Below and above-ground carbon distribution along a rainfall gradient. A case of the Zambezi teak forests,Zambia

Understanding carbon (C) stocks or biomass in forests is important to examine how forests mitigate climate change. To estimate biomass in stems, branches and roots takes intensive fieldwork to uproot, cut and weigh the mass of each component. Different models or equations are also required. Our research focussed on the dry tropical Zambezi teak forests and we studied their structure at three sites following a rainfall gradient in Zambia. We sampled 3558 trees at 42 plots covering a combined area of 15ha. Using data from destructive tree samples, we developed mixed-species biomass models to estimate above ground biomass for small (<5 cm diameter at breast height (DBH, 1.3 m above-ground)) and large (≥5 cm DBH) trees involving 90 and 104 trees respectively, that belonged to 12 species. A below-ground biomass model was developed from seven trees of three species (16–44 cm DBH) whose complete root systems were excavated. Three stump models were also derived from these uprooted trees. Finally, we determined the C fractions from 194 trees that belonged to 12 species. The analysis revealed that DBH was the only predictor that significantly correlated to both above-ground and below-ground biomass. We found a mean root-to-shoot ratio of 0.38:0.62. The C fraction in leaves ranged from 39% to 42%, while it varied between 41% and 46% in wood. The C fraction was highest at the Kabompo site that received the highest rainfall, and lowest at the intermediate Namwala site. The C stocks varied between 15 and 36 ton C ha⁻¹ and these stocks where highest at the wetter Kabompo site and lowest at the drier Sesheke site. Our results indicate that the projected future rainfall decrease for southern Africa, will likely reduce the C storage potential of the Zambezi teak forests, thereby adversely affecting their mitigating role in climate change.     

Climatic signals in tree rings of <Emphasis Type="Italic">Burkea africana</Emphasis> and <Emphasis Type="Italic">Pterocarpus angolensis</Emphasis> from semiarid forests in Namibia

Tree-ring studies contribute worldwide to the understanding of climate and its relation to tree growth. Long tree-ring chronologies serve as climate proxies for the reconstruction of past, pre-instrument climate and its recent change. In tropical regions, the availability of exactly dated tree-ring chronologies is limited. The dendroclimatic potential of two dominant species from dry forests in northern Namibia was examined in the study presented in this paper. Both species (Burkea africana Hook and Pterocarpus angolensis DC) were sampled at two sites (ca. 900 km apart), and the response to several climatic variables, including ENSO indices, is studied. All specimens showed distinct growth rings and cross-dating between radii was successful for all trees. Species-specific mean curves were built for both sites. The mean curves of different species of the same site synchronised significantly, allowing the construction of a site-specific chronology. Synchronisation between sites was not possible, but spectral analysis of the chronologies implied that both show similar long-term (6.7 year) oscillation patterns. B. africana is more sensitive to rainfall variation than P. angolensis at both sites. Growth response to rainfall was positive, but a time-lag in the reaction occurred between the sites, corresponding to the time-lag of the beginning of the rainy season. Air temperature showed a negative correlation with stem increment at both sites. The response at the westernmost site to two ENSO indices indicates a tree growth decrease during El Niño years, which are generally dry in southern Africa.     

Effect of climate on tree growth in the Pampa biome of Southeastern South America: First tree-ring chronologies from Uruguay

Tree-ring research in the highland tropics and subtropics represents a major frontier for understanding climate-growth relationships. Nonetheless, there are many lowland regions – including the South American Pampa biome – with scarce tree ring data. We present the first two tree-ring chronologies for Scutia buxifolia in subtropical Southeastern South America (SESA), using 54 series from 29 trees in two sites in northern and southern Uruguay. We cross-dated annual rings and compared tree growth from 1950 to 2012 with regional climate variability, including rainfall, temperature and the Palmer Drought Severity Index – PDSI, the El Niño Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). Overall, ring width variability was highly responsive to climate signals linked to water availability. For example, tree growth was positively correlated with accumulated rainfall in the summer-fall prior to ring formation for both chronologies. Summer climate conditions were key for tree growth, as shown by a negative effect of hot summer temperatures and a positive correlation with PDSI in late austral summer. The El Niño phase in late spring/early summer favored an increase in rainfall and annual tree growth, while the La Niña phase was associated with less rainfall and reduced tree growth. Extratropical climate factors such as SAM had an equally relevant effect on tree growth, whereby the positive phase of SAM had a negative effect over radial growth. These findings demonstrate the potential for dendroclimatic research and climate reconstruction in a region with scarce tree-ring data. They also improve the understanding of how climate variability may affect woody growth in native forests – an extremely limited ecosystem in the Pampa biome.     

