Age-dependent tree-ring growth responses to climate in Qilian juniper (Sabina przewalskii Kom.)

Qilian juniper (Sabina przewalskii kom.) is one of the dominant tree species on Qinghai-Tibetan Plateau and has been used in dendroclimatological studies. Here we designed a test to examine whether or not the climate–growth responses in tree rings of Qilian Juniper vary with the change in tree's age. A total number of 135 increment cores were sampled from Qilian Juniper trees at five sites, in which 112 cores were selected and grouped into five 100-year age classes for analysis of age-dependent climate–growth relationships. Chronology statistics, response functions and ANOVA F-test were used to test the consistency of five age-class mean chronologies (AGCs). The results showed that mean sensitivity (MS) and standard deviation (SD) did not change significantly with age. Response function analysis indicated that (a) climate accounts for a high amount of variance in tree-ring widths; (b) tree-ring growth has significant positive correlation with mean monthly air temperature of previous October and November, and with total monthly precipitation of current January and June, while has significant negative correlation with mean monthly air temperature of current May; and (c) AGC-2, AGC-3 and AGC-4 have stronger response to climate change than AGC-1 and AGC-5. The ANOVA F-test showed that generally there are significant differences between the first age class and other four age classes, but among the four classes in which trees are older than 200 years, the differences are usually insignificant. Overall the long-lived Qilian Juniper is still an ideal tree species for dendroclimatic reconstruction.     

Climate/growth relations and teleconnections for a <Emphasis Type="Italic">Hymenaea courbaril</Emphasis> (Leguminosae) population inhabiting the dry forest on karst

Key message

Both water availability and temperature modulate the growth of Hymenaea courbaril on karst in Central Brazil. There is evidence of teleconnections between South Atlantic SST and tree growth.

Abstract

Tropical dry forests have low annual precipitation and long dry seasons. Water availability, the main restrictive growth factor, becomes more pronounced in the shallow and highly porous soil of karst regions. Understanding how climate regulates tree growth in stressful environments is essential for predicting climate change impacts on trees. The aim of this study was to build a tree-ring chronology of Hymenaea courbaril growing in a karst dry forest and evaluate how local climate and teleconnections modulate its growth. To accomplish this, increment cores of 19 individuals were sampled in Terra Ronca State Park located in Goiás State, Central Brazil. After surface polishing, tree rings were identified, measured, dated, and a tree-ring chronology was built with 17 individuals. The chronology was correlated with local and regional climate data (temperature, precipitation, air humidity). We also tested teleconnections with sea surface temperature (SST) of the Equatorial Pacific and South Atlantic. Results show that air humidity, precipitation amount, and its distribution during the transition period between dry and wet seasons positively regulate this species growth. On the other hand, growth is negatively correlated with temperature during the middle of the previous year’s dry season. Additionally, growth is negatively correlated with SST of the Southern Atlantic, but not with Equatorial Pacific. These relationships between climate and growth indicate that predicted increases in regional temperature and decreases in water availability may limit the growth of H. courbaril in karst dry forests.

     

Growth–climate relationships along an elevation gradient on a southeast-facing mountain slope in the semi-arid eastern Qaidam Basin,northeastern Tibetan Plateau

Key message

Both temperature and precipitation are strong factors of radial tree growth at all elevations in the semi-arid study area, except at the upper treeline where temperature becomes the major controlling factor.

Abstract

Several recent studies across the Tibetan Plateau found consistent growth–climate relations at all elevations from the lower treelines to the upper treelines. These findings seem to challenge the general principle of dendroclimatology that precipitation serves as the controlling factor of radial tree growth at lower elevations while temperature serves as the controlling factor at higher elevations in semi-arid regions. Such conclusions also question the potential of temperature reconstruction using ring-width data in these regions if precipitation remains the dominant factor of tree growth at the upper treelines. In this study, radial growth of Qilian juniper (Sabina przewalskii Kom.) was examined along an elevation gradient between ~3820 and 4230 m in the mountains east of the Qaidam Basin, northeastern Tibetan Plateau, to determine the limiting factors of radial tree growth at different elevations. Rotated principal component analysis revealed two modes of variation patterns. The first mode presents mostly tree ring data from the lower elevation zones (3820–4100 m) and contains strong signals of precipitation variation. The second mode represents the higher elevation zones (approx. 4100–4230 m) and contains strong signals of both temperature and precipitation variations. When signals of precipitation variation are removed from the tree ring data using partial correlation, the growth–temperature relationships become more evident on the upper slope. When correlations between individual tree-ring series and climate variables were examined, we discovered that there were better chances of finding tree ring samples strongly correlated to temperature variables (r = 0.6 or higher) at the elevation zone within ~100 m of the upper treeline, but uncommon at lower elevations. We also found that topographic variables, such as slope gradient and growing-season direct solar radiation may have minor influences on the growth–climate relationships.

