaecyparis thyoides L. (B.S.P.)) are now vanishing due to saltwater intrusion and anthropogenic landscape alterations. This study utilizes a historic, anthropogenic disturbance to provide insight into the AWC response to salinization. A major straightening and dredging project in the 1920s, including 16 oxbow cuts, allowed brackish water to move upstream in the St. Jones River in Dover, Delaware, leading to the die-off of an AWC swamp. The sampled AWC experienced climate change, storms, hydrologic alterations, and sea-level rise. Annual ring width and suppression event chronologies were developed from dead AWC and were compared to groupings of climate variables in the predisturbance (1895–1920) and postdisturbance (1928–1958) periods. Results of the dendrochronological analysis indicate that the AWC in this study died at an average age of 49.3 years, earlier than typically expected for such species. After the straightening and dredging, the AWC experienced changes in growth response to temperature while suppression events became positively correlated with elevated temperature (p = 0.024) and high precipitation (p = 0.019). The system also showed signs of becoming more sensitive to storm events in the postdisturbance period.

基于树轮记录的阿尔泰山中段1798年以来6-7月平均最低气温变化研究

PDF HTML阅读 XML下载 导出引用 引用提醒 基于树轮记录的阿尔泰山中段1798年以来6-7月平均最低气温变化研究 DOI: 10.5846/stxb201912312835 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 中国沙漠气象科学研究基金（Sqj2017004）；国家自然科学基金（41861006）；甘肃省高等学校科研项目（2018C-02） Changes of mean minimum temperature in June-July since 1798 in central Altay Mountain recorded by tree rings Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:通过分析新疆阿尔泰山中段西伯利亚落叶松树轮宽度年表与气候因子的相关关系证明6-7月平均最低气温是研究区树木径向生长的主控气候因子（r=0.649，P<0.001）。利用线性回归方法构建了阿尔泰山中段1798-2017年6-7月平均最低气温方程，通过计算重建方程方差解释量（41.1%）和利用逐一剔除法对重建方程各项参数进行了稳定性检验，证明了重建方程是稳定可靠的。分析重建的平均最低气温年际变化表明，研究区经历了4个暖期（1906-1919年、1922-1935年、1945-1960年和1997-2017年）和4个冷期（1816-1831年、1840-1867年、1869-1886年和1888-1905年），并且与相邻地区平均气温重建序列冷暖变化阶段一致。基于多窗谱分析结果发现重建6-7月平均最低气温序列存在2a、2.4a、2.8-3a、11a、20-22a左右的变化周期，表明研究区气候变化主要受厄尔尼诺-南方涛动（ENSO）、太阳黑子活动和全球海温变化（SST）驱动。本研究为系统掌握阿尔泰山气候变化规律和科学预测未来气候变化提供了依据。 Abstract:The analysis of the relationship between the tree ring width chronology of Larix sibirica and climatic factors in central Altay Mountain, Xinjiang indicates that the mean minimum temperature from June to July is the main climatic factors for the radial growth of trees (r=0.649, P<0.001). Mean minimum temperature equation from June to July in the past 220 years in central Altay Mountain was constructed using the linear regression method, and the interpretation of the variance of the reconstructed equation was 41.1%. The leave-one-out method was used to test the stability of the reconstruction equation, and various test parameters proved that the reconstruction equation was stable and reliable. Inter-annual changes in the reconstructed mean minimum temperature indicated that there are four warm periods (1906-1919, 1922-1935, 1945-1960, and 1997-2017) and four cold periods (1816-1831, 1840-1867, 1869-1886, and 1888-1905) in the study area. These are consistent with the cold and warm stages of the reconstruction sequence of the mean temperature in the adjacent area. The reconstructed sequence with change periods of about 2a, 2.4a, 2.8-3a, 11a, and 20-22a based on the multi-taper analysis indicates that climate change is mainly driven by the global sea surface temperature (SST), sunspots and ENSO (El Niño-Southern Oscillation) in the study area. The reconstructed mean minimum temperature provides a basis for systematically mastering regularity and scientifically predicting future tendency of climate change in the Altay Mountain. 参考文献 相似文献 引证文献

Ring widths of Rhododendron shrubs reveal a persistent winter warming in the central Himalaya

