Tree growth across the Nepal Himalaya during the last four centuries

The climate of Nepal has changed rapidly over the recent decades, but most instrumental records of weather and hydrology only extend back to the 1980s. Tree rings can provide a longer perspective on recent environmental changes, and since the early 2000s, a new round of field initiatives by international researchers and Nepali scientists have more than doubled the size of the country’s tree-ring network. In this paper, we present a comprehensive analysis of the current tree-ring width network for Nepal, and use this network to estimate changes in forest growth nation-wide during the last four centuries. Ring-width chronologies in Nepal have been developed from 11 tree species, and half of the records span at least 290 years. The Nepal tree-ring width network provides a robust estimate of annual forest growth over roughly the last four centuries, but prior to this point, our mean ring-width composite fluctuates wildly due to low sample replication. Over the last four centuries, two major events are prominent in the all-Nepal composite: (i) a prolonged and widespread growth suppression during the early 1800s; and (ii) heightened growth during the most recent decade. The early 19th century decline in tree growth coincides with two major Indonesian eruptions, and suggests that short-term disturbances related to climate extremes can exert a lasting influence on the vigor of Nepal’s forests. Growth increases since AD 2000 are mainly apparent in high-elevation fir, which may be a consequence of the observed trend towards warmer temperatures, particularly during winter. This synthesis effort should be useful to establish baselines for tree-ring data in Nepal and provide a broader context to evaluate the sensitivity or behavior of this proxy in the central Himalayas.

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Using the International Tree-Ring Data Bank (ITRDB) records as century-long benchmarks for land-surface models

10.5194/gmd-2020-29 ◽

2020 ◽

Author(s):

Jina Jeong ◽

Jonathan Barichivich ◽

Philippe Peylin ◽

Vanessa Haverd ◽

Matthew J. McGrath ◽

...

Keyword(s):

Data Processing ◽

Tree Ring ◽

Land Surface ◽

Environmental Changes ◽

Ring Width ◽

Data Bank ◽

Tree Ring Width ◽

Land Surface Models ◽

Tree Ring Data ◽

Surface Models

Abstract. The search for a long-term benchmark for land-surface models (LSM) has brought tree-ring data to the attention of the land-surface community as they record growth well before human-induced environmental changes became important. The most comprehensive archive of publicly shared tree-ring data is the International Tree-ring Data Bank (ITRDB). Many records in the ITRDB have, however, been collected almost exclusively with a view on maximizing an environmental target signal (e.g. climate), which has resulted in a biased representation of forested sites and landscapes and thus limits its use as a data source for benchmarking. The aim of this study is to propose advances in land-surface modelling and data processing to enable the land-surface community to re-use the ITRDB data as a much-needed century-long benchmark. Given that tree-ring width is largely explained by phenology, tree size, and climate sensitivity, LSMs that intend to use it as a benchmark should at least simulate tree phenology, size-dependent growth, differently-sized trees within a stand, and responses to changes in temperature, precipitation and atmospheric CO2 con¬cen¬tra¬tions. Yet, even if LSMs were capable of accurately simulating tree-ring width, sampling biases in the ITRDB need to be accounted for. This study proposes two solutions: exploiting the observation that the variation due to size-related growth by far exceeds the variation due to environmental changes; and simulating a size-structured population of trees. Combining the proposed advances in modelling and data processing resulted in four complementary benchmarks - reflecting different usage of the information contained in the ITRDB - each described by two metrics rooted in statistics that quantify the performance of the benchmark. Although the proposed benchmarks are unlikely to be precise, they advance the field by providing a much-needed large-scale constraint on changes in the simulated maximum tree diameter and annual growth increment for the transition from pre-industrial to present-day environmental conditions over the past century. Hence, the proposed benchmarks open up new ways of exploring the ITRDB archive, stimulate the dendrochronological community to refine its sampling protocols to produce new and spatially unbiased tree-ring networks, and help the modelling community to move beyond the short-term benchmarking of LSM.

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Tree-ring growth curves as sources of climatic information

Quaternary Research ◽

10.1016/j.yqres.2004.06.005 ◽

2004 ◽

Vol 62 (2) ◽

pp. 126-133 ◽

Cited By ~ 28

Author(s):

Mukhtar M. Naurzbaev ◽

Malcolm K. Hughes ◽

Eugene A. Vaganov

Keyword(s):

