Search

The escalating impact of climate change on global terrestrial ecosystems demands a robust prediction of the trees' growth patterns and physiological adaptation for sustainable forestry and successful conservation efforts. Understanding these dynamics at an intra‐annual resolution can offer deeper insights into tree responses under various future climate scenarios. However, the existing approaches to infer cambial or leaf phenological change are mainly focused on certain climatic zones (such as higher latitudes) or species with foliage discolouration during the fall season. In this study, we demonstrated a novel approach (INTRAGRO) to combine intra‐annual circumference records generated by dendrometers coupled to the output of climate models to predict future tree growth at intra‐annual resolution using a series of supervised and unsupervised machine learning algorithms. INTRAGRO performed well using our dataset, that is dendrometer data of P. roxburghii Sarg. from the subtropical mid‐elevation belt of Nepal, with robust test statistics. Our growth prediction shows enhanced tree growth at our study site for the middle and end of the 21st century. This result is remarkable since the predicted growing season by INTRAGRO is expected to shorten due to changes in seasonal precipitation. INTRAGRO's key advantage is the opportunity to analyse changes in trees' intra‐annual growth dynamics on a global scale, regardless of the investigated tree species, regional climate and geographical conditions. Such information is important to assess tree species' growth performance and physiological adaptation to growing season change under different climate scenarios. [ABSTRACT FROM AUTHOR]

Palaeoclimatic evidence is necessary to place the current warming and drying trends of the Mediterranean region in a long‐term perspective of pre‐industrial variability. Annually resolved and absolutely dated climate proxies that extend back into medieval times are, however, limited to a few sites only. Here we present a network of long ring width chronologies from Pinus nigra tree‐line sites in northern Corsica (France) that cohere exceptionally well over centuries and support the development of a single high‐elevation pine chronology extending back to 974 CE. We apply various detrending methods to these data to retain high‐to‐low frequency ring width variability and scale the resulting chronologies against instrumental precipitation and drought observations to produce hydroclimate reconstructions for the last millennium. Proxy calibration and transfer are challenged by a lack of high‐elevation meteorological data, however, limiting our understanding of precipitation changes in sub‐alpine tree‐line environments. Our new reconstructions extend beyond existing records and provide evidence for low‐frequency precipitation variability in the central‐western Mediterranean from 974–2016 CE. Comparison with a European scale drought reconstruction network shows that regional predictor chronologies are needed to accurately estimate long‐term hydroclimate variability on Corsica. [ABSTRACT FROM AUTHOR]

To develop a high‐resolution paleoclimate proxy record facilitating adaptation measures on drought impacts, we constructed a regional composite tree‐ring chronology of teak (Tectona grandis) by combining three local site chronologies from southern Myanmar. Our regional tree‐ring record is strongly correlated with the November–April self‐calibrated Palmer drought severity index and enabled us to reconstruct drought variability for the period 1802–2016. The reconstruction explained 46.5% of the actual self‐calibrated Palmer drought severity index variance. Over the past two centuries, we detected one extreme (1812) and six severe drought years (1810, 1811, 1816, 1852, 1887, and 1980). Dry periods coincided with six major famines that occurred in India. Spatial correlation analyses revealed that drought occurrence is linked to broader‐scale atmospheric circulations of the Pacific and Indian Oceans, especially during the positive phase of the El Niño–Southern Oscillation. Our reconstruction provides a useful historical perspective for assessing adaptation measures intent on mitigating future drought impacts in Myanmar. Plain Language Summary: We developed a 226‐year‐long ring‐width regional chronology of teak by combining three site chronologies from southern Myanmar. Teak growth is mainly controlled by moisture availability during the dry season, making teak a suitable species for assessing drought variation in southern Myanmar. We reconstructed a 215‐year drought history and find prolonged droughts occurred in 1808–1823, 1837–1843, 1863–1876, 1883–1891, 1895–1901, 1908–1912, 1922–1930, 1941–1945, 1952–1963, 1976–1994, and 2010–2015. We also found a strong association between drought variability in southern Myanmar and sea surface temperatures in the Pacific and Indian Oceans, as well as the El Niño–Southern Oscillation phenomenon. The results are useful to devise necessary policies and strategies for coping with the adverse impacts of drought and protecting the livelihoods of regional populations. Key Points: The radial growth of teak in southern Myanmar is mainly limited by moisture availability during the dry seasonDry episodes in the past 200 years in southern Myanmar coincided with six major famines in India and other regional drought reconstructionsDrought variations in southern Myanmar may be linked to large‐scale climate drivers, mainly tropical SST variations and El Niño events [ABSTRACT FROM AUTHOR]