Himalayan Mountains provide unique opportunities for the extension of shrub-ring based dendroclimatology beyond the upper tree limit. However, little is known about limiting climate factors of shrub growth under harsh environmental conditions. We established a new ring-width chronology of a Himalayan shrub rhododendron (Rhododendron campanulatum D. Don) at the upper Krummholz treeline in the Mt. Gaurishankar massif, central Himalaya, Nepal. Bootstrapped correlation analysis showed positive relationships between radial growth and temperatures of all months from previous November to current October. Correlations were the highest with winter (December-February) minimum temperature (r = 0.781, p < 0.001), indicating that radial growth of R. campanulatum is strongly sensitive to winter minimum temperature. The linear regression model explained 61 % of the actual winter minimum temperature variance during the calibration period 1960–2013. Periods of low and high minimum winter temperatures in the central Himalaya were consistent with cool and warm episodes found by other regional winter temperature reconstructions from the Himalayas and the Tibetan Plateau. Spatial correlation analysis with land surface temperatures revealed the spatial representativeness of our reconstruction for a larger geographical territory over the Himalayas and the Tibetan Plateau. Furthermore, winter temperature in the central Himalaya is teleconnected with the December-February India-Burma trough. The persistent increasing winter temperature in recent decades in the central Himalaya coincides with continental-scale warming. Alpine vegetation in humid regions of the Himalayas may benefit from winter warming via an earlier start and extension of the growing season, as long as moisture availability is sufficient.

Increasing climate sensitivity of subtropical conifers along an aridity gradient

Subtropical forests are an important but still poorly understood component of the global carbon cycle and global biodiversity. If climate continues to change as anticipated, increasing drought may affect the composition and structure of many subtropical forests. Understanding the environmental conditions that determine drought sensitivity across subtropical ecosystems and trees species will help accurately predict their response to climate change and inform the best mitigation and protection strategies. To identify the broad-scale drivers of drought sensitivity, we collected a large network of ring-width chronologies along a broad climate gradient that spans from east to west of the Yunnan-Guizhou Plateau (YGP), in southwestern China. Our network includes growth data from 10 trees species in 28 old growth subtropical coniferous sites. We used tree ring analyses, Redundancy Analysis (RDA), and linear mixed effects models to assess how drought responses varied geographically, climatically, and taxonomically. We found that aridity exerted the strongest limitation in our study area, implying that subtropical forest responses to drought may be more complex than commonly assumed. Moreover, we found that drought intensity during dry season, proxied by aridity index, is a stronger driver of drought sensitivity than stand characteristics and microenvironment. Further increases in drought frequency and dry season drought intensity in the region associated with climate change may pose a larger-than-expected threat to the growth, and ultimately persistence, of many subtropical coniferous forests.

Growth performance of planted population of Pinus roxburghii in central Nepal

BackgroundClimate change has altered the various ecosystem processes including forest ecosystem in Himalayan region. Although the high mountain natural forests including treelines in the Himalayan region are mainly reported to be temperature sensitive, the temperature-related water stress in an important growth-limiting factor for middle elevation mountains. And there are very few evidences on growth performance of planted forest in changing climate in the Himalayan region. A dendrochronological study was carried out to verify and record the impact of warming temperature tree growth by using the tree cores of Pinus roxburghii from Batase village of Dhulikhel in Central Nepal with sub-tropical climatic zone. For this total, 29 tree cores from 25 trees of P. roxburghii were measured and analyzed.ResultA 44-year long tree ring width chronology was constructed from the cores. The result showed that the radial growth of P. roxburghii was positively correlated with pre-monsoon (April) rainfall, although the correlation was not significant and negatively correlated with summer rainfall. The strongest negative correlation was found between radial growth and rainfall of June followed by the rainfall of January. Also, the radial growth showed significant positive correlation with that previous year August mean temperature and maximum temperature, and significant negative correlation between radial growth and maximum temperature (Tmax) of May and of spring season (March-May), indicating moisture as the key factor for radial growth. Despite the overall positive trend in the basal area increment (BAI), we have found the abrupt decline between 1995 and 2005 AD.ConclusionThe results indicated that chir pine planted population was moisture sensitive, and the negative impact of higher temperature during early growth season (March-May) was clearly seen on the radial growth. We emphasize that the forest would experience further moisture stress if the trend of warming temperatures continues. The unusual decreasing BAI trend might be associated with forest management processes including resin collection and other disturbances. Our results showed that the planted pine forest stand is sub-healthy due to major human intervention at times. Further exploration of growth climate response from different climatic zones and management regimes is important to improve our understanding on the growth performance of mid-hill pine forests in Nepal.