Comparison of whole wood and cellulose carbon and oxygen isotope series from Pinus nigra ssp. laricio (Corsica/France)

Stable isotopes in tree rings have widely been used for palaeoclimate reconstructions since tree rings record climatic information at annual resolution. However, various wood components or different parts of an annual tree-ring may differ in their isotopic compositions. Thus, sample preparation and subsequent laboratory analysis are crucial for the isotopic signal retained in the final tree-ring isotope series used for climate reconstruction and must therefore be considered for the interpretation of isotope–climate relationships. This study focuses on wood of Corsican Pine trees (Pinus nigra ssp. laricio) as this tree species allows to reconstruct the long-term climate evolution in the western Mediterranean. In a pilot study, we concentrated on methodological issues of sample preparation techniques in order to evaluate isotope records measured on pooled whole tree-ring cellulose and whole tree-ring bulk wood samples. We analysed 80-year long carbon and oxygen chronologies of Corsican Pine trees growing near the upper tree line on Corsica. Carbon and oxygen isotope records of whole tree-ring bulk wood and whole tree-ring cellulose from a pooled sample of 5 trees were correlated with the climate parameters monthly precipitation, temperature and the self-calibrating Palmer Drought Severity Index (sc-PDSI). Results show that the offsets in carbon and oxygen isotopes of bulk wood and cellulose are not constant over time. Both isotopes correlate with climate parameters from late winter and summer. The carbon and oxygen isotope ratios of cellulose are more sensitive to climatic variables than those of bulk wood. The results of this study imply that extraction of cellulose is a pre-requisite for the reconstruction of high-resolution climate records from stable isotope series of P. nigra ssp. laricio.     

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.     

Climate–growth relationships of the dominant tree species from semi-arid savanna woodland in Ethiopia

Long-term climate–growth relationships, were examined in tree rings of four co-occurring tree species from semi-arid Acacia savanna woodlands in Ethiopia. The main purpose of the study was to prove the presence of annual tree rings, evaluate the relationship between radial growth and climate parameters, and evaluate the association of El Niño and drought years in Ethiopia. The results showed that all species studied form distinct growth boundaries, though differences in distinctiveness were revealed among the species. Tree rings of the evergreen Balanites aegyptiaca were separated by vessels surrounding a thin parenchyma band and the growth boundary of the deciduous acacias was characterized by thin parenchyma bands. The mean annual diameter increment ranged from 3.6 to 5.0 mm. Acacia senegal and Acacia seyal showed more enhanced growth than Acacia tortilis and B. aegyptiaca. High positive correlations were found between the tree-ring width chronologies and precipitation data, and all species showed similar response to external climate forcing, which supports the formation of one tree-ring per year. Strong declines in tree-ring width correlated remarkably well with past El Niño Southern Oscillation (ENSO) events and drought/famine periods in Ethiopia. Spectral analysis of the master tree-ring chronology indicated occurrences of periodic drought events, which fall within the spectral peak equivalent to 2–8 years. Our results proved the strong linkage between tree-ring chronologies and climate, which sheds light on the potential of dendrochronological studies developing in Ethiopia. The outcome of this study has important implications for paleoclimatic reconstructions and in restoration of degraded lands.     

Climate–growth analysis of Qilian juniper across an altitudinal gradient in the central Qilian Mountains, northwest China

In the context of global warming, it is of high importance to assess the influence of climatic change and geographic factors on the radial growth of high-elevation trees. Using tree-ring data collected from four stands of Qilian juniper (Juniperus przewalskii Kom.) across an altitudinal gradient in the central Qilian Mountains, northwest China, we compared the radial growth characteristics and climate–growth relationships at different elevations. Results indicated that there was little difference in the tree-ring parameters of the four chronologies. Correlation analyses both for unfiltered and 10-year high-passed data of monthly climatic variables and chronologies were presented to investigate the climatic forcing on tree growth, and results revealed that the correlation patterns were consistent among the four sites, especially for high-passed data. We employed the principal components analysis method to obtain the first principal component (PC1) of the four chronologies and computed the correlations between PC1 and climate factors. The PC1 correlated significantly with winter (November–January) temperature, prior August and current May temperature, and precipitation in the previous September and current January and April, indicating that tree growth in this region was mainly limited by cold winter temperature and drought in early growing season and prior growing season (prior August and September). However, the climate–growth relationships were unstable; with an increase in temperature, the sensitivity of tree growth to temperature had decreased over the past few decades. Considering the instability of the climate–growth relationships, climate reconstructions based on tree rings in the study area should be approached with more caution.     

