Beyond tree-ring widths: Stable isotopes sharpen the focus on climate responses of temperate forest trees

Tree rings provide an indispensable tool for assessing a tree's response to variability in its environment, oftentimes also providing a means of reconstructing that variability beyond instrumental records. The wood that trees produce is laid down sequentially, creating an archive of temporally ordered material that is rich in physiological and environmental information. This is made all the more useful because trees are globally distributed, can live for thousands of years and in some cases remain intact long after they die

A 26-year stable isotope record of humidity and El Niño-enhanced precipitation in the spines of saguaro cactus, Carnegiea gigantea

Seasonal and annual variations of rainfall and humidity are recorded in the carbon and oxygen stable isotope ratios of sequentially grown spines found on the columnar cactus, Carnegiea gigantea. A 26-year long composite δ 18 O and δ 13 C isotope record from the spines of five saguaro cacti was created using bomb radiocarbon and semi-annual variations in δ 13 C. Once dating errors in the composite record are corrected, mean annual spine δ 18 O is negatively correlated (P 2) in the maximum annual spine δ 18 O are positively correlated (P < 0.01) with the Southern Oscillation Index (SOI). We attribute these decreases to enhanced winter rainfall associated with the El Niño phase of the El Niño-Southern Oscillation. Minimum annual δ 13 C is negatively correlated with TAP (P < 0.05) and mean nighttime VPD (P < 0.05). These results bolster proposed mechanistic models of isotopic variation in the spines of columnar cactus and demonstrate how isotopic spine series may be used as climate proxies in regions of the Americas where trees suitable for traditional or isotopic dendrochonology are absent. © 2010

Progress in Australian dendroclimatology: Identifying growth limiting factors in four climate zones

Dendroclimatology can be used to better understand past climate in regions such as Australia where instrumental and historical climate records are sparse and rarely extend beyond 100 years. Here we review 36 Australian dendroclimatic studies which cover the four major climate zones of Australia; temperate, arid, subtropical and tropical. We show that all of these zones contain tree and shrub species which have the potential to provide high quality records of past climate. Despite this potential only four dendroclimatic reconstructions have been published for Australia, one from each of the climate zones: A 3592 year temperature record for the SE-temperate zone, a 350 year rainfall record for the Western arid zone, a 140 year rainfall record for the northern tropics and a 146 year rainfall record for SE-subtropics. We report on the spatial distribution of tree-ring studies, the environmental variables identified as limiting tree growth in each study, and identify the key challenges in using tree-ring records for climate reconstruction in Australia. We show that many Australian species have yet to be tested for dendroclimatological potential, and that the application of newer techniques including isotopic analysis, carbon dating, wood density measurements, and anatomical analysis, combined with traditional ring-width measurements should enable more species in each of the climate zones to be used, and long-term climate records to be developed across the entire continent

Seasonal photosynthetic gas exchange and water-use efficiency in a constitutive CAM plant, the giant saguaro cactus (Carnegiea gigantea)

Crassulacean acid metabolism (CAM) and the capacity to store large quantities of water are thought to confer high water use efficiency (WUE) and survival of succulent plants in warm desert environments. Yet the highly variable precipitation, temperature and humidity conditions in these environments likely have unique impacts on underlying processes regulating photosynthetic gas exchange and WUE, limiting our ability to predict growth and survival responses of desert CAM plants to climate change

Daily to decadal patterns of precipitation, humidity, and photosynthetic physiology recorded in the spines of the columnar cactus, Carnegiea gigantea

Isotopic analyses of cactus spines grown serially from the apex of long‐lived columnar cactuses may be useful for climatological and ecological studies if time series can be reliably determined from spines. To characterize the timescales over which spines may record this information, we measured spine growth in saguaro cactus over days, months, and years with time‐lapse photography, periodic marking, and postbomb radiocarbon dating and then analyzed isotopic variability over these same timescales and compared these measurements to local climate. We used daily increments of growth, visible as transverse bands of light and dark tissue in spines, as chronometers to develop diurnally resolved d13C and d18O records from three spines grown in series over a 70 day period. We also constructed a 22 year record of d13C variations from spine tips arranged in chronological sequence along the side of a 4 m tall, single‐stemmed saguaro. We evaluated two mechanisms potentially responsible for daily, weekly, and annual variability in d13C values of spines; both related to vapor pressure deficit (VPD). Our data suggest that stomatal conductance is unlikely to be the determinant of d13C variation in spines. We suggest that either VPD‐induced changes in the balance of nighttime‐ and daytime‐ assimilated CO2 or mesophyll‐limited diffusion of CO2 at night are the most likely determinant of d13C variation in spines. Intra‐annual and interannual variability of d18O in spine tissue appears to be controlled by the mass balance of 18O‐depleted water taken up after rain events and evaporative enrichment of 18O in tissue water between rains. We were able to estimate the annual growth and areole generation rate of a saguaro cactus from its 22 yearlong isotopic record because VPD, rainfall, and evaporation exhibit strong annual cycles in the Sonoran Desert and these variations are recorded in the oxygen and carbon isotope ratios of spines

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

© 2018 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

The effects of α-cellulose extraction and blue-stain fungus on retrospective studies of carbon and oxygen isotope variation in live and dead trees

