The science of tropical dendrochronology is now emerging in regions where tree-ring dating had previously not been considered possible. Here, we combine wood anatomical microsectioning techniques and ...radiocarbon analysis to produce the first tree-ring chronology with verified annual periodicity for a new dendrochronological species,
(commonly known as "algarrobo blanco") in the tropical Andes of Bolivia. First, we generated a preliminary chronology composed of six trees using traditional dendrochronological methods (i.e., cross-dating). We then measured the
C content on nine selected tree rings from two samples and compared them with the Southern Hemisphere (SH) atmospheric
C curves, covering the period of the bomb
C peak. We find consistent offsets of 5 and 12 years, respectively, in the calendar dates initially assigned, indicating that several tree rings were missing in the sequence. In order to identify the tree-ring boundaries of the unidentified rings we investigated further by analyzing stem wood microsections to examine anatomical characteristics. These anatomical microsections revealed the presence of very narrow terminal parenchyma defining several tree-ring boundaries within the sapwood, which was not visible in sanded samples under a stereomicroscope. Such newly identified tree rings were consistent with the offsets shown by the radiocarbon analysis and allowed us to correct the calendar dates of the initial chronology. Additional radiocarbon measurements over a new batch of rings of the corrected dated samples resulted in a perfect match between the dendrochronological calendar years and the
C dating, which is based on good agreement between the tree-ring
C content and the SH
C curves. Correlations with prior season precipitation and temperature reveal a strong legacy effect of climate conditions prior to the current
growing season. Overall, our study highlights much potential to complement traditional dendrochronology in tree species with challenging tree-ring boundaries with wood anatomical methods and
C analyses. Taken together, these approaches confirm that
can be accurately dated and thereby used in climatic and ecological studies in tropical and subtropical South America.
Climate change significantly impacts global forests, leading to tree decline and dieback. To cope with climate change, trees develop several functional traits, such as intra-annual density ...fluctuations (IADFs) in tree rings. The formation of these traits facilitates trees to optimize resource allocation, allowing them to withstand periods of stress and eventually recover when the conditions become favourable again. This study focuses on a Pinus pinaster Aiton forest in a warm, drought-prone Mediterranean area, comparing two growing seasons with different weather patterns. The innovative continuous monitoring approach used in this study combines high-resolution monitoring of sap flow (SF), analysis of xylogenesis and quantitative wood anatomy. Our results revealed the high plasticity of P. pinaster in water use and wood formation, shedding light on the link between IADFs and tree conductance. Indeed, the capacity to form large cells in autumn (as IADFs) improves the total xylem hydraulic conductivity of this species. For the first time, a continuous SF measurement system captured the dynamics of bimodal SF during the 2022 growing season in conjunction with the bimodal growth pattern observed through xylogenesis monitoring. These results highlight the intricate interplay between environmental conditions, water use, wood formation and tree physiology, providing valuable insights into the acclimation mechanisms employed by P. pinaster to cope with weather fluctuations.
In the last decades, forests have been seriously threatened by the effects of climate change. In Mediterranean regions, increasing fire occurrence and drought have a substantial impact on forests, ...possibly pushing them towards tipping points. Indeed, although trees could survive to fire events of medium severity in the short term, severe defoliation and environmental stressors could affect the capacity to transport water and to fix and use carbon, amplifying the possibility of a delayed post fire mortality. Therefore, it is urgent to better understand trees eco-physiological processes in response to wildfire in order to plan suitable forest management strategies. In this research an innovative continuous monitoring system of sap flow and micro-stationary climatic conditions of trees was combined with dendro-anatomical analyses and xylem cavitation vulnerability studies to assess fire impact on a Pinus pinaster forest affected by a severe fire and compared to an unburned control site. Xylem analyses showed that the forest-fire did not influence the xylem hydraulic parameters and did not increased vulnerability to embolism. However, burned trees with high defoliation rate, presented reduced assimilation capacity and carbon availability for growth, as well as a limited development of thicker xylem conduit walls compared to unburned trees. Furthermore, continuous monitoring highlighted an increase in sap flow of defoliated trees compared to the control ones during the hottest and driest months of the year indicating a higher stomatal conductance. Overall, our results suggested that although fire did not affect the xylem hydraulics properties of the vascular system, the severe crown damage caused growth reduction and transpiration dysfunction in the monitored period. Those effect could negatively affect the survival of burned trees, especially in areas subjected to hot and dry periods.
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•Fire caused limited growth and low formation of thicker xylem.•Fire-damaged trees showed a trade-off between carbon assimilation and water loss.•Fire did not induce an increase in cavitation vulnerability.•First application of a continuous system of sap flow measurements in a burnt forest.
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.
This Special Issue presents recent advancements in tropical dendrochronology in the tropical and subtropical Americas, focusing on the identification of new species for dendrochronological studies, ...the assessment of climate information contained in tree-ring records, and systematic reviews of past research. The studies included in this issue significantly contribute to our understanding of tree species suitable for dendrochronology and the improvement of dating techniques. Moreover, they delve into the relationships between climate variables and tree growth, offering insights into the response of tropical forests to environmental change and providing tools for reconstructing past climate conditions. These studies also shed light on the challenges associated with accurately distinguishing annual ring boundaries in tropical species with complex anatomical structures and emphasize the importance of integrating complementary dating methods and visualization techniques to enhance the reliability of dendrochronological studies in the tropics. By synthesizing diverse research findings, this Special Issue offers a comprehensive overview of tropical dendrochronology in the American (sub) tropics, revealing gaps in knowledge, and suggesting potential avenues for future research. Ultimately, these advancements promote a deeper understanding of tropical forests, their role in the global climate system, and the need for their sustainable management and conservation.
