A tree-centered approach to assess impacts of extreme climatic events on forests

Ajut Marie Curie IF fellowship (No 659191); COST Action FP1106 STReES

Growth-Ring Boundary Anatomy And Dendrochronological Potential In A Moist Tropical Forest In Northeastern Bangladesh

We present the microscopic analysis of growth-ring boundary anatomy of 27 tree species from a moist tropical forest in Bangladesh and evaluate their dendrochronological potential. We observed high inter-species variability in the anatomical features that define growth-ring boundaries. Marginal parenchyma, fibre zones, and thick-walled latewood fibres were identified as the dominant anatomical features delineating growth-ring boundaries. The evaluation of growth-ring boundary distinctness in thin-sections and scanned images revealed that 25 out of 27 studied species (93%) showed distinct to fairly distinct growth-ring boundaries. Cluster analysis of wood anatomical features was used to select an additional 5 species for further investigation. Ring-width series of these species crossdated well within the same tree. Between trees crossdating was also successful in all 5 species. The Gleichlaufigkeit (GLK; i.e. the proportion of agreement/disagreement of inter-annual growth tendencies among the trees) varied among species between 0.55 and 0.71. A strong synchronization of tree-ring series between trees suggests that growth rings are annual and influenced by common environmental factors. The derived tree-ring series, estimated tree ages, and growth trajectories underline the high potential of our study area for answering a variety of climatological, ecological and archaeological questions by applying den-drochronology. This study will therefore provide a new endeavor in tropical dendrochronology of South Asian moist tropical forests.This item is part of the Tree-Ring Research (formerly Tree-Ring Bulletin) archive. For more information about this peer-reviewed scholarly journal, please email the Editor of Tree-Ring Research at [email protected]

Tree ring inferred summer temperature variations over the last millennium in Western Himalaya, India

We report the first millennium-long reconstruction of mean summer (May-June-July-August) temperature extending back to AD 940 derived from tree-ring width data of Himalayan pencil juniper (Juniperus polycarpos C. Koch) from the monsoon-shadow zone in the western Himalaya, India. Centennial-scale variations in the reconstruction reveal periods of protracted warmth encompassing the 11-15th centuries. A decreasing trend in mean summer temperature occurred since the 15th century with the 18-19th centuries being the coldest interval of the last millennium, coinciding with the expansion of glaciers in the western Himalaya. Since the late 19th century summer temperatures increased again. However, current warming may be underestimated due to a weakening in tree growth-temperature relationship noticeable in the latter part of the 20th century. Mean summer temperature over the western Himalaya shows a positive correlation with summer monsoon intensity over north central India. Low-frequency variations in mean summer temperature anomalies over northwestern India are consistent with tree-ring inferred aridity in western North America. These far-distance linkages reported here for the first time underscore the utility of long-term temperature records from the western Himalayan region in understanding global-scale climatic patterns

General characteristics of temperature variation in China during the last two millennia

Three alternate China-wide temperature composites covering the last 2000 years were established by combining multiple paleoclimate proxy records obtained from ice cores, tree rings, lake sediments and historical documents. Five periods of temperature variation can be identified: a warm stage in AD 0–240, a cold interval between AD 240 and 800, a return to warm conditions from AD 800–1400, including the Medieval Warm Period between AD 800–1100, the cool Little Ice Age period between 1400–1920, and the present warm stage since 1920. Regional temperature variation is found during AD 800–1100, when warm conditions occurred in Eastern China and in the northeastern Tibetan Plateau and in AD 1150–1380, when the southern Tibetan Plateau experienced a warm interval. In contrast, evidence for cool conditions during the LIA is more consistent among the proxy records. The temperature reconstructions for China and the Northern Hemisphere show good agreement over the past millennium

Recent ecological responses to climate variability and human impacts in the Nianbaoyeze Mountains (eastern Tibetan Plateau) inferred from pollen, diatom and tree-ring data

The Tibetan Plateau is a region that is highly sensitive to recent global warming, but the complexity and heterogeneity of its mountainous landscape can result in variable responses. In addition, the scarcity and brevity of regional instrumental and palaeoecological records still hamper our understanding of past and present patterns of environmental change. To investigate how the remote, high-alpine environments of the Nianbaoyeze Mountains, eastern Tibetan Plateau, are affected by climate change and human activity over the last similar to 600 years, we compared regional tree-ring studies with pollen and diatom remains archived in the dated sediments of Dongerwuka Lake (33.22A degrees N, 101.12A degrees E, 4,307 m a.s.l.). In agreement with previous studies from the eastern Tibetan Plateau, a strong coherence between our two juniper-based tree-ring chronologies from the Nianbaoyeze and the Anemaqin Mountains was observed, with pronounced cyclical variations in summer temperature reconstructions. A positive directional trend to warmer summer temperatures in the most recent decades, was, however, not observed in the tree-ring record. Likewise, our pollen and diatom spectra showed minimal change over the investigated time period. Although modest, the most notable change in the diatom relative abundances was a subtle decrease in the dominant planktonic Cyclotella ocellata and a concurrent increase in small, benthic fragilarioid taxa in the similar to 1820s, suggesting higher ecosystem variability. The pollen record subtly indicates three periods of increased cattle grazing activity (similar to 1400-1480 AD, similar to 1630-1760 AD, after 1850 AD), but shows generally no significant vegetation changes during past similar to 600 years. The minimal changes observed in the tree-ring, diatom and pollen records are consistent with the presence of localised cooling centres that are evident in instrumental and tree-ring data within the southeastern and eastern Tibetan Plateau. Given the minor changes in regional temperature records, our complacent palaeoecological profiles suggest that climatically induced ecological thresholds have not yet been crossed in the Nianbaoyeze Mountains region

Pinus roxburghii stand dynamics at a heavily impacted site in Nepal: Research through an educational fieldweek

The fieldweek associated with the 4th Asian Dendrochronological Association Conference was an excellent opportunity for education, networking, and research. The participants and group leaders worked together for five days in an area that was new to some of the group leaders and new to some of the participants which enabled us to learn about forest ecology around Kathmandu and Nagarkot, Nepal. The fieldweek was an excellent networking opportunity and the group leaders and participants bonded which strengthened international research in dendrochronology and continues to foster new research collaborations. All of the group leaders and participants had the opportunity to learn about tree-ring formation in Pinus roxburghii at 1500 masl elevation, to explore its wood anatomy, and to examine specific research questions in our field area. In the end we developed a better understanding of the stand-age structure of a stand of trees in Nagarkot, explored the erosion history from exposed roots, and investigated tree health issues on closely related sites. We found that P. roxburghii poses some dating issues with false and micro rings at this elevation, but we were still able to develop a tree-ring chronology from this species and make preliminary assessments of stand dynamics and health. (C) 2016 Elsevier GmbH. All rights reserved