Comparison of tree-ring growth and eddy covariance-based ecosystem productivities in three different-aged pine plantation forests

This study utilized dendrochronology and long-term (2003–2017) eddy covariance (EC) carbon flux data to investigate the relationships between tree growth and gross ecosystem productivity (GEPEC) in different-age (15-, 42- and 78-year old) pine plantation forests in the Great Lakes region in eastern North America and found that tree-ring growth in these different-age pine forests was significantly (p < 0.05) correlated with observed annual GEPEC values. Forests play a major role in the global carbon cycle. Understanding the dynamics of the forest carbon cycle and its driving factors is challenging. This study utilized dendrochronology and long-term (2003–2017) eddy covariance (EC) carbon flux data to investigate the relationships between tree growth and gross and net ecosystem productivities (GEPEC and NEPEC) in different-age (15-, 42- and 78-year old) pine plantation forests in the Great Lakes region in eastern North America. Tree growth in these different-age pine forests was significantly (p < 0.05) correlated with observed annual GEPEC values, while coherence between tree growth and NEPEC was relatively poor. Current-year and 1-year lagged ring-width chronologies and climate variables, including spring (April–May) temperature (TSPR) and Standardized Potential Evapotranspiration Index (SPEISUM) over the summer months (June–August) were used to test ten different linear regression models to simulate tree-ring-based GEP (GEPTR) values at all three sites. This analysis showed that current-year growth was the best predictor of GEPTR at all three sites, when compared to observed GEPEC, except during drought years, when GEPTR was underestimated. Current-year tree growth models were then used to reconstruct GEPTR over the life span of each stand. These reconstructions showed low GEPTR values from 1978 to 1988 and from 2002 to 2007. Low GEPTR in late 1970s occurred in response to below average temperatures when there were no major drought periods, while low GEPTR in early 2000s occurred following drought-like conditions in 2002. However, in recent years relatively higher GEPTR was observed at all three different-age forest sites. This interdisciplinary study will help to improve our understanding of carbon exchanges and the key environmental controls and associated uncertainties on tree growth in these different-age plantation stands in eastern North America. It will also help to determine how these forests may respond to climate change.

Micro-site conditions affect Fennoscandian forest growth

The long tradition of dendroclimatological studies in Fennoscandia is fostered by the exceptional longevity and temperature sensitivity of tree growth, as well as the existence of well-preserved subfossil wood in shallow lakes and extent peat bogs. Although some of the world’s longest ring width and density-based climate reconstructions have been developed in northern Fennoscandia, it is still unclear if differences in micro-site ecology matter, and if so, whether they have been considered sufficiently in previous studies. We developed a Fennoscandia-wide network of 44 Scots pine ring width chronologies from 22 locations between 59°–70 °N and 16°–31 °E, to assess the effects of moist lakeshores and dry inland micro-sites on tree growth. Our network reveals a strong dependency of pine growth on July temperature, which is also reflected in latitude. Differences in forest productivity between moist and dry micro-sites are likely caused by associated effects on soil temperature. While trees at moist micro-sites at western locations exhibit higher growth rates, this pattern is reversed in the continental eastern part of the network, where increased ring widths are found at drier sites. In addition to the latitudinal increase in growth sensitivity to July temperature, pines at moist sites exhibit an increased dependency of summer warmth. The highest temperature sensitivity and growth coherency, and thus greatest suitability for summer temperature reconstructions, is found in those regions where July mean temperatures range between 11.5 and 13.5 °C, and May precipitation totals do not exceed 100 mm. Our study not only provides guidance for the selection of sampling sites for tree ring-based climate reconstructions, but also reveals the effect of micro-site ecology on Fennoscandian forest growth. The manifestation of micro-site effects varies substantially over the Fennoscandian boreal forest and is predominately triggered by the geographical setting of the stand as expressed by differing abiotic site factors.

Streamflow Variability Indicated by False Rings in Bald Cypress (Taxodium distichum (L.) Rich.)

Despite growing in wet lowland and riparian settings, Taxodium distichum (L.) Rich. (bald cypress) has a strong response to hydroclimate variability, and tree ring chronologies derived from bald cypress have been used extensively to reconstruct drought, precipitation and streamflow. Previous studies have also demonstrated that false rings in bald cypress appear to be the result of variations in water availability during the growing season. In this study 28 trees from two sites located adjacent to the Choctawhatchee River in Northwestern Florida, USA were used to develop a false ring record extending from 1881 to 2014. Twenty false ring events were recorded during the available instrumental era (1931–2014). This record was compared with daily and monthly streamflow data from a nearby gage. All 20 of the false-ring events recorded during the instrumental period occurred during years in which greatly increased streamflow occurred late in the growing season. Many of these wet events appear to be the result of rainfall resulting from landfalling tropical cyclones. We also found that the intra-annual position of false rings within growth rings reflects streamflow variability and combining the false-ring record with tree ring width chronologies improves the estimation of overall summer streamflow by 14%. Future work using these and other quantitative approaches for the identification and measurement of false ring variables in tree rings may improve tree-ring reconstructions of streamflow and potentially the record of tropical cyclone rainfall events.