Climate-related environmental and humanitarian crisis are important challenges in the Great Horn of Africa ( GHA). In the absence of long-term past climate records in the region, tree-rings are valuable climate proxies, reflecting past climate variations and complementing climate records prior to the instrumental era. We established annually resolved multi-century tree-ring chronology from Juniperus procera trees in northern Ethiopia, the longest series yet for the GHA. The chronology correlates significantly with wet-season ( r = .64, p < .01) and annual ( r = .68, p < .01) regional rainfall. Reconstructed rainfall since A.D. 1811 revealed significant interannual variations between 2.2 and 3.8 year periodicity, with significant decadal and multidecadal variations during 1855-1900 and 1960-1990. The duration of negative and positive rainfall anomalies varied between 1-7 years and 1-8 years. Approximately 78.4% (95%) of reconstructed dry (extreme dry) and 85.4% (95%) of wet (extreme wet) events lasted for 1 year only and corresponded to historical records of famine and flooding, suggesting that future climate change studies should be both trend and extreme event focused. The average return periods for dry (extreme dry) and wet (extreme wet) events were 4.1 (8.8) years and 4.1 (9.5) years. Extreme-dry conditions during the 19th century were concurrent with drought episodes in equatorial eastern Africa that occurred at the end of the Little Ice Age. El Niño and La Niña events matched with 38.5% and 50% of extreme-dry and extreme-wet events. Equivalent matches for positive and negative Indian Ocean Dipole events were weaker, reaching 23.1 and 25%, respectively. Spatial correlations revealed that reconstructed rainfall represents wet-season rainfall variations over northern Ethiopia and large parts of the Sahel belt. The data presented are useful for backcasting climate and hydrological models and for developing regional strategic plans to manage scarce and contested water resources. Historical perspectives on long-term regional rainfall variability improve the interpretation of recent climate trends. [ABSTRACT FROM AUTHOR]

ABSTRACT In this study, we examine the relationship between short- and long-term effects of precipitation deficits, integrated in a drought index called 'Joint Deficit Index ( JDI)', and tree-ring growth of oak trees ( Quercus infectoria) in the Javan-Roud region, Kermanshah province (Iran). Precipitation data from regional climate stations cover the period 1968-2008, and the tree-ring width chronology span over the period 1818-2008. This chronology is highly correlated with the JDI (January-September) series for the instrumental period ( P < 0.01). Therefore, the regional JDI was reconstructed using a simple linear regression model which accounts for 40% of JDI (January-September) variances over the instrumental period. Reconstructed drought periods persisted on average for 2 years, and some severe drought lasted for 3-4 years. However, one 7-year drought was reconstructed over the period 1923-1929. The most severe droughts occurred in the periods 1960-1963 and 1999-2001. While the reconstructed JDIs have no significant correlation with the North Atlantic Oscillation, a significant negative correlation was observed with the Southern Oscillation Index in November and December of pre growth during the common period from 1877 to 2008. An appropriate agreement was found between our reconstruction and historical famines in Iran and also reconstructed results from neighbouring countries in the east (China) and west (Turkey and other countries around the Mediterranean Sea), particularly for the most severe droughts. The highest agreement was achieved with regions in the pathway of westerly storm tracks travelling via the Mediterranean region into Iran. [ABSTRACT FROM AUTHOR]

The Modjo watershed has experienced significant land use/land cover (LULC) change and soil erosion. This study examines changes in surface runoff generation and soil erosion in response to the LULC dynamics. To simulate runoff and sediment yield, the geographic information system-interfaced Soil and Water Assessment Tool (SWAT) model was used. Model sensitivity, calibration and validation analyses were carried out, and the efficiency of the model was evaluated using simulated and measured discharge data. The two scenario model simulation goodness-of-fit measures verified that the SWAT model performed very well during calibration and validation periods for daily and monthly time steps (Nash-Sutcliffe efficiency > 0·79 and root mean square error-observation standard deviation ratio < 0·4). Although the computed values of per cent bias fulfilled a satisfactory standard (greater than −11·8%), the model results tended to overestimate discharge. Consequent to the LULC change, an overall increase in the amount of surface runoff (14·2%) and sediment yield (37%) was observed relative to the baseline (1973) simulation scenario. Mean annual soil loss rate was estimated at 24·2 Mg ha−1 y−1. Nearly 95·2% of the watershed is experiencing moderate to severe soil loss rates ranging from 14·7 to 37·5 Mg ha−1 y−1. In the remaining parts of the watershed, soil loss rates range from 4·4 to 14·7 Mg ha−1 y−1. Surface runoff generation and soil erosion varied widely by soil, LULC types and slope positions. The observed environmental change would lead to further land degradation, with negative implications on the livelihoods of local people unless appropriate conservation measures are implemented. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Long-term instrumental records that provide estimates about the natural range of long-term climate fluctuation are lacking in Iran. Ring-width chronologies were developed from two oak sites in the central Zagros Mountains, dating back to 1705 A.D. Due to high correlations between the local site chronologies, a mean regional chronology ( RC) was calculated. Correlations with regionalized climate data showed significant negative correlations with maximum temperature in December of the previous year and February, May, June and August of the current year. However, May-June maximum temperatures of the current growing season showed the highest negative correlation coefficient with regional tree growth patterns. Based on this relationship, maximum temperature of May-June was reconstructed over the last 170 years (1840-2010). The average length of cold periods was shorter than that of warm periods. Further sampling may allow the analysis of long-term climatic trends in this region. [ABSTRACT FROM AUTHOR]