     

Recent reduction in the frequency of frost accounts for most of the increased growth of a high elevation spruce forest in northwestern China

Key message

Using process-based models in combination with dendrochronological measurements provides a way to explain recent increased tree growth in northwestern China.

Abstract

Dendrochronological studies of tree rings in a 250-year-old Qinghai spruce (Picea crassifolia) forest in the Qilian Mountains of northwestern China indicate a 60 % sustained increase in tree-ring growth between 1980 and 2009 compared with any time since 1785. Over the same period, the maximum, minimum, and average temperatures all increased by nearly 2 °C during the growing season (May through September), the frequency of frost decreased 18 days, precipitation remained unchanged, while atmospheric concentrations of CO₂ increased by 48 ppm. To explain how the changes in climatic variables might cause the increase in tree growth, we parameterized a process-based growth model (3-PG, physiological processes predicting growth) with values from the literature and performed a series of sensitivity tests. The results of our analysis indicated that a reduction in frost frequency during the growing season, which allows stomata to remain open, enhanced gross photosynthesis by 42 %. Up to a 20 % increase in P _G could be attributed to rising atmospheric CO₂ between 1980 and 2009, with half of this attributed to increased light interception from a simulated 0.4 increase in canopy leaf area index. The increase in average and maximum temperatures had little direct effect on gross photosynthesis with the optimum temperature set between 9 and 10 °C. Indirectly, the increase in monthly average minimum temperature during the growing season, although small, crossed a threshold that reduced the impact of frost. Our analyses show the value of combining dendrochronological measurements with a process-based model to gain a more holistic understanding of how environmental factors interact to affect tree growth.

     

Annual and intra-annual growth dynamics of <Emphasis Type="Italic">Myricaria elegans</Emphasis> shrubs in arid Himalaya

Key message

To disentangle complex drivers of Myricaria elegans growth in arid Himalaya, we combined tree-ring analysis with detailed dendrometer records. We found that the combination of winter frost, summer floods, and strong summer diurnal temperature fluctuations control annual and intra-annual growth dynamics. The relative importance of these drivers is, however, changing with ongoing climate change.

Abstract

High-mountain areas are among the most sensitive environments to climate change. Understanding how different organisms cope with ongoing climate change is now a major topic in the ecology of cold environments. Here, we investigate climate drivers of the annual and intra-annual growth dynamics of Myricaria elegans, a 3–6 m tall tree/shrub, in a high-elevation cold desert in Ladakh, a rapidly warming region in the NW Himalayas. As Myricaria forms narrow stands around glacier streams surrounded by the desert, we hypothesized that its growth between 3800 and 4100 m will be primarily limited by low temperatures and summer floods. We found that warmer and less snowy conditions in April and May enhance earlywood production. Latewood formation is mostly driven by the June–July temperatures (T). The positive effect of warmer summers on both annual and intra-annual growth is related to fluctuating daily T (from +30 to 0 °C). In particular, dendrometer measurements over a 2-year period showed that net daily growth increments increased when the summer night T remained above 6 °C. While high night T during generally cold desert nights promoted growth, high daytime T caused water stress and growth inhibition. The growth–temperature dependency has gradually weakened due to accelerated warming since the 1990s. In addition, positive latewood responses to high March precipitation during the colder 1960s–1980s have become negative during the warmer 1990s–2000s, reflecting an intensification of summer floods. Latewood width increased while earlywood width decreased from the 1990s, indicating a prolonged growing season and a higher risk of drought-induced embolism in earlywood vessels. Due to a multiplicity of environmental drivers including winter frost, intensified floods and strong summer diurnal T fluctuations, Myricaria growth is not controlled by a single climate parameter. Similar results are increasingly reported from other Himalayan treelines, showing that ongoing climate change will trigger complex and probably spatially variable responses in tree growth. Our study showed that these complex climatic signals can be disentangled by a combination of long-term data from tree-rings with detailed, but short-term, records from dendrometers.