Tree Ring ◽

Regional Growth ◽

Ring Width ◽

Growth Curves ◽

Elevational Gradient ◽

Forest Growth ◽

Tree Ring Width ◽

Cambial Age ◽

Tree Ring Data ◽

Subfossil Wood

Regional growth curves (RGCs) have been recently used to provide a new basis for removing nonclimatic trend from tree-ring data. Here we propose a different use for RGCs and explore their properties along two transects, one meridional and the other elevational. RGCs consisting of mean ring width plotted against cambial age were developed for larch samples from 34 sites along a meridional transect (55–72°N) in central Siberia, and for 24 sites on an elevational gradient (1120 and 2350 m a.s.l.) in Tuva and neighboring Mongolia at approximately 51°N. There are systematic gradients of the parameters of the RGCs, such as I0-maximum tree-ring width near pith, and Imin, the asymptotic value of tree-ring width in old trees. They are smaller at higher latitude and elevation. Annual mean temperature and mean May–September temperature are highly correlated with latitude here, and hence RGC parameters are correlated with these climatic variables. Correlations with precipitation are more complex, and contradictory between meridional and elevational transects. The presence of a similar gradient in the elevational transect is consistent with temperature being the causal factor for both gradients, rather than, for example, latitude-dependent patterns of seasonal photoperiod change. Taking ring measurements from collections of relict and subfossil wood, the RGC–latitude and RGC–temperature relationships are used to estimate paleo-temperatures on centennial time scales. These estimates are consistent with earlier "traditional" dendroclimatic approaches, and with independent information on the northern extent of forest growth in the early mid-Holocene. It may be possible to use this same approach to make estimates of century-scale paleo-temperatures in other regions where abundant relict wood is present.

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Forward modelling of tree-ring width and comparison with a global network of tree-ring chronologies

Climate of the Past ◽

10.5194/cp-10-437-2014 ◽

2014 ◽

Vol 10 (2) ◽

pp. 437-449 ◽

Cited By ~ 49

Author(s):

P. Breitenmoser ◽

S. Brönnimann ◽

D. Frank

Keyword(s):

Data Assimilation ◽

Tree Ring ◽

Ring Width ◽

Global Network ◽

Threshold Temperature ◽

Tree Ring Width ◽

Data Set ◽

Observation Operator ◽

Tree Ring Data ◽

Wide Range

Abstract. We investigate relationships between climate and tree-ring data on a global scale using the process-based Vaganov–Shashkin Lite (VSL) forward model of tree-ring width formation. The VSL model requires as inputs only latitude, monthly mean temperature, and monthly accumulated precipitation. Hence, this simple, process-based model enables ring-width simulation at any location where monthly climate records exist. In this study, we analyse the growth response of simulated tree rings to monthly climate conditions obtained from the CRU TS3.1 data set back to 1901. Our key aims are (a) to assess the VSL model performance by examining the relations between simulated and observed growth at 2287 globally distributed sites, (b) indentify optimal growth parameters found during the model calibration, and (c) to evaluate the potential of the VSL model as an observation operator for data-assimilation-based reconstructions of climate from tree-ring width. The assessment of the growth-onset threshold temperature of approximately 4–6 °C for most sites and species using a Bayesian estimation approach complements other studies on the lower temperature limits where plant growth may be sustained. Our results suggest that the VSL model skilfully simulates site level tree-ring series in response to climate forcing for a wide range of environmental conditions and species. Spatial aggregation of the tree-ring chronologies to reduce non-climatic noise at the site level yielded notable improvements in the coherence between modelled and actual growth. The resulting distinct and coherent patterns of significant relationships between the aggregated and simulated series further demonstrate the VSL model's ability to skilfully capture the climatic signal contained in tree-ring series. Finally, we propose that the VSL model can be used as an observation operator in data assimilation approaches to reconstruct past climate.

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Peer review report 2 on “Forward modeling of tree-ring width improves simulation of forest growth responses to drought”

Agricultural and Forest Meteorology ◽

10.1016/j.agrformet.2016.11.050 ◽

2016 ◽

Vol 217 ◽

pp. 225-226

Author(s):

Anonymous

Keyword(s):

Peer Review ◽

Tree Ring ◽

Ring Width ◽

Forward Modeling ◽

Forest Growth ◽

Tree Ring Width ◽

Growth Responses

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A 406-year non-growing-season precipitation reconstruction in the southeastern Tibetan Plateau

Climate of the Past ◽

10.5194/cp-17-2381-2021 ◽

2021 ◽

Vol 17 (6) ◽

pp. 2381-2392

Author(s):

Maierdang Keyimu ◽

Zongshan Li ◽

Bojie Fu ◽

Guohua Liu ◽

Fanjiang Zeng ◽

...