Recent growth increase in endemic Juglans boliviana from the tropical Andes

The spatial coverage of tree-ring chronologies in tropical South America is low compared to the extratropics, particularly in remote regions. Tree-ring dating from such tropical sites is limited by the generally weak temperature seasonality, complex coloration, and indistinct anatomical morphology in some tree species. As a result, there is a need to complement traditional methods of dendrochronology with innovative and independent approaches. Here, we supplement traditional tree-ring methods via the use of radiocarbon analyses to detect partial missing rings and/or false rings, and wood anatomical techniques to precisely delineate tree-ring boundaries. In so doing we present and confirm the annual periodicity of the first tree-ring width (TRW) chronology spanning from 1814 to 2017 for Juglans boliviana (‘nogal’), a tree species growing in a mid-elevation tropical moist forest in northern Bolivia. We collected 25 core samples and 4 cross-sections from living and recently harvested canopy-dominant trees, respectively. The sampled trees were growing in the Madidi National Park and had a mean age of 115 years old, with certain trees growing for over 200 years. Comparison of (residual and standard) TRW chronologies to monthly climate variables shows significant negative relationships to prior year May-August maximum temperatures (r = −0.54, p < 0.05) and positive relationships to dry season May-October precipitation (r = 0.60, p < 0.05) before the current year growing season. Additionally, the radial growth of Juglans boliviana shows a significant positive trend since 1979. Our findings describe a new and promising tree species for dendrochronology due to its longevity and highlight interdisciplinary techniques that can be used to expand the current tree-ring network in Bolivia and the greater South American tropics.     

Dendrochronology in the tropics using tree-rings of Pinus kesiya

The recent decade has witnessed considerable progress in the number of tree-ring studies using the tropical conifer taxa, Pinus kesiya. Several tree-ring networks have been established in less explored regions in Northeast India, Southwest China and Vietnam. The seasonal climate response of P. kesiya tree-rings has been examined and used to reconstruct temperature and soil moisture variability over the past century and augment the short instrumental records in South and Southeast Asia. In addition to standard approaches, the application of stable isotope, wood density, and blue intensity measurements indicates a significant development in P. kesiya studies. This review elaborates the future prospects of using multiple tree-ring parameters to establish discrete proxies besides tree-ring width. We recommend blue intensity as a cost-effective alternative to quantitative wood anatomy in tropical pines, and call for routine assessments of the temporal stability of climate-growth responses to identify and study potentially non-stationary climate signals. Efforts should be made towards developing extensive networks of long P. kesiya tree-ring chronologies to extend regional climate reconstructions.     

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.     

Tree-ring distinctness,dating potential and climatic sensitivity of laurel forest tree species in Tenerife Island

Macaronesian laurel forests are the only remnants of a subtropical palaeoecosystem dominant during the Tertiary in Europe and northern Africa. These biodiverse ecosystems are restricted to cloudy and temperate insular environments in the North Atlantic Ocean. Due to their reduced distribution area, these forests are particularly vulnerable to anthropogenic disturbances and changes in climatic conditions. The assessment of laurel forest trees’ response to climate variation by dendrochronological methods is limited because it was assumed that the lack of marked seasonality would prevent the formation of distinct annual tree rings. The aims of this study were to identify the presence of annual growth rings and to assess the dendrochronological potential of the most representative tree species from laurel forests in Tenerife, Canary Islands. We sampled increment cores from 498 trees of 12 species in two well-preserved forests in Tenerife Island. We evaluated tree-ring boundary distinctness, dating potential, and sensitivity of tree-ring growth to climate and, particularly, to drought occurrence. Eight species showed clear tree-ring boundaries, but synchronic annual tree rings and robust tree-ring chronologies were only obtained for Laurus novocanariensis, Ilex perado subsp. platyphylla, Persea indica and Picconia excelsa, a third of the studied species. Tree-ring width depended on water balance and drought occurrence, showing sharp reductions in growth in the face of decreased water availability, a response that was consistent among species and sites. Inter-annual tree-ring width variation was directly dependent on rainfall input in the humid period, from previous October to current April. The four negative pointer years 1995, 1999, 2008 and 2012 corresponded to severe drought events in the study area. This study gives the first assessment of dendrochronological potential and tree-ring climate sensitivity of tree species from the Tenerife laurel forest, which opens new research avenues for dendroecological studies in Macaronesian laurel forests.     