Tree-ring carbon and oxygen isotope ratios from live and recently dead trees may reveal important mechanisms of tree mortality. However, wood decay in dead trees may alter the δ13C and δ18O values of whole wood obscuring the isotopic signal associated with factors leading up to and including physiological death. We examined whole sapwood and α-cellulose from live and dead specimens of ponderosa pine (Pinus ponderosa), one-seed juniper (Juniperous monosperma), piñon pine (Pinus edulis) and white fir (Abies concolor), including those with fungal growth and beetle frass in the wood, to determine if α-cellulose extraction is necessary for the accurate interpretation of isotopic compositions in the dead trees. We found that the offset between the δ13C or δ18O values of α-cellulose and whole wood was the same for both live and dead trees across a large range of inter-annual and regional climate differences. The method of α-cellulose extraction, whether Leavitt-Danzer or Standard Brendel modified for small samples, imparts significant differences in the δ13C (up to 0.4‰) and δ18O (up to 1.2‰) of α-cellulose, as reported by other studies. There was no effect of beetle frass or blue-stain fungus (Ophiostoma) on the δ13C and δ18O of whole wood or α-cellulose. The relationships between whole wood and α-cellulose δ13C for ponderosa, piñon and juniper yielded slopes of ~1, while the relationship between δ18O of whole wood and α-cellulose was less clear. We conclude that there are few analytical or sampling obstacles to retrospective studies of isotopic patterns of tree mortality in forests of the western United States. Published in 2011 by John Wiley & Sons, Ltd

Identifying drivers of leaf water and cellulose stable isotope enrichment in Eucalyptus in northern Australia

Several previous studies have investigated the use of the stable hydrogen and oxygen isotope composi- tions in plant materials as indicators of palaeoclimate. However, accurate interpretation relies on a detailed understanding of both physiological and environmental drivers of the variations in isotopic enrichments that occur in leaf water and associated organic compounds. To pro- gress this aim we measured δ18O and δ2H values in euca- lypt leaf and stem water and δ18O values in leaf cellulose, along with the isotopic compositions of water vapour, across a north-eastern Australian aridity gradient. Here we compare observed leaf water enrichment, along with pre- viously published enrichment data from a similar north Australian transect, to Craig–Gordon-modelled predic- tions of leaf water isotopic enrichment. Our investigation of model parameters shows that observed 18O enrichment across the aridity gradients is dominated by the relation- ship between atmospheric and internal leaf water vapour pressure while 2H enrichment is driven mainly by variation in the water vapour—source water isotopic disequilibrium. During exceptionally dry and hot conditions (RH 37 °C) we observed strong deviations from Craig– Gordon predicted isotope enrichments caused by partial stomatal closure. The atmospheric–leaf vapour pressure relationship is also a strong predictor of the observed leaf cellulose δ18O values across one aridity gradient. Our find- ing supports a wider applicability of leaf cellulose δ18O composition as a climate proxy for atmospheric humidity conditions during the leaf growing season than previously documented

Convergence of evidence supports a Chuska Mountains origin for the Plaza Tree of Pueblo Bonito, Chaco Canyon

© 2020 by the Society for American Archaeology. The iconic Plaza Tree of Pueblo Bonito is widely believed to have been a majestic pine standing in the west courtyard of the monumental great house during the peak of the Chaco Phenomenon (AD 850-1140). The ponderosa pine (Pinus ponderosa) log was discovered in 1924, and since then, it has been included in birth and life narratives of Pueblo Bonito, although these ideas have not been rigorously tested. We evaluate three potential growth origins of the tree (JPB-99): Pueblo Bonito, Chaco Canyon, or a distant mountain range. Based on converging lines of evidence-documentary records, strontium isotopes (87Sr/86Sr), and tree-ring provenance testing-we present a new origin for the Plaza Tree. It did not grow in Pueblo Bonito or even nearby in Chaco Canyon. Rather, JPB-99 originated from the Chuska Mountains, over 50 km west of Chaco Canyon. The tree was likely carried to Pueblo Bonito sometime between AD 1100 and 1130, although why it was left in the west courtyard, what it meant, and how it might have been used remain mysteries. The origin of the Plaza Tree of Pueblo Bonito underscores deep cultural and material ties between the Chaco Canyon great houses and the Chuska landscape

The climate reconstruction potential of Acacia cambagei (gidgee) for semi-arid regions of Australia using stable isotopes and elemental abundances

To provide multi-centennial, annually-resolved records of climate for arid and semi-arid areas of Australia it is necessary to investigate the potential climate signals in tree species in this large region. Using a stable isotope and x-ray fluorescence approach to dendrochronology in Acacia cambagei, this study demonstrates short (10 years) proxies of temperature and precipitation are possible. Because rings in A. cambagei are difficult to see, precluding traditional dendrochronology, we used elemental abun- dances of Ca and Sr as an annual chronometer back to 1962. Radiocarbon analysis confirmed that our dating of wood from two trees. We compared d13C and d18O from the a-cellulose of the dated wood over the most recent 10 years (n 1⁄4 10) to local climate records demonstrating significant relationships be- tween d18O and precipitation (r 1⁄4 0.85, p < 0.002); mean monthly maximum temperature (r 1⁄4 0.69, p < 0.03); and drought indexes (CRU scPDSI 0.5 , r 1⁄4 0.89, p < 0.001) for February and March. Acacia cambagei may be useful in developing regional networks of climate proxies for drought. Using modern trees, in combination with architectural timbers, it may be possible to construct a multi-century, annually-resolved proxy-record of rainfall and temperature for semi-arid north-eastern Australia