Questions El Niño Southern Oscillation ( ENSO) is a strong driver of climatic and ecosystem variability in coastal NW Peru. La Niña amplifies the already dry local conditions, and led to depleted ecosystems in 2011. However, the 2012 La Niña event triggered rainfall far above the average. (1) Did plant species diversity, primary productivity and vegetation assemblages change along a climatic gradient between two climatologically different La Niña years; (2) Is there a difference in explanatory power of environmental predictors between the 2 yr; and (iii) is it possible to predict the observed vegetation patterns spatially? Location Transect along a climatic gradient in the Sechura Desert of Piura, NW Peru (corresponds to the terrestrial part of the El Niño region 1 + 2) - a region of extremely high climatic variability. Methods We visited 50 30 m × 30 m randomly sampled plots in 2011 and 2012. A Procrustes analysis of two non-metric multidimensional scaling ( NMDS) ordinations provided information on the temporal change of species assemblages. Variation partitioning revealed the differences in explanatory power of the predictors. We employed a generalized additive model ( GAM) to fit the scores of the first ordination axis with a floristic gradient map as a result. Results Generally, higher rainfall resulted in a positive feedback when considering biodiversity, productivity and vegetation assemblages. The floristic gradient map resulting from the GAM displayed the spatial distribution of the three main assemblages along the climatic gradient. Edaphic variables added no independent portion to the explanation of the vegetation assemblages, but explained in conjunction with topography and NDVI a considerable amount of the variance. Conclusions Strong Atlantic easterly winds crossing the Andes can boost plant growth even during a La Niña situation. This underscores the need for a deeper understanding of ENSO-related climate variability of ENSO. Combining vegetation maps with accurate predictions of such climatic anomalies would aid the effective execution of conservation and recovery strategies. Additionally, coupling an unconstrained ordination with a GAM appears to be a promising tool for vegetation mapping, especially in the presence of a non-linear gradient. [ABSTRACT FROM AUTHOR]

Copyright of Biotropica is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We present an intra-annual stable carbon isotope (δ13C) study based on a labeling experiment to illustrate differences in temporal patterns of recent carbon allocation to wood structures of two functional types of trees, Podocarpus falcatus (a late-successional evergreen conifer) and Croton macrostachyus (a deciduous broadleaved pioneer tree), in a tropical mountain forest in Ethiopia., Dendrometer data, wood anatomical thin sections, and intra-annual δ13C analyses were applied., Isotope data revealed a clear annual growth pattern in both studied species. For P. falcatus, it was possible to synchronize annual δ13C peaks, wood anatomical structures and monthly precipitation patterns. The labeling signature was evident for three consecutive years. For C. macrostachyus, isotope data illustrate a rapid decline of the labeling signal within half a year., Our δ13C labeling study indicates a distinct difference in carryover effects between trees of different functional types. A proportion of the labeled δ13C is stored in reserves of wood parenchyma for up to 3 yr in P. falcatus. By contrast, C. macrostachyus shows a high turnover of assimilates and a carbon carryover effect is only detectable in the subsequent year. [ABSTRACT FROM AUTHOR]

Monthly mean (TEM), maximum ( Tmax) and minimum ( Tmin) surface air temperatures at 119 meteorological stations on the Yunnan Plateau (YP, Southwest China) were analysed for temporal trends and spatial variation patterns during the period 1961-2004. Linear trend analyses revealed that annual temperature over the YP increased at a rate of 0.3 °C/decade during the period 1961-2004, while warming trend of 0.33 °C/decade and 0.26 °C/decade was observed for winter and summer temperatures, respectively. Warming trends of nighttime minimum temperature are more pronounced than those of daytime maximum temperature, especially during winter season. Consequently, a decreasing trend of diurnal temperature ranges (DTR = Tmax − Tmin) was observed. Five spatial patterns of temperature variability were objectively defined by rotated empirical orthogonal function (EOF) analysis, which are associated with distinct temporal temperature variations and geographical area over the YP. Annual temperature increases were found to be most pronounced in the southern and northwestern (high-elevation) parts of the YP, whereas the hot-dry valleys along the Yangtze and Red River basins experienced cooling during the past four decades. Copyright © 2010 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