Keyword(s):

Tibetan Plateau ◽

Tree Ring ◽

Tree Growth ◽

Ring Width ◽

Growing Season ◽

Climatic Conditions ◽

Forest Growth ◽

Drought Severity ◽

Precipitation Reconstruction ◽

Southeastern Tibetan Plateau

Abstract. Trees record climatic conditions during their growth, and tree rings serve as proxy to reveal the features of the historical climate of a region. In this study, we collected tree-ring cores of hemlock forest (Tsuga forrestii) from the northwestern Yunnan area of the southeastern Tibetan Plateau (SETP) and created a residual tree-ring width (TRW) chronology. An analysis of the relationship between tree growth and climate revealed that precipitation during the non-growing season (NGS) (from November of the previous year to February of the current year) was the most important constraining factor on the radial tree growth of hemlock forests in this region. In addition, the influence of NGS precipitation on radial tree growth was relatively uniform over time (1956–2005). Accordingly, we reconstructed the NGS precipitation over the period spanning from 1600–2005. The reconstruction accounted for 28.5 % of the actual variance during the common period of 1956–2005. Based on the reconstruction, NGS was extremely dry during the years 1656, 1694, 1703, 1736, 1897, 1907, 1943, 1982 and 1999. In contrast, the NGS was extremely wet during the years 1627, 1638, 1654, 1832, 1834–1835 and 1992. Similar variations of the NGS precipitation reconstruction series and Palmer Drought Severity Index (PDSI) reconstructions of early growing season from surrounding regions indicated the reliability of the present reconstruction. A comparison of the reconstruction with Climate Research Unit (CRU) gridded data revealed that our reconstruction was representative of the NGS precipitation variability of a large region in the SETP. Our study provides the first historical NGS precipitation reconstruction in the SETP which enriches the understanding of the long-term climate variability of this region. The NGS precipitation showed slightly increasing trend during the last decade which might accelerate regional hemlock forest growth.

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Independent Aridity and Drought Pieces of Evidence Based on Meteorological Data and Tree Ring Data in Southeast Banat, Vojvodina, Serbia

Atmosphere ◽

10.3390/atmos10100586 ◽

2019 ◽

Vol 10 (10) ◽

pp. 586 ◽

Cited By ~ 1

Author(s):

Milivoj B. Gavrilov ◽

Wenling An ◽

Chenxi Xu ◽

Milica G. Radaković ◽

Qingzhen Hao ◽

...

Keyword(s):

Tree Ring ◽

Air Temperature ◽

Meteorological Data ◽

Ring Width ◽

Surface Air Temperature ◽

Aridity Index ◽

Precipitation Trend ◽

Positive Temperature ◽

Tree Ring Width ◽

Tree Ring Data

In this study, aridity data and tree ring data were collected in Northern Serbia, in Southeast (SE) Banat, a subregion within Vojvodina, and Vojvodina at large. They were each investigated independently. The De Martonne Aridity Index and the Forestry Aridity Index are derived from examining the relationship between precipitation and surface air temperature data sets sourced from seven meteorological stations in SE Banat, and from 10 meteorological stations located in Vojvodina as a whole. Vojvodina is a large territory and used as the control area, for the period 1949–2017. The Palmer Drought Severity Index was derived for the period 1927–2016, for both SE Banat and the totality of Vojvodina. The results of the Tree Ring Width Index were obtained from samples collected in or around the villages of Vlajkovac and Šušara, both located in SE Banat, for the period 1927–2017. These tree ring records were compared with three previous aridity and drought indices, and the meteorological data on the surface air temperature and the precipitation, with the objective being to evaluate the response of tree growth to climate dynamics in the SE Banat subregion. It was noted that the significant positive temperature trends recorded in both areas were too insufficient to trigger any trends in aridity or the Tree Ring Width Index, as neither displayed any change. Instead, it appears that these climatic parameters only changed in response to the precipitation trend, which remained unchanged during the investigated period, rather than in response to the temperature trend. It appears that the forest vegetation in the investigated areas was not affected significantly by climate change in response to the dominant temperature increase.

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Development of tree-ring width chronologies and tree-growth response to climate in the mountains surrounding the Issyk-Kul Lake, Central Asia

Dendrochronologia ◽

10.1016/j.dendro.2014.03.002 ◽

2014 ◽

Vol 32 (3) ◽

pp. 230-236 ◽

Cited By ~ 14

Author(s):

Tongwen Zhang ◽

Yujiang Yuan ◽

Qing He ◽

Wenshou Wei ◽

Mamatkanov Diushen ◽

...