     

An interpreted language implementation of the Vaganov–Shashkin tree-ring proxy system model

We describe the implementation of the Vaganov–Shashkin tree-ring growth model (VSM) in MATLAB. VSM, originally written in Fortran, mimics subdaily and daily resolution processes of cambial growth as a function of soil moisture, air temperature, and insolation, with environmental forcing modeled as the principle of limiting factors. The re-implementation in a high level interpreted language, while sacrificing speed, provides opportunities to systematically evaluate model parameters, generate large ensembles of simulated tree-ring chronologies, and embed proxy system modeling within data assimilation approaches to climate reconstruction. We provide a versioned code repository and examples of model applications which permit process-level understanding of tree ring width variations in response to environmental variations and boundary conditions.     

Growth partitioning within beech trees (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.) varies in response to summer heat waves and related droughts

Key message

Beech growth variability and climate sensitivity are much higher in the crown top than in the bole. The most notable bole–crown discrepancies occurred in response to extreme climate conditions.

Abstract

To characterize growth partitioning within the tree and its responses to climate, we studied eight dominant beech trees (Fagus sylvatica L.) of a pure, even-aged 98-year-old stand in Belgium. We sampled ten disks along the stem from breast height to treetop and examined the inter-annual patterns of, and discrepancies between, ring-area and volume increments by performing detailed stem analysis and dendroecological investigations. Although the common inter-annual variation among all increment series was high, we observed increasing growth variability and climate sensitivity with height, leading to notable bole–crown discrepancies. Both the common inter-annual variation and bole–crown discrepancies were mainly driven by summer heat waves and related droughts of the previous year, and spring droughts of the current year. Despite these discrepancies, the radial growth at breast height can be considered a good estimate of the tree volume increment but not for the purpose of focusing on climatic effects of isolated years. Extreme climatic conditions increase the risk of inaccurate estimations. The results of the present study are discussed in relation to tree ecophysiology hypotheses.

     

<Emphasis Type="Italic">Araucaria araucana</Emphasis> tree-ring chronologies in Argentina: spatial growth variations and climate influences

Seventeen tree-ring chronologies from the conifer Araucaria araucana (Molina) K. Koch have been analyzed across its range of distribution in Argentina. We studied the growth patterns and determined the main climatic factors influencing A. araucana radial growth. All the chronologies show a strong common signal observed by the high amount of variance explained by the first principal component (PC1) and the high mean correlation (r = 0.597) between the chronologies over the 1676–1974 interval. On this basis, we developed a regional chronology that is 866 years long (A.D. 1140–2006) and includes 621 tree-ring series. Based on the PC2 scores, chronologies were clearly separated by elevation in high- and low-elevation records. Regional tree growth is strongly negatively related to temperatures during summer and fall in the previous-growing season and spring in the current-growing season, respectively. A positive association of tree growth with precipitation is recorded during spring in the current growing season. These results suggest a close relationship between A. araucana tree growth and water availability on a regional scale. This observation is also consistent with a positive and significant correlation between our A. araucana regional record and a reconstruction of November–December rainfall for northern Patagonia inferred from the xeric Austrocedrus chilensis during the past 400 years. Negative correlations between A. araucana regional growth and the sea surface temperature in the Niño 3.4 region reflect the occurrence of above-mean summer temperatures in the region during positive tropical Pacific SST anomalies. The negative relationship with the Antarctic Oscillation (AAO) results from reduced precipitation in our study region during the positive phase of the AAO. The effect of elevation on water availability is consistent with significant correlations between ring-width variations at lower elevations and the Palmer Drought Severity Index during spring and summer in the current growing season. Our study emphasizes the high dendroclimatological potential of A. araucana chronologies for reconstructing past climate variations in northern Patagonia during the past millennium.     