Annual Growth Ring Patterns in Brachystegia spiciformis Reveal Influence of Precipitation on Tree Growth1

The availability of exactly dated tree‐ring chronologies is limited in tropical regions. However, these chronologies could contribute widely to studies of the influence of natural and human‐induced factors on tropical forests. We examine the potential for building a chronology based on three sites in the miombo woodland of western Zambia. Brachystegia spiciformis Benth., a dominant species from this vegetation type, is used. Response of the chronology to several climatic factors is examined. All specimens showed very clear growth rings, and cross‐dating between radii of a tree was successful for all trees. Site chronologies could be constructed after cross‐dating of growth ring series of individual trees. The mean growth ring curves of the three sites were significantly similar, allowing for the construction of a regional chronology. Correlation function analysis between the tree‐ring chronology and regional climatic variables revealed that climate at the core of the rainy season, in December and January, has an explicit influence on tree growth. Where precipitation and relative humidity in these months influence tree growth positively, temperature correlates in a negative way. Some 20 percent of the variance in the B. spiciformis tree‐ring chronology is accounted for by wet season rainfall. The successful cross‐dating and correlation between a tree‐ring chronology and climate demonstrated in this study indicate annual ring formation in B. spiciformis trees and sensitivity to climatic conditions.     

Annual variation and influence of climate on the ring width and wood hydrosystem of Prosopis flexuosa DC trees using image analysis

We developed chronologies based on the width of tree rings, total area of vessels, and the number of vessels per tree ring of the Prosopis flexuosa wood samples from the xerophytic woodlands of central Argentina. We evaluated the influence of climate on these tree-ring characteristics considering the period from 1940 to 2004 (65 years). The width of the rings, the number of vessels, and the total area of vessels were positively influenced by regional precipitation corresponding to the seasonalized November to December period, which reflects the importance of the water availability in the initial stage of the formation of the wood. The width of the rings and the total area of vessels were negatively influenced by temperature during the same period, while the number of vessels was not significantly correlated with temperature. The high temperatures in spring increase evapotranspiration, which reduces water availability to plants and results in an inverse growth response. This study was the first to develop chronologies based on anatomical characters of wood from the arid and semiarid regions of South America and with significant applications in ecological and climatic studies.     

A lonely dot on the map: Exploring the climate signal in tree-ring density and stable isotopes of clanwilliam cedar,South Africa

Clanwilliam cedar (Widdringtonia cedarbergensis; WICE), a long-lived conifer with distinct tree rings in Cape Province, South Africa, has potential to provide a unique high-resolution climate proxy for southern Africa. However, the climate signal in WICE tree-ring width (TRW) is weak and the dendroclimatic potential of other WICE tree-ring parameters therefore needs to be explored. Here, we investigate the climatic signal in various tree-ring parameters, including TRW, Minimum Density (MND), Maximum Latewood Density (MXD), Maximum Latewood Blue Intensity (MXBI), and stable carbon and oxygen isotopes (δ¹⁸O and δ¹³C) measured in WICE samples collected in 1978. MND was negatively influenced by early spring (October-November) precipitation whereas TRW was positively influenced by spring November-December precipitation. MXD was negatively influenced by autumn (April-May) temperature whereas MXBI was not influenced by temperature. Both MXD and MXBI were negatively influenced by January-March and January-May precipitation respectively. We did not find a significant climate signal in either of the stable isotope time series, which were measured on a limited number of samples. WICE can live to be at least 356 years old and the current TRW chronology extends back to 1564 CE. The development of full-length chronologies of alternative tree-ring parameters, particularly MND, would allow for an annually resolved, multi-century spring precipitation reconstruction for this region in southern Africa, where vulnerability to future climate change is high.     