Keyword(s):

Central Asia ◽

Tree Ring ◽

Tree Growth ◽

Growth Response ◽

Ring Width ◽

Tree Ring Width

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Assimilation of Pseudo-Tree-Ring-Width observations into an Atmospheric General Circulation Model

10.5194/cp-2016-92 ◽

2016 ◽

Cited By ~ 1

Author(s):

Walter Acevedo ◽

Bijan Fallah ◽

Sebastian Reich ◽

Ulrich Cubasch

Keyword(s):

Tree Ring ◽

Tree Growth ◽

General Circulation ◽

Climate Model ◽

Global Climate Model ◽

Ring Width ◽

Circulation Model ◽

Forward Model ◽

Limiting Factors ◽

Tree Ring Width

Abstract. We investigate the assimilation of Tree-Ring-Width (TRW) chronologies into an atmospheric global climate model using Ensemble Kalman Filter (EnKF) techniques and a process-based tree-growth forward model as observation operator. Our results, within a perfect-model experiment setting, indicate that the non-linear response of tree-growth to surface temperature and soil moisture does deteriorate the operation of the time-averaged (EnKF) methodology. Moreover, this skill loss appeared significantly sensitive to the structure of growth rate function, used to represent the Principle of Limiting Factors (PLF)s within the forward model. On the other hand, it was observed that the error reduction achieved by assimilating a particular pseudo-TRW chronology is modulated by the strength of the yearly internal variability of the model at the chronology site. This result might help the dendrochronology community to optimize their sampling efforts. In our experiments, the ''online'' (with cycling) paleao Data Assimilation (DA) approach did not outperform the ''offline'' (no-cycling) one, despite its considerable additional implementation complexity.

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On the ‘Divergence Problem’ in the Alatau Mountains, Central Asia: A Study of the Responses of Schrenk Spruce Tree-Ring Width to Climate under the Recent Warming and Wetting Trend

Atmosphere ◽

10.3390/atmos10080473 ◽

2019 ◽

Vol 10 (8) ◽

pp. 473 ◽

Cited By ~ 3

Author(s):

Zhang ◽

Jiang ◽

Bagila ◽

Ainur ◽

...

Keyword(s):

Central Asia ◽

Tree Ring ◽

Tree Growth ◽

Tree Species ◽

Climatic Factors ◽

Ring Width ◽

Tree Ring Width ◽

Recent Warming ◽

Divergence Problem ◽

The Stability

The divergence problem, which manifests as an unstable response relationship between tree-ring growth and climatic factors under the background of global warming, poses a challenge to both the traditional theory of dendroclimatology and the reliability of climatic reconstructions based on tree-ring data. Although Schrenk spruce, as the dominant tree species in the Tianshan Mountains, is frequently applied in the dendrochronological studies, the understanding of the divergence problem of this tree species is still limited. This study conducted correlation analysis between climatic factors and tree-ring width chronologies from 51 living and healthy specimens of Schrenk spruce at sites of high and low elevation in the Alatau Mountains to determine the stability of the response. The results revealed that the tree-ring width of the spruce specimens was correlated positively with precipitation and correlated negatively with temperature. Although the variations of the two tree-ring chronologies were similar, the radial growth of the spruce at the low elevation was found more sensitive to climatic factors. Furthermore, the sensitivity of tree growth to climate demonstrated an obvious increase after an abrupt change of climate under the background of the recent warming and wetting trend. Increased drought stress, calculated based on climatic data, was regarded as the main reason for this phenomenon. The results supply the gap of the stability of climatic response of tree growth in Central Asia to some extent.

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Last 1100 yr of precipitation variability in western central Asia as revealed by tree-ring data from the Pamir-Alay

Quaternary Research ◽

10.1017/qua.2018.21 ◽

2018 ◽

Vol 91 (1) ◽

pp. 81-95 ◽

Cited By ~ 6

Author(s):

Magdalena Opała-Owczarek ◽

Tadeusz Niedźwiedź

Keyword(s):

Central Asia ◽

Tree Ring ◽

Tree Growth ◽

Palmer Drought Severity Index ◽

Ring Width ◽

Severity Index ◽

Drought Severity ◽

Mountainous Area ◽

Transfer Function Method ◽

Tree Ring Data

AbstractWe developed a 1108 yr chronology of tree-ring widths, based on 64 Himalayan pencil juniper (Juniperus semiglobosa Regel) trees, for the Pamir-Alay Mountains, central Asia. Dendroclimatological analysis demonstrates that precipitation has significant effects on tree growth in the semiarid mountainous area of northwestern Tajikistan located on the edge of the great midlatitude Karakum and Kyzylkum deserts. The highest level of linear correlation (r=0.67) is observed between tree growth and seasonalised winter (previous December–February) precipitation. Our studies also show that moisture (precipitation/Palmer Drought Severity Index) from the previous June to the current September was the dominant climatic factor accounting for interannual variations in tree-ring width, suggesting that this should be considered in climate reconstruction. Using the transfer function method, we reconstructed the region’s drought history over the period AD 908–2015. The results of this moisture reconstruction showed that the most recent millennium was characterised by series of dry and wet stages. The driest periods occurred before 1000, 1200–1250, and at the end of the eighteenth century and beginning of the nineteenth century. The wettest conditions existed in 1650–1700 and after 1990.

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