Individual and time-varying tree-ring growth to climate sensitivity of Pinus tabuliformis Carr. and Sabina przewalskii Kom. in the eastern Qilian Mountains, China

Individual tree-ring width chronologies and mean chronologies from Pinus tabuliformis Carr. (Chinese pine) and Sabina przewalskii Kom. (Qilian juniper) tree cores were collected and analyzed from two sites in the eastern Qilian Mountains of China. The chronologies were used to analyze individual and time-varying tree-ring growth to climate sensitivity with monthly mean air temperature and total precipitation data for the period 1958–2008. Climate–growth relationships were assessed with correlation functions and their stationarity and consistency over time were measured using moving correlation analysis. Individuals’ growth–climate correlations suggested increased percentages of individuals are correlated with certain variables (e.g., current June temperature at the P. tabuliformis site; previous June, December and current May temperature and May precipitation at the S. przewalskii site). These same climatic variables also correspond to the mean chronology correlations. A decreased percentage of individuals correlated with these climatic variables indicates a reduced sensitivity of the mean chronology. Moving correlation analysis indicated a significant change over time in the sensitivity of trees to climatic variability. Our results suggested: (1) that individual tree analysis might be a worthwhile tool to improve the quality and reliability of the climate signal from tree-ring series for dendroclimatology research; and (2) time-dependent fluctuations of climate growth relationships should be taken into account when assessing the quality and reliability of reconstructed climate signals.     

不同生境和去趋势方法下的祁连圆柏径向生长对气候的响应

利用青海不同生境祁连圆柏树木年轮样本,采用3种不同去趋势方法建立树轮年表,结合青海30个气象站的气象资料,分析不同生境和去趋势方法下祁连圆柏径向生长对气候的响应差异。结果表明,祁连山区,生长季前期的平均气温是祁连圆柏树木径向生长的主要限制性因子,NEP树轮标准化宽度年表与生长季前期冬季平均气温相关最好;在柴达木盆地,生长季降水量是该地区树木径向生长的限制性因子,SPL树轮年表对生长季降水量相关较好;在青南高原,祁连圆柏径向生长对春季温度响应最为敏感,而SPL年表与春季温度呈现明显的负相关关系,相关系数达-0.606;而在青海东部地区,祁连圆柏树木径向生长对气候的响应总体不显著。位于青海西部和北部的柴达木盆地和祁连山区祁连圆柏径向生长受西风气候的影响显著,尤其是柴达木盆地,其气候受西风主导;而青南高原受西南季风影响更为显著,该地区祁连圆柏径向生长同时受西南季风气候和海拔高度两方面影响;在青海东部,祁连圆柏径向生长受东亚季风影响更为显著。     

VS-oscilloscope: A new tool to parameterize tree radial growth based on climate conditions

It is generally assumed in dendroecological studies that annual tree-ring growth is adequately determined by a linear function of local or regional precipitation and temperature with a set of coefficients that are temporally invariant. However, various researchers have maintained that tree-ring records are the result of multivariate, often nonlinear biological and physical processes. To describe critical processes linking climate variables with tree-ring formation, the process-based tree-ring Vaganov–Shashkin model (VS-model) was successfully used. However, the VS-model is a complex tool requiring a considerable number of model parameters that should be re-estimated for each forest stand. Here we present a new visual approach of process-based tree-ring model parameterization (the so-called VS-oscilloscope) which allows the simulation of tree-ring growth and can be easily used by researchers and students. The VS-oscilloscope was tested on tree-ring data for two species (Larix gmeliniiand Picea obovata) growing in the permafrost zone of Central Siberia. The parameterization of the VS-model provided highly significant positive correlations (p < 0.0001) between simulated growth curves and original tree-ring chronologies for the period 1950–2009. The model outputs have shown differences in seasonal tree-ring growth between species that were well supported by the field observations. To better understand seasonal tree-ring growth and to verify the VS-model findings, a multi-year natural field study is needed, including seasonal observation of the thermo-hydrological regime of the soil, duration and rate of tracheid development, as well as measurements of their anatomical features.     

Photomorphogenesis in <Emphasis Type="Italic">Dracaena draco</Emphasis>

Key message

Sunlight is a key environmental factor in growth, flowering and shaping of the Dracaena draco tree. Unidirectional light deforms the tree and may cause it to tilt.

Abstract

Dracaena draco, a tree-like monocot, lives in cycles of vegetative growth and flowering. The cycles, as well as the tree growth form, are under genetic control. What controls their length has been unknown before. We propose that it is sunlight. Our trees of the same origin, growing for 20 years in the garden in varying sunlight conditions, started to flower when 9–12, 16 and 18–19 years old, for those growing in full sun, part shade and shade, respectively. In full sun, they grow shorter trunks than those in shade, catching overhead sun. Their branches also had shorter or longer growth and flowering cycles depending on sunlight availability. D. draco tree exhibited strong phototropic response and its crown was organized by the direction of growing tips. In full and in overhead sun, it had a regular form but asymmetrical in unidirectional, oblique sunlight. An asymmetrical crown and the absence of reaction wood may cause the D. draco tree tilting and progressive loss of balance.