We present a 620-year long ring width record from the middle Qilian Mountains, where it is presently controlled by the Westerlies. The chronology was developed from Qilian juniper ( Sabina przewalskii) growing at sites near the western distribution limit of the species in the northern Qilian Mountains, Gansu Province, China. A linear regression model between ring width and annual (July to June) precipitation accounts for 34.9% of the observed instrumental precipitation variance during the period 1952 to 2007. Spatial correlation analyses between the reconstruction and gridded precipitation data shows that the annual precipitation reconstruction captures regional climatic variations over the Qilian Mountains and the nearby Hexi Corridor. We also show the scaled standard chronology adjusted to the mean and variance of the instrumental data. Relatively wet periods are identified for AD 1390-1413, 1425-1450, 1530-1649, 1792-1920, 1937-1949 and 1980-1985. Dry conditions prevailed during AD 1414-1424, 1451-1529, 1650-1791, 1921-1936, 1950-1979 and 1986-2007. In comparison with the regression-based reconstruction, the scaled reconstruction indicates considerably wetter conditions during 1390-1413, 1425-1450, 1570-1630 and 1790-1920. The interval AD 1451-1529 was the most intense and longest drought epoch in the Hexi Corridor over the past six centuries. This drought was not only recorded in the Qilian Mountains but also occurred in northern and eastern China. It might be caused by a substantial weakening of the Asian summer monsoon induced by the joint effects of solar and volcanic activities at that time. Our results also suggest that the Hexi Corridor was under the control of the Asian monsoon circulation on inter-decadal to centennial timescales in the past centuries. Copyright © 2010 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

The article presents a study on the temperature history recorded by tree rings in the Tibetan Plateau (TP), China during 1612-1998. The study develops two ring-width index chronologies such as traditionally standardized chronology (TSC) and regional curve standardization (RCS) for detrending. The results show that low-frequency and high-frequency temperature variations are captured by RCS and TSC reconstructions, and the response patterns of RSC chronology to climate data are similar to the TSC.

The article discusses a tree ring-based drought reconstruction in the central Hengduan Mountains in north-western Yunnan, China. The study involved developing four tree ring-width chronologies of three species. It was found that there are correlations existing among the chronologies, and that the first principal component makes up 60.5% of total variance in 1655-2005. Also, radial growth was observed to be affected by precipitation and relative humidity and Palmer drought severity index (PDSI), whereas tree growth is negatively affected by temperature in March.

Aim Our main aim is to determine if ring-width variations in Empetrum hermaphroditum reflect regional or local topoclimate signals in an alpine environment. In the case that topoclimate provides the dominant signal, a secondary aim is to link these to spatial distribution patterns of different vegetation types. Location The study area is situated in the middle alpine belt in the Vågåmo region, Central Norwegian Scandes. Sampling sites cover different topoclimates: ridges, north-facing slopes and south-facing slopes. Methods We constructed ring-width chronologies of E. hermaphroditum for each type of microsite for the common period 1951–2004. Climate data were prepared on an hourly, daily and growing-season time scale. Climate–growth relationships were evaluated using bivariate correlations and regression tree methods for continuous time-series analyses. In addition, extreme growth anomalies (pointer years) were compared with the climate conditions in those years. The impact of water supply on wood anatomy was determined by correlating the conductive area (percentage of vessel per growth ring) with a running mean (sum) of 10-day intervals for temperature and precipitation. Results This study indicates that mean summer (June–August) temperatures determine the width of the growth rings of E. hermaphroditum irrespective of topoclimate. The length of the growing season, which is the most differentiating climatic factor between microsites, does not substantially alter the anatomical ring structure. Microsite differences in mean growth rates are attributed to the higher frequency of warm days. Extremely warm days limit ring-width development at south-facing slopes, while plants at ridges and north-facing slopes still benefit from higher temperatures. As a consequence, pointer years are not developed synchronously at all microsites. Vessel formation is affected by available moisture, especially in the later part of the growing season. Main conclusions Topoclimate induces slight modifications of annual growth-ring increments of E. hermaphroditum at different microsites. In contrast to the distribution patterns of vegetation types that are determined by snow cover, growth-ring variations are related to summer temperature conditions, and the prominent regional climate signal is still reflected at all microsites. This offers the opportunity to reconstruct climatic change in alpine regions from dwarf shrub ring-width chronologies. [ABSTRACT FROM AUTHOR]