Millennium-Scale Crossdating and Inter-Annual Climate Sensitivities of Standing California Redwoods

Extremely decay-resistant wood and fire-resistant bark allow California’s redwoods to accumulate millennia of annual growth rings that can be useful in biological research. Whereas tree rings of Sequoiadendron giganteum (SEGI) helped formalize the study of dendrochronology and the principle of crossdating, those of Sequoia sempervirens (SESE) have proven much more difficult to decipher, greatly limiting dendroclimatic and other investigations of this species. We overcame these problems by climbing standing trees and coring trunks at multiple heights in 14 old-growth forest locations across California. Overall, we sampled 1,466 series with 483,712 annual rings from 120 trees and were able to crossdate 83% of SESE compared to 99% of SEGI rings. Standard and residual tree-ring chronologies spanning up to 1,685 years for SESE and 1,538 years for SEGI were created for each location to evaluate crossdating and to examine correlations between annual growth and climate. We used monthly values of temperature, precipitation, and drought severity as well as summer cloudiness to quantify potential drivers of inter-annual growth variation over century-long time series at each location. SESE chronologies exhibited a latitudinal gradient of climate sensitivities, contrasting cooler northern rainforests and warmer, drier southern forests. Radial growth increased with decreasing summer cloudiness in northern rainforests and a central SESE location. The strongest dendroclimatic relationship occurred in our southernmost SESE location, where radial growth correlated negatively with dry summer conditions and exhibited responses to historic fires. SEGI chronologies showed negative correlations with June temperature and positive correlations with previous October precipitation. More work is needed to understand quantitative relationships between SEGI radial growth and moisture availability, particularly snowmelt. Tree-ring chronologies developed here for both redwood species have numerous scientific applications, including determination of tree ages, accurate dating of fire-return intervals, archaeology, analyses of stable isotopes, long-term climate reconstructions, and quantifying rates of carbon sequestration.     

Consistency of growth response to precipitation by Pseudopiptadenia contorta in two Atlantic Forest remnants

Tree growth sensitivity to climate can vary over space and time. This variability generates inconsistency in growth response to climate, which makes it difficult to assess the effects of past climate and global climate change on tree growth. A previous short-term study of Pseudopiptadenia contorta found a consistent growth response to climate in distinct locations, which raises the question, is the growth response of P. contorta to climate consistent over the long-term? We aimed to assess whether there is a common pattern of variation in tree-ring width, build tree-ring width chronologies, and verify the consistency of the climate-growth response of P. contorta in two Atlantic Forest remnants. Wood samples were collected in Reserva Biológica de Poço das Antas (RBPA) and Reserva Biológica de Tinguá (RBT) in the state of Rio de Janeiro, Brazil. Conventional dendrochronology methods were used for cross-dating, to build chronologies and to assess the climate-growth relationship. A common growth pattern was detected for P. contorta, and two tree-ring width chronologies were constructed. A congruent growth response was found for trees of RBPA and RBT to annual and spring precipitation as well as precipitation in the rainy months. Other climate-growth relationships were detected with other precipitation and temperature variables. Considering that P. contorta is a widespread species, occurring in other Brazilian biomes and forest formations, it is a promising model for developing further dendrochronological research including regional networks of replicated site chronologies, which could facilitate the reconstruction of historical climatic series and predictions of future impacts of climate change in tropical areas.     

Characteristics of a multi-species conifer network of wood properties chronologies from Southern Australia

Progress in quantitative wood anatomy has resulted in a growing number of increasingly understood proxies from the tree-ring archive. Much of this work has been based on tree species in the Northern Hemisphere. Here, we present and examine a relatively dense network of wood property chronologies (wood density, tracheid radial diameter, cell wall thickness and ring width) from several species in Tasmania, southern Australia. We ask how the relationships amongst the different types of chronologies differ within and amongst species. We also consider how each chronology responds to monthly climate. In general terms, and similar to findings in the Northern Hemisphere, relationships between the various wood properties and climate are stronger than those between climate and ring width chronologies. An important exception to this is the highest elevation Lagarostrobos franklinii site. Additionally, strongest response to climate for the wood properties generally occurs for the concurrent growing season compared to the prior growing season for ring width. Relationships amongst the various chronology types differ for the various species, with L. franklinii also showing some variation in these relationships by site (possibly associated with elevation). Results suggest there is considerable value in further exploring the potential for developing anatomical wood chronologies for climate reconstruction from other species for which ring widths do not exhibit a strong climate signal.     