     

Growth trends and climate responses of Norway spruce along elevational gradients in East-Central Europe

Key message

Decadal growth variability of Norway spruce increases with elevation. Recent temperature sensitivity and growth enhancement are limited to trees growing in the zone adjacent to timberline.

Abstract

Growth trends and climate responses of forest trees along elevational gradients are not fully understood. A deeper insight is, however, fundamental for predicting ecosystem functioning and productivity under future climate change. Supplementary to the effects of elevation and regional provenance on tree growth are sample depth, uneven representation of sample age and varying site conditions. Furthermore, there is only a limited number of studies addressing growth changes along elevational gradients, while at the same time applying tree-ring standardization methods that are sensitive to trend preservation. Here, we introduce 12 novel tree-ring width chronologies of Norway spruce (Picea abies[L.] Karst.) from four elevational belts encompassing montane forests and the local timberline in three regions in East-Central Europe between 15° and 19°E. Each chronology is characterized by sufficient sample replication and a comparable age structure between 1906 and 2010. Tree growth near timberline revealed substantial medium-frequency variability and sharply increasing ring widths since the 1980s. Medium-frequency growth variability of lower elevation trees was, however, relatively small, and growth rates over the last decade were either stable or even decreased. During the last four decades, Norway spruce from higher elevations exhibited a reduced response to autumn temperatures preceding ring formation. In contrast, trees from the lower-montane zone increased their sensitivity to drought during the same time. Our results emphasize not only different but also instable growth trends and climate responses of forest trees along altitudinal gradients, which should be considered in future forest management strategies.

     

Regional chronologies of <Emphasis Type="Italic">Cedrela</Emphasis><Emphasis Type="Italic">fissilis</Emphasis> and <Emphasis Type="Italic">Cedrela angustifolia</Emphasis> in three forest types and their relation to climate

Key message

Although tree-ring chronologies of Cedrela fissilis and Cedrela angustifolia showed a common climatic signal, local conditions influence growth, suggesting that forest guidelines should be appropriate to the species and context.

Abstract

Cedrela species are highly valued because of the quality of their timber. Understanding the behaviour of each different Cedrela species and their ecology is of importance to ensuring that forest harvesting and management do not endanger the survival of natural populations. These species grow in a wide range of environmental gradients and different types of forests in Bolivia. This study used dendrochronological methods to analyse growth–precipitation relationships of two Cedrela species coming from three locations with different environmental conditions: dry Chiquitano (Concepción), Chiquitano transitional Amazonian (Guarayos), and Bolivian-Tucuman montane forests (Postrervalle). The rainy season in all locations runs from October to April and the dry season runs from May to September. Twelve Cedrela fissilis specimens were sampled from dry Chiquitano, 11 Cedrela fissilis specimens from Chiquitano transitional Amazonian, and 30 Cedrela angustifolia specimens from Bolivian-Tucuman montane forests. The samples were crossdated and exhibited a common signal between trees from three sites, despite tree rings from the Chiquitano transitional Amazonian forest being narrower and displaying blurred bands of parenchyma in the boundaries. Significant inter-series correlation was found for the C. fissilis species series from dry Chiquitano with r = 0.261 (p < 0.01) and Chiquitano transitional Amazonian forests with r = 0.284 (p < 0.01), and for Cedrela angustifolia from Bolivian-Tucuman montane forests with r = 0.374 (p < 0.01). Mean annual growth was 2.07, 1.92, and 2.82 mm year^?1 at the three sites, respectively. Cedrela species from dry Chiquitano and Bolivian-Tucuman montane forests were sensitive to precipitation from October to April of the current growth year (wettest season) and to low temperatures from May to July of the current growth year (driest season). Samples from Chiquitano transitional Amazonian were more sensitive to precipitation during late rainy season (March, April, and May of the current growth year) and high temperatures during the rainy months (November–December). Growth differences between sites and species in response to climate variations and local conditions should be taken into account and handled with different forest management guidelines.

     

Aleppo pine vulnerability to climate stress is independent of site productivity of forest stands in southeastern Spain

Key message

Clim ate is the main driver of Aleppo pine radial growth variability irrespective of site pro ductivity, with the climate effects on tree growth more limiting from 1970 onwards.

Abstract

Forest management adaptation to climate change requires identifying the previously most vulnerable stands and the possible climate impacts on forests. This study evaluates whether site index, as an indicator of forest productivity, is related to climate–growth responses and assesses the way in which local site factors modulate climate–tree growth relationships. Tree-ring width series and soil characteristics were obtained from six Pinus halepensis stands with different site indices and similar climate. Dendrochronological methods were used to compare tree climate–growth responses among sites and to study temporal trends in inter-annual growth variability and climate–growth relationships (before and after 1970). The influence of topographic and soil features on tree growth was assessed by means of partial least squares. Stands with low site indices tended to present higher mean sensitivities and greater percentages of missing rings, this relation being modulated mainly by clay percentage and nutrient status in soil. Climate is the major Aleppo pine radial growth driver in the study area with similar growth–climate relationship among sites. Radial growth was mainly influenced by spring temperature and precipitation and previous autumn–winter precipitation. This relationship was stronger after 1970 than before this year, showing also a 2-month advancement of the most influential climate variables after 1970, from May to March. These results and the increasing temporal trend found in mean sensitivity after 1970 highlight the vulnerability of these stands to climate change. Site index was not found to be directly related to stand vulnerability, although local site factors modulate in part the tree-growth response.     

祁连山中部低海拔地区青海云杉径向生长的气候响应机制

利用生理模型开展树木径向生长的气候响应机制研究对理解树木生长的生理机制、预估气候变化情景下森林生态系统的变化、提供森林保护管理的建议有重要意义。以祁连山中部低海拔地区青海云杉树轮记录为依据,利用Vaganov-Shashkin模型模拟青海云杉(Picea crassifolia)的径向生长,探讨青海云杉径向生长的生理机制。结果表明:降水对祁连山中部低海拔地区青海云杉径向生长起着决定性作用,5—8月份的降水直接影响当年青海云杉的径向生长,9月份的降水量影响翌年青海云杉的径向生长。根据本研究结果,水分是限制青海云杉径向生长的主要因子,建议青海云杉人工林种植时,可在5—8月份对青海云杉增加灌溉量。     

Dendrochronological potential of <Emphasis Type="Italic">Millettia stuhlmannii</Emphasis> in Mozambique

Key message

This study demonstrates that Millettia stuhlmannii produces annual growth rings responsive to seasonal climate and should be useful for dendrochronology.

Abstract

Millettia stuhlmannii is a highly valuable and potentially overexploited timber species indigenous to southeastern Africa. It is of particular economic importance in Mozambique though relatively little is known about its growth rate or response to climate. This study investigates whether M. stuhlmannii is potentially useful for dendrochronology—that is whether this species forms annual growth rings that are responsive to external forcing such as climate. Five methods were used to determine whether M. stuhlmannii growth rings are indeed annual in nature, including analysis of ring anatomy, dating trees of known age, cambial wounding, classical cross-dating, and comparison of annual growth to climate variables. Growth rings of Millettia stuhlmannii are distinct and well formed, young trees from plantations of known age formed an appropriate number of distinct annual rings, trees showed distinct wood reaction to cambial wounding, adding exactly one complete ring in one calendar year, cross-dating within and between trees was somewhat successful, and annual growth is significantly correlated with wet season precipitation. Results of this study indicate that M. stuhlmannii is a potentially useful species for dendrochronology. These findings should allow a better understanding of this species’ growth dynamics and ecology, as well as its response to climate variability in the past and potentially to future climate change.

     

Climate variability,tree increment patterns and ENSO-related carbon sequestration reduction of the tropical dry forest species <Emphasis Type="Italic">Loxopterygium huasango</Emphasis> of Southern Ecuador

Key message

Striking hydro-climatic differences of 2 years (wet; dry) dramatically control the increment pattern of L. huasango in varying extent, even causing a “growth collapse” during the La Niña drought 2010/2011.