Growth response of Sabina tibetica to climate factors along an elevation gradient in south Tibet

We examine the climate significance in tree-ring chronologies retrieved from Sabina tibetica Kom. (Tibetan juniper) at two sites ranging in elevation from 4124 to 4693 m above sea level (a.s.l.) in the Namling region, south Tibet. The study region is under the control of semi-arid plateau temperate climate. The samples were grouped into high- and low-elevation classes and standard ring-width chronologies for both classes were developed. Statistical analysis revealed a decreasing growth rate yet increasing chronology reliability with increasing elevation. Overall, correlation analyses showed that radial growth in S. tibetica at the study sites was controlled by similar climatic factors, regardless of elevation; these factors comprised early winter (November) and early summer (May–June) temperatures as well as annual precipitation (July–June). Slight differences in the correlation between tree growth along the elevation gradient and climate variables were examined. The correlations with early winter temperature varied from significantly positive at the low-elevation site to weakly positive at the high-elevation site, whereas the correlations between radial growth and early summer temperature increased from weakly negative at the low-elevation sites to strongly negative at the high-elevation sites. The abundant precipitation through the year may have masked variations in tree growth on different elevation aspects. Our results will aid future dendroclimatological studies of Namling tree rings in south Tibet and demonstrate the potential of S. tibetica Kom. for improving our understanding of environmental impacts on tree growth.     

Anomalous ring identification in two Australian subtropical Araucariaceae species permits annual ring dating and growth-climate relationship development

Almost all Australian tropical and subtropical regions lack annually-resolved long-term (multi-decadal to centennial scale) instrumental climate records. Reconstructing climate in these regions requires the use of sparse climate proxy records such as tree rings. Tree rings often archive annually-resolved centennial-scale climate information. However, many tropical and subtropical species have short life-spans, the timbers are poorly preserved, and there is a belief that the proxy records of these species are often compromised by ring anomalies. Additionally, for many species the relationship between climate (e.g. temperature and/or rainfall) and tree growth has not been established. These factors have led to tree-ring data being underutilized in the Australian subtropics. Trees in the Araucariaceae family, a common family in northern and eastern Australia, are both longer lived than many species in the Australian subtropics, present growth rings that are annual in nature, and their growth is known to vary with climate. In this study we examine two subtropical Araucariaceae species, Araucaria cunninghamii and Araucaria bidwillii, and quantify the relationship between their radial growth and climate variability. Ring anomalies including false, faint, locally absent, and pinching rings, are found to be present in these species, however, bomb-pulse radiocarbon dating of A. cunninghamii samples together with a whole tree approach helped to identify annual growth patterns despite such anomalous ring boundaries. Additionally, to determine which climate variables most influence growth in these species, dendrometers were installed at two locations in subtropical Southeast Queensland, Australia. We found that rainfall variability drives annual ring growth, while temperature constrains the onset and conclusion of the growth season each year. Our results demonstrate that through the use of A. cunninghamii and A. bidwillii trees which demonstrate annual growth in relation to climate variables there is potential to develop centennial scale climate reconstructions from the Australian subtropics. We provide recommendations on how to best identify ring anomalies in these species to help in the future development of long-term chronologies and climate reconstructions.     

芦芽山华北落叶松(Larix principis-rupprechtii)树轮宽度年表对气候因子的响应

在芦芽山地区采集3个不同海拔的华北落叶松(Larix principis-rupprechtii),在传统去趋势的基础上,采用"signal-free"方法对拟合曲线进行修正,避免了中等频率的气候信息引起的拟合偏差,最终建立3个不同海拔树轮宽度标准年表(STD)。同时以10a为界对上述年表进行滤波处理,得到3个低频年表。年表特征值表明,随着海拔升高,年轮平均轮宽变窄,敏感性和高频信息增强,低频信息减弱,这可能与逐渐恶劣的生境有关。中、低海拔年表的低频信息更一致,中、高海拔的高频信息更接近,而高、低海拔无论是标准年表还是高频、低频年表相似性均较差。树轮气候响应分析显示,低海拔STD年表与5月最低温负相关最为显著,STD和低频年表均与5、6月份土壤温度显著负相关,说明生境暖干,树木主要受生长季的干旱胁迫;中海拔STD年表与当年5月最高温正相关最为显著,STD和低频年表与土壤温度相关均不显著,说明生境逐渐变得冷湿,生长季的低温成为树木生长的限制因子;高海拔STD年表与气象要素相关不显著,低频年表与当年4月土壤温度正相关,说明高海拔最为冷湿,并有季节性冻土分布,生长季的土壤低温成为树木生长的限制因子。因此,全球变暖的趋势将更有利于高海拔树木的生长,而低海拔树木的干旱胁迫进一步加剧。