Abstract

We present the first multi-year long time series of local climate data in the seasonally dry tropical forest in Southern Ecuador and related growth dynamics of Loxopterygium huasango, a deciduous tree species. Local climate was investigated by installing an automatically weather station in 2007 and the daily tree growth variability was measured with high-resolution point dendrometers. The climatic impact on growth behaviour was evaluated. Hydro-climatic variables, like precipitation and relative humidity, were the most important factors for controlling tree growth. Changes in rainwater input affected radial increment rates and daily amplitudes of stem diameter variations within the study period from 2009 to 2013. El Niño Southern Oscillation (ENSO) related variations of tropical Pacific Ocean sea surface temperatures influenced the trees’ increment rates. Average radial increments showed high inter-annual (up to 7.89 mm) and inter-individual (up to 3.88 mm) variations. Daily amplitudes of stem diameter variations differed strongly between the two extreme years 2009 (wet) and 2011 (dry). Contrary to 2009, the La Niña drought in 2011 caused a rapid reduction of the daily amplitudes, indicating a total cessation (‘growth collapse’) of stem increment under ENSO-related drought conditions and demonstrating the high impact of climatic extreme events on carbon sequestration of the dry tropical forest ecosystem.

     

Dendroclimatological potential of three juniper species from the Turkestan range,northwestern Pamir-Alay Mountains,Uzbekistan

Key message

Intensity and magnitude of the growth-climate relationship depends on juniper species and sites. Juniperus seravschanica at low elevations shows highest potential for April–September drought reconstruction in the Turkestan range (Pamir-Alay), Uzbekistan.

Abstract

We present a detailed dendroclimatological study of three juniper species, Juniperus seravschanica Kom., Juniperus semiglobosa Regel and Juniperus turkistanica Kom., sampled at six sites of different elevation (2100–2700 m a.s.l.), exposition (west and south) and steepness (10°–30°) in the Zaamin National Park, Turkestan range, Pamir-Alay mountain system in eastern Uzbekistan. Simple correlation statistics and redundancy analyses were applied to detect species- and site-specific climate responses during the twentieth century, which were additionally investigated in the high-frequency domain by identifying extreme growth years. Our results show that tree-ring formation of J. seravschanica at our low-elevation site is strongly limited by April to September drought conditions, while J. semiglobosa inherits a weak and variable climate response with respect to elevation. J. turkistanica growth at high altitudes is positively associated with warm spring and summer temperatures. Species-specific growth extremes are triggered by incoming air masses from the Atlantic and Arctic, highlighting the connection of synoptic climate regimes across Eurasia. From a dendroclimatic perspective, J. seravschanica exhibits a high potential for reconstructing past drought and pluvials, but under sustained temperature rise also J. semiglobosa will likely increase its sensitivity to drought. Moreover, J. turkistanica at its distribution limit at the tree line is a suitable proxy of summer temperature. Our findings clearly demonstrate that a careful selection of the site, overall topography and elevation as well as the different juniper species are important for successfully reconstructing past climate in Uzbekistan.

     

Cambial dormancy induced growth rings in <Emphasis Type="Italic">Heritiera fomes</Emphasis> Buch.- Ham.: a proxy for exploring the dynamics of Sundarbans,Bangladesh

Key message

Cambial marking experiment and cambial activity analysis offer strong evidence on existence of annual growth rings in Heritiera fomes and revealing the potential of dendrochronological applications in Bangladesh mangroves.

Abstract

Despite enormous significance in coastal protection, biodiversity conservation and livelihood support to the local communities, mangrove ecosystems have been continuously degrading mainly due to anthropogenic disturbances and climate change. Time series based on dated tree ring is an option to identify the causes of forest dilapidation. In this study, we investigated the structure and periodicity of the growth ring in Heritiera fomes, the flagship tree species of the Bangladesh Sundarbans, combining cambial marking experiment and cambial activity analysis. Distinct growth rings were found which are delineated by a band of marginal parenchyma, predominantly one cell wide but up to three and occasionally interrupted with fiber. Of the 13 trees with cambium marking experiment, one growth ring was found in each tree during a year. The dormant cambium was characterized by the abrupt boundary between xylem and cambial zone, absence of enlarging or differentiating cambial derivatives, lower number of cambial cells and thicker radial walls in cambial cells. Growth ring anomalies, i.e., wedging and partially missing rings were also found. In most of the cases, the lower part of the eccentric discs had low radial increment (<0.75 mm) and therefore the growth ring in that area merged with previous one and produced wedging or partially missing ring. However, the existence of annual rings suggests its great potential for future dendrochronological applications to reveal the dynamics of vegetation and climate in Sundarbans.